Jeffrey Leung - Academia.edu (original) (raw)
Papers by Jeffrey Leung
Frontiers in Plant Science
Epigenetics refers to the mode of inheritance independent of mutational changes in the DNA. Early... more Epigenetics refers to the mode of inheritance independent of mutational changes in the DNA. Early evidence has revealed methylation, acetylation, and phosphorylation of histones, as well as methylation of DNA as part of the underlying mechanisms. The recent awareness that many human diseases have in fact an epigenetic basis, due to unbalanced diets, has led to a resurgence of interest in how epigenetics might be connected with, or even controlled by, metabolism. The Next-Generation genomic technologies have now unleashed torrents of results exposing a wondrous array of metabolites that are covalently attached to selective sites on histones, DNA and RNA. Metabolites are often cofactors or targets of chromatin-modifying enzymes. Many metabolites themselves can be acetylated or methylated. This indicates that the acetylome and methylome can actually be deep and pervasive networks to ensure the nuclear activities are coordinated with the metabolic status of the cell. The discovery of novel histone marks also raises the question on the types of pathways by which their corresponding metabolites are replenished, how they are corralled to the specific histone residues and how they are recognized. Further, atypical cytosines and uracil have also been found in eukaryotic genomes. Although these new and extensive connections between metabolism and epigenetics have been established mostly in animal models, parallels must exist in plants, inasmuch as many of the basic components of chromatin and its modifying enzymes are conserved. Plants are chemical factories constantly responding to stress. Plants, therefore, should lend themselves readily for identifying new endogenous metabolites that are also modulators of nuclear activities in adapting to stress.
Plant physiology, 2017
Changing from unsustainable to renewable agriculture requires boosting water-use efficiency in cr... more Changing from unsustainable to renewable agriculture requires boosting water-use efficiency in crops. Because abscisic acid (ABA) reinforces a plant's capacity to withstand drought, the mode of action of this hormone has thus long attracted biophysicists, ecophysiologists, geneticists, and molecular biologists alike. In Arabidopsis (Arabidopsis thaliana), 14 STARTdomain proteins compose the family of cytosolic ABA receptors (Ma et al., 2009; Park et al., 2009). One founding mutant, PYRABACTIN RESISTANCE1 (PYR1), is in fact a namesake based on a genetic screen for seeds that can germinate in the synthetic ABA agonist pyrabactin (Park et al., 2009). An analog, quinabactin, was later found to activate strongly four ABA receptors (PRY1, PYL1-PYL3), resulting in seed germination inhibition and stomatal closure. Several plant species treated with this compound did improve water-use efficiency (Okamoto et al., 2013), hinting at its potential in agriculture. In this issue, Ye et al. (2017) identified and characterized in detail ABA ANTAGONIST1 (AA1) by screening for chemicals that can reverse the inhibitory effect of ABA on Arabidopsis seed germination. AA1 can oppose all known elementary ABA responses tested, ranging from stomatal movements to expression of reporter genes. Also, among known antagonists, AA1 can block all ABA receptors, at least by bonding with some of the same amino acid residues as ABA. An interesting twist is that the authors went further to probe two little-noticed ABA functions using AA1. Higher ABA levels were known to associate with senescing vegetative tissues and ripening fruits, although the significance of these results had not been clear. Ye et al. demonstrated that AA1 can suspend, in a dose-dependent manner, the progress of senescence in leaves and ABA-induced tomato ripening. Why is the above an important development? Permanent adaptation requires the plant to optimize the trade-off between H 2 O and CO 2 for photosynthesis (Raschke, 1976). In simplest terms, while closed stomates help to retain H 2 O in plant tissues, they also tend to keep CO 2 out. Many drought-hardy plant species compensate, for example, by recycling malate as the carbon source (Crassulacean acid metabolism). As this is not the case for most crops, ABA antagonists could become decisive tools to redress this trade deficit in CO 2 .
eLife, 2016
Despite being composed of immobile cells, plants reorient along directional stimuli. The hormone ... more Despite being composed of immobile cells, plants reorient along directional stimuli. The hormone auxin is redistributed in stimulated organs leading to differential growth and bending. Auxin application triggers rapid cell wall acidification and elongation of aerial organs of plants, but the molecular players mediating these effects are still controversial. Here we use genetically-encoded pH and auxin signaling sensors, pharmacological and genetic manipulations available for Arabidopsis etiolated hypocotyls to clarify how auxin is perceived and the downstream growth executed. We show that auxin-induced acidification occurs by local activation of H+-ATPases, which in the context of gravity response is restricted to the lower organ side. This auxin-stimulated acidification and growth require TIR1/AFB-Aux/IAA nuclear auxin perception. In addition, auxin-induced gene transcription and specifically SAUR proteins are crucial downstream mediators of this growth. Our study provides strong e...
Symposia of the Society For Experimental Biology, Feb 1, 1998
The semi-dominant abi1-1 mutation of Arabidopsis interferes with multiple aspects of abscisic aci... more The semi-dominant abi1-1 mutation of Arabidopsis interferes with multiple aspects of abscisic acid signal transduction resulting in reduced seed dormancy and sensitivity of root growth in ABA. Furthermore, the mutant transpires excessively as a result of abnormal stomatal regulation leading to a wilty phenotype. The ABI1 gene has been cloned. The carboxyl-terminal domain of the predicted ABI1 protein is related to the 2C class of serine-threonine phosphatases while no overt homology was found in the extended amino terminus. A combination of in vitro assays and yeast mutant complementation studies confirmed that ABI1 is a functional protein phosphatase 2C. The abi1-1 mutation converts the amino acid glycine180 to aspartic acid, and in the above test systems, causes a partial loss of the phosphatase activity. In transgenic Nicotiana benthamiana guard cells, the abi1-1 gene causes a reduction in the background current of the outward-rectifying potassium channels, and also in the abscisic acid-sensitivity of both the outward- and the inward-rectifying potassium channels in the plasma membrane. However, normal sensitivity of both potassium channels to, and stomatal closure in, abscisic acid was recovered in the presence of H7 and staurosporine, both broad-range protein kinase antagonists. These results suggest the aberrant potassium channel behavior as a major consequence of abi1-1 action and implicate ABI1 as part of a phosphatase/kinase pathway that modulates the sensitivity of guard-cell potassium channels to abscisic acid-evoked signal cascades.
Methods in Molecular Biology, Feb 1, 1998
30 Cloning Genes of Arabidopsis thaliana by Chromosome Walking Jeffrey Leung and Jerome Giraudat ... more 30 Cloning Genes of Arabidopsis thaliana by Chromosome Walking Jeffrey Leung and Jerome Giraudat 1. Introduction Chromosome walking is a versatile ... CIC* 420 1152 YAC4 (Columbia) 17 Yupc 250 2300 YAC4 (?) 16 EG1 160 2300 YAC41 (Columbia) 14 abil 120 2100 ...
Molecular Plant, 2016
Plants rely on a diverse set of small-molecule hormones to regulate every aspect of their biologi... more Plants rely on a diverse set of small-molecule hormones to regulate every aspect of their biological processes including development, growth, and adaptation. Since the discovery of the first plant hormone, auxin, hormones have always been at the frontier of plant biology. Although the physiological functions of most plant hormones have been studied for decades, the last 15-20 years have seen dramatic progress in our understanding of the molecular mechanisms of hormone actions. The publication of the whole-genome sequences of the model systems of Arabidopsis and rice, together with the advent of multidisciplinary approaches, has opened the door to successful experimentation on plant hormone actions. To discuss the latest advances and future frontiers in hormone biology, almost 10 years ago, a group of young Chinese talent, mainly recruited overseas scientists, organized the 286th Xiangshan Science Conference on Plant Hormones and Green Revolution on October 18-20, 2006, in Beijing, China. One of the fruitful achievements of this milestone meeting was a consensus that Chinese plant biologists should carry out interdisciplinary cooperation and integrated studies on the molecular mechanisms of hormone actions.
Molecular plant, Jan 13, 2015
SnRK2 kinases, PP2C phosphatases and the PYR/PYL/RCAR receptors constitute the core abscisic acid... more SnRK2 kinases, PP2C phosphatases and the PYR/PYL/RCAR receptors constitute the core abscisic acid (ABA) signaling module that is thought to contain all of the intrinsic properties to self-regulate the hormone signal output. Here we identify Casein Kinase (CK)2 as a novel negative regulator of SnRK2. CK2 phosphorylates a cluster of conserved serines at the ABA box of SnRK2, increasing its binding to PP2C and triggering protein degradation. Consequently, CK2 action has implications on SnRK2 protein levels, as well as kinase activity and its response to abiotic stimuli.
Hedden/Plant, 2006
Marion-Poll, A. and Leung, J.(2007) Abscisic Acid Synthesis, Metabolism and Signal Transduction, ... more Marion-Poll, A. and Leung, J.(2007) Abscisic Acid Synthesis, Metabolism and Signal Transduction, in Annual Plant Reviews Volume 24: Plant Hormone Signaling (eds P. Hedden and SG Thomas), Blackwell Publishing Ltd, Oxford, UK. doi: 10.1002/ ...
Advances in Botanical Research, 2011
ABSTRACT Drought tolerance actually embodies several protective mechanisms deployed by plants com... more ABSTRACT Drought tolerance actually embodies several protective mechanisms deployed by plants commensurate with the stress severity and duration. Against mild drought, one of the most rapid defensive measures is the closing of the stomatal pore, caused by ...
Science Signaling, 2011
The soluble receptors of abscisic acid (ABA) have been identified in Arabidopsis thaliana. The 14... more The soluble receptors of abscisic acid (ABA) have been identified in Arabidopsis thaliana. The 14 proteins in this family, bearing the double name of PYRABACTIN RESISTANCE/PYRABACTIN-LIKE (PYR/PYL) or REGULATORY COMPONENTS OF ABA RECEPTOR (RCAR) (collectively referred to as PYR/PYL/RCAR), contain between 150 and 200 amino acids with homology to the steroidogenic acute regulatory-related lipid transfer (START) protein. Structural studies of these receptors have provided rich insights into the early mechanisms of ABA signaling. The binding of ABA to PYR/PYL/RCAR triggers the pathway by inducing structural changes in the receptors that allows them to sequester members of the clade A negative regulating protein phosphatase 2Cs (PP2Cs). This liberates the class III ABA-activated Snf1-related kinases (SnRK2s) to phosphorylate various targets. In guard cells, a specific SnRK2, OPEN STOMATA 1 (OST), stimulates H(2)O(2) production by NADPH oxidase respiratory burst oxidase protein F and inhibits potassium ion influx by the inward-rectifying channel KAT1. OST1, the kinase CPK23, the calcium-dependent kinase CPK21, and the counteracting PP2Cs modulate the slow anion channel SLAC1, a pathway that contributes to stomatal responses to diverse stimuli, including ABA and carbon dioxide. A minimal ABA response pathway that leads to activation of the SLAC1 homolog, SLAH3, and presumably stomatal closure has been reconstituted in vitro. The identification of the soluble receptors and core components of the ABA signaling pathway provides promising targets for crop design with higher resilience to water deficit while maintaining biomass.
Plant Science, 2006
The Arabidopsis mitogen-activated kinase MPK6 transmits a diversity of stress signals. However, m... more The Arabidopsis mitogen-activated kinase MPK6 transmits a diversity of stress signals. However, much less is known about resetting mechanisms subsequent to the stress response. We show that MPK6 is a potential target of abscisic acid-insensitive 1 (ABI1), a protein phosphatase 2C that acts as a key element in attenuating abscisic acid (ABA)-dependent stress signaling. MPK6 can bind to ABI1 in vitro and in yeast, and that a complex containing these two proteins can be co-precipitated from transfected Arabidopsis cells. In whole plants, MPK6 is hyper-reactive to osmotic stress in mutants compromised in ABI1 activity, but not in its closest functional homolog ABI2. Moreover, conditional expression of a dominant-negative form of mpk6 renders plants hypersensitive to ABA. MPK6 enhances the synthesis of ethylene [1]. ABI1 may therefore down modulate ethylene as part of the resetting mechanism after stress.
Plos One, 2013
The Arabidopsis kinase OPEN STOMATA 1 (OST1) plays a key role in regulating drought stress signal... more The Arabidopsis kinase OPEN STOMATA 1 (OST1) plays a key role in regulating drought stress signalling, particularly stomatal closure. We have identified and investigated the functions of the OST1 ortholog in Z. mays (ZmOST1). Ectopic expression of ZmOST1 in the Arabidopsis ost1 mutant restores the stomatal closure phenotype in response to drought. Furthermore, we have identified the transcription factor, ZmSNAC1, which is directly phosphorylated by ZmOST1 with implications on its localization and protein stability. Interestingly, ZmSNAC1 binds to the ABA-box of ZmOST1, which is conserved in SnRK2s activated by ABA and is part of the contact site for the negative-regulating clade A PP2C phosphatases. Taken together, our results indicate that ZmSNAC1 is a substrate of ZmOST1 and delineate a novel osmotic stress transcriptional pathway in maize.
The Plant Journal, 2014
Faced with declining soil-water potential, plants synthesize abscisic acid (ABA), which then trig... more Faced with declining soil-water potential, plants synthesize abscisic acid (ABA), which then triggers stomatal closure to conserve tissue moisture. Closed stomates, however, also create several physiological dilemmas. Among these, the large CO2 influx required for net photosynthesis will be disrupted. Depleting CO2 in the plant will in turn bias stomatal opening by suppressing ABA sensitivity, which then aggravates transpiration further. We have investigated the molecular basis of how C3 plants resolve this H2 O-CO2 conflicting priority created by stomatal closure. Here, we have identified in Arabidopsis thaliana an early drought-induced spermidine spermine-N(1) -acetyltransferase homolog, which can slow ABA-mediated stomatal closure. Evidence from genetic, biochemical and physiological analyses has revealed that this protein does so by acetylating the metabolite 1,3-diaminopropane (DAP), thereby turning on the latter's intrinsic activity. Acetylated DAP triggers plasma membrane electrical and ion transport properties in an opposite way to those by ABA. Thus in adapting to low soil-water availability, acetyl-DAP could refrain stomates from complete closure to sustain CO2 diffusion to photosynthetic tissues.
Abscisic acid (ABA) mediates seed maturation and adaptive responses t o environmental stress. In ... more Abscisic acid (ABA) mediates seed maturation and adaptive responses t o environmental stress. In Arabidopsis, the ABA-INSENSITIVEl (ABll) protein phosphatase 2C is required for proper ABA responsiveness both in seeds and in vegetative tissues. To determine whether the lack of recessive alleles at the corresponding locus could be explained by the existence of redundant genes, we initiated a search for ABl7 homologs. One such homolog turned out t o be the A612 locus, whose abi2-7 mutation was previously known t o decrease ABA sensitivity. Whereas abi7-7 is (semi)dominant, abi2-7 has been described as recessive and maternally controlled at the germination stage. Unexpectedly, the sequence of the abi2-7 mutation showed that it converts Gly-168 t o Asp, which is precisely the same amino acid substitution found in abi7-7 and at the coincidental position within the A B l l phosphatase domain (Gly-180 t o Asp). In vitro assays and functional complementation studies in yeast confirmed that the AB12 protein is an active protein phosphatase 2C and that the abi2-7 mutation reduced phosphatase activity as well as affinity t o Mg2+. Although a number of differences between the two mutants in adaptive responses t o stress have been reported, quantitative comparisons of other major phenotypes showed that the effects of both abi7-7 and abi2-7 on these processes are nearly indistinguishable. Thus, the homologous ABll and AB12 phosphatases appear t o assume partially redundant functions in ABA signaling, which may provide a mechanism t o maintain informational homeostasis.
European Journal of Biochemistry, 1996
Mutations at the ABIl (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause... more Mutations at the ABIl (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause a reduction in sensitivity to the plant hormone abscisic acid. The sequence of ABZl predicts a protein composed of an N-terminal domain that contains motifs for an EF-hand Caz+-binding site, and a Cterminal domain with similarities to protein serinekhreonine phosphatases 2C. We report here two sets of experimental evidence that indicate that ABIl has typical protein phosphatase 2C activity. First, expression of the ABIl C-terminal domain partially complemented the temperature-sensitive growth defect of a Saccharomyces cerevisiae protein phosphatase 2C mutant. Second, recombinant proteins that contained the ABIl C-terminal domain displayed in vitro phosphatase activity towards 'ZP-labelled casein, and this activity displayed Mg2+ or Mn'+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C. Characterisation of recombinant proteins that contained various portions of ABIl indicated that the putative EF-hand motif is unlikely to mediate Caz+ regulation of the ABIl phosphatase activity at physiological CaZ+ concentrations, and may represent an EF-hand analogue rather than an EF-hand homologue. The abil-l mutation appeared to cause significant reduction in the phosphatase activity of ABII. These results are discussed in relation to the dominant phenotype of abil-1 over the wild-type allele in plants, and to the possible role of ABIl in abscisic acid signalling.
Biologie aujourd'hui, 2012
The combined daily consumption of fresh water ranges from 200 to 700 liters per capita per day in... more The combined daily consumption of fresh water ranges from 200 to 700 liters per capita per day in most developed countries, with about 70% being used for agricultural needs. Unlike other resources such as the different forms of energy, water has no other alternatives. With the looming prospect of global water crisis, the recent laudable success in deciphering the early steps in the signal transduction of the "stress hormone" abscisic acid (ABA) has ignited hopes that crops can be engineered with the capacity to maintain productivity while requiring less water input. Although ABA was first discovered in plants, it has resurfaced in the human brain (and many other non-plant organisms : sea sponge, some parasites, hydra to name a few), suggesting that its existence may be widespread. In humans, more amazingly, ABA has shown anti-inflammatory and antiviral properties. Even its receptors and key signaling intermediates have homologs in the human genome suggesting that evolution...
The Plant Journal, 1997
The influence of the plant water-stress hormone abscisic acid (ABA) on anion channel activity and... more The influence of the plant water-stress hormone abscisic acid (ABA) on anion channel activity and its interaction with protein kinase and phosphatase antagonists was examined in stomatal guard cells of wild-type Nicotiana benthamiana L. and of transgenic plants expressing the dominant-negative (mutant) Arabidopsis abi1-1 protein phosphatase. Intact guard cells were impaled with double-barrelled micro-electrodes and membrane current was recorded under voltage clamp in the presence of 15 mM CsCl and 15 mM tetraethylammonium chloride (TEA-Cl) to eliminate K+ channel currents. Under these conditions, the free-running voltage was situated close to 0 mV (+9 +/- 6 mV, n = 18) and the membrane under voltage clamp was dominated by anion channel current (ICl) as indicated from tall current reversal near the expected chloride equilibrium potential, current sensitivity to the anion channel blockers 9-anthracene carboxylic acid and niflumic acid, and by its voltage-dependent kinetics. Pronounced activation of ICl was recorded on stepping from a conditioning voltage of -250 mV to voltages between -30 and +50 mV, and the current deactivated with a voltage-dependent halftime at more negative voltages (tau approximately equal to 0.3 sec at -150 mV). Challenge with 20 microM ABA increased the steady-state current conductance, gCl, near 0 mV by 1.2- to 2.6-fold and at -150 mV by 4.5- to sixfold with a time constant of 40 +/- 4 sec, and it slowed ICl deactivation as much as fourfold at voltages near -50 mV, introducing two additional voltage-sensitive kinetic components to these current relaxations. Neither the steady-state and kinetic characteristics of ICl nor its sensitivity to ABA were influenced by H7 or staurosporine, both broad-range protein kinase antagonists. However, the protein phosphatase 1/2A antagonist calyculin A mimicked the effects of ABA on gCl and current relaxations on its own and exhibited a synergistic interaction with ABA, enhancing ICl sensitivity to ABA three- to four-fold. Quantitatively similar current characteristics were recorded from guard cells of abi1-1 transgenic N. benthamiana, indicating that the abi1-1 protein phosphatase does not influence the anion current or its response to ABA directly. These results demonstrate that ABA stimulates ICl and modulates its voltage sensitivity. Furthermore, they show that ABA promotes ICl, either by introducing additional long-lived states of the channel or by activating a second anion channel with similar permeation characteristics but with a very long dwell time in the open state. Overall, the data are broadly consistent with the view that ABA action engenders coordinate control of ICl together with guard cell K+ channels to effect solute loss and stomatal closure.
The Plant Journal, 2002
In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure... more In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure of the stomatal pores. This process is vital for plants to conserve water by reducing transpirational water loss. Moreover, recent studies have demonstrated the advantages of the Arabidopsis stomatal guard cell for combining genetic, molecular and biophysical approaches to characterise ABA action. However, genetic dissection of stomatal regulation has been limited by the dif®culty of identifying a reliable phenotype for mutant screening. Leaf temperature can be used as an indicator to detect mutants with altered stomatal control, since transpiration causes leaf cooling. In this study, we optimised experimental conditions under which individual Arabidopsis plants with altered stomatal responses to drought can be identi®ed by infrared thermography. These conditions were then used to perform a pilot screen for mutants that displayed a reduced ability to close their stomata and hence appeared colder than the wild type. Some of the mutants recovered were de®cient in ABA accumulation, and corresponded to alleles of the ABA biosynthesis loci ABA1, ABA2 and ABA3. Interestingly, two of these novel aba2 alleles were able to intragenically complement the aba2±1 mutation. The remaining mutants showed reduced ABA responsiveness in guard cells. In addition to the previously known abi1±1 mutation, we isolated mutations at two novel loci designated as OST1 (OPEN STOMATA 1) and OST2. Remarkably, ost1 and ost2 represent, to our knowledge, the ®rst Arabidopsis mutations altering ABA responsiveness in stomata and not in seeds.
Frontiers in Plant Science
Epigenetics refers to the mode of inheritance independent of mutational changes in the DNA. Early... more Epigenetics refers to the mode of inheritance independent of mutational changes in the DNA. Early evidence has revealed methylation, acetylation, and phosphorylation of histones, as well as methylation of DNA as part of the underlying mechanisms. The recent awareness that many human diseases have in fact an epigenetic basis, due to unbalanced diets, has led to a resurgence of interest in how epigenetics might be connected with, or even controlled by, metabolism. The Next-Generation genomic technologies have now unleashed torrents of results exposing a wondrous array of metabolites that are covalently attached to selective sites on histones, DNA and RNA. Metabolites are often cofactors or targets of chromatin-modifying enzymes. Many metabolites themselves can be acetylated or methylated. This indicates that the acetylome and methylome can actually be deep and pervasive networks to ensure the nuclear activities are coordinated with the metabolic status of the cell. The discovery of novel histone marks also raises the question on the types of pathways by which their corresponding metabolites are replenished, how they are corralled to the specific histone residues and how they are recognized. Further, atypical cytosines and uracil have also been found in eukaryotic genomes. Although these new and extensive connections between metabolism and epigenetics have been established mostly in animal models, parallels must exist in plants, inasmuch as many of the basic components of chromatin and its modifying enzymes are conserved. Plants are chemical factories constantly responding to stress. Plants, therefore, should lend themselves readily for identifying new endogenous metabolites that are also modulators of nuclear activities in adapting to stress.
Plant physiology, 2017
Changing from unsustainable to renewable agriculture requires boosting water-use efficiency in cr... more Changing from unsustainable to renewable agriculture requires boosting water-use efficiency in crops. Because abscisic acid (ABA) reinforces a plant's capacity to withstand drought, the mode of action of this hormone has thus long attracted biophysicists, ecophysiologists, geneticists, and molecular biologists alike. In Arabidopsis (Arabidopsis thaliana), 14 STARTdomain proteins compose the family of cytosolic ABA receptors (Ma et al., 2009; Park et al., 2009). One founding mutant, PYRABACTIN RESISTANCE1 (PYR1), is in fact a namesake based on a genetic screen for seeds that can germinate in the synthetic ABA agonist pyrabactin (Park et al., 2009). An analog, quinabactin, was later found to activate strongly four ABA receptors (PRY1, PYL1-PYL3), resulting in seed germination inhibition and stomatal closure. Several plant species treated with this compound did improve water-use efficiency (Okamoto et al., 2013), hinting at its potential in agriculture. In this issue, Ye et al. (2017) identified and characterized in detail ABA ANTAGONIST1 (AA1) by screening for chemicals that can reverse the inhibitory effect of ABA on Arabidopsis seed germination. AA1 can oppose all known elementary ABA responses tested, ranging from stomatal movements to expression of reporter genes. Also, among known antagonists, AA1 can block all ABA receptors, at least by bonding with some of the same amino acid residues as ABA. An interesting twist is that the authors went further to probe two little-noticed ABA functions using AA1. Higher ABA levels were known to associate with senescing vegetative tissues and ripening fruits, although the significance of these results had not been clear. Ye et al. demonstrated that AA1 can suspend, in a dose-dependent manner, the progress of senescence in leaves and ABA-induced tomato ripening. Why is the above an important development? Permanent adaptation requires the plant to optimize the trade-off between H 2 O and CO 2 for photosynthesis (Raschke, 1976). In simplest terms, while closed stomates help to retain H 2 O in plant tissues, they also tend to keep CO 2 out. Many drought-hardy plant species compensate, for example, by recycling malate as the carbon source (Crassulacean acid metabolism). As this is not the case for most crops, ABA antagonists could become decisive tools to redress this trade deficit in CO 2 .
eLife, 2016
Despite being composed of immobile cells, plants reorient along directional stimuli. The hormone ... more Despite being composed of immobile cells, plants reorient along directional stimuli. The hormone auxin is redistributed in stimulated organs leading to differential growth and bending. Auxin application triggers rapid cell wall acidification and elongation of aerial organs of plants, but the molecular players mediating these effects are still controversial. Here we use genetically-encoded pH and auxin signaling sensors, pharmacological and genetic manipulations available for Arabidopsis etiolated hypocotyls to clarify how auxin is perceived and the downstream growth executed. We show that auxin-induced acidification occurs by local activation of H+-ATPases, which in the context of gravity response is restricted to the lower organ side. This auxin-stimulated acidification and growth require TIR1/AFB-Aux/IAA nuclear auxin perception. In addition, auxin-induced gene transcription and specifically SAUR proteins are crucial downstream mediators of this growth. Our study provides strong e...
Symposia of the Society For Experimental Biology, Feb 1, 1998
The semi-dominant abi1-1 mutation of Arabidopsis interferes with multiple aspects of abscisic aci... more The semi-dominant abi1-1 mutation of Arabidopsis interferes with multiple aspects of abscisic acid signal transduction resulting in reduced seed dormancy and sensitivity of root growth in ABA. Furthermore, the mutant transpires excessively as a result of abnormal stomatal regulation leading to a wilty phenotype. The ABI1 gene has been cloned. The carboxyl-terminal domain of the predicted ABI1 protein is related to the 2C class of serine-threonine phosphatases while no overt homology was found in the extended amino terminus. A combination of in vitro assays and yeast mutant complementation studies confirmed that ABI1 is a functional protein phosphatase 2C. The abi1-1 mutation converts the amino acid glycine180 to aspartic acid, and in the above test systems, causes a partial loss of the phosphatase activity. In transgenic Nicotiana benthamiana guard cells, the abi1-1 gene causes a reduction in the background current of the outward-rectifying potassium channels, and also in the abscisic acid-sensitivity of both the outward- and the inward-rectifying potassium channels in the plasma membrane. However, normal sensitivity of both potassium channels to, and stomatal closure in, abscisic acid was recovered in the presence of H7 and staurosporine, both broad-range protein kinase antagonists. These results suggest the aberrant potassium channel behavior as a major consequence of abi1-1 action and implicate ABI1 as part of a phosphatase/kinase pathway that modulates the sensitivity of guard-cell potassium channels to abscisic acid-evoked signal cascades.
Methods in Molecular Biology, Feb 1, 1998
30 Cloning Genes of Arabidopsis thaliana by Chromosome Walking Jeffrey Leung and Jerome Giraudat ... more 30 Cloning Genes of Arabidopsis thaliana by Chromosome Walking Jeffrey Leung and Jerome Giraudat 1. Introduction Chromosome walking is a versatile ... CIC* 420 1152 YAC4 (Columbia) 17 Yupc 250 2300 YAC4 (?) 16 EG1 160 2300 YAC41 (Columbia) 14 abil 120 2100 ...
Molecular Plant, 2016
Plants rely on a diverse set of small-molecule hormones to regulate every aspect of their biologi... more Plants rely on a diverse set of small-molecule hormones to regulate every aspect of their biological processes including development, growth, and adaptation. Since the discovery of the first plant hormone, auxin, hormones have always been at the frontier of plant biology. Although the physiological functions of most plant hormones have been studied for decades, the last 15-20 years have seen dramatic progress in our understanding of the molecular mechanisms of hormone actions. The publication of the whole-genome sequences of the model systems of Arabidopsis and rice, together with the advent of multidisciplinary approaches, has opened the door to successful experimentation on plant hormone actions. To discuss the latest advances and future frontiers in hormone biology, almost 10 years ago, a group of young Chinese talent, mainly recruited overseas scientists, organized the 286th Xiangshan Science Conference on Plant Hormones and Green Revolution on October 18-20, 2006, in Beijing, China. One of the fruitful achievements of this milestone meeting was a consensus that Chinese plant biologists should carry out interdisciplinary cooperation and integrated studies on the molecular mechanisms of hormone actions.
Molecular plant, Jan 13, 2015
SnRK2 kinases, PP2C phosphatases and the PYR/PYL/RCAR receptors constitute the core abscisic acid... more SnRK2 kinases, PP2C phosphatases and the PYR/PYL/RCAR receptors constitute the core abscisic acid (ABA) signaling module that is thought to contain all of the intrinsic properties to self-regulate the hormone signal output. Here we identify Casein Kinase (CK)2 as a novel negative regulator of SnRK2. CK2 phosphorylates a cluster of conserved serines at the ABA box of SnRK2, increasing its binding to PP2C and triggering protein degradation. Consequently, CK2 action has implications on SnRK2 protein levels, as well as kinase activity and its response to abiotic stimuli.
Hedden/Plant, 2006
Marion-Poll, A. and Leung, J.(2007) Abscisic Acid Synthesis, Metabolism and Signal Transduction, ... more Marion-Poll, A. and Leung, J.(2007) Abscisic Acid Synthesis, Metabolism and Signal Transduction, in Annual Plant Reviews Volume 24: Plant Hormone Signaling (eds P. Hedden and SG Thomas), Blackwell Publishing Ltd, Oxford, UK. doi: 10.1002/ ...
Advances in Botanical Research, 2011
ABSTRACT Drought tolerance actually embodies several protective mechanisms deployed by plants com... more ABSTRACT Drought tolerance actually embodies several protective mechanisms deployed by plants commensurate with the stress severity and duration. Against mild drought, one of the most rapid defensive measures is the closing of the stomatal pore, caused by ...
Science Signaling, 2011
The soluble receptors of abscisic acid (ABA) have been identified in Arabidopsis thaliana. The 14... more The soluble receptors of abscisic acid (ABA) have been identified in Arabidopsis thaliana. The 14 proteins in this family, bearing the double name of PYRABACTIN RESISTANCE/PYRABACTIN-LIKE (PYR/PYL) or REGULATORY COMPONENTS OF ABA RECEPTOR (RCAR) (collectively referred to as PYR/PYL/RCAR), contain between 150 and 200 amino acids with homology to the steroidogenic acute regulatory-related lipid transfer (START) protein. Structural studies of these receptors have provided rich insights into the early mechanisms of ABA signaling. The binding of ABA to PYR/PYL/RCAR triggers the pathway by inducing structural changes in the receptors that allows them to sequester members of the clade A negative regulating protein phosphatase 2Cs (PP2Cs). This liberates the class III ABA-activated Snf1-related kinases (SnRK2s) to phosphorylate various targets. In guard cells, a specific SnRK2, OPEN STOMATA 1 (OST), stimulates H(2)O(2) production by NADPH oxidase respiratory burst oxidase protein F and inhibits potassium ion influx by the inward-rectifying channel KAT1. OST1, the kinase CPK23, the calcium-dependent kinase CPK21, and the counteracting PP2Cs modulate the slow anion channel SLAC1, a pathway that contributes to stomatal responses to diverse stimuli, including ABA and carbon dioxide. A minimal ABA response pathway that leads to activation of the SLAC1 homolog, SLAH3, and presumably stomatal closure has been reconstituted in vitro. The identification of the soluble receptors and core components of the ABA signaling pathway provides promising targets for crop design with higher resilience to water deficit while maintaining biomass.
Plant Science, 2006
The Arabidopsis mitogen-activated kinase MPK6 transmits a diversity of stress signals. However, m... more The Arabidopsis mitogen-activated kinase MPK6 transmits a diversity of stress signals. However, much less is known about resetting mechanisms subsequent to the stress response. We show that MPK6 is a potential target of abscisic acid-insensitive 1 (ABI1), a protein phosphatase 2C that acts as a key element in attenuating abscisic acid (ABA)-dependent stress signaling. MPK6 can bind to ABI1 in vitro and in yeast, and that a complex containing these two proteins can be co-precipitated from transfected Arabidopsis cells. In whole plants, MPK6 is hyper-reactive to osmotic stress in mutants compromised in ABI1 activity, but not in its closest functional homolog ABI2. Moreover, conditional expression of a dominant-negative form of mpk6 renders plants hypersensitive to ABA. MPK6 enhances the synthesis of ethylene [1]. ABI1 may therefore down modulate ethylene as part of the resetting mechanism after stress.
Plos One, 2013
The Arabidopsis kinase OPEN STOMATA 1 (OST1) plays a key role in regulating drought stress signal... more The Arabidopsis kinase OPEN STOMATA 1 (OST1) plays a key role in regulating drought stress signalling, particularly stomatal closure. We have identified and investigated the functions of the OST1 ortholog in Z. mays (ZmOST1). Ectopic expression of ZmOST1 in the Arabidopsis ost1 mutant restores the stomatal closure phenotype in response to drought. Furthermore, we have identified the transcription factor, ZmSNAC1, which is directly phosphorylated by ZmOST1 with implications on its localization and protein stability. Interestingly, ZmSNAC1 binds to the ABA-box of ZmOST1, which is conserved in SnRK2s activated by ABA and is part of the contact site for the negative-regulating clade A PP2C phosphatases. Taken together, our results indicate that ZmSNAC1 is a substrate of ZmOST1 and delineate a novel osmotic stress transcriptional pathway in maize.
The Plant Journal, 2014
Faced with declining soil-water potential, plants synthesize abscisic acid (ABA), which then trig... more Faced with declining soil-water potential, plants synthesize abscisic acid (ABA), which then triggers stomatal closure to conserve tissue moisture. Closed stomates, however, also create several physiological dilemmas. Among these, the large CO2 influx required for net photosynthesis will be disrupted. Depleting CO2 in the plant will in turn bias stomatal opening by suppressing ABA sensitivity, which then aggravates transpiration further. We have investigated the molecular basis of how C3 plants resolve this H2 O-CO2 conflicting priority created by stomatal closure. Here, we have identified in Arabidopsis thaliana an early drought-induced spermidine spermine-N(1) -acetyltransferase homolog, which can slow ABA-mediated stomatal closure. Evidence from genetic, biochemical and physiological analyses has revealed that this protein does so by acetylating the metabolite 1,3-diaminopropane (DAP), thereby turning on the latter's intrinsic activity. Acetylated DAP triggers plasma membrane electrical and ion transport properties in an opposite way to those by ABA. Thus in adapting to low soil-water availability, acetyl-DAP could refrain stomates from complete closure to sustain CO2 diffusion to photosynthetic tissues.
Abscisic acid (ABA) mediates seed maturation and adaptive responses t o environmental stress. In ... more Abscisic acid (ABA) mediates seed maturation and adaptive responses t o environmental stress. In Arabidopsis, the ABA-INSENSITIVEl (ABll) protein phosphatase 2C is required for proper ABA responsiveness both in seeds and in vegetative tissues. To determine whether the lack of recessive alleles at the corresponding locus could be explained by the existence of redundant genes, we initiated a search for ABl7 homologs. One such homolog turned out t o be the A612 locus, whose abi2-7 mutation was previously known t o decrease ABA sensitivity. Whereas abi7-7 is (semi)dominant, abi2-7 has been described as recessive and maternally controlled at the germination stage. Unexpectedly, the sequence of the abi2-7 mutation showed that it converts Gly-168 t o Asp, which is precisely the same amino acid substitution found in abi7-7 and at the coincidental position within the A B l l phosphatase domain (Gly-180 t o Asp). In vitro assays and functional complementation studies in yeast confirmed that the AB12 protein is an active protein phosphatase 2C and that the abi2-7 mutation reduced phosphatase activity as well as affinity t o Mg2+. Although a number of differences between the two mutants in adaptive responses t o stress have been reported, quantitative comparisons of other major phenotypes showed that the effects of both abi7-7 and abi2-7 on these processes are nearly indistinguishable. Thus, the homologous ABll and AB12 phosphatases appear t o assume partially redundant functions in ABA signaling, which may provide a mechanism t o maintain informational homeostasis.
European Journal of Biochemistry, 1996
Mutations at the ABIl (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause... more Mutations at the ABIl (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause a reduction in sensitivity to the plant hormone abscisic acid. The sequence of ABZl predicts a protein composed of an N-terminal domain that contains motifs for an EF-hand Caz+-binding site, and a Cterminal domain with similarities to protein serinekhreonine phosphatases 2C. We report here two sets of experimental evidence that indicate that ABIl has typical protein phosphatase 2C activity. First, expression of the ABIl C-terminal domain partially complemented the temperature-sensitive growth defect of a Saccharomyces cerevisiae protein phosphatase 2C mutant. Second, recombinant proteins that contained the ABIl C-terminal domain displayed in vitro phosphatase activity towards 'ZP-labelled casein, and this activity displayed Mg2+ or Mn'+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C. Characterisation of recombinant proteins that contained various portions of ABIl indicated that the putative EF-hand motif is unlikely to mediate Caz+ regulation of the ABIl phosphatase activity at physiological CaZ+ concentrations, and may represent an EF-hand analogue rather than an EF-hand homologue. The abil-l mutation appeared to cause significant reduction in the phosphatase activity of ABII. These results are discussed in relation to the dominant phenotype of abil-1 over the wild-type allele in plants, and to the possible role of ABIl in abscisic acid signalling.
Biologie aujourd'hui, 2012
The combined daily consumption of fresh water ranges from 200 to 700 liters per capita per day in... more The combined daily consumption of fresh water ranges from 200 to 700 liters per capita per day in most developed countries, with about 70% being used for agricultural needs. Unlike other resources such as the different forms of energy, water has no other alternatives. With the looming prospect of global water crisis, the recent laudable success in deciphering the early steps in the signal transduction of the "stress hormone" abscisic acid (ABA) has ignited hopes that crops can be engineered with the capacity to maintain productivity while requiring less water input. Although ABA was first discovered in plants, it has resurfaced in the human brain (and many other non-plant organisms : sea sponge, some parasites, hydra to name a few), suggesting that its existence may be widespread. In humans, more amazingly, ABA has shown anti-inflammatory and antiviral properties. Even its receptors and key signaling intermediates have homologs in the human genome suggesting that evolution...
The Plant Journal, 1997
The influence of the plant water-stress hormone abscisic acid (ABA) on anion channel activity and... more The influence of the plant water-stress hormone abscisic acid (ABA) on anion channel activity and its interaction with protein kinase and phosphatase antagonists was examined in stomatal guard cells of wild-type Nicotiana benthamiana L. and of transgenic plants expressing the dominant-negative (mutant) Arabidopsis abi1-1 protein phosphatase. Intact guard cells were impaled with double-barrelled micro-electrodes and membrane current was recorded under voltage clamp in the presence of 15 mM CsCl and 15 mM tetraethylammonium chloride (TEA-Cl) to eliminate K+ channel currents. Under these conditions, the free-running voltage was situated close to 0 mV (+9 +/- 6 mV, n = 18) and the membrane under voltage clamp was dominated by anion channel current (ICl) as indicated from tall current reversal near the expected chloride equilibrium potential, current sensitivity to the anion channel blockers 9-anthracene carboxylic acid and niflumic acid, and by its voltage-dependent kinetics. Pronounced activation of ICl was recorded on stepping from a conditioning voltage of -250 mV to voltages between -30 and +50 mV, and the current deactivated with a voltage-dependent halftime at more negative voltages (tau approximately equal to 0.3 sec at -150 mV). Challenge with 20 microM ABA increased the steady-state current conductance, gCl, near 0 mV by 1.2- to 2.6-fold and at -150 mV by 4.5- to sixfold with a time constant of 40 +/- 4 sec, and it slowed ICl deactivation as much as fourfold at voltages near -50 mV, introducing two additional voltage-sensitive kinetic components to these current relaxations. Neither the steady-state and kinetic characteristics of ICl nor its sensitivity to ABA were influenced by H7 or staurosporine, both broad-range protein kinase antagonists. However, the protein phosphatase 1/2A antagonist calyculin A mimicked the effects of ABA on gCl and current relaxations on its own and exhibited a synergistic interaction with ABA, enhancing ICl sensitivity to ABA three- to four-fold. Quantitatively similar current characteristics were recorded from guard cells of abi1-1 transgenic N. benthamiana, indicating that the abi1-1 protein phosphatase does not influence the anion current or its response to ABA directly. These results demonstrate that ABA stimulates ICl and modulates its voltage sensitivity. Furthermore, they show that ABA promotes ICl, either by introducing additional long-lived states of the channel or by activating a second anion channel with similar permeation characteristics but with a very long dwell time in the open state. Overall, the data are broadly consistent with the view that ABA action engenders coordinate control of ICl together with guard cell K+ channels to effect solute loss and stomatal closure.
The Plant Journal, 2002
In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure... more In response to drought, plants synthesise the hormone abscisic acid (ABA), which triggers closure of the stomatal pores. This process is vital for plants to conserve water by reducing transpirational water loss. Moreover, recent studies have demonstrated the advantages of the Arabidopsis stomatal guard cell for combining genetic, molecular and biophysical approaches to characterise ABA action. However, genetic dissection of stomatal regulation has been limited by the dif®culty of identifying a reliable phenotype for mutant screening. Leaf temperature can be used as an indicator to detect mutants with altered stomatal control, since transpiration causes leaf cooling. In this study, we optimised experimental conditions under which individual Arabidopsis plants with altered stomatal responses to drought can be identi®ed by infrared thermography. These conditions were then used to perform a pilot screen for mutants that displayed a reduced ability to close their stomata and hence appeared colder than the wild type. Some of the mutants recovered were de®cient in ABA accumulation, and corresponded to alleles of the ABA biosynthesis loci ABA1, ABA2 and ABA3. Interestingly, two of these novel aba2 alleles were able to intragenically complement the aba2±1 mutation. The remaining mutants showed reduced ABA responsiveness in guard cells. In addition to the previously known abi1±1 mutation, we isolated mutations at two novel loci designated as OST1 (OPEN STOMATA 1) and OST2. Remarkably, ost1 and ost2 represent, to our knowledge, the ®rst Arabidopsis mutations altering ABA responsiveness in stomata and not in seeds.