The Arabidopsis ATR1 Myb transcription factor controls indolic glucosinolate homeostasis (original) (raw)
Related papers
2013
In the model cruciferous plant, Arabidopsis thaliana, tryptophan (Trp) is a focal point for growth and defense as it is used for the production of secondary metabolites including the growth hormone indole-3-acetic acid (IAA, or auxin), and two classes of defense compounds: indole glucosinolates (IGs) and camalexin. Trp metabolism in plants is of general importance to agriculture because animals (including humans) cannot synthesize Trp and must obtain it from their diet. Questions remain about the synthesis and regulation of Trp and how it relates to secondary metabolism in Arabidopsis. In this thesis it is shown that IGs are a sink for Trp metabolism because auxotrophic mutants deficient in Trp production are suppressed in combination with the IG-deficient cyp79B2 cyp79B3 mutant and enhanced in combination with IG overproducing mutant, atr1D. vi Because Trp auxotrophic mutants were found to produce IGs, the four predicted Arabidopsis Trp Synthase Beta genes (TSB1, TSB2, TSB3 and TSBt2) were examined for their role in Trp primary and secondary metabolism. It was determined that members of this gene family, while being redundant for enzyme activity, may have unique functions in channeling Trp to different secondary endpoints. tsb1 tsb2 plants display a healthier phenotype and produce lower IG levels than the single tsb1 mutants, in contrast to tsb1 tsbt2 plants, which have elevated IG production and an enhanced auxotrophic phenotype. tsb2 tsbt2 plants are indiscernible from WT. Gene expression in Trp biosynthetic pathway steps, IG biosynthesis genes, and regulatory TFs is dysregulated in these mutants. In a second part of this thesis, transcriptional regulation of IG synthesis was examined with respect to tissue specificity and stress. In collaboration with Judith Bender's laboratory at Brown University, the function of a subfamily of three Myb transcription factors that have been implicated in regulating IG biosynthesis genes was studied. Using combinations of Myb knockout mutants and GUS reporter plants, tissue specific roles for MYB34 and MYB51 in root and shoot tissues, respectively, were found. In addition, roles were discovered for MYB34 in mediating anti-herbivory signals, and for both MYB51 and MYB122 in regulating defense against microbial pathogens. vii
The Plant Journal, 2007
Glucosinolates are a class of plant secondary metabolites that serve as antiherbivore compounds in plant defence. A previously identified Arabidopsis thaliana activation-tagged line, displaying altered levels of secondary metabolites, was shown here to be affected in the content of indolic and aliphatic glucosinolates. The observed chemotype was caused by activation of the R2R3-MYB transcription factor gene HIG1 (HIGH INDOLIC GLUCOSINOLATE 1, also referred to as MYB51). HIG1/MYB51 was shown to activate promoters of indolic glucosinolate biosynthetic genes leading to increased accumulation of indolic glucosinolates. The corresponding loss-of-function mutant hig1-1 contained low levels of glucosinolates. Overexpression of the related transcription factor ATR1/MYB34, which had previously been described as a regulator of indolic glucosinolate and indole-3-acetic acid homeostasis, in the hig1-1 mutant background led to a partial rescue of the mutant chemotype along with a severe high-auxin growth phenotype. Overexpression of MYB122, another close homologue of HIG1/MYB51, did not rescue the hig1-1 chemotype, but caused a high-auxin phenotype and increased levels of indolic glucosinolates in the wild-type. By contrast, overexpression of HIG1/MYB51 resulted in the specific accumulation of indolic glucosinolates without affecting auxin metabolism and plant morphology. Mechanical stimuli such as touch or wounding transiently induced the expression of HIG1/ MYB51 but not of ATR1/MYB34, and HIG1/MYB51 overexpression reduced insect herbivory as revealed by dual-choice assays with the generalist lepidopteran herbivore, Spodoptera exigua. We hypothesize that HIG1/ MYB51 is a regulator of indolic glucosinolate biosynthesis that also controls responses to biotic challenges.
Identification of an Arabidopsis Aminotransferase that Facilitates Tryptophan and Auxin Homeostasis
2015
IAA plays a critical role in regulating numerous aspects of plant growth and development. While there is much genetic support for tryptophan-dependent (Trp-D) IAA synthesis pathways, there is little genetic evidence for tryptophan-independent (Trp-I) IAA synthesis pathways. Using Arabidopsis, we identified two mutant alleles of ISS1 (Indole Severe Sensitive) that display indole-dependent IAA overproduction phenotypes including leaf epinasty and adventitious rooting. Stable isotope labeling showed that iss1, but not WT, uses primarily Trp-I IAA synthesis when grown on indole-supplemented medium. In contrast, both iss1 and WT use primarily Trp-D IAA synthesis when grown on unsupplemented medium. iss1 seedlings produce 8-fold higher levels of IAA when grown on indole and surprisingly have a 174-fold increase in Trp. These findings indicate that the iss1 mutant???s increase in Trp-I IAA synthesis is due to a loss of Trp catabolism. ISS1 was identified as At1g80360, a predicted aromatic ...
The Plant Journal, 2006
Glucosinolates are a group of secondary metabolites that function as defense substances against herbivores and micro-organisms in the plant order Capparales. Indole glucosinolates (IGS), derivatives of tryptophan, may also influence plant growth and development. In Arabidopsis thaliana, indole-3-acetaldoxime (IAOx) produced from tryptophan by the activity of two cytochrome P450 enzymes, CYP79B2 and CYP79B3, serves as a precursor for IGS biosynthesis but is also an intermediate in the biosynthetic pathway of indole-3-acetic acid (IAA). Another cytochrome P450 enzyme, CYP83B1, funnels IAOx into IGS. Although there is increasing information about the genes involved in this biochemical pathway, their regulation is not fully understood. OBP2 has recently been identified as a member of the DNA-binding-with-one-finger (DOF) transcription factors, but its function has not been studied in detail so far. Here we report that OBP2 is expressed in the vasculature of all Arabidopsis organs, including leaves, roots, flower stalks and petals. OBP2 expression is induced in response to a generalist herbivore, Spodoptera littoralis, and by treatment with the plant signalling molecule methyl jasmonate, both of which also trigger IGS accumulation. Constitutive and inducible overexpression of OBP2 activates expression of CYP83B1. In addition, auxin concentration is increased in leaves and seedlings of OBP2 over-expression lines relative to wild-type, and plant size is diminished due to a reduction in cell size. RNA interference-mediated OBP2 blockade leads to reduced expression of CYP83B1. Collectively, these data provide evidence that OBP2 is part of a regulatory network that regulates glucosinolate biosynthesis in Arabidopsis.
Plant Physiology, 2021
Arabidopsis (Arabidopsis thaliana) defenses against herbivores are regulated by the jasmonate (JA) hormonal signaling pathway, which leads to the production of a plethora of defense compounds. Arabidopsis defense compounds include tryptophan-derived metabolites, which limit Arabidopsis infestation by the generalist herbivore two-spotted spider mite, Tetranychus urticae. However, the phytochemicals responsible for Arabidopsis protection against T. urticae are unknown. Here, we used Arabidopsis mutants disrupted in the synthesis of tryptophan-derived secondary metabolites to identify phytochemicals involved in the defense against T. urticae. We show that of the three tryptophan-dependent pathways found in Arabidopsis, the indole glucosinolate (IG) pathway is necessary and sufficient to assure tryptophan-mediated defense against T. urticae. We demonstrate that all three IGs can limit T. urticae herbivory, but that they must be processed by myrosinases to hinder T. urticae oviposition. ...
Genetics, 2015
IAA plays a critical role in regulating numerous aspects of plant growth and development. While there is much genetic support for tryptophan-dependent (Trp-D) IAA synthesis pathways, there is little genetic evidence for tryptophan-independent (Trp-I) IAA synthesis pathways. Using Arabidopsis, we identified two mutant alleles of ISS1 (Indole Severe Sensitive) that display indole-dependent IAA overproduction phenotypes including leaf epinasty and adventitious rooting. Stable isotope labeling showed that iss1, but not WT, uses primarily Trp-I IAA synthesis when grown on indole-supplemented medium. In contrast, both iss1 and WT use primarily Trp-D IAA synthesis when grown on unsupplemented medium. iss1 seedlings produce 8-fold higher levels of IAA when grown on indole and surprisingly have a 174-fold increase in Trp. These findings indicate that the iss1 mutant's increase in Trp-I IAA synthesis is due to a loss of Trp catabolism. ISS1 was identified as At1g80360, a predicted aromati...
Molecular Plant, 2014
The MYB34, MYB51, and MYB122 transcription factors are known to regulate indolic glucosinolate (IG) biosynthesis in Arabidopsis thaliana. To determine the distinct regulatory potential of MYB34, MYB51, and MYB122, the accumulation of IGs in different parts of plants and upon treatment with plant hormones were analyzed in A. thaliana seedlings. It was shown that MYB34, MYB51, and MYB122 act together to control the biosynthesis of I3M in shoots and roots, with MYB34 controlling biosynthesis of IGs mainly in the roots, MYB51 regulating biosynthesis in shoots, and MYB122 having an accessory role in the biosynthesis of IGs. Analysis of glucosinolate levels in seedlings of myb34, myb51, myb122, myb34 myb51 double, and myb34 myb51 myb122 triple knockout mutants grown in the presence of abscisic acid (ABA), salicylic acid (SA), jasmonate (JA), or ethylene (ET) revealed that: (1) MYB51 is the central regulator of IG synthesis upon SA and ET signaling, (2) MYB34 is the key regulator upon ABA and JA signaling, and (3) MYB122 plays only a minor role in JA/ET-induced glucosinolate biosynthesis. The myb34 myb51 myb122 triple mutant is devoid of IGs, indicating that these three MYB factors are indispensable for IG production under standard growth conditions.