María Elena Alvarez - Academia.edu (original) (raw)

Papers by María Elena Alvarez

Biochemical Journal, 1990

Complex arrangements of filamentous structures have been isolated from vegetative cells of the fu... more Complex arrangements of filamentous structures have been isolated from vegetative cells of the fungus Neurospora crassa. They were enriched by differential centrifugation and purified by permeation chromatography. The filamentous structures are made up of units of 8-10 nm diameter and were isolated in bundles of up to six to nine units. The main constituent of these structures is a polypeptide with an apparent molecular mass of 59 kDa (P59Nc), which represents 4-5% of the total N. crassa proteins. The filamentous structures are cold-stable and are not affected by high-ionic-strength solutions or by the presence of 10 mM-EDTA or 1% (w/v) Triton X-100; they were disassembled by raising the pH of the solution or by using Tris-based buffers. The disassembled form assembled into structures sedimentable at 105,000 g after dialysis against the isolation buffer. The sedimentable structures were organized in the form of regular aggregates of 42-45 nm polypeptides and reacted weakly with anti...

Frontiers in Plant Science

In plants, the establishment of broad and long-lasting immunity is based on programs that control... more In plants, the establishment of broad and long-lasting immunity is based on programs that control systemic resistance and immunological memory or “priming”. Despite not showing activated defenses, a primed plant induces a more efficient response to recurrent infections. Priming might involve chromatin modifications that allow a faster/stronger activation of defense genes. The Arabidopsis chromatin regulator “Morpheus Molecule 1” (MOM1) has been recently suggested as a priming factor affecting the expression of immune receptor genes. Here, we show that mom1 mutants exacerbate the root growth inhibition response triggered by the key defense priming inducers azelaic acid (AZA), β-aminobutyric acid (BABA) and pipecolic acid (PIP). Conversely, mom1 mutants complemented with a minimal version of MOM1 (miniMOM1 plants) are insensitive. Moreover, miniMOM1 is unable to induce systemic resistance against Pseudomonas sp. in response to these inducers. Importantly, AZA, BABA and PIP treatments ...

Genetics, 1992

P59Nc is a 59-kD polypeptide associated with 8-10-nm diameter cellular filaments in normal Neuros... more P59Nc is a 59-kD polypeptide associated with 8-10-nm diameter cellular filaments in normal Neurospora crassa strains. Abnormally sized and shaped bundles of these structures are present in N. crassa strains carrying mutations at the locus sn (snowflake). By using molecular cloning and restriction fragment length polymorphism (RFLP) segregation analysis strategies we show here that sn is not the genetic locus of P59Nc. Several P59Nc cDNAs were cloned from a N. crassa lambda GT11 library after immunoscreening with specific polyclonal anti-P59Nc antibodies. Additional longer cDNAs were obtained from a N. crassa cDNA-lambda ZAP library. When used as probes in Southern blots of total DNA from wild-type strains, multicent-2 (a multiple mutant strain), and snowflake mutants, the P59Nc cDNAs revealed comparable patterns of hybridizing bands for all of the restriction enzymes tested. Analysis of segregation of BclI and ClaI RFLPs, detected in the genomic region of the P59Nc gene (locus cfp: ...

Molecular Plant-Microbe Interactions®, 2020

This article is part of the Top 10 Unanswered Questions in MPMI invited review series.The past fe... more This article is part of the Top 10 Unanswered Questions in MPMI invited review series.The past few decades have seen major discoveries in the field of molecular plant-microbe interactions. As the result of technological and intellectual advances, we are now able to answer questions at a level of mechanistic detail that we could not have imagined possible 20 years ago. The MPMI Editorial Board felt it was time to take stock and reassess. What big questions remain unanswered? We knew that to identify the fundamental, overarching questions that drive our research, we needed to do this as a community. To reach a diverse audience of people with different backgrounds and perspectives, working in different areas of plant-microbe interactions, we queried the more than 1,400 participants at the 2019 International Congress on Molecular Plant-Microbe Interactions meeting in Glasgow. This group effort resulted in a list of ten, broad-reaching, fundamental questions that influence and inform our...

Plant Physiology, 2020

Arabidopsis (Arabidopsis thaliana) OXIDATION RESISTANCE2 (AtOXR2) is a mitochondrial protein belo... more Arabidopsis (Arabidopsis thaliana) OXIDATION RESISTANCE2 (AtOXR2) is a mitochondrial protein belonging to the Oxidation Resistance (OXR) protein family, recently described in plants. We analyzed the impact of AtOXR2 in Arabidopsis defense mechanisms against the hemibiotrophic bacterial pathogen Pseudomonas syringae. oxr2 mutant plants are more susceptible to infection by the pathogen and, conversely, plants overexpressing AtOXR2 (oeOXR2 plants) show enhanced disease resistance. Resistance in these plants is accompanied by higher expression of WRKY transcription factors, induction of genes involved in salicylic acid (SA) synthesis, accumulation of free SA, and overall activation of the SA signaling pathway. Accordingly, defense phenotypes are dependent on SA synthesis and SA perception pathways, since they are lost in isochorismate synthase1/salicylic acid induction deficient2 and nonexpressor of pathogenesis-related genes1 (npr1) mutant backgrounds. Overexpression of AtOXR2 leads to faster and stronger oxidative burst in response to the bacterial flagellin peptide flg22. Moreover, AtOXR2 affects the nuclear localization of the transcriptional coactivator NPR1, a master regulator of SA signaling. oeOXR2 plants have increased levels of total glutathione and a more oxidized cytosolic redox cellular environment under normal growth conditions. Therefore, AtOXR2 contributes to establishing plant protection against infection by P. syringae acting on the activity of the SA pathway.

The Plant journal : for cell and molecular biology, Jan 20, 2018

Pattern recognition receptors (PRR) and nucleotide-binding leucine-rich repeat proteins (NLR) are... more Pattern recognition receptors (PRR) and nucleotide-binding leucine-rich repeat proteins (NLR) are major components of the plant immune system responsible for pathogen detection. To date, the transcriptional regulation of PRR/NLR genes is poorly understood. Some PRR/NLR genes are affected by epigenetic changes of neighboring transposable elements (TEs) (cis-regulation). We analyzed whether these genes can also respond to changes in the epigenetic marks of distal pericentromeric TEs (trans-regulation). We found that Arabidopsis tissues infected with Pseudomonas syringae pv. tomato (Pst) initially induced the expression of pericentromeric TEs, and then repressed it by RNA-directed DNA methylation (RdDM). The latter response was accompanied by the accumulation of small RNAs (sRNAs) mapping to the TEs. Curiously these sRNAs also mapped to distal PRR/NLR genes, which were controlled by RdDM but remained induced in the infected tissues. Then, we used non-infected mom1 (Morpheus' molecu...

Plant physiology, Jan 21, 2017

The activation of phosphoinositide-specific phospholipase C (PI-PLC) is one of the earliest respo... more The activation of phosphoinositide-specific phospholipase C (PI-PLC) is one of the earliest responses triggered by the recognition of several microbe-associated molecular patterns (MAMPs) in plants. The Arabidopsis PI-PLC gene family is composed of nine members. Previous studies suggested a role for PLC2 in MAMP-triggered immunity (MTI) as it is rapidly phosphorylated in vivo upon treatment with the bacterial MAMP flg22. Here we analyzed the role of PLC2 in plant immunity using an artificial microRNA to silence PLC2 expression in Arabidopsis. We found that PLC2-silenced plants are more susceptible to the type III secretion system-deficient bacterial strain Pseudomonas syringae pv. tomato (Pst) DC3000 hrcC- (Pst DC3000 hrcC-) and to the non-adapted pea powdery mildew Erysiphe pisi. However, PLC2-silenced plants display normal susceptibility to virulent (Pst DC3000) and avirulent P. syringae strains (Pst DC3000 AvrRPM1), conserving typical hypersensitive response (HR) features. In res...

Frontiers in Plant Science, 2015

Plants facing adverse conditions usually alter proline (Pro) metabolism, generating changes that ... more Plants facing adverse conditions usually alter proline (Pro) metabolism, generating changes that help restore the cellular homeostasis. These organisms synthesize Pro from glutamate (Glu) or ornithine (Orn) by two-step reactions that share 1 pyrroline-5-carboxylate (P5C) as intermediate. In the catabolic process, Pro is converted back to Glu using a different pathway that involves Pro dehydrogenase (ProDH), P5C dehydrogenase (P5CDH), and P5C as intermediate. Little is known about the coordination of the catabolic and biosynthetic routes under stress. To address this issue, we analyzed how P5CDH affects the activation of Pro synthesis, in Arabidopsis tissues that increase ProDH activity by transient exposure to exogenous Pro, or infection with Pseudomonas syringae pv. tomato. Wild-type (Col-0) and p5cdh mutant plants subjected to these treatments were used to monitor the Pro, Glu, and Orn levels, as well as the expression of genes from Pro metabolism. Col-0 and p5cdh tissues consecutively activated ProDH and Pro biosynthetic genes under both conditions. However, they manifested a different coordination between these routes. When external Pro supply was interrupted, wild-type leaves degraded Pro to basal levels at which point Pro synthesis, mainly via Glu, became activated. Under the same condition, p5cdh leaves sustained ProDH induction without reducing the Pro content but rather increasing it, apparently by stimulating the Orn pathway. In response to pathogen infection, both genotypes showed similar trends. While Col-0 plants seemed to induce both Pro biosynthetic routes, p5cdh mutant plants may primarily activate the Orn route. Our study contributes to the functional characterization of P5CDH in biotic and abiotic stress conditions, by revealing its capacity to modulate the fate of P5C, and prevalence of Orn or Glu as Pro precursors in tissues that initially consumed Pro.

Plant Signaling & Behavior, 2011

Molecular Plant-Microbe Interactions®, 2006

Plant tissues display major alterations upon the perception of microbial pathogens. Changes of cy... more Plant tissues display major alterations upon the perception of microbial pathogens. Changes of cytoplasmic and apo-plastic components that sense and transduce plant defenses have been extensively characterized. In contrast, less information is available about modifications affecting the plant nuclear genome under these circumstances. Here, we investigated whether the Arabidopsis thaliana DNA methylation status is altered in tissues responding to the attack of Pseudomonas syringae pv. tomato DC3000. We applied amplified fragment length polymorphism analysis to monitor cytosine methylation at anonymous 5′-CCGG-3′ and 5′-GATC-3′ sites in naïve and infected samples. Plant genomic fragments reducing methylation upon infection, including peri/centromeric repeats such as the 180-bp unit, Athila retrotansposon, and a portion of the nuclear insertion of mitochondrial DNA, were isolated and characterized. P. syringae pv. tomato-induced hypomethylation was detected by high-performance liquid c...

Plant Physiology, 2005

Programmed cell death, developmental senescence, and responses to pathogens are linked through co... more Programmed cell death, developmental senescence, and responses to pathogens are linked through complex genetic controls that are influenced by redox regulation. Here we show that the Arabidopsis (Arabidopsis thaliana) low vitamin C mutants, vtc1 and vtc2, which have between 10% and 25% of wild-type ascorbic acid, exhibit microlesions, express pathogenesis-related (PR) proteins, and have enhanced basal resistance against infections caused by Pseudomonas syringae. The mutants have a delayed senescence phenotype with smaller leaf cells than the wild type at maturity. The vtc leaves have more glutathione than the wild type, with higher ratios of reduced glutathione to glutathione disulfide. Expression of green fluorescence protein (GFP) fused to the nonexpressor of PR protein 1 (GFP-NPR1) was used to detect the presence of NPR1 in the nuclei of transformed plants. Fluorescence was observed in the nuclei of 6- to 8-week-old GFP-NPR1 vtc1 plants, but not in the nuclei of transformed GFP-N...

Molecular Plant-Microbe Interactions®, 2004

Accumulation of free L-proline (Pro) is a typical stress response incited by osmotic injuries in ... more Accumulation of free L-proline (Pro) is a typical stress response incited by osmotic injuries in plants and microorganisms. Although the protective role of Pro in osmotic stress is not well understood, it is thought to function as compatible osmolyte or as a scavenger of reactive oxygen species (ROS). Here we show that, in Arabidopsis thaliana, Pro biosynthesis can be activated by incompatible plant—pathogen interactions triggering a hypersensitive response (HR). Pro accumulates in leaf tissues treated with Pseudomonas syringae pv. tomato avirulent strains (avrRpt2 and avrRpm1) but remains unchanged in leaves infected with isogenic virulent bacteria. Incompatible interactions lead to transcriptional activation of AtP5CS2, but not AtP5CS1, encoding the rate limiting enzyme in Pro biosynthesis pyrroline-5-carboxylate synthase (P5CS). AtP5CS2:GUS and AtP5CS2:LUC transgenes were induced inside and around the HR lesions produced by avirulent Pseudomonas spp. in transgenic plants. Pro acc...

Molecular Plant-Microbe Interactions®, 2013

Salicylic acid (SA) is one of the key hormones that orchestrate the pathogen-induced immune respo... more Salicylic acid (SA) is one of the key hormones that orchestrate the pathogen-induced immune response in plants. This response is often characterized by the activation of a local hypersensitive reaction involving programmed cell death, which constrains proliferation of biotrophic pathogens. Here, we report the identification and functional characterization of an SA-induced legume lectin-like protein 1 (SAI-LLP1), which is coded by a gene that belongs to the group of early SA-activated Arabidopsis genes. SAI-LLP1 expression is induced upon inoculation with avirulent strains of Pseudomonas syringae pv. tomato via an SA-dependent mechanism. Constitutive expression of SAI-LLP1 restrains proliferation of P. syringae pv. tomato Avr-Rpm1 and triggers more cell death in inoculated leaves. Cellular and biochemical evidence indicates that SAI-LLP1 is a glycoprotein located primarily at the apoplastic side of the plasma membrane. This work indicates that SAI-LLP1 is involved in resistance to P....

Molecular Plant Pathology, 2010

SUMMARYIn eukaryotic genomes, gene expression and DNA recombination are affected by structural ch... more SUMMARYIn eukaryotic genomes, gene expression and DNA recombination are affected by structural chromatin traits. Chromatin structure is shaped by the activity of enzymes that either introduce covalent modifications in DNA and histone proteins or use energy from ATP to disrupt histone–DNA interactions. The genomic ‘marks’ that are generated by covalent modifications of histones and DNA, or by the deposition of histone variants, are susceptible to being altered in response to stress. Recent evidence has suggested that proteins generating these epigenetic marks play crucial roles in the defence against pathogens. Histone deacetylases are involved in the activation of jasmonic acid‐ and ethylene‐sensitive defence mechanisms. ATP‐dependent chromatin remodellers mediate the constitutive repression of the salicylic acid‐dependent pathway, whereas histone methylation at the WRKY70 gene promoter affects the activation of this pathway. Interestingly, bacterial‐infected tissues show a net redu...

Eukaryotic Cell, 2003

We show that Neurospora crassa has a single histone H1 gene, hH1 , which encodes a typical linker... more We show that Neurospora crassa has a single histone H1 gene, hH1 , which encodes a typical linker histone with highly basic N- and C-terminal tails and a central globular domain. A green fluorescent protein-tagged histone H1 chimeric protein was localized exclusively to nuclei. Mutation of hH1 by repeat-induced point mutation (RIP) did not result in detectable defects in morphology, DNA methylation, mutagen sensitivity, DNA repair, fertility, RIP, chromosome pairing, or chromosome segregation. Nevertheless, hH1 mutants had mycelial elongation rates that were lower than normal on all tested carbon sources. This slow linear growth phenotype, however, was less evident on medium containing ethanol. The pyruvate decarboxylase gene, cfp , was abnormally derepressed in hH1 mutants on ethanol-containing medium. This derepression was also found when an ectopically integrated fusion of the cfp gene promoter to the reporter gene hph was analyzed. Thus, Neurospora histone H1 is required for the...

Current Biology, 1996

Background: Avirulent pathogens elicit a battery of plant defenses, often accompanied by collapse... more Background: Avirulent pathogens elicit a battery of plant defenses, often accompanied by collapse of the challenged cells. In soybean cells, sustained accumulation of H 2 O 2 from an oxidative burst cues localized host cell death. Such hypersensitive cell death appears to be an active process, but little is known about the mechanisms underlying cellular collapse. Results: We show that H 2 O 2 stimulates a rapid influx of Ca 2+ into soybean cells, which activates a physiological cell death program resulting in the generation of large (~50 kb) DNA fragments and cell corpse morphology-including cell shrinkage, plasma membrane blebbing and nuclear condensationcharacteristic of apoptosis. In contrast, H 2 O 2 induction of the cellular protectant gene glutathione S-transferase is Ca 2+-independent. Apoptosis in soybean cells and leaf tissue was induced by avirulent Pseudomonas syringae pv. glycinea but was not observed at comparable stages of the compatible interaction with the isogenic virulent strain, which fails to elicit a hypersensitive response. Apoptosis was also observed at the onset of the hypersensitive response in Arabidopsis leaves inoculated with avirulent P. syringae pv. tomato and in tobacco cells treated with the fungal peptide cryptogein, which is involved in the induction of non-host resistance to Phytophthora cryptogea. Conclusions: These observations establish a signal function for Ca 2+ downstream of the oxidative burst in the activation of a physiological cell death program in soybean cells that is similar to apoptosis in animals. That the characteristic cell corpse morphology is also induced in Arabidopsis and tobacco by different avirulence signals suggests that apoptosis may prove to be a common, but not necessarily ubiquitous, feature of incompatible plant-pathogen interactions. Emerging similarities between facets of hypersensitive disease resistance and the mammalian native immune system indicate that apoptosis is a widespread defence mechanism in eukaryotes.

Cell, 1998

wild-type and salicylic acid-deficient tobacco lines (Vernooij et al., 1994; Pallas et al., 1996)... more wild-type and salicylic acid-deficient tobacco lines (Vernooij et al., 1994; Pallas et al., 1996) indicate that salicylic acid is not an essential mobile signal. One of the earliest events in the HR is a burst of oxidative metabolism leading to the generation of super

Applied and Environmental Microbiology, 2005

Using the genes encoding the 2,4-dinitrotoluene degradation pathway enzymes, the nonpathogenic ps... more Using the genes encoding the 2,4-dinitrotoluene degradation pathway enzymes, the nonpathogenic psychrotolerant rhizobacterium Pseudomonas fluorescens ATCC 17400 was genetically modified for degradation of this priority pollutant. First, a recombinant strain designated MP was constructed by conjugative transfer from Burkholderia sp. strain DNT of the pJS1 megaplasmid, which contains the dnt genes for 2,4-dinitrotoluene degradation. This strain was able to grow on 2,4-dinitrotoluene as the sole source of carbon, nitrogen, and energy at levels equivalent to those of Burkholderia sp. strain DNT. Nevertheless, loss of the 2,4-dinitrotoluene degradative phenotype was observed for strains carrying pJS1. The introduction of dnt genes into the P.fluorescens ATCC 17400 chromosome, using a suicide chromosomal integration Tn 5 -based delivery plasmid system, generated a degrading strain that was stable for a long time, which was designated RE. This strain was able to use 2,4-dinitrotoluene as a...

Molecular plant pathology, Jan 26, 2015

Natural and synthetic elicitors have significantly contributed to the study of plant immunity. Pa... more Natural and synthetic elicitors have significantly contributed to the study of plant immunity. Pathogen-derived proteins and carbohydrates, that bind to immune receptors allowed fine dissection of some defense pathways. Lipids of different nature that act as defense elicitors have also been studied, but their specific effects have been less characterized, and their receptors have not been identified. In animal cells, nanoliposomes of the synthetic cationic lipid 3-tetradecylamino-tert-butyl-N-tetradecylpropionamidine (diC14) activate the TLR4-dependent immune cascade. We here investigated if this lipid induces Arabidopsis defense responses. At the local level, diC14 activated early and late defense gene markers (FRK1, WRKY29, ICS1 and PR1) acting in a dose dependent manner. This lipid induced the salicylic acid (SA)-, but not jasmonic acid (JA)-, dependent pathway and protected plants against Pseudomonas syringae pv. tomato (Pst), but not Botrytis cinerea. diC14 was not toxic for pl...

The Plant Journal, 2022

SUMMARYDNA glycosylases are critical enzymes that recognize small base lesions in DNA and trigger... more SUMMARYDNA glycosylases are critical enzymes that recognize small base lesions in DNA and trigger their repair to preserve genome integrity. The Arabidopsis MBD4‐like (MBD4L) DNA glycosylase improves tolerance to genotoxic stress. This enzyme is encoded by a single gene carrying an exonic intron (exitron) at its 5′ region. Although alternative splicing (AS) of exitrons (protein‐coding cryptic introns within exons) is suspected to increase protein diversity, phenotypes associated to exitron removal or retention are only known for a few genes. Here, we show that AS of the MBD4L exitron determines the generation of two enzyme isoforms with different subnuclear localization. Both isoforms conserve the catalytic domain but are directed to either the nucleoplasm or the nucleolus. Interestingly, heat stress regulates the AS of the MBD4L exitron and increases the relative abundance of the nucleolar variant. This process depends on the splicing factors NTR1 and RS31. Next, we generated trans...