Phosphorylation is required for the pathogen defense function of the Arabidopsis PEN3 ABC transporter.

The Arabidopsis PEN3 ABC transporter accumulates at sites of pathogen detection, where it is involved in defense against a number of pathogens. Perception of PAMPs by pattern recognition receptors initiates recruitment of PEN3 and also leads to PEN3 phosphorylation at multiple amino acid residues. Whether PAMP-induced phosphorylation of PEN3 is important for its defense function or focal recruitment has not been addressed. In this study, we evaluated the role of PEN3 phosphorylation in modulating the localization and defense function of the transporter. We report that PEN3 phosphorylation is critical for its function in defense, but dispensable for recruitment to powdery mildew penetration sites. These results indicate that PAMP-induced phosphorylation is likely to regulate the transport activity of PEN3

EDR2 negatively regulates salicylic acid-based defenses and cell death during powdery mildew infections of Arabidopsis thaliana

<p>Abstract</p> <p>Background</p> <p>The hypersensitive necrosis response (HR) of resistant plants to avirulent pathogens is a form of programmed cell death in which the plant sacrifices a few cells under attack, restricting pathogen growth into adjacent healthy tissues. In spite of the importance of this defense response, relatively little is known about the plant components that execute the cell death program or about its regulation in response to pathogen attack.</p> <p>Results</p> <p>We isolated the <it>edr2-6 </it>mutant, an allele of the previously described <it>edr2 </it>mutants. We found that <it>edr2-6 </it>exhibited an exaggerated chlorosis and necrosis response to attack by three pathogens, two powdery mildew and one downy mildew species, but not in response to abiotic stresses or attack by the bacterial leaf speck pathogen. The chlorosis and necrosis did not spread beyond inoculated sites suggesting that EDR2 limits the initiation of cell death rather than its spread. The pathogen-induced chlorosis and necrosis of <it>edr2-6 </it>was correlated with a stimulation of the salicylic acid defense pathway and was suppressed in mutants deficient in salicylic acid signaling. <it>EDR2 </it>encodes a novel protein with a pleckstrin homology and a StAR transfer (START) domain as well as a plant-specific domain of unknown function, DUF1336. The pleckstrin homology domain binds to phosphatidylinositol-4-phosphate <it>in vitro </it>and an EDR2:HA:GFP protein localizes to endoplasmic reticulum, plasma membrane and endosomes.</p> <p>Conclusion</p> <p><it>EDR2 </it>acts as a negative regulator of cell death, specifically the cell death elicited by pathogen attack and mediated by the salicylic acid defense pathway. Phosphatidylinositol-4-phosphate may have a role in limiting cell death via its effect on EDR2. This role in cell death may be indirect, by helping to target EDR2 to the appropriate membrane, or it may play a more direct role.</p

Cellulose-derived oligomers act as damage-associated molecular patterns and trigger defense-like responses

The plant cell wall, often the site of initial encounters between plants and their microbial pathogens, is composed of a complex mixture of cellulose, hemicellulose, and pectin polysaccharides as well as proteins. The concept of damage-associated molecular patterns (DAMPs) was proposed to describe plant elicitors like oligogalacturonides (OGs), which can be derived by the breakdown of the pectin homogalacturon by pectinases. OGs act via many of the same signaling steps as pathogen- or microbe-associated molecular patterns (PAMPs) to elicit defenses and provide protection against pathogens. Given both the complexity of the plant cell wall and the fact that many pathogens secrete a wide range of cell wall-degrading enzymes, we reasoned that the breakdown products of other cell wall polymers may be similarly biologically active as elicitors and may help to reinforce the perception of danger by plant cells. Our results indicate that oligomers derived from cellulose are perceived as signal molecules in Arabidopsis (Arabidopsis thaliana), triggering a signaling cascade that shares some similarities to responses to well-known elicitors such as chitooligomers and OGs. However, in contrast to other known PAMPs/DAMPs, cellobiose stimulates neither detectable reactive oxygen species production nor callose deposition. Confirming our idea that both PAMPs and DAMPs are likely to cooccur at infection sites, cotreatments of cellobiose with flg22 or chitooligomers led to synergistic increases in gene expression. Thus, the perception of cellulose-derived oligomers may participate in cell wall integrity surveillance and represents an additional layer of signaling following plant cell wall breakdown during cell wall remodeling or pathogen attack

Moonlighting Function of Phytochelatin Synthase1 in Extracellular Defense against Fungal Pathogens

13 Pág.Phytochelatin synthase (PCS) is a key component of heavy metal detoxification in plants. PCS catalyzes both the synthesis of the peptide phytochelatin from glutathione and the degradation of glutathione conjugates via peptidase activity. Here, we describe a role for PCS in disease resistance against plant pathogenic fungi. The pen4 mutant, which is allelic to cadmium insensitive1 (cad1/pcs1) mutants, was recovered from a screen for Arabidopsis mutants with reduced resistance to the nonadapted barley fungal pathogen Blumeria graminis f. sp. hordei PCS1, which is found in the cytoplasm of cells of healthy plants, translocates upon pathogen attack and colocalizes with the PEN2 myrosinase on the surface of immobilized mitochondria. pcs1 and pen2 mutant plants exhibit similar metabolic defects in the accumulation of pathogen-inducible indole glucosinolate-derived compounds, suggesting that PEN2 and PCS1 act in the same metabolic pathway. The function of PCS1 in this pathway is independent of phytochelatin synthesis and deglycination of glutathione conjugates, as catalytic-site mutants of PCS1 are still functional in indole glucosinolate metabolism. In uncovering a peptidase-independent function for PCS1, we reveal this enzyme to be a moonlighting protein important for plant responses to both biotic and abiotic stresses.This work was supported by the National Science Foundation and the Carnegie Institution for Science (S.S.), Stanford University (Graduate Fellowship to M.S.), the Max Planck Society (P.S.L.), the Deutsche Forschungsgemeinschaft (DFG; grants SPP1212 to P.S.L., GR 938 to E.G., and LI 1317/2-1 to V.L.), the Spanish Ministry of Economy and Competitiveness (MINECO; grants BIO2015-64077-R and BIO2012-32910 to A.M.), and the Polish National Science Centre (grant 2012/07/E/NZ2/04098 to P.B.).Peer reviewe

YODA MAPK kinase kinase regulates a novel immunity pathway conferring broad-spectrum resistance to pathogens

Plant mitogen-activated protein kinase (MAPK) casca des transduce environmental molecular signals and developmental cues into cellular responses. Among these signals are the pathogen-associated molecular patterns (PAMPs) that upon recognition by plant pattern recognition receptors (PRR), including Receptor-Like Kinases (RLKs), activate MAPK cascades that regulate PAMP-triggered immunity responses (PTI)

ATL9, a RING Zinc Finger Protein with E3 Ubiquitin Ligase Activity Implicated in Chitin- and NADPH Oxidase-Mediated Defense Responses

Pathogen associated molecular patterns (PAMPs) are signals detected by plants that activate basal defenses. One of these PAMPs is chitin, a carbohydrate present in the cell walls of fungi and in insect exoskeletons. Previous work has shown that chitin treatment of Arabidopsis thaliana induced defense-related genes in the absence of a pathogen and that the response was independent of the salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) signaling pathways. One of these genes is ATL9 ( = ATL2G), which encodes a RING zinc-finger like protein. In the current work we demonstrate that ATL9 has E3 ubiquitin ligase activity and is localized to the endoplasmic reticulum. The expression pattern of ATL9 is positively correlated with basal defense responses against Golovinomyces cichoracearum, a biotrophic fungal pathogen. The basal levels of expression and the induction of ATL9 by chitin, in wild type plants, depends on the activity of NADPH oxidases suggesting that chitin-mediated defense response is NADPH oxidase dependent. Although ATL9 expression is not induced by treatment with known defense hormones (SA, JA or ET), full expression in response to chitin is compromised slightly in mutants where ET- or SA-dependent signaling is suppressed. Microarray analysis of the atl9 mutant revealed candidate genes that appear to act downstream of ATL9 in chitin-mediated defenses. These results hint at the complexity of chitin-mediated signaling and the potential interplay between elicitor-mediated signaling, signaling via known defense pathways and the oxidative burst

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

A Mutant of Arabidopsis Thaliana Deficient in Chloroplast Dicarboxylate Transport Activity

176 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.The photorespiratory pathway in C3 plants is comprised of reactions occurring in three organelles, chloroplasts, peroxisomes, and mitochondria. This pathway therefore provides a unique opportunity for studying transport systems and their role in mediating interactions between organelles. This study is concerned with the characterization and physiological analysis of a mutant of Arabidopsis thaliana (L.) Heyn. defective in dicarboxylate transport across the chloroplast envelope. This mutant was recovered in a screen for photorespiratory mutants and exhibits the growth requirement for high CO(,2) (1% CO(,2), balance air) common to such mutants. This growth requirement is inherited as a simple, recessive, nuclear mutation and the locus defined by this mutation has been designated dct (dicarboxylate transport). Evidence used to support the conclusion that the altered photorespiratory phenotype in the mutant was due to a defect in chloroplast dicarboxylate transport was obtained using both indirect and direct measures of transport. Chloroplast reactions dependent upon transport for a supply of substrates were assayed. Glutamate synthase and glutamate-oxaloacetate aminotransferase were assayed on intact chloroplasts and found missing in the mutant. Transport activity was also measured directly using the silicone oil filter centrifugation technique. Malate, 2-oxoglutarate, glutamate and aspartate uptake were severely reduced or missing in chloroplasts from the mutant.The loss of dicarboxylate transport activity in the chloroplast envelope disrupted photorespiratory metabolism, apparently by limiting chloroplast glutamate synthase activity. The consequent reduction of glutamate supply restricted glycine formation and ammonia refixation in the photo-respiratory carbon and nitrogen cycles.The mutant plants are capable of normal growth under nonphotorespiratory conditions. Thus the primary physiological function of the chloroplast dicarboxylate transporter appears to be its role in linking fluxes though the photorespiratory carbon and nitrogen cycles. The shuttling of reducing equivalents between the chloroplast and the cytoplasm via malate/oxaloacetate or malate/aspartate shuttle systems is a function of minor importance.The mutant has also been useful in delineating the specificity of the dicarboxylate transporter. Glutamine transport is normal in the mutant suggesting this compound is not carried on the same transporter as malate, aspartate, glutamate or 2-oxoglutarate. This result contradicts reports based on kinetic studies of spinach and pea chloroplasts.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD