Negative Regulator Of Plant Immunity Research Articles

Functional screening of the Arabidopsis 2C protein phosphatases family identifies PP2C15 as a negative regulator of plant immunity by targeting BRI1-associated receptor kinase 1.

Genetic engineering using negative regulators of plant immunity has the potential to provide a huge impetus in agricultural biotechnology to achieve a higher degree of disease resistance without reducing yield. Type 2C protein phosphatases (PP2Cs) represent the largest group of protein phosphatases in plants, with a high potential for negative regulatory functions by blocking the transmission of defence signals through dephosphorylation. Here, we established a PP2C functional protoplast screen using pFRK1::luciferase as a reporter and found that 14 of 56 PP2Cs significantly inhibited the immune response induced by flg22. To verify the reliability of the system, a previously reported MAPK3/4/6-interacting protein phosphatase, PP2C5, was used; it was confirmed to be a negative regulator of PAMP-triggered immunity (PTI). We further identified PP2C15 as an interacting partner of BRI1-associated receptor kinase 1 (BAK1), which is the most well-known co-receptor of plasma membrane-localized pattern recognition receptors (PRRs), and a central component of PTI. PP2C15 dephosphorylates BAK1 and negatively regulates BAK1-mediated PTI responses such as MAPK3/4/6 activation, defence gene expression, reactive oxygen species bursts, stomatal immunity, callose deposition, and pathogen resistance. Although plant growth and 1000-seed weight of pp2c15 mutants were reduced compared to those of wild-type plants, pp2c5 mutants did not show any adverse effects. Thus, our findings strengthen the understanding of the mechanism by which PP2C family members negatively regulate plant immunity at multiple levels and indicate a possible approach to enhance plant resistance by eliminating specific PP2Cs without affecting plant growth and yield.

CRISPR-targeted mutagenesis of mitogen-activated protein kinase phosphatase 1 improves both immunity and yield in wheat.

Plants have evolved a sophisticated immunity system for specific detection of pathogens and rapid induction of measured defences. Over- or constitutive activation of defences would negatively affect plant growth and development. Hence, the plant immune system is under tight positive and negative regulation. MAP kinase phosphatase1 (MKP1) has been identified as a negative regulator of plant immunity in model plant Arabidopsis. However, the molecular mechanisms by which MKP1 regulates immune signalling in wheat (Triticum aestivum) are poorly understood. In this study, we investigated the role of TaMKP1 in wheat defence against two devastating fungal pathogens and determined its subcellular localization. We demonstrated that knock-down of TaMKP1 by CRISPR/Cas9 in wheat resulted in enhanced resistance to rust caused by Puccinia striiformis f. sp. tritici (Pst) and powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt), indicating that TaMKP1 negatively regulates disease resistance in wheat. Unexpectedly, while Tamkp1 mutant plants showed increased resistance to the two tested fungal pathogens they also had higher yield compared with wild-type control plants without infection. Our results suggested that TaMKP1 interacts directly with dephosphorylated and activated TaMPK3/4/6, and TaMPK4 interacts directly with TaPAL. Taken together, we demonstrated TaMKP1 exert negative modulating roles in the activation of TaMPK3/4/6, which are required for MAPK-mediated defence signalling. This facilitates our understanding of the important roles of MAP kinase phosphatases and MAPK cascades in plant immunity and production, and provides germplasm resources for breeding for high resistance and high yield.

Plant U-box E3 ligases PUB20 and PUB21 negatively regulate pattern-triggered immunity in Arabidopsis.

Plant U-box E3 ligases PUB20 and PUB21 are flg22-triggered signaling components and negatively regulate immune responses. Plant U-box proteins (PUBs) constitute a class of E3 ligases that are associated with various stress responses. Among the class IV PUBs featuring C-terminal Armadillo (ARM) repeats, PUB20 and PUB21 are closely related homologs. Here, we show that both PUB20 and PUB21 negatively regulate innate immunity in plants. Loss of PUB20 and PUB21 function leads to enhanced resistance to surface inoculation with the virulent bacterium Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). However, the resistance levels remain unaffected after infiltration inoculation, suggesting that PUB20 and PUB21 primarily function during the early defense stages. The enhanced resistance to Pst DC3000 in PUB mutant plants (pub20-1, pub21-1, and pub20-1/pub21-1) correlates with extensive flg22-triggered reactive oxygen production, strong MPK3 activation, and enhanced transcriptional activation of early immune response genes. Additionally, PUB mutant plants (except pub21-1) exhibit constitutive stomatal closure after Pst DC3000 inoculation, implying the significant role of PUB20 in stomatal immunity. Comparative analyses of flg22 responses between PUB mutants and wild-type plants reveals that the robust activation of the pattern-induced immune responses may enhance resistance against Pst DC3000. Notably, the hypersensitivity responses triggered by RPM1/avrRpm1 and RPS2/avrRpt2 are independent of PUB20 and PUB21. These results suggest that PUB20 and PUB21 knockout mutations affect bacterial invasion, likely during the early stages, acting as negative regulators of plant immunity.

Glycine-serine-rich effector PstGSRE4 in Puccinia striiformis f. sp. tritici targets and stabilizes TaGAPDH2 that promotes stripe rust disease.

Puccinia striiformis f. sp. tritici (Pst) secretes effector proteins that enter plant cells and manipulate host processes. In a previous study, we identified a glycine-serine-rich effector PstGSRE4, which was proven to regulate the reactive oxygen species (ROS) pathway by interacting with TaCZSOD2. In this study, we further demonstrated that PstGSRE4 interacts with wheat glyceraldehyde-3-phosphate dehydrogenase TaGAPDH2, which is related to ROS signalling. In wheat, silencing of TaGAPDH2 by virus-induced gene silencing increased the accumulation of ROS induced by the Pst virulent race CYR31. Overexpression of TaGAPDH2 decreased the accumulation of ROS induced by the avirulent Pst race CYR23. In addition, TaGAPDH2 suppressed Pst candidate elicitor Pst322-triggered cell death by decreasing ROS accumulation in Nicotiana benthamiana. Knocking down TaGAPDH2 expression attenuated Pst infection, whereas overexpression of TaGAPDH2 promoted Pst infection, indicating that TaGAPDH2 is a negative regulator of plant defence. In N. benthamiana, PstGSRE4 stabilized TaGAPDH2 through inhibition of the 26S proteasome-mediated destabilization. Overall, these results suggest that TaGAPDH2 is hijacked by the Pst effector as a negative regulator of plant immunity to promote Pst infection in wheat.

The Botrytis cinerea effector BcXYG1 suppresses immunity in Fragaria vesca by targeting FvBPL4 and FvACD11.

Botrytis cinerea is one of the most destructive pathogens in strawberry cultivation. Successful infection by B. cinerea requires releasing a large number of effectors that interfere with the plant's immune system. One of the effectors required by B. cinerea for optimal virulence is the secreted protein BcXYG1, which is thought to associate with proteins near the plasma membrane of the host plant to induce necrosis. However, the host proteins that associate with BcXYG1 at the plasma membrane are currently unknown. We found that BcXYG1 binds to FvBPL4 and FvACD11 at the plasma membrane. Both FvBPL4 and FvACD11 are negative regulators of plant immunity in strawberry. Our results demonstrate that degradation of FvBPL4 by BcXYG1 promotes disease resistance while stabilization of FvACD11 by BcXYG1 suppresses the immune response. These findings suggest that BcXYG1 suppresses plant immunity and promotes B. cinerea infection by regulating FvBPL4 and FvACD11 protein levels.

CRISPR/Cas9 editing of Downy mildew resistant 6 (DMR6-1) in grapevine leads to reduced susceptibility to Plasmopara viticola.

Downy mildew of grapevine (Vitis vinifera), caused by the oomycete Plasmopara viticola, is an important disease that is present in cultivation areas worldwide, and using resistant varieties provides an environmentally friendly alternative to fungicides. DOWNY MILDEW RESISTANT 6 (DMR6) from Arabidopsis is a negative regulator of plant immunity and its loss of function confers resistance to downy mildew. In grapevine, DMR6 is present in two copies, named VvDMR6-1 and VvDMR6-2. Here, we describe the editing of VvDMR6-1 in embryogenic calli using CRISPR/Cas9 and the regeneration of the edited plants. All edited plants were found to be biallelic and chimeric, and whilst they all showed reduced growth compared with non-transformed control plants, they also had reduced susceptibility to P. viticola. Comparison between mock-inoculated genotypes showed that all edited lines presented higher levels of salicylic acid than controls, and lines subjected to transformation presented higher levels of cis-resveratrol than controls. Our results identify VvDMR6-1 as a promising target for breeding grapevine cultivars with improved resistance to downy mildew.

S-nitrosylation switches the Arabidopsis redox sensor protein, QSOX1, from an oxidoreductase to a molecular chaperone under heat stress

The Arabidopsis quiescin sulfhydryl oxidase 1 (QSOX1) thiol-based redox sensor has been identified as a negative regulator of plant immunity. Here, we have found that small molecular weight proteins of QSOX1 were converted to high molecular weight (HMW) complexes upon exposure to heat stress and that this was accompanied by a switch in QSOX1 function from a thiol-reductase to a molecular chaperone. Plant treatment with S-nitrosoglutathione (GSNO), which causes nitrosylation of cysteine residues (S-nitrosylation), but not with H2O2, induced HMW QSOX1 complexes. Thus, functional switching of QSOX1 is induced by GSNO treatment. Accordingly, simultaneous treatment of plants with heat shock and GSNO led to a significant increase in QSOX1 chaperone activity by increasing its oligomerization. Consequently, transgenic Arabidopsis overexpressing QSOX1 (QSOX1OE) showed strong resistance to heat shock, whereas qsox1 knockout plants exhibited high sensitivity to heat stress. Plant treatment with GSNO under heat stress conditions increased their resistance to heat shock. We conclude that S-nitrosylation allows the thiol-based redox sensor, QSOX1, to respond to various external stresses in multiple ways.

SlWRKY16 and SlWRKY31 of tomato, negative regulators of plant defense, involved in susceptibility activation following root-knot nematode Meloidogyne javanica infection

The involvement of WRKY transcription factors in plant-nematode interactions, and in particular, how these WRKYs participate in regulating the complex morphological and physiological changes occurring after nematode infection, are the topic of active research. We characterized the functional role of the unstudied tomato WRKY genes SlWRKY16 and SlWRKY31 in regulating tomato roots’ response to infection by the root-knot nematode Meloidogyne javanica. Using promoter–GUS reporter gene fusions and qRT-PCR, we show that both SlWRKYs are predominantly expressed during the first half of the parasitic life stages, when feeding-site induction and construction occur. Expression of SlWRKY16 increased sharply 15 days after inoculation, whereas SlWRKY31 was already induced earlier, but reached its maximum expression at this time. Both genes were downregulated at the mature female stage. To determine biological function, we produced transgenic lines overexpressing SlWRKY16 and SlWRKY31 in tomato hairy roots. Overexpression of both genes resulted in enhanced M. javanica infection, reflected by increased galling occurrence and reproduction. Expression profiling of marker genes responsive to defense-associated phytohormones indicated reductions in salicylic acid defense-related PR-1 and jasmonic acid defense-related PI in inoculated roots overexpressing SlWRK16 and SlWRKY31, respectively. Our results suggest that SlWRKY16 and SlWRKY31 function as negative regulators of plant immunity induced upon nematode infection.

Activated Expression of Rice DMR6-like Gene OsS3H Partially Explores the Susceptibility to Bacterial Leaf Streak Mediated by Knock-Out OsF3H04g.

Downy Mildew Resistance 6-like (DMR6-like) genes are identified as salicylic acid (SA) hydroxylases and negative regulators of plant immunity. Previously, we identified two rice DMR6-like genes, OsF3H03g, and OsF3H04g, that act as susceptible targets of transcription activator-like effectors (TALEs) from Xanthomonas oryzae pv. oryzicola (Xoc), which causes bacterial leaf streak (BLS) in rice. Furthermore, all four homologs of rice DMR6-like proteins were identified to predominantly carry the enzyme activity of SA 5-hydroxylase (S5H), negatively regulate rice broad-spectrum resistance, and cause the loss of function of these OsDMR6s, leading to increased resistance to rice blast and bacterial blight (BB). Here, we curiously found that an OsF3H04g knock-out mutant created by T-DNA insertion, osf3h04g, was remarkedly susceptible to BLS and BB and showed an extreme reduction in SA content. OsF3H04g knock-out rice lines produced by gene-editing were mildly susceptible to BLS and reduced content of SA. To explore the susceptibility mechanism in OsF3H04g loss-of-function rice lines, transcriptome sequencing revealed that another homolog, OsS3H, had induced expression in the loss-of-function OsF3H04g rice lines. Furthermore, we confirmed that a great induction of OsS3H downstream and genomically adjacent to OsF3H04g in osf3h04g was primarily related to the inserted T-DNA carrying quadruple enhancer elements of 35S, while a slight induction was caused by an unknown mechanism in gene-editing lines. Then, we found that the overexpression of OsS3H increased rice susceptibility to BLS, while gene-editing mediated the loss-of-function OsS3H enhanced rice resistance to BLS. However, the knock-out of both OsF3H04g and OsS3H by gene-editing only neutralized rice resistance to BLS. Thus, we concluded that the knock-out of OsF3H04g activated the expression of the OsS3H, partially participating in the susceptibility to BLS in rice.

Nucleoredoxin gene SINRX1 negatively regulates tomato immunity by activating SA signaling pathway

The tomato (Solanum lycopersicum) is widely consumed globally and renowned for its health benefits, including the reduction of cardiovascular disease and prostate cancer risk. However, tomato production faces significant challenges, particularly due to various biotic stresses such as fungi, bacteria, and viruses. To address this challenges, we employed the CRISPR/Cas9 system to modify the tomato NUCLEOREDOXIN (SlNRX) genes (SlNRX1 and SlNRX2) belonging to the nucleocytoplasmic THIOREDOXIN subfamily. CRISPR/Cas9-mediated mutations in SlNRX1 (slnrx1) plants exhibited resistance against bacterial leaf pathogen Pseudomonas syringae pv. maculicola (Psm) ES4326, as well as the fungal pathogen Alternaria brassicicola. However, the slnrx2 plants did not display resistance. Notably, the slnrx1 demonstrated elevated levels of endogenous salicylic acid (SA) and reduced levels of jasmonic acid after Psm infection, in comparison to both wild-type (WT) and slnrx2 plants. Furthermore, transcriptional analysis revealed that genes involved in SA biosynthesis, such as ISOCHORISMATE SYNTHASE 1 (SlICS1) and ENHANCED DISEASE SUSCEPTIBILITY 5 (SlEDS5), were upregulated in slnrx1 compared to WT plants. In addition, a key regulator of systemic acquired resistance, PATHOGENESIS-RELATED 1 (PR1), exhibited increased expression in slnrx1 compared to WT. These findings suggest that SlNRX1 acts as a negative regulator of plant immunity, facilitating infection by the Psm pathogen through interference with the phytohormone SA signaling pathway. Thus, targeted mutagenesis of SlNRX1 is a promising genetic means to enhance biotic stress resistance in crop breeding.

JMJ28 guides sequence-specific targeting of ATX1/2-containing COMPASS-like complex in Arabidopsis

Despite extensive investigations in mammals and yeasts, the importance and specificity of COMPASS-like complex, which catalyzes histone 3 lysine 4 methylation (H3K4me), are not fully understood in plants. Here, we report that JMJ28, a Jumonji C domain-containing protein in Arabidopsis, recognizes specific DNA motifs through a plant-specific WRC domain and acts as an interacting factor to guide the chromatin targeting of ATX1/2-containing COMPASS-like complex. JMJ28 associates with COMPASS-like complex invivo via direct interaction with RBL. The DNA-binding activity of JMJ28 is essential for both the targeting specificity of ATX1/2-COMPASS and the deposition of H3K4me at specific loci but exhibit functional redundancy with alternative COMPASS-like complexes at other loci. Finally, we demonstrate that JMJ28 is a negative regulator of plant immunity. In summary, our findings reveal a plant-specific recruitment mechanism of COMPASS-like complex. These findings help to gain deeper insights into the regulatory mechanism of COMPASS-like complex in plants.

Verticillium dahliae Effector VdCE11 Contributes to Virulence by Promoting Accumulation and Activity of the Aspartic Protease GhAP1 from Cotton.

Verticillium dahliae is a soilborne plant fungal pathogen that causes Verticillium wilt, a disease that reduces the yields of many economically important crops. Despite its worldwide distribution and harmful impacts, much remains unknown regarding how the numerous effectors of V. dahliae modulate plant immunity. Here, we identified the intracellular effector VdCE11 that induces cell death and defense responses in Nicotiana benthamiana to counter leaf pathogens such as Sclerotinia sclerotiorum and Botrytis cinerea. VdCE11 also contributes to the virulence of V. dahliae in cotton and Arabidopsis. Yeast two-hybrid library screening and immunoprecipitation revealed that VdCE11 interacts physically with the cotton aspartic protease GhAP1. GhAP1 and its Arabidopsis homolog AtAP1 are negative regulators of plant immunity, since disruption of either increased the resistance of cotton or Arabidopsis to V. dahliae. Further, VdCE11 plays a role in promoting the accumulation of the AP1 proteins and increasing its hydrolase activity. Taken together, these results indicate a novel mechanism regulating virulence whereby the secreted effector VdCE11 increases cotton susceptibility to V. dahliae by promoting the accumulation and activity of GhAP1. IMPORTANCE Verticclium dahliae is a plant fungal pathogen that causes a destructive vascular disease on a large number of plant hosts, resulting in great threat to agricultural production. In this study, we identified a V. dahliae effector VdCE11 that induces cell death and defense responses in Nicotiana benthamiana. Meanwhile, VdCE11 contributes to the virulence of V. dahliae in cotton and Arabidopsis. Yeast two-hybrid library screening and immunoprecipitation revealed that VdCE11 interacts physically with the cotton aspartic protease GhAP1. GhAP1 and its Arabidopsis homolog AtAP1 are negative regulators of plant immunity since disruption of either increased the resistance of cotton or Arabidopsis to V. dahliae. Further research showed that VdCE11 plays a role in promoting the accumulation of the AP1 proteins and increasing its hydrolase activity. These results suggested that a novel mechanism regulating virulence whereby VdCE11 increases susceptibility to V. dahliae by promoting the accumulation and activity of GhAP1 in the host.

Homeostasis of Arabidopsis R protein RPS2 is negatively regulated by the RING-type E3 ligase MUSE16.

The homeostasis of resistance (R) proteins in plants must be tightly regulated to ensure precise activation of plant immune responses upon pathogen infection, while avoiding autoimmunity and growth defects when plants are uninfected. It is known that CPR1, an F-box protein in the SCF E3 complex, functions as a negative regulator of plant immunity through targeting the resistance (R) proteins SNC1 and RPS2 for degradation. However, whether these R proteins are also targeted by other E3 ligases is unclear. Here, we isolated Arabidopsis MUSE16, which encodes a RING-type E3 ligase, from a forward genetic screen and suggest that it is a negative regulator of plant immunity. Unlike CPR1, knocking out MUSE16 alone in Arabidopsis is not enough to result in defense-related dwarfism, since only RPS2 out of the tested R proteins accumulated in the muse16 mutants. Thus, our study identifies a novel E3 ligase involved in the degradation of nucleotide-binding and leucine-rich repeat (NLR) R proteins, support the idea that ubiquitin-mediated degradation is a fine-tuned mechanism for regulating the turnover of R proteins in plants, and that the same R protein can be targeted by different E3 ligases for regulation of its homeostasis.

The Emerging Role of PP2C Phosphatases in Tomato Immunity.

The antagonistic effect of plant immunity on growth likely drove evolution of molecular mechanisms that prevent accidental initiation and prolonged activation of plant immune responses. Signaling networks of pattern-triggered and effector-triggered immunity, the two main layers of plant immunity, are tightly regulated by the activity of protein phosphatases that dephosphorylate their protein substrates and reverse the action of protein kinases. Members of the PP2C class of protein phosphatases have emerged as key negative regulators of plant immunity, primarily from research in the model plant Arabidopsis thaliana, revealing the potential to employ PP2C proteins to enhance plant disease resistance. As a first step towards focusing on the PP2C family for both basic and translational research, we analyzed the tomato genome sequence to ascertain the complement of the tomato PP2C family, identify conserved protein domains and signals in PP2C amino acid sequences, and examine domain combinations in individual proteins. We then identified tomato PP2Cs that are candidate regulators of single or multiple layers of the immune signaling network by in-depth analysis of publicly available RNA-seq datasets. These included expression profiles of plants treated with fungal or bacterial pathogen-associated molecular patterns, with pathogenic, nonpathogenic, and disarmed bacteria, as well as pathogenic fungi and oomycetes. Finally, we discuss the possible use of immunity-associated PP2Cs to better understand the signaling networks of plant immunity and to engineer durable and broad disease resistance in crop plants. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

A serine-rich effector from the stripe rust pathogen targets a Raf-like kinase to suppress host immunity.

Puccinia striiformis f. sp. tritici (Pst) is an important obligate pathogen in wheat (Triticum aestivum L.) and secretes effectors into plant cells to promote infection. Identifying host targets of effector proteins and clarifying their roles in pathogen infection is essential for understanding pathogen virulence. In this study, we identified a serine-rich effector, Pst27791, from Pst that suppresses cell death in Nicotiana benthamiana. Stable overexpression of Pst27791 in wheat suppressed reactive oxygen species accumulation and the salicylic acid-dependent defense response. Transgenic wheat expressing the RNA interference construct of Pst27791 exhibited high resistance to Pst virulent isolate CYR31, indicating its importance in pathogenesis. Pst27791 interacting with wheat rapidly accelerated fibrosarcoma (Raf)-like kinase TaRaf46 in yeast and in planta. Knocking down TaRaf46 expression in wheat attenuated Pst infection and increased wheat immunity. The overexpression of TaRaf46 decreased wheat resistance to Pst and repressed MAPK activation in wheat. Pst27791 may stabilize TaRaf46 through the inhibition of proteasome-mediated degradation in N. benthamiana. The ability of Pst27791 to enhance Pst colonization was compromised when TaRaf46 was silenced, suggesting that the virulence of Pst27791 is mediated by TaRaf46. Overall, these results indicate that Raf-like kinase TaRaf46 is exploited by the Pst effector as a negative regulator of plant immunity to promote infection in wheat.

SlCML55, a novel Solanum lycopersicum calmodulin-like gene, negatively regulates plant immunity to Phytophthora pathogens

Calmodulin-like (CML) proteins are important decoders for intracellular Ca2+ variation controlling diverse cellular functions by regulating the activity of various target proteins. The functions of many CMLs, especially their roles as negative regulators of plant immunity, have not been clarified. The Solanum lycopersicum gene SlCML55, a novel CML gene with a susceptibility-inducing function in Nicotiana benthamiana, was identified in a tomato cDNA library. Silencing of SlCML55 inhibits Phytophthora capsici infection, indicating that SlCML55 negatively regulates plant immunity in tomato. Confocal laser scanning microscopy showed eGFP:SlCML55 to localize to the cytosol and nucleus. SlCML55 was highly expressed in roots compared to other tissues and downregulated during the early stage of P. capsici infection, especially at 3 hours post-infection. Expression of SlCML55 was regulated by Ca2+ and peaked at 6 h after external administration of CaCl2. Expression of SlCML55 was also largely downregulated under disease resistance-related hormone (SA, JA and ET) treatments. Furthermore, silencing SlCML55 promoted PR1 expression and viral defense, as stimulated via the SA immune pathway. Taken together, our findings indicate that SlCML55 acts as a negative regulator during pathogen infection in tomato in association with the SA signaling pathway.

AtMC1 Associates With LSM4 to Regulate Plant Immunity Through Modulating Pre-mRNA Splicing.

Alternative splicing of pre-mRNAs is an important gene regulatory mechanism shaping the transcriptome. AtMC1 is an Arabidopsis thaliana type I metacaspase that positively regulates the hypersensitive response. Here, we found that AtMC1 is involved in the regulation of plant immunity to the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and is physically associated with Sm-like4 (LSM4), which is involved in pre-mRNA splicing. AtMC1 and LSM4 protein levels both increased with their coexpression as compared with their separate expression invivo. Like AtMC1, LSM4 negatively regulates plant immunity to P. syringae pv. tomato DC3000 infection. By RNA sequencing, AtMC1 was shown to modulate the splicing of many pre-mRNAs, including 4CL3, which is a negative regulator of plant immunity. Thus, AtMC1 plays a regulatory role in pre-mRNA splicing, which might contribute to AtMC1-mediated plant immunity.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

HbLFG1, a Rubber Tree (Hevea brasiliensis) Lifeguard Protein, Can Facilitate Powdery Mildew Infection by Suppressing Plant Immunity.

Powdery mildew causes substantial losses in crop and economic plant yields worldwide. Although powdery mildew infection of rubber trees (Hevea brasiliensis), caused by the biotrophic fungus Erysiphe quercicola, severely threatens natural rubber production, little is known about the mechanism by which E. quercicola adapts to H. brasiliensis to invade the host plant. In barley and Arabidopsis thaliana, lifeguard (LFG) proteins, which have topological similarity to BAX INHIBITOR-1, are involved in host plant susceptibility to powdery mildew infection. In this study, we characterized an H. brasiliensis LFG protein (HbLFG1) with a focus on its function in regulating defense against powdery mildew. HbLFG1 gene expression was found to be upregulated during E. quercicola infection. HbLFG1 showed conserved functions in cell death inhibition and membrane localization. Expression of HbLFG1 in Nicotiana benthamiana leaves and A. thaliana Col-0 was demonstrated to significantly suppress callose deposition induced by conserved pathogen-associated molecular patterns chitin and flg22. Furthermore, we found that overexpression of HbLFG1 in H. brasiliensis mesophyll protoplasts significantly suppressed the chitin-induced burst of reactive oxygen species. Although A. thaliana Col-0 and E. quercicola displayed an incompatible interaction, Col-0 transformants overexpressing HbLFG1 were shown to be susceptible to E. quercicola. Collectively, the findings of this study provide evidence that HbLFG1 acts as a negative regulator of plant immunity that facilitates E. quercicola infection in H. brasiliensis.

A teosinte-derived allele of a MYB transcription repressor confers multiple disease resistance in maize

Natural alleles that control multiple disease resistance (MDR) are valuable for crop breeding. However, only one MDR gene has been cloned in maize, and the molecular mechanisms of MDR remain unclear in maize. In this study, through map-based cloning we cloned a teosinte-derived allele of a resistance gene, Mexicana lesion mimic 1 (ZmMM1), which causes a lesion mimic phenotype and confers resistance to northern leaf blight (NLB), gray leaf spot (GLS), and southern corn rust (SCR) in maize. Strong MDR conferred by the teosinte allele is linked with polymorphisms in the 3′ untranslated region of ZmMM1 that cause increased accumulation of ZmMM1 protein. ZmMM1 acts as a transcription repressor and negatively regulates the transcription of specific target genes, including ZmMM1-target gene 3 (ZmMT3), which functions as a negative regulator of plant immunity and associated cell death. The successful isolation of the ZmMM1 resistance gene will help not only in developing broad-spectrum and durable disease resistance but also in understanding the molecular mechanisms underlying MDR.

EDS1-interacting J protein 1 is an essential negative regulator of plant innate immunity in Arabidopsis.

Plants have evolved precise mechanisms to optimize immune responses against pathogens. ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) plays a vital role in plant innate immunity by regulating basal resistance and effector-triggered immunity. Nucleocytoplasmic trafficking of EDS1 is required for resistance reinforcement, but the molecular mechanism remains elusive. Here, we show that EDS1-INTERACTING J PROTEIN1 (EIJ1), which acts as a DnaJ protein-like chaperone in response to pathogen infection, functions as an essential negative regulator of plant immunity by interacting with EDS1. The loss-of-function mutation of EIJ1 did not affect plant growth but significantly enhanced pathogen resistance. Upon pathogen infection, EIJ1 relocalized from the chloroplast to the cytoplasm, where it interacted with EDS1, thereby restricting pathogen-triggered trafficking of EDS1 to the nucleus and compromising resistance at an early infection stage. During disease development, EIJ1 was gradually degraded, allowing the nuclear accumulation of EDS1 for transcriptional resistance reinforcement. The avirulent strain Pst DC3000 (AvrRps4) abolished the repressive action of EIJ1 by rapidly inducing its degradation in the effector-triggered immunity response. Thus, our findings show that EIJ1 is an essential EDS1-dependent negative regulator of innate plant immunity and provide a mechanistic understanding of how the nuclear versus cytoplasmic distribution of EDS1 is regulated during the immune response.