Gene silencing guided by small RNAs governs a broad range of cellular processes in eukaryotes. Small RNAs are important components of plant immunity because they contribute to pathogen-triggered transcription reprogramming and directly target pathogen RNAs. Recent research suggests that silencing of pathogen genes by plant small RNAs occurs not only during viral infection but also in nonviral pathogens through a process termed host-induced gene silencing, which involves trans-species small RNA trafficking. Similarly, small RNAs are also produced by eukaryotic pathogens and regulate virulence. This review summarizes the small RNA pathways in both plants and filamentous pathogens, including fungi and oomycetes, and discusses their role in host–pathogen interactions. We highlight secondarysmall interfering RNAs of plants as regulators of immune receptor gene expression and executors of host-induced gene silencing in invading pathogens. The current status and prospects of trans-species gene silencing at the host–pathogen interface are discussed.
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The PTI ‐suppressing Avr2 effector from Fusarium oxysporum suppresses mono‐ubiquitination and plasma membrane dissociation of BIK1
Plant pathogens use effector proteins to target host processes involved in pathogen perception, immune signalling, or defence outputs. Unlike foliar pathogens, it is poorly understood how root‐invading pathogens suppress immunity. The Avr2 effector from the tomato root‐ and xylem‐colonizing pathogen
- NSF-PAR ID:
- 10441589
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Molecular Plant Pathology
- Volume:
- 24
- Issue:
- 10
- ISSN:
- 1464-6722
- Page Range / eLocation ID:
- p. 1273-1286
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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SUMMARY Plant intracellular immune receptors, primarily nucleotide‐binding, leucine‐rich repeat proteins (NLRs), detect pathogen effector proteins and activate NLR‐triggered immunity (NTI). Recently, ‘sensor’ NLRs have been reported to function with ‘helper’ NLRs to activate immunity. We investigated the role of two helper NLRs, Nrc2 and Nrc3, on immunity in tomato to the bacterial pathogen
Pseudomonas syringae pv. tomato (Pst ) mediated by the sensor NLR Prf and the Pto kinase. Annrc2/nrc3 mutant no longer activated Prf/Pto‐mediated NTI toPst containing the effectors AvrPto and AvrPtoB. Annrc3 mutant showed intermediate susceptibility between wild‐type plants and aPrf mutant, while annrc2 mutant developed only mild disease. These observations indicate that Nrc2 and Nrc3 act additively in Prf‐/Pto‐mediated immunity. We examined at what point Nrc2 and Nrc3 act in the Prf/Pto‐mediated immune response. In thenrc2/3 mutant, programmed cell death (PCD) normally induced by constitutively active variants of AvrPtoB, Pto, or Prf was abolished, but that induced by M3Kα or Mkk2 was not. PCD induced by a constitutively active Nrc3 was also abolished in aNicotiana benthamiana line with reduced expression ofPrf . MAPK activation triggered by expression of AvrPto in the wild‐type tomato plants was completely abolished in thenrc2 /3 mutant. These results indicate that Nrc2 and Nrc3 act with Prf/Pto and upstream of MAPK signaling. Nrc2 and Nrc3 were not required for PCD triggered by Ptr1, another sensor NLR‐mediatingPst resistance, although these helper NLRs do appear to be involved in resistance to certainPst race 1 strains -
null (Ed.)Abstract Ligand-induced endocytosis of the immune receptor FLAGELLIN SENSING2 (FLS2) is critical for maintaining its proper abundance in the plasma membrane (PM) to initiate and subsequently down regulate cellular immune responses to bacterial flagellin or flg22-peptide. The molecular components governing PM abundance of FLS2, however, remain mostly unknown. Here, we identified Arabidopsis (Arabidopsis thaliana) DYNAMIN-RELATED PROTEIN1A (DRP1A), a member of a plant-specific family of large dynamin GTPases, as a critical contributor to ligand-induced endocytosis of FLS2 and its physiological roles in flg22-signaling and immunity against Pseudomonas syringae pv. tomato DC3000 bacteria in leaves. Notably, drp1a single mutants displayed similar flg22-defects as those previously reported for mutants in another dynamin-related protein, DRP2B, that was previously shown to colocalize with DRP1A. Our study also uncovered synergistic roles of DRP1A and DRP2B in plant growth and development as drp1a drp2b double mutants exhibited severely stunted roots and cotyledons, as well as defective cell shape, cytokinesis, and seedling lethality. Furthermore, drp1a drp2b double mutants hyperaccumulated FLS2 in the PM prior to flg22-treatment and exhibited a block in ligand-induced endocytosis of FLS2, indicating combinatorial roles for DRP1A and DRP1B in governing PM abundance of FLS2. However, the increased steady-state PM accumulation of FLS2 in drp1a drp2b double mutants did not result in increased flg22 responses. We propose that DRP1A and DRP2B are important for the regulation of PM-associated levels of FLS2 necessary to attain signaling competency to initiate distinct flg22 responses, potentially through modulating the lipid environment in defined PM domains.more » « less
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null (Ed.)At the host–pathogen interface, the protein composition of the plasma membrane (PM) has important implications for how a plant cell perceives and responds to invading microbial pathogens. A plant's ability to modulate its PM composition is critical for regulating the strength, duration, and integration of immune responses. One mechanism by which plant cells reprogram their cell surface is vesicular trafficking, including secretion and endocytosis. These trafficking processes add or remove cargo proteins (such as pattern-recognition receptors, transporters, and other proteins with immune functions) to or from the PM via small, membrane-bound vesicles. Clathrin-coated vesicles (CCVs) that form at the PM and trans-Golgi network/early endosomes have emerged as the prominent vesicle type in the regulation of plant immune responses. In this review, we discuss the roles of the CCV core, adaptors, and accessory components in plant defense signaling and immunity against various microbial pathogens.more » « less
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Abstract Pathogen pressure on hosts can lead to the evolution of genes regulating the innate immune response. By characterizing naturally occurring polymorphisms in immune receptors, we can better understand the molecular determinants of pathogen recognition. ZAR1 is an ancient
Arabidopsis thaliana NLR (Nucleotide‐binding [NB] Leucine‐rich‐repeat [LRR] Receptor) that recognizes multiple secreted effector proteins from the pathogenic bacteriaPseudomonas syringae andXanthomonas campestris through its interaction with receptor‐like cytoplasmic kinases (RLCKs). ZAR1 was first identified for its role in recognizingP. syringae effector HopZ1a, through its interaction with the RLCK ZED1. To identify additional determinants of HopZ1a recognition, we performed a computational screen for ecotypes from the 1001 Genomes project that were likely to lack HopZ1a recognition, and tested ~300 ecotypes. We identified ecotypes containing polymorphisms in ZAR1 and ZED1. Using our previously establishedNicotiana benthamiana transient assay and Arabidopsis ecotypes, we tested for the effect of naturally occurring polymorphisms on ZAR1 interactions and the immune response. We identified key residues in the NB or LRR domain of ZAR1 that impact the interaction with ZED1. We demonstrate that natural diversity combined with functional assays can help define the molecular determinants and interactions necessary to regulate immune induction in response to pathogens.
