Molecular Plant-microbe Interactions最新文献

Crops are constantly exposed to pathogenic microbes. Rust fungi are examples of these harmful microorganisms, which have a major economic impact on wheat production. To protect themselves from pathogens like rust fungi, plants employ a multilayered immune system that includes immunoreceptors encoded by resistance genes. Significant efforts have led to the isolation of numerous resistance genes against rust fungi in cereals, especially in wheat. However, the evolution of virulence of rust fungi hinders the durability of resistance genes as a strategy for crop protection. Rust fungi, like other biotrophic pathogens, secrete an arsenal of effectors to facilitate infection, and these are the molecules that plant immunoreceptors target for pathogen recognition and mounting defense responses. When recognized, these effector proteins are referred to as avirulence (Avr) effectors. Despite the many predicted effectors in wheat rust fungi, only five Avr genes have been identified, all from wheat stem rust. Knowledge of the Avr genes and their variation in the fungal population will inform deployment of the most appropriate wheat disease-resistance genes for breeding and farming. The review provides an overview of methodologies as well as the validation techniques that have been used to characterize Avr effectors from wheat stem rust. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Plant pathogens manipulate the cellular environment of the host to facilitate infection and colonization that often lead to plant diseases. To accomplish this, many specialized pathogens secrete virulence proteins called effectors into the host cell, which subvert processes such as immune signaling, gene transcription, and host metabolism. Phytophthora infestans, the causative agent of potato late blight, employs an expanded repertoire of RxLR effectors with WY domains to manipulate the host through direct interaction with protein targets. However, our understanding of the molecular mechanisms underlying the interactions between WY effectors and their host targets remains limited. In this study, we performed a structural and biophysical characterization of the P. infestans WY effector Pi04314 in complex with the potato Protein Phosphatase 1-c (PP1c). We elucidate how Pi04314 uses a WY domain and a specialized C-terminal loop carrying a KVxF motif that interact with conserved surfaces on PP1c, known to be used by host regulatory proteins for guiding function. Through biophysical and in planta analyses, we demonstrate that Pi04314 WY or KVxF mutants lose their ability to bind PP1c. The loss of PP1c binding correlates with changes in PP1c nucleolar localization and a decrease in lesion size in plant infection assays. This study provides insights into the manipulation of plant hosts by pathogens, revealing how effectors exploit key regulatory interfaces in host proteins to modify their function and facilitate disease. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Fungal pathogens deploy a set of molecules (proteins, specialized metabolites, and sRNAs), so-called effectors, to aid the infection process. In comparison to other plant pathogens, smut fungi have small genomes and secretomes of 20 Mb and around 500 proteins, respectively. Previous comparative genomic studies have shown that many secreted effector proteins without known domains, i.e., novel, are conserved only in the Ustilaginaceae family. By analyzing the secretomes of 11 species within Ustilaginaceae, we identified 53 core homologous groups commonly present in this lineage. By collecting existing mutants and generating additional ones, we gathered 44 Ustilago maydis strains lacking single core effectors as well as 9 strains containing multiple deletions of core effector gene families. Pathogenicity assays revealed that 20 of these 53 mutant strains were affected in virulence. Among the 33 mutants that had no obvious phenotypic changes, 13 carried additional, sequence-divergent, structurally similar paralogs. We report a virulence contribution of seven previously uncharacterized single core effectors and of one effector family. Our results help to prioritize effectors for understanding U. maydis virulence and provide genetic resources for further characterization. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Molecular Plant-Microbe Interactions Vol. 37 No. 2

Rapidly evolving bacterial pathogens pose a unique challenge for long-term plant disease management. In this study, we investigated the types and rate of mutations in bacterial populations during seasonal disease epidemics. Two phylogenetically distinct strains of the bacterial spot pathogen, Xanthomonas perforans, were marked, released in tomato fields, and recaptured at several time points during the growing season. Genomic variations in recaptured isolates were identified by comparative analysis of their whole-genome sequences. In total, 180 unique variations (116 substitutions, 57 insertions/deletions, and 7 structural variations) were identified from 300 genomes, resulting in the overall host-associated mutation rate of ∼0.3 to 0.9/genome/week. This result serves as a benchmark for bacterial mutation during epidemics in similar pathosystems. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

In plants, plasmodesmata establish cytoplasmic continuity between cells to allow for communication and resource exchange across the cell wall. While plant pathogens use plasmodesmata as a pathway for both molecular and physical invasion, the benefits of molecular invasion (cell-to-cell movement of pathogen effectors) are poorly understood. To establish a methodology for identification and characterization of the cell-to-cell mobility of effectors, we performed a quantitative live imaging-based screen of candidate effectors of the fungal pathogen Colletotrichum higginsianum. We predicted C. higginsianum effectors by their expression profiles, the presence of a secretion signal, and their predicted and in planta localization when fused to green fluorescent protein. We assayed for cell-to-cell mobility of nucleocytosolic effectors and identified 14 that are cell-to-cell mobile. We identified that three of these effectors are "hypermobile," showing cell-to-cell mobility greater than expected for a protein of that size. To explore the mechanism of hypermobility, we chose two hypermobile effectors and measured their impact on plasmodesmata function and found that even though they show no direct association with plasmodesmata, each increases the transport capacity of plasmodesmata. Thus, our methods for quantitative analysis of cell-to-cell mobility of candidate microbe-derived effectors, or any suite of host proteins, can identify cell-to-cell hypermobility and offer greater understanding of how proteins affect plasmodesmal function and intercellular connectivity. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Plant disease resistance (R) gene-mediated effector-triggered immunity (ETI) is usually associated with hypersensitive response (HR) and provides robust and race-specific disease resistance against pathogenic infection. The activation of ETI and HR in plants is strictly regulated, and improper activation will lead to cell death. Xa27 is an executor-type R gene in rice induced by the TAL effector AvrXa27 and confers disease resistance to Xanthomonas oryzae pv. oryzae (Xoo). Here we reported the characterization of a transgenic line with lesion mimic phenotype, designated as Spotted leaf and resistance 1 (Slr1), which was derived from rice transformation with a genomic subclone located 5,125 bp downstream of the Xa27 gene. Slr1 develops spontaneous lesions on its leaves caused by cell death and confers disease resistance to both Xoo and Xanthomonas oryzae pv. oryzicola. Further investigation revealed that the Slr1 phenotype resulted from the ectopic expression of an Xa27 paralog gene, designated as Xa27B, in the inserted DNA fragment at the Slr1 locus driven by a truncated CaMV35Sx2 promoter in reverse orientation. Disease evaluation of IRBB27, IR24, and Xa27B mutants with Xoo strains expressing dTALE-Xa27B confirmed that Xa27B is a functional executor-type R gene. The functional XA27B-GFP protein was localized to the endoplasmic reticulum and apoplast. The identification of Xa27B as a new functional executor-type R gene provides additional genetic resources for studying the mechanism of executor-type R protein-mediated ETI and developing enhanced and broad-spectrum disease resistance to Xoo through promoter engineering. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Embedded in the plasma membrane of plant cells, receptor kinases (RKs) and receptor proteins (RPs) act as key sentinels, responsible for detecting potential pathogenic invaders. These proteins were originally characterized more than three decades ago as disease resistance (R) proteins, a concept that was formulated based on Harold Flor's gene-for-gene theory. This theory implies genetic interaction between specific plant R proteins and corresponding pathogenic effectors, eliciting effector-triggered immunity (ETI). Over the years, extensive research has unraveled their intricate roles in pathogen sensing and immune response modulation. RKs and RPs recognize molecular patterns from microbes as well as dangers from plant cells in initiating pattern-triggered immunity (PTI) and danger-triggered immunity (DTI), which have intricate connections with ETI. Moreover, these proteins are involved in maintaining immune homeostasis and preventing autoimmunity. This review showcases seminal studies in discovering RKs and RPs as R proteins and discusses the recent advances in understanding their functions in sensing pathogen signals and the plant cell integrity and in preventing autoimmunity, ultimately contributing to a robust and balanced plant defense response. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2024.

The plant hormone indole-3-acetic acid (IAA), also known as auxin, plays important roles in plant growth and development, as well as in several plant-microbe interactions. IAA also acts as a microbial signal and in many bacteria regulates metabolism, stress responses, and virulence. In the bacterial plant pathogen Pseudomonas syringae pv. tomato strain DC3000 (PtoDC3000), exposure to IAA results in large-scale transcriptional reprogramming, including the differential expression of several known virulence genes. However, how PtoDC3000 senses and responds to IAA and what aspects of its biology are regulated by IAA is not understood. To investigate the mechanisms involved in perceiving and responding to IAA, we carried out a genetic screen for mutants with altered responses to IAA. One group of mutants of particular interest carried disruptions in the aefR gene encoding a TetR family transcriptional regulator. Gene expression analysis confirmed that the aefR mutants have altered responses to IAA. Thus, AefR is the first demonstrated auxin response regulator in PtoDC3000. We also investigated several aspects of PtoDC3000 biology that are regulated by both AefR and IAA, including antibiotic resistance, motility, and virulence. The observation that the aefR mutant has altered virulence on Arabidopsis, suggests that the sector of the IAA response regulated by aefR is important during pathogenesis. Our findings also provide evidence that AefR plays a role in coordinating changes in gene expression during the transition from early to late stages of infection. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The permanent organs of grapevines (Vitis vinifera L.), like those of other woody perennials, are colonized by various unrelated pathogenic ascomycete fungi secreting cell wall-degrading enzymes and phytotoxic secondary metabolites that contribute to host damage and disease symptoms. Trunk pathogens differ in the symptoms they induce and the extent and speed of damage. Isolates of the same species often display a wide virulence range, even within the same vineyard. This study focuses on Eutypa lata, Neofusicoccum parvum, and Phaeoacremonium minimum, causal agents of Eutypa dieback, Botryosphaeria dieback, and Esca, respectively. We sequenced 50 isolates from viticulture regions worldwide and built nucleotide-level, reference-free pangenomes for each species. Through examination of genomic diversity and pangenome structure, we analyzed intraspecific conservation and variability of putative virulence factors, focusing on functions under positive selection and recent gene family dynamics of contraction and expansion. Our findings reveal contrasting distributions of putative virulence factors in the core, dispensable, and private genomes of each pangenome. For example, carbohydrate active enzymes (CAZymes) were prevalent in the core genomes of each pangenome, whereas biosynthetic gene clusters were prevalent in the dispensable genomes of E. lata and P. minimum. The dispensable fractions were also enriched in Gypsy transposable elements and virulence factors under positive selection (polyketide synthase genes in E. lata and P. minimum, glycosyltransferases in N. parvum). Our findings underscore the complexity of the genomic architecture in each species and provide insights into their adaptive strategies, enhancing our understanding of the underlying mechanisms of virulence. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.