ZAR1 resistosome and helper NLRs: Bringing in calcium and inducing cell death

Constructing a Novel Disease Resistance Mechanism Model for Cruciferous Crops: An Example From Black Rot

Cruciferous crops are essential components of global agricultural production due to their rich nutritional value and extensive economic benefits. Black rot caused by Xanthomonas campestris pv. campestris (Xcc) has caused significant losses to cruciferous crops. Therefore, studying the resistance mechanisms of cruciferous crops to improve the disease resistance of cruciferous crops is of significant practical importance. This review introduces the biological characteristics and epidemiological patterns of the Xcc. The main resistance mechanisms including the physical barrier functions, immune responses, systemic resistance, regulation of photosynthesis, antimicrobial effects of secondary metabolites, production and regulation of reactive oxygen species, and the signalling pathways of salicylic acid, jasmonic acid and ethylene of cruciferous crops to Xcc are also summarised. Comprehensive knowledge of these resistance mechanisms will provide theoretical support for enhancing disease resistance in crops.

Plant NAC transcription factors in the battle against pathogens

BACKGROUND

The NAC transcription factor family, which is recognized as one of the largest plant-specific transcription factor families, comprises numerous members that are widely distributed among various higher plant species and play crucial regulatory roles in plant immunity.

RESULTS

In this paper, we provided a detailed summary of the roles that NAC transcription factors play in plant immunity via plant hormone pathways and reactive oxygen species pathways. In addition, we conducted in-depth investigations into the interactions between NAC transcription factors and pathogen effectors to summarize the mechanism through which they regulate the expression of defense-related genes and ultimately affect plant disease resistance.

CONCLUSIONS

This paper presented a comprehensive overview of the crucial roles that NAC transcription factors play in regulating plant disease resistance through their involvement in diverse signaling pathways, acting as either positive or negative regulators, and thus provided references for further research on NAC transcription factors.

Diversity and Evolution of NLR Genes in Citrus Species

NLR genes are crucial components of the effector-triggered immunity (ETI) system, responsible for recognizing pathogens and initiating immune responses. Although NLR genes in many plant species have been extensively studied, the diversity of NLR genes in citrus remains largely unknown. Our analysis revealed significant variations in the copy numbers of NLR genes among these species. Gene duplication and recombination were identified as the major driving forces behind this diversity. Additionally, horizontal gene transfer (HGT) emerged as the principal mechanism responsible for the increase in NLR gene copy number in A. buxifolia. The citrus NLR genes were classified into four categories: TIR-NBS-LRR (TNL), CC-NBS-LRR (CNL), RPW8-NBS-LRR (RNL), and NL. Our findings indicate that TNL, RNL, and CNL genes originated from NL genes through the acquisition of TIR and RPW8 domains, along with CC motifs, followed by the random loss of corresponding domains. Phylogenetic analysis suggested that citrus NLR genes originated alongside the species and underwent adaptive evolution, potentially playing crucial roles in the global colonization of citrus. This study provides important insights into the diversity of citrus NLR genes and serves as a foundational dataset for future research aimed at breeding disease-resistant citrus varieties.

Effector-triggered and self-regulated plant resistance to insects

Despite many years of research, the molecular mechanisms underlying the activation and regulation of host plant resistance (HPR) to insects remain elusive. Recently, Guo et al. reported that a nucleotide-binding leucine-rich repeat NLR protein activates HPR through direct recognition of an insect effector and that autophagy-mediated degradation of this effector negatively regulates HPR.

Staying vigilant: NLR monitors virus invasion

Phytohormones play important roles in plant immunity. Recently, Chen et al. discovered that the tomato spotted wilt virus attacks the plant hormone receptor to promote infection. Plants evolved an immune receptor to mimic the attacked hormone receptors to recognize the virus, thereby activating a robust immune response.

SNP-based bulk segregant analysis revealed disease resistance QTLs associated with northern corn leaf blight in maize

Maize (Zea mays L.) is the most important food security crop worldwide. Northern corn leaf blight (NCLB), caused by Exserohilum turcicum, severely reduces production causing millions of dollars in losses worldwide. Therefore, this study aimed to identify significant QTLs associated with NCLB by utilizing next-generation sequencing-based bulked-segregant analysis (BSA). Parental lines GML71 (resistant) and Gui A10341 (susceptible) were used to develop segregating population F₂. Two bulks with 30 plants each were further selected from the segregating population for sequencing along with the parental lines. High throughput sequencing data was used for BSA. We identified 10 QTLs on Chr 1, Chr 2, Chr 3, and Chr 5 with 265 non-synonymous SNPs. Moreover, based on annotation information, we identified 27 candidate genes in the QTL regions. The candidate genes associated with disease resistance include AATP1, At4g24790, STICHEL-like 2, BI O 3-BIO1, ZAR1, SECA2, ABCG25, LECRK54, MKK7, MKK9, RLK902, and DEAD-box ATP-dependent RNA helicase. The annotation information suggested their involvement in disease resistance-related pathways, including protein phosphorylation, cytoplasmic vesicle, protein serine/threonine kinase activity, and ATP binding pathways. Our study provides a substantial addition to the available information regarding QTLs associated with NCLB, and further functional verification of identified candidate genes can broaden the scope of understanding the NCLB resistance mechanism in maize.

Nucleotide-binding leucine-rich repeat proteins: a missing link in controlling cell fate and plant adaptation to hostile environment?

Programmed cell death is a tightly regulated genetically controlled process that leads to cell suicide and eliminates cells that are either no longer needed or damaged/harmful. Nucleotide-binding leucine-rich repeat proteins have recently emerged as a novel class of Ca2+-permeable channels that operate in plant immune responses. This viewpoint argues that the unique structure of this channel, its permeability to other cations, and specificity of its operation make it an ideal candidate to mediate cell signaling and adaptive responses not only to pathogens but also to a broad range of abiotic stress factors.

Transcriptional Coactivators: Driving Force of Plant Immunity

Salicylic acid (SA) is a plant defense signal that mediates local and systemic immune responses against pathogen invasion. However, the underlying mechanism of SA-mediated defense is very complex due to the involvement of various positive and negative regulators to fine-tune its signaling in diverse pathosystems. Upon pathogen infections, elevated level of SA promotes massive transcriptional reprogramming in which Non-expresser of PR genes 1 (NPR1) acts as a central hub and transcriptional coactivator in defense responses. Recent findings show that Enhanced Disease Susceptibility 1 (EDS1) also functions as a transcriptional coactivator and stimulates the expression of PR1 in the presence of NPR1 and SA. Furthermore, EDS1 stabilizes NPR1 protein level, while NPR1 sustains EDS1 expression during pathogenic infection. The interaction of NPR1 and EDS1 coactivators initiates transcriptional reprogramming by recruiting cyclin-dependent kinase 8 in the Mediator complex to control immune responses. In this review, we highlight the recent breakthroughs that considerably advance our understanding on how transcriptional coactivators interact with their functional partners to trigger distinct pathways to facilitate immune responses, and how SA accumulation induces dynamic changes in NPR1 structure for transcriptional reprogramming. In addition, the functions of different Mediator subunits in SA-mediated plant immunity are also discussed in light of recent discoveries. Taken together, the available evidence suggests that transcriptional coactivators are essential and potent regulators of plant defense pathways and play crucial roles in coordinating plant immune responses during plant-pathogen interactions.