Transcriptome Sequence Analysis of the Defense Responses of Resistant and Susceptible Cucumber Strains to Podosphaera xanthii

CsWRKY11 cooperates with CsNPR1 to regulate SA-triggered leaf de-greening and reactive oxygen species burst in cucumber

Salicylic acid (SA) is a multi-functional phytohormone, regulating diverse processes of plant growth and development, especially triggering plant immune responses and initiating leaf senescence. However, the early SA signaling events remain elusive in most plant species apart from Arabidopsis, and even less is known about the multi-facet mechanism underlying SA-regulated processes. Here, we report the identification of a novel regulatory module in cucumber, CsNPR1-CsWRKY11, which mediates the regulation of SA-promoted leaf senescence and ROS burst. Our analyses demonstrate that under SA treatment, CsNPR1 recruits CsWRKY11 to bind to the promoter of CsWRKY11 to activate its expression, thus amplifying the primary SA signal. Then, CsWRKY11 cooperates with CsNPR1 to directly regulate the expression of both chlorophyll degradation and ROS biosynthesis related genes, thereby inducing leaf de-greening and ROS burst. Our study provides a solid line of evidence that CsNPR1 and CsWRKY11 constitute a key module in SA signaling pathway in cucumber, and gains an insight into the interconnected regulation of SA-triggered processes.

Comparative transcriptomic profiling of the two-stage response of rice to Xanthomonas oryzae pv. oryzicola interaction with two different pathogenic strains

BACKGROUND

Two-tiered plant immune responses involve cross-talk among defense-responsive (DR) genes involved in pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), effector-triggered immunity (ETI) and effector-triggered susceptibility (ETS). Bacterial leaf streak (BLS), caused by Xanthomonas oryzae pv. oryzicola (Xoc) is an important bacterial disease that causes serious threats to rice yield and quality. Transcriptomic profiling provides an effective approach for the comprehensive and large-scale detection of DR genes that participate in the interactions between rice and Xoc.

RESULTS

In this study, we used RNA-seq to analyze the differentially expressed genes (DEGs) in susceptible rice after inoculation with two naturally pathogenic Xoc strains, a hypervirulent strain, HGA4, and a relatively hypovirulent strain, RS105. First, bacterial growth curve and biomass quantification revealed that differential growth occurred beginning at 1 day post inoculation (dpi) and became more significant at 3 dpi. Additionally, we analyzed the DEGs at 12 h and 3 days post inoculation with two strains, representing the DR genes involved in the PTI and ETI/ETS responses, respectively. Gene Ontology (GO) functional and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed on the common DEGs, which included 4380 upregulated and 4019 downregulated genes and 930 upregulated and 1383 downregulated genes identified for the two strains at 12 h post inoculation (hpi) and 3 dpi, respectively. Compared to those at 12 hpi, at 3 dpi the number of common DEGs decreased, while the degree of differential expression was intensified. In addition, more disease-related GO pathways were enriched, and more transcription activator-like effector (TALE) putative target genes were upregulated in plants inoculated with HGA4 than in those inoculated with RS105 at 3 dpi. Then, four DRs were randomly selected for the BLS resistance assay. We found that CDP3.10, LOC_Os11g03820, and OsDSR2 positively regulated rice resistance to Xoc, while OsSPX3 negatively regulated rice resistance.

CONCLUSIONS

By using an enrichment method for RNA-seq, we identified a group of DEGs related to the two stages of response to the Xoc strain, which included four functionally identified DR genes.

Transcriptomic Analysis of the Response of Susceptible and Resistant Bitter Melon (Momordica charantia L.) to Powdery Mildew Infection Revealing Complex Resistance via Multiple Signaling Pathways

The challenge of mitigating the decline in both yield and fruit quality due to the intrusion of powdery mildew (PM) fungus looms as a pivotal concern in the domain of bitter melon cultivation. Yet, the intricate mechanisms that underlie resistance against this pathogen remain inscrutable for the vast majority of bitter melon variants. In this inquiry, we delve deeply into the intricate spectrum of physiological variations and transcriptomic fluctuations intrinsic to the PM-resistant strain identified as '04-17-4' (R), drawing a sharp contrast with the PM-susceptible counterpart, designated as '25-15' (S), throughout the encounter with the pathogenic agent Podosphaera xanthii. In the face of the challenge presented by P. xanthii, the robust cultivar displays an extraordinary capacity to prolong the initiation of the pathogen's primary growth stage. The comprehensive exploration culminates in the discernment of 6635 and 6954 differentially expressed genes (DEGs) in R and S strains, respectively. Clarification through the lens of enrichment analyses reveals a prevalence of enriched DEGs in pathways interconnected with phenylpropanoid biosynthesis, the interaction of plants with pathogens, and the signaling of plant hormones. Significantly, in the scope of the R variant, DEGs implicated in the pathways of plant-pathogen interaction phenylpropanoid biosynthesis, encompassing components such as calcium-binding proteins, calmodulin, and phenylalanine ammonia-lyase, conspicuously exhibit an escalated tendency upon the encounter with P. xanthii infection. Simultaneously, the genes governing the synthesis and transduction of SA undergo a marked surge in activation, while their counterparts in the JA signaling pathway experience inhibition following infection. These observations underscore the pivotal role played by SA/JA signaling cascades in choreographing the mechanism of resistance against P. xanthii in the R variant. Moreover, the recognition of 40 P. xanthii-inducible genes, encompassing elements such as pathogenesis-related proteins, calmodulin, WRKY transcription factors, and Downy mildew resistant 6, assumes pronounced significance as they emerge as pivotal contenders in the domain of disease control. The zenith of this study harmonizes multiple analytical paradigms, thus capturing latent molecular participants and yielding seminal resources crucial for the advancement of PM-resistant bitter melon cultivars.

Deciphering the molecular basis of abiotic stress response in cucumber (Cucumis sativus L.) using RNA-Seq meta-analysis, systems biology, and machine learning approaches

Abiotic stress in cucumber (Cucumis sativus L.) may trigger distinct transcriptome responses, resulting in significant yield loss. More insight into the molecular underpinnings of the stress response can be gained by combining RNA-Seq meta-analysis with systems biology and machine learning. This can help pinpoint possible targets for engineering abiotic tolerance by revealing functional modules and key genes essential for the stress response. Therefore, to investigate the regulatory mechanism and key genes, a combination of these approaches was utilized in cucumber subjected to various abiotic stresses. Three significant abiotic stress-related modules were identified by gene co-expression network analysis (WGCNA). Three hub genes (RPL18, δ-COP, and EXLA2), ten transcription factors (TFs), one transcription regulator, and 12 protein kinases (PKs) were introduced as key genes. The results suggest that the identified PKs probably govern the coordination of cellular responses to abiotic stress in cucumber. Moreover, the C2H2 TF family may play a significant role in cucumber response to abiotic stress. Several C2H2 TF target stress-related genes were identified through co-expression and promoter analyses. Evaluation of the key identified genes using Random Forest, with an area under the curve of ROC (AUC) of 0.974 and an accuracy rate of 88.5%, demonstrates their prominent contributions in the cucumber response to abiotic stresses. These findings provide novel insights into the regulatory mechanism underlying abiotic stress response in cucumber and pave the way for cucumber genetic engineering toward improving tolerance ability under abiotic stress.

The pivotal role of MYB transcription factors in plant disease resistance

MAIN CONCLUSION

MYB transcription factors are essential for diverse biology processes in plants. This review has focused on the potential molecular actions of MYB transcription factors in plant immunity. Plants possess a variety of molecules to defend against disease. Transcription factors (TFs) serve as gene connections in the regulatory networks controlling plant growth and defense against various stressors. As one of the largest TF families in plants, MYB TFs coordinate molecular players that modulate plant defense resistance. However, the molecular action of MYB TFs in plant disease resistance lacks a systematic analysis and summary. Here, we describe the structure and function of the MYB family in the plant immune response. Functional characterization revealed that MYB TFs often function either as positive or negative modulators towards different biotic stressors. Moreover, the MYB TF resistance mechanisms are diverse. The potential molecular actions of MYB TFs are being analyzed to uncover functions by controlling the expression of resistance genes, lignin/flavonoids/cuticular wax biosynthesis, polysaccharide signaling, hormone defense signaling, and the hypersensitivity response. MYB TFs have a variety of regulatory modes that fulfill pivotal roles in plant immunity. MYB TFs regulate the expression of multiple defense genes and are, therefore, important for increasing plant disease resistance and promoting agricultural production.