Detection of putative pathogenicity and virulence genes of Erysiphe pisi using genome-wide in-silico search and their suppression by er2 mediated resistance in garden pea

Genome-wide search and gene expression studies reveal candidate effectors with a role in pathogenicity and virulence in Fusarium graminearum

Fusarium graminearum causes Fusarium head blight (FHB) disease in wheat worldwide. Although F. graminearum is reported to secrete several effectors, their role in virulence and pathogenicity is unknown. The study aimed at identifying candidate genes with a role in pathogenicity and virulence using two different host systems, Arabidopsis thaliana and wheat, challenged with F. graminearum TN01. Detached leaf assay and histological studies revealed the virulent nature of TN01. A genome-wide in silico search revealed several candidate genes, of which 23 genes were selected based on reproducibility. Gene expression studies by reverse transcriptase-polymerase chain reaction (RT-PCR) in leaf tissues of Arabidopsis and the two wheat genotypes, the susceptible (Sonalika) and the resistant (Nobeoka Bozu/Nobeoka), compared with mock-treated controls in a time-course study using fungal- and plant-specific genes as internal controls revealed that these genes were differentially regulated. Further, expression of these candidates in F. graminearum-inoculated Sonalika and Nobeoka spikes compared with mock-treated controls revealed their role in pathogenicity and virulence. Gene ontology studies revealed that some of these secretory proteins possessed a role in apoptosis and ceratoplatanin and KP4 killer toxin syntheses. A three-dimensional protein configuration was performed by homology modeling using trRosetta. Further, real-time quantitative PCR (RT-qPCR) studies in F. graminearum-inoculated Arabidopsis and wheat at early time points of inoculation revealed an increased expression of the majority of these genes in Sonalika, suggesting their possible role in pathogenicity, whereas low mRNA abundance was observed for 11 of these genes in the resistant genotype, Nobeoka, compared with Sonalika, indicating their role in virulence of F. graminearum.

Perception and First Defense Responses Against Pseudomonas syringae pv. phaseolicola in Phaseolus vulgaris: Identification of Wall-Associated Kinase Receptors

Common bean (Phaseolus vulgaris) is attacked by several pathogens such as the biotrophic gamma-proteobacterium Pseudomonas syringae pv. phaseolicola. To study the P. syringae pv. phaseolicola-bean interaction during the first stages of infection, leaf discs of a susceptible bean cultivar Riñón were infected with pathogenic P. syringae pv. phaseolicola. Using this experimental system, we tested six new putative wall-associated kinase (WAK) receptors, previously identified in silico. These six P. vulgaris WAKs (PvWAKs) showed high protein sequence homology to the well-described Arabidopsis thaliana WAK1 (AtWAK1) receptor and, by phylogenetic analysis, clustered together with AtWAKs. The expression of PvWAK1 increased at very early stages after the P. syringae pv. phaseolicola infection. Time course experiments were performed to evaluate the accumulation of apoplastic H₂O₂, Ca²⁺ influx, total H₂O₂, antioxidant enzymatic activities, lipid peroxidation, and the concentrations of abscisic acid and salicylic acid (SA), as well as the expression of six defense-related genes: MEKK-1, MAPKK, WRKY33, RIN4, PR1, and NPR1. The results showed that overexpression of PR1 occurred 2 h after P. syringae pv. phaseolicola infection without a concomitant increase in SA levels. Although apoplastic H₂O₂ increased after infection, the oxidative burst was neither intense nor rapid, and an efficient antioxidant response did not occur, suggesting that the observed cellular damage was caused by the initial increase in total H₂O₂ early after infection. In conclusion, Riñón can perceive the presence of P. syringae pv. phaseolicola, but this recognition results in only a modest and slow activation of host defenses, leading to high susceptibility to P. syringae pv. phaseolicola.

Comparative proteomic analysis reveals molecular differences between incompatible and compatible interaction of Erysiphe pisi in garden pea

Comparative proteome analysis of Erysiphe pisi-infected pea genotypes; JI-2480 carrying er2 resistant gene and Arkel, the susceptible genotype by liquid chromatography- mass spectrometry (LCMS/MS QTOF) at 72 h post inoculation (hpi) revealed several differentially abundant proteins (DAPs) of both the host and the pathogen. The functional annotation of proteins through gene enrichment and KEGG pathway analyses revealed strong up-regulation of pathogenesis related protein NPR1, proteins related to defense, transportation and signal transduction, hypersensitive response, cell wall modifications, phenylpropanoid and metabolic pathways in J-72. Significant abundance of membrane-related polypeptides, kinase domains and small GTPase signal transduction-related proteins suggested their major role in plant defense. The abundance of cellular antioxidant protein, catalase and its isozyme along with calreticulin-1 and 2 in J-72 confirmed their intervention in maintaining a redox balance in powdery mildew defense. High abundance levels of Glycolysis-related proteins indicated it as a major pathway for energy source during fungal growth. The majority of pathogenicity and virulence genes were downregulated in J-72 compared to A-72, while four EKA (Effectors homologues to Avk1 and Avra10) like avirulence proteins were significantly upregulated in incompatible interaction suggesting their role in eliciting hypersensitive response in pea against E. pisi.

Comparative transcriptome of compatible and incompatible interaction of Erysiphe pisi and garden pea reveals putative defense and pathogenicity factors

Comparative transcriptome analysis of Erysiphe pisi-infected pea (Pisum sativum) genotypes JI-2480 (resistant) and Arkel (susceptible) at 72 hours post-inoculation (hpi) was carried to detect molecular components involved in compatible and incompatible interactions. Differential gene expression was observed in Arkel and JI-2480 genotype at 72 hpi with E. pisi isolate (Ep01) using EdgeR software. Out of 32 217 transcripts, 2755 transcripts showed significantly altered gene expression in case of plants while 530 were related to E. pisi (P < 0.05). The higher transcript number of differentially expressed genes demonstrated peak activity of pathogenicity genes in plants at 72 hpi. Glycolysis was observed to be the major pathway for energy source during fungal growth. Differential gene expression of plant transcripts revealed significant expression of putative receptor and regulatory sequences involved in defense in the resistant, JI-2480 compared to susceptible, Arkel genotype. Expression of genes involved in defense and hormonal signaling, genes related to hypersensitive response, reactive oxygen species and phenylpropanoid pathway in JI-2480 indicated their crucial role in disease resistance against E. pisi. Down-regulation of transcription factors like-WRKY-28 and up-regulation of several putative pattern recognition receptors in JI-2480 compared to Arkel also suggested activation of host-mediated defense responses against E. pisi in pea.