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

Abstract

The biotrophic fungus, Erysiphe pisi is the chief causal agent of powdery mildew disease of garden pea. A genome-wide search using in-silico approach was carried to detect putative pathogenicity and virulence genes of E. pisi, since information about these genes and their interaction with pea is limited. Nineteen putative pathogenicity gene sequences were detected through genome-wide pathogenicity gene-search and confirmed them to be conserved in E. pisi through genomic PCRs. Fifteen of these genes expressed through reverse transcriptase-polymerase chain reaction (RT-PCR) amplifying expected band size along with fungal and plant specific internal controls. Gene sequencing and annotation revealed them to be Erysiphe-specific. A time course study was carried to monitor expression of nine of these genes through real-time quantitative (qRT)-PCR in Erysiphe-challenged plants of powdery mildew resistant pea genotype, JI-2480 carrying er2 gene and susceptible pea cultivar, Arkel. Expression of these genes was differentially and temporally regulated. They were found mostly related to signaling; cAMP-PKA (cPKA, CRP and AC) and MAPK (MST7) pathways along with MFP, TRE and PEX which are reported pathogenicity factors in other ascomycete members indicating that similar conserved pathways function in E. pisi also. These genes expressed at higher level at initial hours post inoculation (hpi) as early as 6 hpi in Arkel compared to JI-2480 implying them as pathogenicity factors. The elevated level of expression of MFP, TRE, CRP and cPKA gene sequences in E. pisi-challenged JI-2480 genotype at 12 hpi alone suggests these genes to possess a role in avirulence in JI-2480, conferring er2 mediated resistance.