Effector mining from the Erysiphe pisi haustorial transcriptome identifies novel candidates involved in pea powdery mildew pathogenesis

Powdery mildews are significant fungal pathogens that cause crop yield losses of ~25-60%. They are true obligate biotrophs, which means that they depend entirely on living host plants for their survival. To establish biotrophic relationships with their host, these fungi secrete an arsenal of effector molecules, primarily through specialized infection structures termed haustoria.

A research article published in Molecular Plant Pathology by Dr. Chandran’s group describes the identification of 167 effector candidates from the pea powdery mildew Erysiphe pisi (Ep) via high-throughput sequencing of an enriched haustorial cDNA library. Phylogenetic analysis revealed that EpCSEPs are highly diverse, but unlike cereal powdery mildew-CSEPs, exhibit extensive sequence similarity with effectors from other powdery mildews. Quantitative PCR of a subset of EpCSEPs revealed that they are preferentially expressed in haustoria and at distinct infection stages. The functional role of two effector candidates was probed via a double-stranded (ds) RNA-based RNA interference approach. Foliar application of individual EpCSEP-dsRNAs resulted in a marked reduction in disease symptoms, suggesting that these EpCSEPs play important roles in pea powdery mildew pathogenesis. Homology modeling revealed that both EpCSEPs are analogous to fungal ribonucleases, and may possess RNA cleavage activity. To obtain deeper insights into their role as virulence factors, future investigations will focus on the identification of their host targets.

Front cover: Comprehensive profiling of the haustorial transcriptome of the pea powdery mildew Erysiphe pisi identified 167 candidate secreted effector proteins (CSEPs). This CIRCOS plot summarizes key features. Outer squares show protein family (cyan, ribonuclease/ribotoxin; red, MULE transposase domain; orange, aspartic peptidase; green, hydrolase fold; pink, histidine phosphatase; blue, peptidase S8; grey, unknown); circles show CSEPs harbouring the YxC (blue), FxC (pink) or WxC (green) motif; grid shows CSEPs with homologous sequences in E. necator (red), Golovinomyces orontii (green) and Blumeria graminis f. sp. hordei (blue); bars show gene expression (yellow low, red high); radiating neighbour-joining phylogenetic tree in centre.

Full article: https://bsppjournals.onlinelibrary.wiley.com/doi/10.1111/mpp.12862


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