TheParastagonospora nodorumnecrotrophic effector SnTox5 targets the wheat geneSnn5and facilitates entry into the leaf mesophyll

Abstract

AbstractParastagonospora nodorum, causal agent of septoria nodorum blotch, is a destructive necrotrophic fungal pathogen of wheat.P. nodorumis known to secrete several necrotrophic effectors that target wheat susceptibility genes that trigger classical biotrophic resistance responses but resulting in susceptibility rather than resistance. SnTox5 targets the wheat susceptibility geneSnn5to induce necrosis. In this study, we used full genome sequences of 197P. nodorumisolates collected from the US and their disease phenotyping on theSnn5differential line LP29, to perform genome wide association study analysis to localize theSnTox5gene to chromosome 8 ofP. nodorum.SnTox5was validated using gene transformation and CRISPR-Cas9 based gene disruption.SnTox5encoded a small secreted protein with a 22 and 45 amino acid secretion signal and a pro sequence, respectively. TheSnTox5gene is under purifying selection in the Upper Midwest but under strong diversifying selection in the South/East regions of the US. Comparison of wild type and SnTox5-disrupted strains on wheat lines with and without the susceptibility targetSnn5showed that SnTox5 has two functions, 1) facilitating colonization of the mesophyll layer, and 2) targeting Snn5 to induce programmed cell death to provide cellular nutrient to complete its necrotrophic life cycle.