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Characterization of a Sudden Death Syndrome (SDS) Core Effector Using Comparative Genomics between SDS-causing and non-SDS-causing Fusarium species

Hao-Xun Chang: Department of Plant Soil and Microbial Sciences, Michigan State University

<div>In the United States, sudden death syndrome (SDS) is a destructive soybean disease caused by the soil-borne fungus <em>Fusarium virguliforme</em>. Other species including <em>F. azukicola</em>, <em>F. brasiliense</em>, and <em>F. tucumaniae</em> from South America are found to cause SDS foliar symptoms. These fungi produce phytotoxins, which are translocated from infected roots to soybean leaves, and consequently induce interveinal chlorosis and necrosis. With the hypothesis that SDS-causing <em>Fusarium</em> have acquired specialized phytotoxic effectors, this study aims to identify the SDS core effector(s) (SCE) that elicits the distinct SDS foliar symptoms. A comparative genomics approach between nine strains of SDS-causing species and nine strains of non-SDS-causing <em>Fusarium</em> species was performed. These 18 strains have 1,100 to 2,300 putative effectors, but after filtering out orthologous genes, only one putative effector was found for the nine strains of SDS-causing <em>Fusarium</em> species. This SCE of <em>F. virguliforme</em> (FvSCE) is a 228 bp gene without available annotation. The FvSCE was cloned into an overexpression system mediated by <em>Soybean mosaic virus</em>, and the recombined vector was bombarded into soybean leaves to visualize its phytotoxicity. A CRISPR-Cas9-directed split-marker approach was used to create the FvSCE knockout mutant. This study will illuminate the function of FvSCE linked to SDS foliar symptoms and provide novel insights into the evolution of core effectors in plant pathogenic fungi.</div>