Oral: Fungal Pathogenicity
A forward genetic screen in Phomopsis longicolla provides unique insights into pathogenesis
M. ZACCARON (1), S. Sharma (2), W. Fagundes (2), W. Hawkins (2), N. Lawson (2), J. Ridenour (2), J. Smith (2), B. Dhillon (2), J. Rupe (2), B. Bluhm (2) (1) University of Arkansas, U.S.A.; (2) University of Arkansas, U.S.A.
Phomopsis longicola (Hobbs) causes Phomopsis seed decay of soybean (Glycine max), and also causes lesions on soybean stems, pods, and petioles. P. longicola can also exist endophytically within soybean stems, which has given rise to the hypothesis that pathogenesis occurs when the pathogen transitions from endophytic or hemibiotrophic growth to necrotrophy. In this study, a forward genetic screen was performed to elucidate genetic mechanisms underlying necrotrophy, and a RAD-seq approach was adapted to characterize genomic lesions in selected mutants. A collection of 1114 tagged, insertional mutants was created via Agrobacterium-mediated transformation, and mutants were evaluated individually in soybean stems for their ability to induce necrosis and form pycnidia. Six mutants induced significantly less necrosis in soybean stems than the wild-type strain, and four formed significantly fewer pycnidia. No gain-of-function mutations (increased necrosis) were observed. A modified RAD-seq protocol developed to identify the site of insertion was applied to a mutant significantly reduced in its ability to cause stem necrosis; a single copy of the disruption cassette integrated into the presumed promoter region of a cellobiohydrolase. This study describes new tools to dissect the interaction between P. longicola and soybean, and provides new insight into conserved mechanisms underlying stem, pod, and seed necrosis caused by P. longicola.