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Chemical genomics reveals resistant soybean line inhibits Sclerotinia sclerotiorum by targeting its ergosterol biosynthesis pathway

Ashish Ranjan: University of Wisconsin-Madison

<div>In nature, plants employ various strategies to overcome pathogen attacks including production of antimicrobial compounds. We study the interaction between the fungal pathogen, <em>Sclerotinia sclerotiorum</em>, and soybean. While screening soybean lines for resistance to <em>S. sclerotiorum</em>, we observed a distinct red discoloration at the site of inoculation in resistant soybean lines, accompanied by a complete arrest of fungal growth. We hypothesized that the resistant lines produce antifungal compounds in response to <em>S. sclerotiorum</em> challenge. We recovered the red stem extract (RSE), and assessed its effect on fungal growth. <em>S. sclerotiorum</em> growth was markedly inhibited in the presence of RSE. The mode of action and the antifungal activity of RSE were further tested by performing chemical genomics in a yeast mutant library. Mutants of genes involved in phospholipid and ergosterol biosynthesis were significantly sensitive to RSE. The chemical genomics profile of RSE was compared to other known drug profiles, and was found to have significantly similar activity to ergosterol biosynthesis targeting drugs. This was further substantiated by the significant decrease in ergosterol levels in <em>S. sclerotiorum</em> when challenged with RSE. Overall, we show that resistance to <em>S. sclerotiorum</em> in soybean involves the upregulation of antifungal activity, targeting ergosterol biosynthesis in the fungus. This work may help uncover novel bioactive antimicrobial compounds with agricultural and pharmaceutical importance.</div>