The genetic basis of the interaction between Magnaporthe oryzae and Bacillus velezensis strain S4

Abstract

The fungus Magnaporthe oryzae is the causative agent of rice blast, a devastating rice disease. Members of the Bacillus subtilis group are used as biocontrol agents because they produce numerous bioactive secondary metabolites. It was previously shown that soil isolate Bacillus velezensis strain S4 has antifungal activity against M. oryzae. We sought to pinpoint which genes or pathways in strain S4 direct the biosynthesis of the active antifungal molecule(s) and which genes or pathways in M. oryzae respond when exposed to the bacterium or the antifungal. We identified biosynthetic clusters in strain S4 which are likely contributors to the antifungal activity. An uncharacterized putative biosynthetic cluster was identified and selected for genetic inactivation experiments and heterologous expression in Escherichia coli. A preexisting transcriptome profile of M. oryzae during exposure to strain S4 was used to identify genes which may be responding to the presence of the bacterium or its antifungal agent. Treatment of M. oryzae with supernatant from strain S4 causes deformities of its appressoria, hyphae, and conidia and appears to stimulate production of melanin.