Reduced fungal protein acetylation mediates the antimicrobial activity of a rhizosphere bacterium against a phytopathogenic fungus.

Rhizosphere microbes can protect plants from phytopathogens, but the molecular mechanisms are often poorly understood. Here, we report that a rhizosphere bacterium, Bacillus amyloliquefaciens strain TG1-2 displays antimicrobial activity against various phytopathogenic fungi and oomycetes, in a process that is mediated by the NatA acetyltransferase complex in the phytopathogenic fungus Verticillium dahliae. We show that acetylation of the molecular chaperone Hsp83 by NatA facilitates the formation of a co-chaperone complex Hsp83-Sti1-Hsp70 involved in protein quality control. Dysfunction of NatA or disruption of Hsp83 acetylation results in dissociation of the co-chaperon complex, increasing protein degradation and fungal apoptosis. Notably, TG1-2 and its major antimicrobial compound surfactin induce a reduction in Hsp83 acetylation, enhancing protein degradation and fungal apoptosis. Thus, our study provides insights into the mechanisms underlying the antimicrobial action of a rhizosphere strain against phytopathogenic fungi.