Abstract

Plants actively recruit beneficial rhizosphere microorganisms to enhance immunity, though the molecular mechanisms are largely unclear. Here we identified a complete Os MAPK– Os WRKY pathway of rice rhizosphere Bacillus recruitment via root secretion of heptadecanoic acid upon rice blast occurrence. In field trials, enrichment of Bacillus in their rhizospheres was associated with higher disease resistance of rice. Integrated omics analyses demonstrated a strong correlation between the activation of the Os MKK4– Os MPK6 cascade and Bacillus recruitment. Loss-of-function mutants of Os MKK4 and Os MPK6 reduce rhizosphere Bacillus abundance by 82% and 79%, respectively. As the substrates of Os MPK6, Os WRKY24/53/70 transcription factors activate Os KCS2 , which encodes a β‑ketoacyl-CoA synthase involved in heptadecanoic acid biosynthesis. Mutations of Os WRKY24/53/70 or Os KCS2 reduce root-secreted heptadecanoic acid by 15–28% and impair Bacillus colonization. Heptadecanoic acid application recapitulated Bacillus recruitment and disease resistance. Collectively, our results demonstrate that the MAPK pathway regulates heptadecanoic acid synthesis, which controls Bacillus recruitment as well as rice blast disease resistance.