Rice roots recruit Bacillus via the secretion of heptadecanoic acid

Plants actively recruit beneficial rhizosphere microorganisms to enhance immunity, though the molecular mechanisms are largely unclear. Here we identified a complete OsMAPK-OsWRKY 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 OsMKK4-OsMPK6 cascade and Bacillus recruitment. Loss-of-function mutants of OsMKK4 and OsMPK6 reduce rhizosphere Bacillus abundance by 82% and 79%, respectively. As the substrates of OsMPK6, OsWRKY24/53/70 transcription factors activate OsKCS2, which encodes a β‑ketoacyl-CoA synthase involved in heptadecanoic acid biosynthesis. Mutations of OsWRKY24/53/70 or OsKCS2 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.