Root-specific camalexin biosynthesis controls the plant growth-promoting effects of multiple bacterial strains

Significance To address mechanisms by which plants control their associated microorganisms, we designed a screen using a bacterial activity in soil. A detailed analysis of a candidate gene from the screen, CYP71A27 , identified an additional root-specific component of synthesis of camalexin, a natural product involved in plant defense against pathogens. Loss of function of CYP71A27 affected not only the microbiota in soil but also interactions with single plant growth-promoting bacteria. The loss of the promoting effect in the mutants could be complemented chemically by adding camalexin to the bacteria. Thus, our study identified an additional role for camalexin in facilitating interaction with microbes in the rhizosphere and an additional gene for its synthesis.