Dissecting root-specific non-conventional effector-triggered immunity and its role in defense and shifting the microbiome.

Plant roots are extremely heterogeneous and non-photosynthetic tissue that is drastically different from leaves. Pioneering studies have revealed the existence of pattern-triggered immune responses in roots; however, whether roots mount tissue-specific effector-triggered immunity (ETI) is a fundamental question in plant immunity. By utilizing inducible effector-expressing lines, we systematically characterize non-conventional physiological and molecular responses during ETI activation in roots. Root ETI seems to be weaker than leaf ETI, evidenced by restricted cell death in the transition zone and fewer number of differentially expressed genes (DEGs). Root ETI also shows much higher DEG overlap with Pep1-triggered immunity than with Flg22-triggered responses, which is the opposite trend in leaves. We find that both PEPR1/2 receptors and BIK1, WRKY42 are required for induced root ETI responses. By comparing root responses to wild type and the T3SS mutant of Ralstonia solanacearum in the Nd-1 ecotype, we confirm that natural root ETI responses show similarities to induced ETI. Our work reveals tissue-specific features of root ETI and provides new insights into engineering root disease resistance in agriculture.