The bacterial pathogen Pseudomonas syringae DC3000 induces defense responses in diverse maize inbred lines

Phytopathogens translocate virulence (effector) proteins into plant cells to circumvent host immune responses during infection. One such pathogen is Pseudomonas syringae DC3000 (DC3000), which secretes at least thirty-six effectors into host cells, of which a subset elicit host defense responses in crop plant species such as wheat. However, it is unknown whether P. syringae DC3000 is capable of activating immune responses in maize inbreds. We, therefore, screened a diverse maize germplasm collection for effector-dependent recognition of P. syringae DC3000. As a control, we infiltrated Pseudomonas syringae DC3000(D36E) (D36E), a derivative of P. syringae DC3000 that lacks all endogenous effectors. In our evaluations, we observed a variety of responses to P. syringae DC3000 in maize and scored the phenotypes as either no observable response (N) or as one of three responses: weak chlorosis (WC), chlorosis (C) that gives way to cell death, and hypersensitive reaction (HR). Of the twenty-six maize inbreds screened, 13 were scored as N, 2 as WC, 2 as C, and 9 as HR. Importantly, no maize line responded to P. syringae D36E, demonstrating the responses observed are likely dependent upon recognition of one or more P. syringae effectors. Consistent with the phenotypic responses, maize inbred lines that recognize P. syringae DC3000 accumulated detectable hydrogen peroxide within the infiltrated regions. Collectively, our results demonstrate that diverse maize inbred lines likely encode disease resistance proteins that recognize the activities of one or more P. syringae DC3000 effectors.