Dominant, heritable resistance to stewart's wilt in maize is associated with an enhanced vascular defense response to infection with pantoea stewartii

Vascular wilt bacteria such as Pantoea stewartii, the causal agent of Stewart's bacterial wilt of maize (SW), are destructive pathogens that are diffith to control. These bacteria colonize the xylem, where they form biofilms that block sap flow leading to characteristic wilting symptoms. Heritable forms of SW resistance exist and are used in maize breeding programs but the underlying genes and mechanisms are mostly unknown. Here, we show that seedlings of maize inbred lines with panl mutations are highly resistant to SW. However, current evidence suggests that other genes introgressed along with panl are responsible for resistance. Genomic analyses of panl lines were used to identify candidate resistance genes. In-depth comparison of R stewartii interaction with susceptible and resistant maize lines revealed an enhanced vascular defense response in panl lines characterized by accumulation of electron-dense materials in xylem conduits visible by electron microscopy. We propose that this vascular defense response restricts R stewartii spread through the vasculature, reducing both systemic bacterial colonization of the xylem network and consequent wilting. Though apparently unrelated to the resistance phenotype ofpanl lines, we also demonstrate that the effector WtsE is essential for P. stewartii xylem dissemination, show evidence for a nutritional immunity response to P. stewartii that alters xylem sap composition, and present the first analysis of maize transcriptional responses to P. stewartii infection.