Multiple Recognitions of RXLR Effectors Is Associated with Nonhost Resistance of Pepper Against Phytophthora infestans

Nonhost resistance is a plant immune response to resist most pathogens. The molecular basis of nonhost resistance remains poorly understood but recognition of pathogen effectors by immune receptors, a response known as effector-triggered immunity (ETI), has been proposed as a component of nonhost resistance. We demonstrate that the nonhost response of the solanaceous crop plant pepper against the potato late blight pathogen Phytophthora infestans is associated with the recognition of several RXLR-type effectors. Pepper showed a localized cell death response upon inoculation with P. infestans, suggesting that recognition of effectors may contribute to nonhost resistance in this system. To further investigate the basis of the interaction between pepper and P. infestans, we performed transient expression of 54 P. infestans RXLR effectors using optimized heterologous expression methods and showed that nonhost pepper accessions recognized from 2 to 36 effectors. Among the effectors, PexRD8 and Avrblb2 induced cell death on a broad range of pepper accessions. We then analyzed the inheritance of effector-induced cell death. Segregation of effector-induced cell death in an F2 population derived from a cross between two pepper accessions fit a 15:1, 9:7 and 3:1 depending on the effector. This suggests that single or two independent/complementary dominant genes are involved in the recognitions RXLR effectors. Our findings indicate that multiple loci recognizing a series of effectors underpin nonhost resistance of pepper to P. infestans and may confer resistance durability.