AVR2-induced immunity to Phytophthora infestans by unrelated resistance genes of Solanum species

Abstract

Late blight caused by the oomycete Phytophthora infestans, remains the most devastating disease for potato. Wild Solanum species provide a valuable resource of resistance (R) genes. Yet, for educated R gene deployment, molecular knowledge of the corresponding avirulence (Avr) gene is essential. AVR2 is an RXLR effector of P. infestans with an important role in late blight development. AVR2 is recognized by the R2 family from wild Mexican Solanum species and by the dissimilar Rpi-mcq1 family from Peru. Herewith, we present the first example of two sequence unrelated R proteins that recognize the same effector. Interestingly, the recognition of AVR2 by Rpi-mcq1 and R2 displays an overlapping, but not identical specificity. Disease tests with a wide panel of P. infestans isolates on transgenic R2 and Rpi-mcq1 potatoes show different patterns of disease resistance. Studies of the AVR2 family revealed that this is a highly diverse effector family that is differentially expressed in P. infestans isolates. We found new AVR2 alleles and we hypothesize that the AVR2 family is co-evolving with two different R gene families. R2-mediated AVR2 recognition requires the interaction with the BSU-like 1 (BSL1) protein, whereas the Rpi-mcq1-mediated recognition involves a different signaling pathway. These studies contribute to understanding the R-AVR interaction, which is instrumental to improve R gene-based breeding and deployment against late blight in potato.