Identification of Target Proteins Required for Cell Death Induced by Phytophthora infestans Core Effectors Recognized by Nonhost Pepper

Abstract

Phytophthora infestans is one of the most devastating plant pathogenic oomycetes, which causes severe yield loss of Solanum species including economically important crops, such as potato and tomato. Like most successful pathogens, P. infestans secretes diverse sets of effector proteins into host cell to promote pathogen proliferation. Contrary, various plant resistance (R) genes recognize effectors and induce effector-triggered immunity (ETI) to suppress pathogen proliferation. Non-host resistance (NHR), the most common form of immune response of plants, is defined as the resistance of a plant species against all isolates of a pathogen species and durable in nature. In recent researches, effectors are regarded as a key factors for understanding host range and also NHR in terms of ETI. Since pepper is non-host plant against P. infestans, 57 RXLR effectors were predicted in silico using genome information. And these CEs (Core effectors) were transiently expressed in two pepper accessions to identify candidate AVR (avirulence) genes which associated with NHR. Eight CEs induced cell death on CM334 or ECW30R suggesting that these effectors might be recognized by corresponding R genes of pepper. Among them, CE31, CE66 and CE86 (PITG_07550, PITG_15930, and PITG_23226, respectively) were selected for further investigation on their roles in cell death of identifying target proteins. These three putative effectors affected pathogen growth on host plant. And among them, especially with CE86, heat shock proteins (HSPs) 70kDa homologs were identified as potential host target proteins in host plant, Nicotiana benthamiana. Furthermore, exploiting CE31 and CE66 to identify NHR genes which recognize these two effectors by co-expressing with 415 pepper NB-LRR coding genes, but none of these putative R genes induced cell death when co-expressed with selected CEs. In conclusion, screening results from this paper suggest the multiple candidate effectors which possibly involved in NHR of pepper against P. infestans. And three selected effectors (CE31, CE66, and CE86) could be exploited for further experiments to understand more detailed mechanisms of NHR in terms of ETI.