Identification of Asian Soybean Rust (Phakopsora pachyrhizi) Effectors Inducing Hypersensitive Cell Death on Pepper

Abstract

Phakopsora pachyrhizi is a causal agent of Asian Soybean Rust (ASR) notably affecting the yield loss of soybean (Glycine max) and delivers small molecules called effectors into the host cells to suppress the host immunity. Six resistance genes against ASR have been reported in soybean but none of them has cloned. Nonhost resistance (NHR) is the most common defense in nature and defined as a type of resistance to all isolates of a pathogen species. The recognition of effectors by plant resistance (R) genes induces strong resistance response called effector-triggered immunity (ETI), which is considered as an important factor of NHR. Since peppers are nonhost plants against ASR, two pepper cultivars including Capsicum annuum cv. CM334 and ECW-30R were inoculated with 81 effector candidates of P. pachyrhizi to elucidate the nonhost interaction. As results of the screening, five and seventeen effector candidates induced cell death on CM334 and ECW-30R, respectively. Two effector candidates including Pp09 and Pp16 inducing cell death on both cultivars were selected for identification of nonhost R genes. These effector candidates played a role in virulence of not oomycetes but bacterial pathogens on N. benthamiana. To identify R genes of nonhost plant pepper against ASR, in planta interaction between 444 putative pepper R genes and selected candidate effector candidates was conducted. However, none of the putative R genes of pepper interact with any candidate effector candidates of P. pachyrhizi by one-by-one coexpression in N. benthamiana. Taken together, the findings suggested that multiple effector candidates of ASR inducing cell death on peppers have opened up possibilities in the role of ETI in NHR of pepper