Abstract
Nonhost resistance (NHR) is a plant immune response to resist most pathogens. The molecular basis of NHR is poorly understood, but recognition of pathogen effectors by immune receptors, a response known as effector-triggered immunity, has been proposed as a component of NHR.We performed transient expression of 54 Phytophthora infestansRXLR effectors in pepper (Capsicum annuum) accessions. We used optimized heterologous expression methods and analyzed the inheritance of effector-induced cell death in an F2 population derived from a cross between two pepper accessions.Pepper showed a localized cell death response upon inoculation with P. infestans, suggesting that recognition of effectors may contribute to NHR in this system. Pepper accessions recognized as many as 36 effectors. Among the effectors, PexRD8 and Avrblb2 induced cell death in a broad range of pepper accessions. Segregation of effector-induced cell death in an F2 population derived from a cross between two pepper accessions fit 15 : 1, 9 : 7 or 3 : 1 ratios, depending on the effector.Our genetic data suggest that a single or two independent/complementary dominant genes are involved in the recognition of RXLR effectors. Multiple loci recognizing a series of effectors may underpin NHR of pepper to P. infestans and confer resistance durability.
Highlights
Plants are challenged by numerous pathogens including fungi, bacteria and viruses
Nonhost resistance of pepper against P. infestans is associated with hypersensitive cell death
In order to investigate how nonhost pepper plants respond to P. infestans and characterize its nonhost defense response, the detached leaves of pepper, tomato and potato plants were inoculated with a zoospore suspension of P. infestans isolate 88069 (5 9 104 spores mlÀ1)
Summary
Most plants are resistant to most pathogens and disease is the exception in nature (Huitema et al, 2003) This phenomenon is known as nonhost resistance (NHR), an immune response of plant species against all isolates of a microorganism that cause disease on other plant species (Sumit et al, 2012). The mechanism of NHR comprises of several components, including pre-formed and induced immunity (Thordal-Christensen, 2003). Induced immunity includes pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) (Thordal-Christensen, 2003; Zhao et al, 2005; Jones & Dangl, 2006). The relative contribution of ETI and PTI to NHR may relate to the evolutionary divergence time between host and nonhost plants. It was suggested that the relative contribution of ETI increases with decreasing phylogenetic divergence time between two plant species (Schulze-Lefert & Panstruga, 2011)
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