Identification of the Capsicum baccatum NLR Protein CbAR9 Conferring Disease Resistance to Anthracnose

Anthracnose is caused by Colletotrichum species and is one of the most virulent fungal diseases affecting chili pepper (Capsicum) yield globally. However, the noble genes conferring resistance to Colletotrichum species remain largely elusive. In this study, we identified CbAR9 as the causal locus underlying the large effect quantitative trait locus CcR9 from the anthracnose-resistant chili pepper variety PBC80. CbAR9 encodes a nucleotide-binding and leucine-rich repeat (NLR) protein related to defense-associated NLRs in several other plant species. CbAR9 transcript levels were induced dramatically after Colletotrichum capsici infection. To explore the biological function, we generated transgenic Nicotiana benthamiana lines overexpressing CbAR9, which showed enhanced resistance to C. capsici relative to wild-type plants. Transcript levels of pathogenesis-related (PR) genes increased markedly in CbAR9-overexpressing N. benthamiana plants. Moreover, resistance to anthracnose and transcript levels of PR1 and PR2 were markedly reduced in CbAR9-silenced chili pepper fruits after C. capsici infection. Our results revealed that CbAR9 contributes to innate immunity against C. capsici.

Automated summary

In this study, the researchers identified CbAR9 as the genetic locus responsible for resistance to Colletotrichum species in chili peppers. CbAR9 is a gene that encodes an NLR protein related to defense in other plant species, and its expression is significantly induced after infection by Colletotrichum capsici. Overexpression of CbAR9 in Nicotiana benthamiana led to enhanced resistance to C. capsici and increased expression of pathogenesis-related genes, while silencing CbAR9 in chili pepper fruits resulted in reduced resistance to anthracnose and decreased expression of PR1 and PR2 genes after infection. These findings highlight the role of CbAR9 in innate immunity against C. capsici.