Avirulence Proteins AvrBs7 from Xanthomonas gardneri and AvrBs1.1 from Xanthomonas euvesicatoria Contribute to a Novel Gene-for-Gene Interaction in Pepper

Abstract

A novel hypersensitive resistance (HR) in Capsicum baccatum var. pendulum against the bacterial spot of pepper pathogen, Xanthomonas gardneri, was introgressed into C. annuum cv. Early Calwonder (ECW) to create the near-isogenic line designated as ECW-70R. A corresponding avirulence gene avrBs7, in X. gardneri elicited a strong HR in ECW-70R. A homolog of avrBs7, avrBs1.1, was found in X. euvesicatoria 85-10, which showed delayed HR on ECW-70R leaves. Genetic analysis confirmed the presence of a single dominant resistance gene, Bs7, corresponding to the two avr genes. Both AvrBs7 and AvrBs1.1 share a consensus protein tyrosine phosphatase (PTP) active site domain and can dephosphorylate para-nitrophenyl phosphate. Mutation of Cys(265) to Ser in the PTP domain and subsequent loss of enzymatic activity and HR activity indicated the importance of the PTP domain in the recognition of the Avr protein by the Bs7 gene transcripts. Superpositioning of AvrBs7 and AvrBs1.1 homology models indicated variation in the geometry of the loops adjacent to the active sites. These predicted structural differences might be responsible for the differences in HR timing due to differential activation of the resistance gene. Mutating the PTP domain of AvrBs1.1 to match that of AvrBs7 failed to activate HR on ECW-70R, indicating the possibility of differential substrate specificities between AvrBs1.1 and AvrBs7.

Resistência à mancha-bacteriana e características agronômicas de linhas recombinadas de Capsicum annuum L.

“…Genes que conferem resistência à mancha-bacteriana já foram identificados, sendo seis genes dominantes (Bs1,Bs2,Bs3,Bs4, BsT e Bs7) e, pelo menos, dois recessivos (bs5 e bs6) (Stall et al, 2009;Potnis et al, 2012). Há também relatos de pelo menos três genes recessivos controlando a resistência à mancha-bacteriana em um cruzamento entre um pimentão suscetível (UENF 1421) e uma pimenta resistente (UENF 1381) (Riva et al, 2004a).…”

Resistance in Capsicum spp. to anthracnose affected by different stages of fruit development during pre- and post-harvest

“…However, according to Mahasuk et al (2009a), resistant accessions of C. chinense are most commonly used in breeding programs aiming at resistance to anthracnose because this species belongs to the same gene pool as C. annuum, which indicates a greater chance of success in the transfer of resistance genes among species. However, successful crosses were carried out between C. annuum and C. baccatum to transfer the gene Bs7, which confers resistance to bacterial spot in sweet pepper (Potnis et al, 2012), demonstrating that gene transfer between these two species is possible. The accessions UENF 1718 and UENF 1797 belonging to C. baccatum var.…”

Research Article Multiple genetic resistances in Capsicum spp.

“…Nonetheless, other interactive genes with avirulence alleles (avrBsT, avrBs4C and avrBs7) have been described in bacterial isolates, promoting HR. As examples, we may cite BsT (Minsavage et al, 1990), Bs4C (Straub et al, 2012, and Bs7 (Potnis et al, 2012).…”

“…The latter is the most effective among the control measures. Several studies have aimed to understand the interaction between Capsicum and Xanthomonas (Jones et al, 2004;Vallejos et al, 2010;Ryan et al, 2011;Potnis et al, 2012), seeking for resistance sources (Costa et al, 2002;Riva-Souza et al, 2009;Moreira et al, 2013) by characterization of the gene expression (Jones et al, 1998;Riva et al, 2004b;Kiss et al, 2016), genetic inheritance (Riva et al, 2004a), developing molecular markers for resistance genes (Holdsworth and Mazourek, 2015), and use of transgenics (Zipfel and Jones, 2015). Despite these studies, few pure line cultivars that are resistant to BS are available in the seed market.…”