Variability and evolution of NBS-LRR genes in Agave tequilana and their differential response to Lasiodiplodia infection

NBS domain-containing sequences from the Agave tequilana transcriptome shotgun assembly were identified, characterized, and classified based on their physicochemical properties and motif structure, which resulted in a differential response to Lasiodiplodia sp. infection. Agave tequilana is an important crop in Mexico that is susceptible to many pathogens and adverse conditions. In plants, NBS-LRR genes are involved in the physiological response to pathogenic infection. Forty-six partial NBS-LRR sequences were identified in the transcriptome shotgun assembly and were classified into five subclasses (CNL, CN, NL, N, and L) belonging to the non-TIR class in the NBS-LRR family. The identified sequences encode functional NBS-LRR proteins based on physicochemical properties, gene structure and motif analysis, functional annotation, and gene ontology. Phylogenetic analysis showed that these genes were clustered into seven groups (Groups I-VII). These groups were under diversifying selection pressure (Ka/Ks rates < 1) except for Group V (Ka/Ks rate = 1.23) which formed more recently (9 Mya). Specific primers designed for Groups I, II and V showed that the expression response to pathogenic Lasiodiplodia strains varied among the different NBS-LRR gene groups. The highest NBS-LRR gene transcript induction was obtained at 48 h, and the expression peaks were preceded by an increase in the concentration of endogenous salicylic acid, which has been associated with the activation of some NBS-LRR genes, suggesting that each group may have a specific defence response function.