Evolutionary balance between LRR domain loss and young NBS–LRR genes production governs disease resistance in Arachis hypogaea cv. Tifrunner

BACKGROUND: Cultivated peanut (Arachis hypogaea L.) is an important oil and protein crop, but it has low disease resistance; therefore, it is important to reveal the number, sequence features, function, and evolution of genes that confer resistance. Nucleotide-binding site–leucine-rich repeats (NBS–LRRs) are resistance genes that are involved in response to various pathogens. RESULTS: We identified 713 full-length NBS–LRRs in A. hypogaea cv. Tifrunner. Genetic exchange events occurred on NBS–LRRs in A. hypogaea cv. Tifrunner, which were detected in the same subgenomes and also found in different subgenomes. Relaxed selection acted on NBS–LRR proteins and LRR domains in A. hypogaea cv. Tifrunner. Using quantitative trait loci (QTL), we found that NBS–LRRs were involved in response to late leaf spot, tomato spotted wilt virus, and bacterial wilt in A. duranensis (2 NBS–LRRs), A. ipaensis (39 NBS–LRRs), and A. hypogaea cv. Tifrunner (113 NBS–LRRs). In A. hypogaea cv. Tifrunner, 113 NBS–LRRs were classified as 75 young and 38 old NBS–LRRs, indicating that young NBS–LRRs were involved in response to disease after tetraploidization. However, compared to A. duranensis and A. ipaensis, fewer LRR domains were found in A. hypogaea cv. Tifrunner NBS–LRR proteins, partly explaining the lower disease resistance of the cultivated peanut. CONCLUSIONS: Although relaxed selection acted on NBS–LRR proteins and LRR domains, LRR domains were preferentially lost in A. hypogaea cv. Tifrunner compared to A. duranensis and A. ipaensis. The QTL results suggested that young NBS–LRRs were important for resistance against diseases in A. hypogaea cv. Tifrunner. Our results provid insight into the greater susceptibility of A. hypogaea cv. Tifrunner to disease compared to A. duranensis and A. ipaensis.