Genome-wide Identification of Disease Resistance Genes (R Genes) in Wheat

Proteins encoded by plant resistance genes (R genes) detect pathogenic effectors and initiate immune responses. Although R genes in many plant genomes are identified, they are yet to be identified in wheat. The major objectives of this project were to conduct genome-wide identification of the NB-ARC-encoding R genes in wheat (Triticum aestivum L.) and assess their genomic architecture and potential functional divergence. Wheat protein sequences were obtained from the Ensembl Genomes database, and genes were identified using interpro program. Chromosomal locations of the R genes were determined and syntenic analyses were performed. Altogether, 2151 wheat NB-ARC-encoding genes were identified, among which 1298 genes formed 547 gene clusters. Many of these gene clusters included highly similar genes likely formed by tandem duplications. Among the NB-ARC-encoding genes, 1552 ([~]72%) encode Leucine-Rich Repeats (LRRs), 802 are Coiled-Coil (CC) domain-encoding CC-NBS-LRR (CNL) genes and three are Resistance to Powdery mildew 8 (RPW8) domain-encoding RPW8-NBS-LRR (RNL) genes. Surprisingly, five of the NB-ARC-encoding genes encoded a Toll/Interleukin-1 Receptor (TIR), with no LRR, known as TN genes. CNL clades formed similar nesting patterns with a large expansion of CNL-C group like previously reported findings in wheat relatives. Comparisons of the wheat genome with barley (Hordeum vulgare L.) and Tauschs goatgrass (Aegilops tauschii Coss.), showed similar locations for homologous NB-ARC-encoding genes. These results showed that R genes in wheat have diversified through duplication to encode receptors that recognize rapidly evolving pathogenic effectors. Identified R genes in this study have implications in plant breeding, as a source of resistance for crop improvement.