Identification and Distribution of NBS-Encoding Resistance Genes of Dactylis glomerata L. and Its Expression Under Abiotic and Biotic Stress

Orchardgrass ( Dactylis glomerata L.) is drought resistant and tolerant to barren landscapes, making it one of the most important forages for animal husbandry, as well as ecological restoration of rocky landscapes that are undergoing desertification. However, orchardgrass is susceptible to rust, which can significantly reduce its yield and quality. Therefore, understanding the genes that underlie resistance against rust in orchardgrass is critical. The evolution, cloning of plant disease resistance genes, and the analysis of pathogenic bacteria induced expression patterns are important contents in the study of interaction between microorganisms and plants. Genes with nucleotide binding site (NBS) structure are disease-resistant genes ubiquitous in plants and play an important role in plant attacks against various pathogens. Using sequence analysis and re-annotation, we identified 413 NBS resistance genes in orchardgrass. Similar to previous studies, NBS resistance genes containing TIR (toll/interleukin-1 receptor) domain were not found in orchardgrass. The NBS resistance genes can be divided into four types: NBS (up to 264 homologous genes, accounting for 64% of the total number of NBS genes in orchardgrass), NBS-LRR, CC-NBS, and CC-NBS-LRR (minimum of 26 homologous genes, only 6% of the total number of NBS genes in orchardgrass). These 413 NBS resistance genes were unevenly distributed across seven chromosomes where chromosome 5 had up to 99 NBS resistance genes. There were 224 (54%) NBS resistance genes expressed in different tissues (roots, stems, leaves, flowers, and spikes), and we did not detect expression for 45 genes (11%). The remaining 145 (35%) were expressed in some tissues. And we found that 11 NBS resistance genes were differentially expressed under waterlogging stress, 5 NBS resistance genes were differentially expressed under waterlogging and drought stress, and 1 NBS resistance was is differentially expressed under waterlogging and heat stress. Most importantly, we found that 65 NBS resistance genes were significantly expressed in different control groups. On the 7th day of inoculation, 23 NBS resistance genes were differentially expressed in high resistance materials alone, of which 7 NBS resistance genes regulate the “plant–pathogen interaction” pathway by encoding RPM1 . At the same time, 2 NBS resistance genes that were differentially expressed in the high resistance material after inoculation were also differentially expressed in abiotic stress. In summary, the NBS resistance gene plays a crucial role in the resistance of orchardgrass to rust.