Genome-Wide Identification and Expression Analyses of Genes During Nodule Symbiosis in .

Glycoside hydrolase family 18 (GH18) proteins can hydrolyze the β-1,4-glycosidic bonds of chitin, which is a common structure component of insect exoskeletons and fungal cell walls. In this study, 36 genes were identified and subjected to bioinformatic analysis based on the genomic data of . They were distributed in 16 out of 20 tested soybean chromosomes. According to the amino acid sequences, they can be further divided into five subclades. Class III chitinases (22 members) and class V chitinases (6 members) are the major two subclades. The amino acid size of soybean GH18 proteins ranges from 173 amino acids (aa) to 820 aa and the molecular weight ranges from 19.46 kDa to 91.01 kDa. From an evolutionary perspective, soybean genes are closely related to Medicago (17 collinear loci with soybean) and Lotus (23 collinear loci with soybean). Promoter analysis revealed that genes could be induced by environmental stress, hormones, and embryo development. , and were screened out due to their nodulation specific expression and further verified by RT-qPCR. These results provide an elaborate reference for the further characterization of specific genes, especially during nodule formation in soybean.