Genome-wide identification of the GRAS transcription factor family in autotetraploid cultivated alfalfa (Medicago sativa L.) and expression analysis under drought stress

GRAS transcription factors are one of the most important plant-specific gene families and play diverse roles in plant development and abiotic stress. A total of 55 MsGRAS genes were obtained from the autotetraploid cultivated alfalfa genome of XinJiangDaYe. Phylogenetic analysis demonstrated that the MsGRAS genes were classified into 10 subgroups, including HAM, LAS, SCL4/7, DLT, SCR, SCL3, DELLA, PAT1, SHR, and LISCL. Gene structure analysis showed that 92.7% of MsGRAS genes lacked introns. Many hormone- and stress-related cis-regulatory elements have been identified in the promoter regions of MsGRAS genes. A total of 55 MsGRAS genes were unevenly mapped on 32 alfalfa chromosomes, except for MsGRAS53 and MsGRAS55. Gene duplication analysis demonstrated that segmental duplication was the key driving force for the expansion of this gene family during evolution. Expression analysis of 55 MsGRAS genes in various tissues and under drought stress showed that they were differentially expressed. RT-qPCR analysis revealed that the expression of eight selected MsGRAS genes was significantly induced by drought stress. Collectively, our study is the first to investigate GRAS genes in autotetraploid cultivated alfalfa, and these findings will further enrich our knowledge regarding GRAS transcription factor genes and establish a foundation for enhancing drought stress tolerance by genetic engineering in autotetraploid cultivated alfalfa.