Identification and analysis of ADK gene family members in alfalfa (Medicago sativa)

Adenylate Kinase (ADK) is a key enzyme widely distributed in animals and plants that maintains the dynamic balance of cell energy. It plays an important role in growth and stress response. We identified MsADK genes at a genome-wide level based on the alfalfa genome data. Bioinformatics methods were used to analyze the physical and chemical properties, gene structure, chromosome location, promoter cis-acting, phylogenetic relationship, and secondary and tertiary structure of MsADK. Furthermore, MsADK gene expression in different tissues and its response to abiotic stress was analyzed. Ten members of the MsADK gene family were identified in alfalfa and distributed on seven chromosomes; three of these pairs were segmental duplication. The coding regions were between 627 and 1515 bp, with an average length of 768 bp. The number of exons was mostly between three and six. MMsADK protein is hydrophilic, and its subcellular location is diverse, mainly located in the cytoplasm. Phylogenetic analysis showed that MsADK is highly conserved among different species and has a close relationship with legumes. The prediction results of cis-acting elements showed that MsADK promoter regions had many response elements related to hormones, stress, and light. Analysis of MsADK expression pattern in different tissues and under abiotic stress revealed that MsADK expression was higher in stems than in other parts. MsADK1, MsADK3, and MsADK8 were up-regulated under ABA, drought, and salt stress conditions, whereas the remaining MsADK genes were down-regulated. MsADK2 and MsADK5 were down-regulated, while all other MsADK genes were up-regulated under low-temperature stress. Results also showed that MsADK has two regulatory patterns (positive or negative) under different stress conditions. These results will provide candidate genes and a theoretical basis for the genetic improvement of alfalfa based on the ADK gene.