Abstract
The mitochondrial calcium uniporters (MCUs) are a family of calcium unidirectional transporters important for cytoplasmic Ca(2+) signals. Though the MCU proteins in several plant species have been investigated, genome-wide analysis of MCUs in alfalfa is lacking. Here, via genome-wide analysis, a total of 5, 20, and 6 MCU genes were identified in three different alfalfa cultivars, namely Medicago truncatula Jemalong A17, Medicago sativa XinJiangDaYe, and M. sativa Zhongmu No. 1, respectively. They were further phylogenetically classified into three subfamilies. Most MCU genes have only one intron, and gene duplication events of MCU genes were observed within each alfalfa accession and between different accessions. All alfalfa MCU proteins contained a highly conserved MCU domain and 10 conserved motifs, featuring two transmembrane domains and a DI/VME motif. According to the tissue expression data of M. sativa Zhongmu No. 1, MsMCU6.2 was the most abundant transcript with the highest expression in the leaf, and MsMCU5 and MsMCU1.2 showed higher expression levels in the stem than other tissues. We analyzed the expression profiles of five MCU genes (MsMCU1.1/1.2/5/6.1/6.2) under salt, drought, and cold stresses via qRT-PCR assays. All five MCU genes were induced by drought stress, except MsMCU5, whose expression was up-regulated by salt stress, while cold stress slightly altered MsMCU expression. Nine potential interacting proteins and three miRNAs targeting MtMCUs were predicted. These results provide detailed knowledge of alfalfa MCU genes and suggest their potential functions in abiotic stress response.