Identification of 7S Globulin Genes in Mung Bean (Vigna radiata L.) and Their Expression Analysis during Seed Development

In order to elucidate the basic properties of Vigna radiata 7S (Vr7S) globulin genes and their expression patterns during seed growth and development, the physicochemical properties, structural characteristics, protein tertiary structures, phylogenetic relationship and expression profiles of 10 Vr7S globulin genes were studied using bioinformatics and reverse transcription-polymerase chain reaction (RT-PCR). The results showed that the proteins encoded by the Vr7S globulin genes consisted of 246 to 594 amino acid residues, with isoelectric point (pI) ranging from 5.02 to 6.40, and molecular mass ranging from 27.82 to 70.02 kDa. All Vr7S globulin genes contained 3–7 exons, 2–6 introns, and 5–8 conserved motifs. Vr7S B1 had one conserved cupin domain, while the other nine genes contained two cupin domains. Vr7S globulin had four types of tertiary structures including α-helix and β-chain. In the conserved cupin domain, 67 conserved amino acid residues were shared by mung bean and other species, and mung bean 7S globulin genes had the closest homology adzuki bean 7S globulin genes followed by those of French bean, pigeon pea and soybean. The RNA sequencing (RNA-Seq) and RT-PCR expression profiles of mung bean seeds at different development stages showed that the expression level of the Vr7S globulin genes increased with the maturity of mung bean seeds, which was consistent with the expression pattern of 7S globulin genes in other legume species. These results indicated that the Vr7S globulin genes played a positive role in regulating the generation of mung bean seed storage protein. This study may lay a foundation for further analyzing the biological function of the Vr7S globulin genes in the seed development of mung bean.