Identification and Analysis of the MIR399 Gene Family in Grapevine Reveal Their Potential Functions in Abiotic Stress

MiR399 plays an important role in plant growth and development. The objective of the present study was to elucidate the evolutionary characteristics of the gene family in grapevine and investigate its role in stress response. To comprehensively investigate the functions of miR399 in grapevine, nine members of the family were identified based on the genome, using a miRBase database search, located on four chromosomes (Chr 2, Chr 10, Chr 15, and Chr 16). The lengths of the Vvi-miR399 precursor sequences ranged from 82 to 122 nt and they formed stable stem-loop structures, indicating that they could produce microRNAs (miRNAs). Furthermore, our results suggested that the 2 to 20 nt region of miR399 mature sequences were relatively conserved among family members. Phylogenetic analysis revealed that the of dicots ( , tomato, and sweet orange) and monocots (rice and grapevine) could be divided into three clades, and most of the were closely related to sweet orange in dicots. Promoter analysis of showed that the majority of the predicted -elements were related to stress response. A total of 66.7% (6/9) of the promoters harbored drought, GA, and SA response elements, and 44.4% (4/9) of the promoters also presented elements involved in ABA and MeJA response. The expression trend of was consistent in different tissues, with the lowest expression level in mature and young fruits and the highest expression level in stems and young leaves. However, nine and four target genes showed different expression patterns when exposed to low light, high light, heat, cold, drought, and salt stress. Interestingly, a putative target of targeted multiple genes; for example, seven simultaneously targeted . Furthermore, overexpression of and in enhanced tolerance to drought compared with wild-type (WT). In contrast, the survival rate of -overexpressed plants were zero after drought stress. In conclusion, and , which are related to drought tolerance in grapevine, provide candidate genes for future drought resistance breeding.