MiR399 plays an important role in plant growth and development. The objective of the present study was to elucidate the evolutionary characteristics of the MIR399 gene family in grapevine and investigate its role in stress response. To comprehensively investigate the functions of miR399 in grapevine, nine members of the Vvi-MIR399 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 Vvi-MIR399 members of dicots (Arabidopsis, tomato, and sweet orange) and monocots (rice and grapevine) could be divided into three clades, and most of the Vvi-MIR399s were closely related to sweet orange in dicots. Promoter analysis of Vvi-MIR399s showed that the majority of the predicted cis-elements were related to stress response. A total of 66.7% (6/9) of the Vvi-MIR399 promoters harbored drought, GA, and SA response elements, and 44.4% (4/9) of the Vvi-MIRR399 promoters also presented elements involved in ABA and MeJA response. The expression trend of Vvi-MIR399s 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 Vvi-MIR399s 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 Vvi-MIR399 targeted multiple genes; for example, seven Vvi-MIR399s simultaneously targeted VIT_213s0067g03280.1. Furthermore, overexpression of Vvi_MIR399e and Vvi_MIR399f in Arabidopsis enhanced tolerance to drought compared with wild-type (WT). In contrast, the survival rate of Vvi_MIR399d-overexpressed plants were zero after drought stress. In conclusion, Vvi-MIR399e and Vvi-MIR399f, which are related to drought tolerance in grapevine, provide candidate genes for future drought resistance breeding.

Knowledge about the growth vigor of grapevine rootstocks is required for scion-based rootstock selection and rootstock breeding. We performed this trial aiming to evaluate the multiplication and growth vigor of several rootstocks. Thirty-one rootstock genotypes were compared on their multiplication characteristics, phenological periods, and growth indicators across three consecutive seasons. The results suggested that the cuttings of most rootstocks had callus-forming indices (CFIs) over 0.5 except for ‘188-08’ (0.28). The rooting rate of ‘420A’ was 5%, while that of the rest of the rootstocks was greater than 48%. The internode lengths of the one-year-old vines were positively correlated with those (as well as cane lengths and pruning weights) of the adult vines. These rootstocks were grouped into three clusters based on the growth measurements across three seasons. Eight combinations of genetic backgrounds showed various effects on the growth indicators. The high-vigor cluster includes ‘1103P’, ‘5BB’, ‘225Ru’, etc.; the medium-vigor cluster includes ‘Dogridge’, ‘101-14M’, ‘Fercal’, etc.; and the low-vigor cluster includes ‘Gloire’, ‘3309C’, ‘Ganzin1’, etc. The Vitis berlandieri parentage showed a higher vigor heredity, while the V. riparia showed a lower vigor heredity. These findings would contribute to rootstock nursery construction and provide references for vigor-based rootstock selection for grafts and parent selection for rootstock breeding.