Comparative expression analysis of Myb1, Myb14, and Myb15 genes in leaf tissues of grapevine rootstocks under long-term drought stress

Drought is a major environmental constraint in viticulture, strongly influencing grapevine adaptation. Grapevine rootstocks differ in their capacity to cope with water deficit due to their distinct genetic backgrounds, which give rise to diverse tolerance mechanisms. Among the key regulatory components involved in stress responses, MYB transcription factors constitute a large and functionally diverse gene family that modulates both developmental processes and stress-related cellular pathways through interactions with cis-regulatory elements in target gene promoters. In this study, the expression levels of three Myb genes (Myb1, Myb14, and Myb15) were comparatively evaluated using Real-Time PCR analyses in six grapevine rootstocks subjected to long-term (16 days) drought stress (water deficit). The rootstocks included V. berlandieri × V. rupestris (110R, 1103P, and 99R) and V. berlandieri × V. riparia (SO4, 5BB, and 161-49C). The results demonstrated that all examined genes were upregulated under drought stress conditions. Notably, Myb1 exhibited the strongest response, with high and statistically significant increases in expression across all rootstocks. In contrast, Myb14 and Myb15 displayed relatively lower expression levels, with variations depending on the genotype. Among the rootstocks, higher levels of upregulation were observed in SO4 and 161-49C, whereas 1103P exhibited a more limited upregulation response. As a result of the study, these genes were determined to be part of a common transcriptional response to drought stress in grapevine rootstocks; however, the magnitude of this response varied depending on the genotype of the rootstock. These findings provide new insights into drought-responsive MYB transcription factors in grapevine rootstocks and may contribute to future molecular breeding and rootstock selection strategies.