Potato E3 Ubiquitin Ligase StXERICO1 Positively Regulates Drought Resistance by Enhancing ABA Accumulation in Potato and Tobacco and Interacts with the miRNA Novel-miR1730-3p and Proteins StUBC and StTLP

Potato (Solanum tuberosum L.) is sensitive to drought, which severely impacts tuber yield and quality. In this study, we characterized a XERICO gene, encoding a RING-H2 type E3 ubiquitin ligase, StXERICO1, from a diploid potato, investigated its role in enhancing drought resistance and ABA accumulation, and identified its interaction with the miRNA novel-miR1730-3p, as well as its protein interactions with StUBC and StTLP. StXERICO1, with a complete Open Reading Frame (ORF) of 459 bp encoding 152 amino acids, was highly responsive to drought, ABA treatment, and abiotic stresses in potato plants. Overexpression of the StXERICO1 significantly enhanced drought resistance and ABA accumulation in transgenic potato and tobacco plants and exhibited greater sensitivity to ABA treatment, which was associated with the upregulation of expression of ABA biosynthetic genes NCED and CYP707A. Furthermore, our results revealed that StXERICO1 and its encoding protein interacted with miRNAs and other proteins. 5′ RLM-RACE (cDNA terminal rapid amplification) experiment showed that the miRNA novel-miR1730-3p targets 5′ UTR region of the StXERICO1 gene. Dual luciferase assay and virus-based miRNA silencing experiment showed that the novel-miR1730-3p negatively regulates StXERICO1 expression. Moreover, yeast two-hybrid assay indicated that StXERICO1 interacts with StUBC (an E2 ubiquitin ligase) and StTLP (a Tubby-like protein), suggesting that StXERICO1 might function on ABA homeostasis at the post-translational level. These findings elucidate the molecular mechanisms by which StXERICO1, a RING-H2 type E3 ubiquitin ligase, enhances drought resistance through increased ABA accumulation, how its expression is regulated by miRNA, and how it exerts its function through interactions with other proteins. The results also provide a potential candidate gene for subsequent precision molecular breeding aimed at improving crop drought resistance.