Identification of the RING-HCa E3 Ligase Gene Family and Functional Characterization of StDRIP1 in Potato Drought Stress Response

The RING-type E3 ubiquitin ligase plays a significant role in plant responses and adaptations to abiotic stresses such as drought. However, few studies have explored the role of E3 ubiquitin ligases in potato drought stress, especially DRIP1. In this study, 172 StHCa genes were identified across the potato genome. These genes were unevenly distributed on twelve chromosomes and divided into six subclades (group I–VI). The molecular weight of potato HCa proteins ranges from 5445.38 to 143,293.69 Da. More than half of them are acidic proteins and most are unstable. There are 161 hydrophilic proteins, and the subcellular localization analysis indicated that they were mainly located in the nucleus. The co-linearity analysis of StHCa genes showed that 172 genes underwent 40 tandem duplications and 28 segmental duplication events. Potato and tomato share a recent common ancestor and exhibit highly similar evolutionary trajectories. Promoter sequence analysis of the StHCa family identified abundant cis-acting elements associated with light signal transduction, hormone responses, plant growth and development, and abiotic stress responses. These results suggest that the StHCa genes may play important regulatory roles in different environmental signals and developmental stages. Expression profiling revealed that StDRIP1 exhibited higher transcript levels in potato roots than in stems and leaves, and its expression was significantly induced by drought stress. Physiological phenotyping demonstrated that StDRIP1-overexpressing (OE) plants displayed reduced root growth compared with wild-type (WT) plants, with decreases in root length, total root area, total root volume, and root vitality. Under 20% PEG-6000-simulated drought stress, the root expression level of StDRIP1 was higher in OE lines than in WT plants. Furthermore, StDRIP1 overexpression suppressed the activities of antioxidant enzymes (POD, CAT, and SOD) and weakened their osmotic adjustment ability by reducing proline (Pro) accumulation. At the late stage of stress treatment (9 h), the SOD, POD, and CAT activities of OE plants were 5.0%, 19.9%, and 25.1% lower than those of WT plants, respectively. These physiological alterations exacerbated oxidative damage, as evidenced by increased malondialdehyde (MDA) content and elevated electrolyte leakage in OE plants. In summary, this study comprehensively characterized the StHCa gene family in potato, providing a valuable theoretical basis for elucidating the functional mechanism of StDRIP1 in modulating drought stress responses. Collectively, StDRIP1 acts as a negative regulator of potato drought tolerance through two primary mechanisms: (1) repressing root growth and weakening root vitality, thereby reducing the water absorption capacity of roots; and (2) diminishing antioxidant enzyme activities and impairing osmotic homeostasis, which further exacerbates oxidative damage under drought stress.