Characterization of AcSINA1 and Its Regulatory Role in ABA Responses in Kiwifruit (Actinidia chinensis)

Abstract SINA (Seven in Absentia) E3 ubiquitin ligase represents a major class of E3 ligase in the ubiquitin‑proteasome system (UPS) and play critical roles in diverse plant physiological processes. In this study, the kiwifruit (Actinidia chinensis Planch.) AcSINA1 was systematically investigated via bioinformatics, spatiotemporal and stress-responsive expression profiles, and functional analyses. Bioinformatics analysis revealed that AcSINA1 was located on kiwifruit chromosome 3 and encoded a 317 amino acid protein, with a predicted molecular weight of 35 848.65 Da and an isoelectric point of 6.54. Meanwhile, AcSINA1 protein harbored the conserved RING and SINA domains and shared the closest phylogenetic relationship with rice OsSINA3. The gene promoter was enriched in stress and hormone responsive cis‑elements, including elements responsive to abscisic acid (ABA), methyl jasmonate (MeJA), salicylic acid (SA), light, and anaerobic induction. Expression analysis showed that AcSINA1 exhibited the highest transcript abundance in kiwifruit stems. The expression profiling under multiple treatments suggested that AcSINA1 showed significant expression changes in response to ABA, cold, and salt stresses. The GUS staining assay further proofed that AcSINA1 were predominantly expressed in stems and lateral root tips of transgenic Arabidopsis. Functional research revealed that compared with wild type, the transgenic Arabidopsis had a higher germination rate, greater shoot fresh weight, and longer primary root length under ABA treatment at both germination and vegetative stages. These findings enrich our knowledge of plant SINA proteins and lay foundation for breeding new salt-tolerant cultivars.