Genome-wide characterization of BiP gene family and functional analysis of VvBiP3 in Vitis vinifera.

Drought stress exacerbated by climate change severely impairs the growth and quality of horticultural crops. Grapevine (Vitis vinifera L.) is an economically vital fruit species, and exploring stress-tolerant genes lays a foundation for its genetic improvement and sustainable cultivation. BiP proteins serve as pivotal endoplasmic reticulum (ER) molecular chaperones and participate widely in plant abiotic stress acclimation, yet the genomic features and drought-associated functions of grapevine BiP family genes remain largely unclear. In this study, three VvBiP members were identified genome-widely. These genes scatter unevenly on three chromosomes, encoding proteins of 649-667 amino acids with highly conserved motifs and structural characteristics. Cis-element analysis indicated their involvement in hormonal signaling and diverse abiotic stress responses. Transcriptomic data indicated that VvBiP3 exhibited predominant expression in both leaves and berries, with a significant induction observed under drought stress. Its subcellular localization within the ER was further validated. Functional assays revealed that the overexpression of VvBiP3 modulated stomatal movement and maintained photosynthetic capacity in transgenic grape plants subjected to drought stress. Furthermore, biochemical evidence demonstrated that VvbZIP60 directly binds to and activates the VvBiP3 promoter in response to drought. Elevated VvbZIP60 expression upregulated VvBiP3 transcription and facilitated hexose accumulation in grape calli. This work clarifies the grapevine BiP family characteristics and the regulatory mechanism of the VvbZIP60-VvBiP3 module governing drought resistance and sugar metabolism, offering elite gene resources and theoretical references for drought tolerance and quality improvement breeding of grapevine.