Evolution and Functional Dynamics of the BAG Gene Family in Passion Fruit (Passiflora edulis)

B-cell lymphoma 2 (Bcl-2)-associated athanogene (BAG) family proteins are co-chaperones that regulate growth, development, and cell death and are evolutionarily conserved across eukaryotes. The BAG gene family has attracted intense interest in human health research, but its plant counterparts have received little attention. In this study, we conducted a genome-wide scan of the BAG family in passion fruit, a crop of great economic importance. Fifteen PeBAG genes were identified, with all but PeBAG5 having multiple copies. PeBAG members, each characterized by a BAG domain, were categorized into two groups: Group 1 (PeBAG1/2/3/4) with extra ubiquitin domains, and Group 2 (PeBAG5/6-1/6-2) with additional plant-specific calmodulin-binding domains. The transcriptome data suggest that PeBAGs exhibit high gene expression in stems, flowers, and fruit, while PeBAG4-3 and 6-1 upregulated under hormonal and abiotic stresses. qRT-PCR further confirmed the heat stress activation of PeBAG4-3 and 6-1. Subcellular localization in planta revealed varied compartmentalization, with members in the nucleus, cytoplasm, and plastids demonstrating functional divergence. This study provides a guide for investigating and employing PeBAG genes to improve heat resistance in passion fruit.