BAG co-chaperones and phytohormonal signaling in tomato: Molecular regulators of stress resilience, growth, and fruit quality

Tomato (Solanum lycopersicum) is a major horticultural crop and an important model for studying fruit development and stress adaptation. Climate-induced stresses, including drought, salinity, heat, and oxidative damage, pose significant challenges to tomato productivity, emphasizing the need to understand molecular mechanisms that integrate stress responses with developmental processes. Bcl-2-associated athanogene (BAG) proteins, highly conserved co-chaperones, have emerged as key regulators at the intersection of proteostasis, signaling, and programmed cell death. However, despite their emerging importance, comprehensive studies reviewing BAG co-chaperones in tomato are still limited. In this review, we summarize the current knowledge on BAG proteins in tomato, focusing on their structural features, evolutionary divergence from animal BAGs, and functional roles in development and stress tolerance. We examined how SlBAGs interact with Hsp70 chaperones, MAPK signaling cascades, calcium/calmodulin pathways, and the ubiquitin-proteasome system to coordinate cellular responses under diverse abiotic stresses. Special attention is given to their involvement in reactive oxygen species regulation, programmed cell death, senescence, and fruit ripening. Furthermore, we highlighted the gaps in functional characterization, post-translational regulation, and field-level validation of SlBAGs. Finally, we discussed the emerging strategies, including multi-omics approaches, genome editing, and translational breeding, to harness the genetic potential of SlBAGs for developing climate-resilient, high-yielding, and quality-enhanced tomato cultivars.