TPR domain-containing co-chaperones of HSP70 and HSP90 in plants

Protein homeostasis relies on chaperones such as HSP70 and HSP90, which assist in the folding, activation, and turnover of client proteins. Their activity is modulated by co-chaperones, many of which contain tetratricopeptide repeat (TPR) domains. A subset of these, known as carboxylate clamp TPR (CC-TPR) domains, possess distinctive structural features that mediate interactions with the chaperones' C-terminal EEVD motifs. This review focuses on plant TPR-containing co-chaperones, particularly those with CC-TPR domains, because they provide the structural basis for selective HSP70 and HSP90 recognition -a central but understudied aspect of plant proteostasis. We summarize advances in understanding the structure and diversity of plant TPR co-chaperones, and discuss three representative examples: AtRPAP3, a component of the R2T complex; HOP, a co-chaperone integrating hormonal and stress responses; and SGT1, a TPR protein that interacts with HSP90 through a TPR-independent mechanism and is crucial for immunity and development. Comparative evidence reveals both conservation and plant-specific diversification of TPR co-chaperone function, reflecting their adaptation to environmental and developmental cues. We conclude that plant TPR proteins constitute a versatile regulatory layer that coordinates chaperone activity across multiple cellular processes. Understanding their mechanisms will be essential to map the chaperone networks that underpin plant resilience and growth.