Plant heat shock protein Hsp90 enhances stress resistance through integrating protein quality control, chloroplast protection, hormone signal network, and immune defense

There has been groundbreaking progress in identifying unique functions of the plant heat shock protein Hsp90 in stress responses in recent years. However, there is an absence of systematic integration of these new mechanisms in protein quality control, hormone network regulation, chloroplast protection, and immune defense in existing reviews; this article aims to fill this gap. Recent studies have revealed four key mechanisms: (i) Hsp90 forms complexes with E3 ligases to promote polyubiquitination of heat-induced protein aggregates, cooperating with the 26S proteasome for clearance, a pathway hijacked by viruses; (ii) Hsp90 stabilizes the auxin receptor Transport inhibitor response 1 (TIR1), reconstructs root auxin gradients via polarized PIN-FORMED 1 (PIN1), activates abscisic acid (ABA) biosynthesis, and enhances insect resistance through JA signaling; (iii) Hsp90C maintains photosystem renewal, protects chloroplast DNA via CHLOROPLAST-AND-NUCLEUS DUAL-LOCALIZED PROTEIN 1 (CND1) translocation, and stabilizes thylakoid proteins via its CTE domain; and (iv) Hsp90 escorts Chitin Elicitor Receptor Kinase 1 (CERK1) to initiate pattern-triggered immunity (PTI), activates nucleotide binding leucine-rich repeat (NLR) for effector-triggered immunity (ETI), and interacts with Autophagy-related protein 8 (ATG8) to enhance autophagic pathogen clearance. This review integrates key new discoveries since 2012 and identifies core research gaps to address: regulation of optimal threshold of Hsp90 abundance, its combined stress response mechanism, transformation of knowledge from model plants to major food crops. The article provides a clear direction framework for subsequent research.