Small heat shock proteins in plants: Structure, function and role in stress adaptation

Small heat shock proteins (sHSPs) are a diverse group of ATP-independent molecular chaperones that play a vital role in maintaining protein stability in plants under stress conditions. Defined by a conserved α-crystallin domain, these proteins form flexible oligomers capable of binding and stabilizing misfolded proteins, thus preventing aggregation. Plant sHSPs are classified into multiple families and are targeted to specific subcellular compartments such as the cytosol, chloroplasts, mitochondria, endoplasmic reticulum and peroxisomes, highlighting their specialized functions. In addition to safeguarding plants from heat stress, sHSPs contribute to tolerance against (various abiotic stress factors) drought, salinity, oxidative damage and heavy metals. They are also involved in developmental processes including seed maturation and fruit ripening. Structural variability, particularly in terminal regions, facilitates their dynamic interactions with various client proteins. The primary objective of this review is to study the tissue and organelle specific classification of sHSPs across plant lineages, their structural diversification and the implication of these variations on their function. The review also points out the interaction of the sHSPs with other proteins including co-chaperones in the heat shock response (HSR) pathway. However due to limited information on the structure of sHSPs the correlation of structure with the mechanism of oligomer formation and substrate binding still remains incomplete. Further investigation in this direction would reduce this knowledge gap and surely help in developing climate-resilient crops.