Small Heat Shock Proteins: Roles in Development, Desiccation Tolerance and Seed Longevity

Small heat shock proteins are one of the five classes of heat shock proteins, a family named after their expression in response to heat shock. Despite their name some members of this family have been shown to express during a gamut of non-stress conditions in a variety of plant species. Small HSPs have been known to accumulate during plant developmental stages like pollen development, seed maturation stages, early seed germination and also in storage organs. Interestingly, aging induced accumulation of small HSPs has also been observed in a few species. The spatial and temporal accumulation pattern of small HSPs also correlates well with other seed abundant proteins like late embryogenesis abundant (LEA) proteins. Regulation of these developmental stages responsive and non-stress induced small HSPs is also distinct from the heat stress regulated transcript induction in terms of involvement of some novel and exclusive transcription activators like ABI3 and HsfA9. Small HSPs are known to function as molecular chaperone and thus their role in plant development especially during seed development has been discussed in the light of their functional implication during these stages.