Unraveling heat tolerance in bread wheat using physiological and proteomics approaches.

Heat stress significantly impacts global bread wheat productivity. Our study
aimed to identify underlying mechanisms of heat tolerance in wheat flag leaves
and spike tissues. We compared physiology, yield, and protein abundance
changes of wheat genotypes with contrasting heat tolerance (two tolerant
[RAJ3765 and HD2932] and two susceptible [HD2329 and HD2733]) under
short- and long-term heat stress (32°C) at ear peep. This experiment revealed
that heat tolerant genotypes maintained grain yield under short-term heat
exposure by maintaining photosynthesis, membrane stability, chlorophyll
content, pollen viability, and redox homeostasis. Heat stress during ear peep
reduced grain number, above-ground biomass, harvest index less in heat-tolerant than -susceptible genotypes while increased thousand grain weight
and grain protein content, with significant genotype x treatment interactions.
Notably, long-term heat stress reduced thousand grain weight more in heat-susceptible than -tolerant genotypes. We identified 31 and 60 changes in
protein abundances in flag leaves and spike tissues, respectively. Key pathways
in flag leaves included photosynthesis, RNA processing, heat shock proteins,
redox homeostasis, carbohydrate metabolism, chromatin organisation, and
protein breakdown, translation, and translocation. In spikes, prominent
pathways included carbohydrate, lipid, and secondary metabolism, cell wall
and chromatin organisation, redox homeostasis, membrane transport,
methylation, protein folding, breakdown and translocation, RNA processing,
lipid transfer, cell morphogenesis, heat shock proteins, and reproduction. Co-expression analysis revealed proteins correlated with important agronomic
traits. These proteins provided insights into mechanisms of heat tolerance
associated wheat physiology and yield.