Genome survey sequencing of wild cotton (Gossypium robinsonii) reveals insights into proteomic responses of pollen to extreme heat.

Heat stress specifically affects fertility by impairing pollen viability but cotton wild relatives successfully reproduce in hot savannas where they evolved. An Australian arid-zone cotton (Gossypium robinsonii) was exposed to heat events during pollen development then mature pollen was subjected to deep proteomic analysis using 57 023 predicted genes from a genomic database we assembled for the same species. Three stages of pollen development, including tetrads (TEs), uninucleate microspores (UNs) and binucleate microspores (BNs) were exposed to 36°C or 40°C for 5 days and the resulting mature pollen was collected at anthesis (p-TE, p-UN and p-BN, respectively). Using the sequential windowed acquisition of all theoretical mass spectra proteomic analysis, 2704 proteins were identified and quantified across all pollen samples analysed. Proteins predominantly decreased in abundance at all stages in response to heat, particularly after exposure of TEs to 40°C. Functional enrichment analyses demonstrated that extreme heat increased the abundance of proteins that contributed to increased messenger RNA splicing via spliceosome, initiation of cytoplasmic translation and protein refolding in p-TE40. However, other functional categories that contributed to intercellular transport were inhibited in p-TE40, linked potentially to Rab proteins. We ascribe the resilience of reproductive processes in G. robinsonii at temperatures up to 40°C, relative to commercial cotton, to a targeted reduction in protein transport.