Widespread deployment of wheat hybrids has been limited by high seed production costs in a commercial environment. This is due to poor outcrossing characteristics of wheat which can, in part, be attributed to poor female organ receptivity to airborne pollen. Here we underpin a detailed characterization of cross-pollination seed set progression in both emasculated wild-type, and a genetically male-sterile wheat line with a comprehensive RNA-Seq and co-expression analysis. We identify three clear phases in the fertilization window: stigma development and onset of receptivity, effective pollination period, and senescence onset and subsequent tissue deterioration. By profiling female-specific marker genes, we determined that physical emasculation of wild-type 'cv. Chris' (Ms1) advances female development 2 to 3 days relative to genic male sterility (ms1d). Gene networks linked to gibberellic acid homeostasis were found associated with styloid and stigma hair elongation, and increased expression of peroxidases associated with peak receptivity (3 days after floret gaping). Further, changes in the expression of exocyst complex components coincided with the onset of stigma hair senescence. Together the applied clustering and differential expression strategy identified biologically meaningful expression signatures, particularly in stigma hairs, that correlate with the effective pollination period and the observed cross-pollination seed set. Overall, the datasets represent a valuable resource to help identify and/or engineer improved cross-pollination seed set, and ultimately leading to greater insights into this complex biological process and a more cost-effective hybrid seed production system.
Whitford et al. (Fri,) studied this question.