Plant sexual reproduction commences with the interaction of the mature stigma (the receptive portion of the female reproductive organ) and the mature pollen (the male gametophyte). Proteins present at their mature developmental stages are therefore likely to reflect their upcoming reproductive roles. In this study, gel-free shotgun proteomics was used to investigate the proteomes of the mature stigma and pollen grain in two species that are highly related to Canada's most important crops. We identified 7703 and 5608 Brassica carinata stigma and pollen proteins, and 11533 and 2977 triticale stigma and pollen proteins, respectively. These represent the largest Brassicaceae and Triticeae pollen and stigma proteome datasets to date. In addition, this is the first comparative analysis of developing stigmas, and it was performed using isobaric tag for relative and absolute quantification (iTRAQ). There were 251 B. carinata proteins found to be differentially abundant during stigma maturation with 154 proteins that had increased abundance, while 97 decreased in abundance. For triticale, 647 differentially abundant stigma proteins were identified with 305 and 342 proteins increasing and decreasing in abundance respectively.
A comparison of the B. carinata and triticale stigma or pollen proteomes suggested considerable functional conservation between the two species despite their very different morphology. Although the proteomes exhibited similar functional enrichment trends, both species displayed significant differences between their pollen and stigma proteomes, which reflected their functional specialization. Altogether, the results of this study represent an invaluable resource for the further study of pollen and stigma development and interactions, and will potentially facilitate our understanding of plant reproduction in other members of the Brassicaceae (e.g. B. napus, B. oleracea, B. rapa) and Triticeae (wheat, barley, rye).