The Brassica Mature Pollen and Stigma Proteomes: Preparing to Meet

Successful pollination brings together the mature pollen grain and stigma papilla to initiate an intricate series of molecular processes meant to eventually enable sperm cell delivery for fertilization and reproduction. At maturity, the pollen and stigma cells have acquired proteomes comprising the primary molecular effectors required upon their meeting. In Brassica species, knowledge of the roles and global composition of these proteomes is largely lacking. To address this gap, gel-free shotgun proteomics was performed on the mature pollen and stigma of Brassica carinata, a representative of the Brassica family and its many crop species (e.g. B. napus, B. oleracea, B. rapa), which holds considerable potential as a bio-industrial crop. 5608 and 7703 B. carinata mature pollen and stigma proteins were identified, respectively. The pollen and stigma proteomes were found to reflect not only their many common functional and developmental objectives, but also important differences underlying their cellular specialization. Isobaric tag for relative and absolute quantification (iTRAQ) was exploited in the first analysis of a developing Brassicaceae stigma, and uncovered 251 B. carinata proteins that were differentially abundant during stigma maturation, providing insight into proteins involved in the initial phases of pollination.