The stigma, the specialized apex of the gynoecium plays a critical role in pollen capture, discrimination, hydration, germination, and guidance. Species of the Brassicaceae and Poaceae possess dry stigmas as opposed to the wet stigmas found for example in the Solanaceae and Liliaceae. The global proteome underlying stigma development and function remains largely unknown. A total of 2184 and 2275 proteins were identified in triticale and B. napus mature stigma respectively using a combination of 1D SDS PAGE LC-MS/MS, 2D IEF/SDS PAGE LC-MS/MS and OFFGEL Electrophoresis (OGE) LC-MS/MS. Two
search engines, Mascot version 2. 3. 0 (http://www.matrixscience.com) and X! Tandem version 2007.01.01.1 (www.thegpm.org/tandem), were used to search against the Universal Protein Resource (UniProt) Viridiplantae database. Scaffold version 4.0.4 (Proteome Software Inc., Portland, OR, USA) was used to validate MS/MS based peptide and protein identifications. The potential role of identified proteins involved in triticale stigma development, pollen-stigma interactions as well as protection against biotic and abiotic stresses was discussed. Comparisons between triticale stigma transcriptomic
and proteomic data also revealed post-translational as well as post-transcriptional regulation in this tissue. In triticale, comparing the functional distribution of mature stigma proteins and most abundantly expressed genes showed that structural and metabolic processes had high protein to mRNA ratios, whereas regulatory processes and transport had low protein to mRNA ratios, probably reflecting the need for rapid protein production and turnover in response to pollination. The B. napus stigma was found to express many proteins with a wide variety of roles in cellular and organ development.
Comparative proteomic analysis of Brassicaceae and Poaceae stigmas revealed very similar global functional trends despite being very different morphologically, but also demonstrated evident differences in protein composition in particular with respect to glucosinolate and isoprenoid metabolism, photosynthesis and self-incompatibility. To our knowledge, this study represents the first high throughput characterization of the stigma proteome. This work should serve as a solid base for future research meant to investigate the function of these proteins in stigma development and function.