Comparative transcriptome analysis of self-incompatible flower stigmas and self-compatible bud stigmas following self-pollination in broccoli.

DH07 is a DH line of Class I S-haplotype in broccoli (Brassica oleracea var. italica), in which stigmas of flowers show self-incompatibility (SI) and stigmas of buds show self-compatibility (SC). The molecular mechanisms that lead to stigmas at different developmental stages having different responses to self-pollination are yet unknown. In the present study, comparative transcriptome profiling of the stigmas of flowers and buds before and after self-pollination was performed by RNA-sequencing using an Illumina HiSeq 2000. A total of 80,102,897 reads were generated for further analysis in four libraries. Comparisons of the transcriptome profiles before and after self-pollination revealed 579 differentially expressed genes (DEGs) in the stigmas of buds (SBs); of these, 431 DEGs showed increased and 148 DEGs showed decreased transcript abundance after self-pollination in SBs. There were a total of 686 DEGs between unpollinated stigmas of flowers (SFs) and pollinated SFs, among which, 517 DEGs were up regulated and 169 DEGs were down regulated. Following the self-pollination, 379 identified DEGs were common in both SBs and SFs. It was found that ARR7-like and oxysterol-binding family protein related DEGs could play key roles in SI or SC signal transduction. The results obtained in this study would form the foundation for further studies on investigating the molecular mechanisms of SI and SC in Brassica.