Comparative transcriptome analysis of dioecious, unisexual floral development in Ribes diacanthum pall

Ribes diacanthum Pall. (Grossulariaceae), a species with dioecious, unixsexual flowers, has great economic and medicinal value and is widespread in northeastern China. After the initiation of intact floral organs, male flowers develop an abnormal stigma, and female flowers develop fading stamens incapable of pollination. To explore the genes governing dioecious unisexual floral development in R. diacanthum, we used high-throughput sequencing to obtain transcriptome data for male and female inflorescences and analyzed expression patterns of candidate genes at various developmental stages of male and female flowers. The combined transcriptomic data were successfully assembled into 72,791 transcripts (N50 = 1467) and 48,600 unigenes (N50 = 1378); 62% of the unigenes were annotated by NR, Swissprot, KEGG, GO and COG database based on orthology. Analysis of the differentially expressed genes (DEGs) showed that 2785 annotated genes were differentially expressed, and significantly more genes were male-biased than were female-biased in expression in the inflorescences. Both male and female flowers were found to be complete hermaphroditic flowers during early floral development; sex determination was a late event. Several MADS-box genes such as comp53946_c0 (putative AGL11) might be directly correlated with the establishment of sexual dimorphism. The sex-specific transcripts and genes identified may regulate coordinated events during floral development and be involved in the molecular regulation of dioecious, unisexual floral development in R. diacanthum. The transcriptome from the male and the female inflorescences will provide a valuable reference for further functional research on the development of dioecious, unisexual flowers.