Transcriptomic analysis of heteromorphic stamens in Cassia biscapsularis L.

Hermaphroditic flowers have evolved primarily under the selection on male function. Evolutionary modification often leads to stamen differentiation within flowers, or "heteranthery", a phenomenon intrigued scientists since the 18(th) century until recently. However, the genetic basis and molecular regulation mechanism has barely been touched. Here we conducted comparative transcriptome profiling in Cassia biscapsularis L., a heterantherous species with representative patterns of stamen differentiation. Numerous differentially expressed genes (DEGs) were detected between the staminodes (the degenerated stamens) and fertile stamens, while much fewer genes differentially expressed among the three sets of fertile stamens. GO term enrichment and KEGG pathway analysis characterized functional properties of DEGs in different stamen types. Transcripts showing close correlation between expression pattern and stamen types were identified. Transcription factors from the bHLH family were suggested to have taken crucial part in the formation of staminodes. This first global transcriptomic analysis focusing on stamen differentiation opens the door toward a more comprehensive understanding on the molecular regulation of floral organ evolution. Especially, the generated unigene resource would be valuable for developing male sterile lines in agronomy.