Transcriptome profiling of the flowering transition in saffron (Crocus sativus L.)

Saffron, derived from the stigma of Crocus sativus, is not only a valuable traditional Chinese medicine but also the expensive spice and dye. Its yield and quality are seriously influenced by its flowering transition. However, the molecular regulatory mechanism of the flowering transition in C. sativus is still unknown. In this study, we performed morphological, physiological and transcriptomic analyses using apical bud samples from C. sativus during the floral transition process. Morphological results indicated that the flowering transition process could be divided into three stages: an undifferentiated period, the early flower bud differentiation period, and the late flower bud differentiation period. Sugar, gibberellin (GA(3)), auxin (IAA) and zeatin (ZT) levels were steadily upregulated, while starch and abscisic acid (ABA) levels were gradually downregulated. Transcriptomic analysis showed that a total of 60 203 unigenes were identified, among which 19 490 were significantly differentially expressed. Of these, 165 unigenes were involved in flowering and were significantly enriched in the sugar metabolism, hormone signal transduction, cell cycle regulatory, photoperiod and autonomous pathways. Based on the above analysis, a hypothetical model for the regulatory networks of the saffron flowering transition was proposed. This study lays a theoretical basis for the genetic regulation of flowering in C. sativus.