Floral terpenoid volatiles are impacted by light quality. In snapdragon, blue light can significantly enhance the emissions of ocimene and myrcene and the expression of ocimene synthase (AmOCS) and myrcene synthase (AmMYS). However, the mechanisms underlying the response to blue light are largely unknown. In this study, two transcription factors (TFs), AmMYB24 and AmMYB63 were screened which showed high expression level under blue light. AmMYB24 exhibited synchronous expression with AmOCS. Moreover, AmOCS transcript expression was up-regulated in response to AmMYB24 overexpression. This activation is direct and occurs through binding of AmMYB24 to MYBCORECYCATB1 sites in the AmOCS promoter. In addition, AmMYB24 interacts with the blue light signal key receptor AmCRY1 and the transcriptional activation activity of AmMYB24 was decreased in AmCRY1 silencing flowers. Taken together, our results revealed the regulatory pathway of biosynthesis of ocimene induced by blue light mediated by AmMYB24 and AmCRY1. When snapdragon flowers were exposed to blue light, AmCRY1 was first activated, the light signal is transduced to AmMYB24 through interaction with AmCRY1, and finally AmMYB24 activates AmOCS by binding to its MYBCOREATCYCB1 motif, resulting in abundant ocimene emission.

Background Floral secondary metabolites, especially terpenoids, play a key role in plant defense and reproduction. Terpenoids are the most abundant floral volatiles, and their synthesis and release are affected by light quality. Blue light can significantly enhance the emissions of terpenoids as well as the expression of biosynthesis-related genes in snapdragon. However, the regulatory mechanism of blue light-induced terpenoid biosynthesis remains unclear. Results In this study, the transcription factor (TF) PHYTOCHROME-INTERACTING FACTOR 4 (AmPIF4) was identified and found to be lowly expressed under blue light, which was in contrast to the expression of ocimene synthase (AmOCS) and myrcene synthase (AmMYS), 1-deoxy-D-xylulose 5-phosphate (DXP) synthase (AmDXS), and DXP reductoisomerase (AmDXR). AmOCS and AmMYS expression and the relative emissions of ocimene and myrcene were up-regulated in response to AmPIF4 silencing. Moreover, AmPIF4 negatively regulated terpenoid biosynthesis by binding to the promoters of biosynthesis-related genes. The transcriptional activation activity of AmPIF4 was increased in AmCRY1-silenced flowers. In addition, AmPIF4 interacted with AmCRYs (Cryptochromes) and AmCOP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1), which are key blue light signal receptors. Conclusion Overall, our results reveal a novel molecular mechanism involving AmPIF4 that contributes to the blue light-mediated regulation of terpenoid biosynthesis in snapdragon.