Metabolite regulation of cryptochrome activity and flowering time
The UV-A/blue light receptor cryptochrome 2 (cry2) has a central role in photoperiodic flower induction. Important components in cry2 signaling are bHLH transcription factors (CIB1, CIB2, CIB4, CIB5), which associate with cry2 under blue light. These heterodimers then bind to non-canonical E-boxes in the promoter region of FLOWERING LOCUS T (FT) and thereby induce expression of this important flowering gene. Moreover, cry2 interacts with SPA proteins and thereby inhibits the activity of the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENESIS 1 (COP1). COP1 plays a major role in degradation of the FT activator CONSTANS (CO). We have shown that the flavin chromophore of cry2 in the lit state is in the neutral semiquinone form, and formation of this redox state is enhanced by metabolites such as ATP and NADPH. Structure-based site-directed mutagenesis of CRY2 revealed which residues are required for metabolite control. This information will be used for elucidating the role of metabolites in photoperiodic flowering. For this purpose, we plan to express the cry2 variants in situ and to analyze their flowering time, FT expression, and interaction with downstream partners (CIB, SPA, COP1). These studies will be complemented by in vitro studies of recombinant proteins.
Engelhard C., Wang X., Robles D., Moldt J., Essen L.-O., Batschauer A., Bittl R., and Ahmad M. (2014). Cellular metabolites enhance light sensitivity of Arabidopsis cryptochrome through alternate electron transfer pathways. Plant Cell, www.plantcell.org/cgi/doi/10.1105/tpc.114.129809.