Phytochromes transmit photoperiod information via the evening complex in Brachypodium

Abstract

AbstractBackgroundDaylength is a key seasonal cue for animals and plants. In cereals, photoperiodic responses are a major adaptive trait, and alleles of clock genes such asPHOTOPERIOD1 (PPD1)andEARLY FLOWERING3 (ELF3)have been selected for in adapting barley and wheat to northern latitudes. How monocot plants sense photoperiod and integrate this information into growth and development is not well understood.ResultsWe find thatphytochrome C (PHYC)is essential for flowering inBrachypodium distachyon. Conversely, ELF3 acts as a floral repressor andelf3mutants display a constitutive long day phenotype and transcriptome. We find that ELF3 and PHYC occur in a common complex. ELF3 associates with the promoters of a number of conserved regulators of flowering, includingPPD1andVRN1. Consistent with observations in barley, we are able to show thatPPD1overexpression accelerates flowering in short days and is necessary for rapid flowering in response to long days. PHYC is in the active Pfr state at the end of the day, but we observe it undergoes dark reversion over the course of the night.ConclusionsWe propose that PHYC acts as a molecular timer and communicates information on night-length to the circadian clock via ELF3.