Identification of Late BLOOMER2 As a Cycling Dof Factor Homolog Reveals Conserved and Divergent Features of the Flowering Response to Photoperiod in Pea

The molecular pathways responsible for the flowering response to photoperiod have been extensively studied in Arabidopsis and cereals, but remain poorly understood in other major plant groups. Here, we describe a new dominant mutant at the LATE2 locus in pea (Pisum sativum L.) that is late flowering with a reduced response to photoperiod. LATE2 acts downstream of light signalling and the circadian clock to control expression of the main photoperiod-regulated FT gene, FTb2, implying that it plays a primary role in photoperiod measurement. Mapping identified the CYCLING DOF FACTOR gene CDFc1 as a strong candidate for LATE2, and the late2-1D mutant was found to carry a missense mutation in CDFc1which impairs its capacity to bind to the blue-light photoreceptor FKF1 in yeast two-hybrid assays and delays flowering in Arabidopsis when overexpressed. Arabidopsis CDF genes are important negative regulators of CONSTANS (CO) transcription, but we found no effect of LATE2 on transcription of pea CO orthologs, nor on genes in CCT, BBX, PIF or CIB families previously implicated in activation of FT in Arabidopsis.  Our results define a new component of the pea photoperiod response pathway and support the view that photoperiodic regulation of FT expression occurs via a CO-independent pathway.