Fig. 4.

Simplified models of photoperiodic regulation of flowering in (a) Arabidopsis (LD dicot species) based on Valverde et al. [65] and (b) wheat (LD monocot species) based on Chen and Dubcovsky 2012 [87] and Chen et al. 2014 [19]. In Arabidopsis the photoperiodic response is regulated by CONSTANS (CO). In the absence of PHYB, CO proteins accumulate, inducing flowering. In wheat, PPD1/PRR37 is the central regulator of the photoperiodic response. The effects of CO in monocots are observed only in the absence of PPD1/PRR37 [88, 89]. In wheat, PHYB and PHYC are required for the light activation of PPD1/PRR37 so both the phyB-null and phyC-null  mutants exhibit a late-flowering phenotype