Sorghum Phytochrome B Inhibits Flowering in Long Days by Activating Expression of SbPRR37 and SbGHD7, Repressors of SbEHD1, SbCN8 and SbCN12
Figure 5
Model of the photoperiod flowering time pathway in sorghum.
Phytochrome B (PhyB) is mediates light signaling that modulates flowering time in response to photoperiod in sorghum. In LD, PhyB up-regulates the expression of PRR37 and GHD7, two central floral repressors, during the evening phase of LD but with minimal influence in SD. Induction at this time of day is also dependent on output from the circadian clock. PhyB may stabilize and interact with PhyC, a candidate gene for Ma5 a locus that also contributes to photoperiod regulation of flowering time. SbPRR37 activates SbCO expression peaking at dawn. SbPRR37 and SbGhd7 repress expression of the floral inductors SbEHD1, SbCN8, SbCN12 and SbCN15, leading to delayed flowering in long days. In SD or 58 M (phyB-1), expression of the floral repressors SbPRR37 and SbGHD7 is reduced which results in floral initiation once plants have satisfied other requirements for flowering. PhyB was found to mediate repression of SbCN15 regardless of day length.