Analysis of day-length dependent regulation of Ehd1 expression mediated by a floral repressor Ghd7 in rice

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In rice, florigen Hd3a expression is toggled by a 30 minutes difference of day-length reduction. Setting of critical day-length for Hd3a is conferred by precise control of Ehd1 expression. Ghd7 represses Ehd1 to repress Hd3a under long-days. Ghd7 activity is controlled by day-length dependent regulation at both transcriptional and post-transcriptional levels. Contrary, Ehd1 is induced only when blue-light signal coincides with a morning phase set by OsGI, a rice circadian clock component, independently of photoperiods. In here, we identified blue-light signaling pathway required for Ehd1 induction and proposed a model how blue-light signals interact with OsGI to induce Ehd1 expression in the morning. Because blue-light signal is transduced via an ubiquitin-mediated proteolysis, our results indicate that blue-light dependent stabilization of a transacting factor expressed by OsGI can achieve an acute induction of Ehd1 at the morning when Ghd7 repression is released.