Antisense Suppression of the Arabidopsis PIF3 Gene Does not Affect Circadian Rhythms But Causes Early Flowering by Increasing FT Expression

Abstract

Photoperiodic control of flowering is regulated by light and a circadian clock. TOC1, LHY and CCA1 consist both of positive and negative feedback loops and are clock components in Arabidopsis. PIF3, a bHLH transcription factor binds promoter regions of the LHY and CCA1 genes, affects the light induction of these genes and interacts with TOC1 protein. Although PIF3 has been assumed to be involved in the positive feedback regulation of clock components, the molecular nature has not been elucidated. Here we demonstrate that the antisense suppression of the PIF3 gene causes higher levels of mRNA of floral activator genes CO and FT and results in early flowering. Neither the circadian rhythms nor the diurnal rhythms of the clock-controlled genes are affected by the reduction in PIF3 gene expression. We will discuss a possibility that PIF3 may regulate CO and FT expressions without affecting circadian rhythms.