Circadian clock components in Arabidopsis II. LHY/CCA1 regulate the floral integrator gene SOC1 in both GI-dependent and -independent pathways

Abstract

Two myb-related proteins, LHY and CCA1, play key roles in circadian clock function and flowering in Arabidopsis. GI mediates between LHY/CCA1 and floral activators (CO and FT) to promote flowering. The effect of GI on flowering probably involves FT-independent pathways, because ft only partially suppresses the early flowering caused by lhy cca1 or overexpression of GI (GI-ox). LFY, FT, and SOC1 integrate four flowering pathways: the photoperiod, gibberellic acid (GA), vernalization, and autonomous pathways. Roles of SOC1 and LFY in mediating between the clock and control of flowering time have not been elucidated. Here, we demonstrate that SOC1 functioned redundantly with FT to promote flowering via the LHY/CCA1/GI pathway. GI-ox and lhy cca1 increased mRNA levels of the SOC1 and gi partially suppressed the up-regulation in lhy cca1 under SD. The overexpression of LHY (lhy-1) shifted the phase of SOC1 expression, and the gi mutation did not affect the phase shift, suggesting that LHY regulates SOC1 expression both in GI-dependent and independent manners.