CONSTANS Activates SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 through FLOWERING LOCUS T to Promote Flowering in Arabidopsis

Abstract

CONSTANS (CO) regulates flowering time by positively regulating expression of two floral integrators, FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), in Arabidopsis (Arabidopsis thaliana). FT and SOC1 have been proposed to act in parallel pathways downstream of CO based on genetic analysis using weak ft alleles, since ft soc1 double mutants showed an additive effect in suppressing the early flowering of CO overexpressor plants. However, this genetic analysis was inconsistent with the sequential induction pattern of FT and SOC1 found in inducible CO overexpressor plants. Hence, to identify genetic interactions of CO, FT, and SOC1, we carried out genetic and expression analyses with a newly isolated T-DNA allele of FT, ft-10. We found that ft-10 almost completely suppressed the early flowering phenotype of CO overexpressor plants, whereas soc1-2 partially suppressed the phenotype, suggesting that FT is the major output of CO. Expression of SOC1 was altered in gain-or loss-of-function mutants of FT, whereas expression of FT remained unchanged in gain-or loss-of-function mutants of SOC1, suggesting that FT positively regulates SOC1 to promote flowering. In addition, inactivation of FTcaused down-regulation of SOC1 even in plants overexpressing CO, indicating that FT is required for SOC1 induction by CO. Taken together, these data suggest that CO activates SOC1 through FT to promote flowering in Arabidopsis.The phase transition to flowering in plants is precisely controlled by environmental conditions and endogenous developmental cues so that plants produce their progeny under favorable conditions. The response to multiple factors suggests the existence of a complex network regulating this phase transition in plants ( Koornneef et al., 1998). To identify genes that control the transition, mutants that showed accelerated or delayed flowering under different conditions, commonly known as flowering-time mutants, have been isolated (Redei, 1975). These mutants were grouped according to their responses to various physiological conditions and then integrated into genetic pathways to explain the control of flowering time. Four floral promotion pathways have been genetically identified in Arabidopsis (Arabidopsis thaliana): the photoperiod, autonomous, vernalization, and GA pathways . Among these pathways, genes within the photoperiod pathway, or the long-day pathway, play an important role in controlling flowering time (Komeda, 2004), since Arabidopsis is a facultative long-day plant.One of the central regulators in the photoperiod pathway is CONSTANS (CO), which encodes a nuclear protein that contains a CCT motif and two B-box-type zinc-finger domains (Putterill et al., 1995). Loss of CO function delays the phase transition, whereas gain of function of CO accelerates it, suggesting that CO positively regulates flowering time in Arabidopsis. Furthermore, CO mRNA levels show a circadian rhythm under continuous light, such that CO mRNA levels peak at night and are reduced during the day (SuarezLopez et...

Long-distance movement of ArabidopsisFLOWERING LOCUS TRNA participates in systemic floral regulation

“…1E). We grafted ft-10, which contains a T-DNA insertion at first intron of FT gene that greatly knock-down FT RNA accumulation, 32 onto ft-3 stock. Two weeks after grafting, we collected RNA samples from various scions and subjected to RT-PCR analysis.…”

“…Arabidopsis thaliana seeds were obtained from the Arabidopsis Biological Resource Center (ABRC, Ohio) and were grown in growth chambers under a 16/8 h, 22°C/20°C day/night cycle, with white fluorescent light, at light intensity: 100 μmolm -2 s -1 . The ft-10 mutant line was obtained from GABI-Kat (http://www.gabi-kat.de, line ID: 290E08; Yoo et al 2005). Arabidopsis PSUC2-amiRFT and PFD-amiRFT transformants were obtained from Dr Markus Schmid.…”

Flowering-time genes modulate meristem determinacy and growth form in Arabidopsis thaliana

“…The ft-1 mutants flower late only in long days, whereas the 35S:FT transgene triggers an extremely early and photoperiodindependent flowering in wild type 19,20 . The soc1 and ful single mutations slightly delayed the strong early flowering in 35S:FT plants 21,22 (Table 1). Despite the very early flowering of 35S:FT soc1-3 and 35S:FT ful-2 plants, they showed a markedly increased longevity and produced through reiteration of growth many short determinate co-inflorescences, particularly in short days (Supplementary Fig.…”

NO FLOWERING IN SHORT DAY (NFL) is a bHLH transcription factor that promotes flowering specifically under short-day in Arabidopsis

“…Therefore, increased CO protein promotes expression of FT only under LD. FT moves through phloem to the meristem, where it associates with FD, and the FT-FD complex activates expression of SOC1 and downstream floral identity genes, such as AP1 and LFY, to promote flowering (Abe et al, 2005;Corbesier et al, 2007;Michaels et al, 2005;Wigge et al, 2005;Yoo et al, 2005). However, in SD, CO protein peaks in the dark, where it is degraded through the COP1-SPA complex, resulting in a delayed flowering response.…”