The Balance between CONSTANS and TEMPRANILLO Activities Determines FT Expression to Trigger Flowering

Abstract

Seasonal changes in day length influence flowering time in many plant species. In Arabidopsis, flowering is accelerated by exposure to long day (LD). Those inductive photoperiods are perceived in leaves [1] and initiate a long-distance signaling mediated by CO and FT. CO is expressed in the phloem according to a circadian rhythm [2-4]. Only under LD does CO induce FT expression as high levels of CO in the evening coincide with the external light that stabilizes CO protein [4, 5]. Subsequently, FT protein travels through the phloem to the shoot apex where, together with FD, it initiates flowering [6-12]. Despite the photoperiodic induction, a mechanism of floral repression is needed to avoid precocious flowering. We show that TEMPRANILLO genes (TEM1 and TEM2) act as novel direct FT repressors. Molecular and genetic analyses suggest that a quantitative balance between the activator CO and the repressor TEM determines FT levels. Moreover, developmental TEM downregulation marks the timing of flowering, as it shifts the CO/TEM balance in favor of CO activity, allowing FT transcript to reach the threshold level required to trigger flowering. We envision that this might be a general mechanism between long-day plants to ensure a tight regulation of flowering time.

EMBRYONIC FLOWER1 and ULTRAPETALA1 Act Antagonistically on Arabidopsis Development and Stress Response

“…AGL24, FPF1, and SPL9 promote flowering (Kania et al, 1997;Melzer et al, 1999;Michaels et al, 2003;Schwarz et al, 2008;Wang et al, 2009), whereas FLC, TEM1, TFL1, MAF2, and MAF3 repress flowering (Michaels and Amasino, 1999;Ratcliffe et al, 2003;Castillejo and Pelaz, 2008).…”

Transcriptional Mechanism of Jasmonate Receptor COI1-Mediated Delay of Flowering Time in Arabidopsis

“…Under favorable conditions, light signaling and the circadian clock coordinately control the activity of CO, which directly regulates the transcription of FT to promote flowering (Suárez-López et al, 2001;An et al, 2004;Imaizumi et al, 2005;Sawa et al, 2007;Fornara et al, 2009). On the other hand, the expression of FT is also negatively regulated by several transcriptional repressors, such as FLOWERING LOCUS C (Helliwell et al, 2006;Searle et al, 2006), SHORT VEGETATIVE PHASE (Lee et al, 2007), TEMPRANILLO1 (Castillejo and Pelaz, 2008), and SCHLAFMŰTZE (SMZ) (Mathieu et al, 2009). Under unfavorable conditions for flowering or during the juvenile developmental phases, these repressors, as well as their related transcriptional regulators, bind to specific cis-elements in the FT locus and repress its expression to prevent precocious flowering (Song et al, 2013).…”

TEMPRANILLO genes link photoperiod and gibberellin pathways to control flowering in Arabidopsis

“…We have previously found that the TEMPRANILLO (TEM) genes have a pivotal role in the direct repression of FT and counteract the activator CONSTANS (CO) 3 . A quantitative balance between TEM and CO, both regulated by light and the circadian clock, controls FT accumulation in LD 3 .…”

“…A quantitative balance between TEM and CO, both regulated by light and the circadian clock, controls FT accumulation in LD 3 . In addition, it has recently been suggested that GIGANTEA, an output from the circadian clock, directly regulates FT expression through neutralization of TEM (1 and 2) and SHORT VEGETATIVE PHASE 4 , two FT repressors 3,5,6 .…”