PHYTOCHROME-DEPENDENT LATE-FLOWERING accelerates flowering through physical interactions with phytochrome B and CONSTANS

Abstract

In flowering plants, light is one of the major environmental stimuli that determine the timing of the transition from the vegetative to reproductive phase. In Arabidopsis, phytochrome B (phyB); phyA; cryptochrome 2; and FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 are major photoreceptors that regulate flowering. Unlike phyA; cryptochrome 2; and FLAVIN-BINDING, KELCH REPEAT, F-BOX 1, phyB delays flowering mainly by destabilizing the CONSTANS (CO) protein, whose reduction leads to decreased expression of a florigen gene, FLOWERING LOCUS T. However, it remains unclear how the phyB-mediated CO destabilization is mechanistically regulated. Here, we identify a unique PHYTOCHROME-DEPENDENT LATE-FLOWERING (PHL) gene, which is mainly involved in the phyBdependent regulation of flowering. Plants with mutant phl exhibited a late-flowering phenotype, especially under long-day conditions. The late-flowering phenotype of the phl mutant was completely overridden by a phyB mutation, indicating that PHL normally accelerates flowering by countering the inhibitory effect of phyB on flowering. Accordingly, PHL physically interacted with phyB both in vitro and in vivo in a red light-dependent manner. Furthermore, in the presence of phyB under red light, PHL interacted with CO as well. Taken together, we propose that PHL regulates photoperiodic flowering by forming a phyB-PHL-CO tripartite complex.light signaling | FT

Red Light-Mediated Degradation of CONSTANS by the E3 Ubiquitin Ligase HOS1 Regulates Photoperiodic Flowering in Arabidopsis

“…As previously described, phyB mutant plants grown under continuous RL displayed a conspicuous early flowering phenotype (Reed et al, 1993;Endo et al, 2013), indicating that this wavelength delays flowering time in Arabidopsis. We have also grown Col, hos1, and the double hos1 phyB mutant under continuous RL, and we observed that hos1 flowering time is not as delayed as in the wild type, but later than in the phyB mutant ( Figure 3A).…”

“…In addition, several factors have been shown to interact with phyB and regulate photoperiodic flowering. The PHYTOCHROME-DEPENDENT LATE FLOWERING (PHL) nuclear protein accelerates flowering by suppressing the inhibitory effect of phyB on flowering time (Endo et al, 2013). PHL interacts physically with phyB in a RL-dependent manner and, in the presence of active phyB, PHL interacts with CO as well (Endo et al, 2013).…”

“…The PHYTOCHROME-DEPENDENT LATE FLOWERING (PHL) nuclear protein accelerates flowering by suppressing the inhibitory effect of phyB on flowering time (Endo et al, 2013). PHL interacts physically with phyB in a RL-dependent manner and, in the presence of active phyB, PHL interacts with CO as well (Endo et al, 2013). The VASCULAR PLANT ONE-ZINC FINGER1 (VOZ1) and VOZ2 transcription factors are required for proper regulation of flowering time and cold stress responses in Arabidopsis (Yasui et al, 2012;Celesnik et al, 2013;Nakai et al, 2013).…”

Circadian Clock and Photoperiodic Flowering in Arabidopsis: CONSTANS Is a Hub for Signal Integration

“…PhyB-dependent regulation of CO stability can be explained by two distinct mechanisms [i.e. HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE1 (HOS1) and PHYTOCHROME-DEPENDENT LATE-FLOWERING (PHL)] (Endo et al, 2013;Lazaro et al, 2015). In the morning, HOS1 E3 ubiquitin ligase restricts accumulation of CO protein by degrading it (Lazaro et al, 2012(Lazaro et al, , 2015.…”

“…In addition, HOS1 physically interacts with phyB and CO. PhyB-dependent CO destabilization can therefore operate through HOS1 in the morning. PhyB-dependent destabilization of CO can be relieved in the afternoon by PHL (Endo et al, 2013). In the afternoon, PHL functions as a positive regulator of flowering by countering the inhibitory effect of phyB on CO stability.…”