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Proc Natl Acad Sci U S A. 2013 Oct 29;110(44):18017-22. doi: 10.1073/pnas.1310631110. Epub 2013 Oct 14.

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

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Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan.


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 phyB-dependent 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.


FT; light signaling

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