2 research outputs found
Phosphorylation of CONSTANS and its COP1-dependent degradation during photoperiodic flowering of Arabidopsis
Seasonal flowering involves responses to changes in day length. In Arabidopsis thaliana, the CONSTANS
(CO) transcription factor promotes flowering in the long days of spring and summer. Late flowering in short
days is due to instability of CO, which is efficiently ubiquitinated in the dark by the CONSTITUTIVE PHOTOMORPHOGENIC
1 (COP1) E3 ligase complex. Here we show that CO is also phosphorylated. Phosphorylated
and unphosphorylated forms are detected throughout the diurnal cycle but their ratio varies, with the relative
abundance of the phosphorylated form being higher in the light and lower in the dark. These changes
in relative abundance require COP1, because in the cop1 mutant the phosphorylated form is always more
abundant. Inactivation of the PHYTOCHROME A (PHYA), CRYPTOCHROME 1 (CRY1) and CRYPTOCHROME 2
(CRY2) photoreceptors in the phyA cry1 cry2 triple mutant most strongly reduces the amount of the phosphorylated
form so that unphosphorylated CO is more abundant. This effect is caused by increased COP1
activity, as it is overcome by introduction of the cop1 mutation in the cop1 phyA cry1 cry2 quadruple
mutant. Degradation of CO is also triggered in red light, and as in darkness this increases the relative abundance
of unphosphorylated CO. Finally, a fusion protein containing truncated CO protein including only the
carboxy-terminal region was phosphorylated in transgenic plants, locating at least one site of phosphorylation
in this region. We propose that CO phosphorylation contributes to the photoperiodic flowering
response by enhancing the rate of CO turnover via activity of the COP1 ubiquitin ligase.Peer reviewe