Researchers at CBGP revealed the molecular mechanism mediating the red light-induced degradation of CO that regulates photoperiodic flowering in Arabidopsis.
Flowering in all plants depends on light, which is perceived in leaves. Light quality, quantity, and relative duration during the day are all variables that influence the timing of the floral transition. Among them, daylength is a major factor in the regulation of flowering time and allows sexual reproduction to take place at an appropriate time of the year and to synchronise flowering with seasons and pollination agents, when this is part of the plant’s adaptive strategy. In Arabidopsis, the ability to distinguish long days (LDs) from short days (SDs) is largely the result of the complex regulation of the CONSTANS (CO) gene, both at the transcriptional and post-translational level. The coincidence of CO expression with light in LD conditions is essential for the promotion of flowering. Besides, different light qualities play specific roles in the photoperiodic response, and while blue and far-red light promote flowering, red light delays it through phytochrome B (phyB) function. It was already known that CO protein stability is controlled by various light signals during the day, but the molecular mechanism mediating the red light-induced degradation of CO that regulates photoperiodic flowering in Arabidopsis remains to be elucidated.
Researchers at CBGP from the ¨Molecular Bases of Plant Developmental Phase Transitions¨ group have revealed a key role for the RING finger E3 UBIQUITIN LIGASE protein HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENES 1 (HOS1) in this mechanism. They present evidence indicating that the degradation of CO under red light is prevented in the hos1 and the phyB mutants and thus HOS1 is involved in the red light-mediated degradation of CO. Besides, they demonstrate that PhyB physically interacts in vivo with HOS1 and CO, suggesting that the mechanism by which CO is degraded under red light relies on the formation of a tripartite complex between these proteins that may be essential to modulate a correct photoperiodic response in Arabidopsis. Red light regulates flowering time in a variety of LD and SD species. Because HOS1, CO, and phyB homologs are found in all plant species, the interaction revealed maybe generally present in all flowering plants. The existence of this protein complex provides a framework that will help elucidate how flowering time is regulated by environmental signals, particularly by red light.
Lazaro, A; Mouriz, A; Piñeiro, M; Jarillo, JA. 2015. "Red light-mediated degradation of CONSTANS by the E3 ubiquitin ligase HOS1 regulates photoperiodic flowering in Arabidopsis". Plant Cell. DOI: 10.1105/tpc.15.00529".