Abstract
Phytochrome B (phyB) is the primary red light photoreceptor in plants, and regulates both growth and development. The relative levels of phyB in the active state are determined by the light conditions, such as direct sunlight or shade, but are also affected by light-independent dark reversion. Dark reversion is a temperature-dependent thermal relaxation process, by which phyB reverts from the active to the inactive state. Here, we show that the homologous phyB-binding proteins PCH1 and PCHL suppress phyB dark reversion, resulting in plants with dramatically enhanced light sensitivity. Moreover, far-red and blue light upregulate the expression of PCH1 and PCHL in a phyB independent manner, thereby increasing the response to red light perceived by phyB. PCH1 and PCHL therefore provide a node for the molecular integration of different light qualities by regulation of phyB dark reversion, allowing plants to adapt growth and development to the ambient environment.
Highlights
Phytochrome B is the primary red light photoreceptor in plants, and regulates both growth and development
PhyA is required for sensing far-red light (FR) and weak light of any wavelength, while Phytochrome B (phyB) is the primary receptor for red light (R)
Yeast two-hybrid (Y2H) screening and MS/MS analyses of immunoprecipitated phyB complexes from extracts of phyB-NLS-GFP expressing Arabidopsis plants, we identified PHOTOPERIODIC CONTROL OF HYPOCOTYL 1 (PCH1) as a phyB interacting protein (Fig. 1a, b; Supplementary Fig. 1a)
Summary
Phytochrome B (phyB) is the primary red light photoreceptor in plants, and regulates both growth and development. PCH1 and PCHL provide a node for the molecular integration of different light qualities by regulation of phyB dark reversion, allowing plants to adapt growth and development to the ambient environment. Phytochromes are red/far-red photoreceptors in plants that play a critical role in the adaptation of growth and development to the environment[1,2,3]. Seedlings lacking functional PCH1 have elongated hypocotyls compared to the wild type when grown in short days[14] Under these conditions, PCH1 transcript and protein levels peak at dusk, enhancing phyB-dependent inactivation of the growth-promoting transcription factor PHYTOCHROME INTERACTING FACTOR 4 (PIF4)[13,14]. PCH1 and PCHL allow plants to adapt to their environment by acting as a node of signal integration that regulates phyB dark reversion
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