A constitutively active allele of phytochrome B maintains circadian robustness in the absence of light.

Jones, M. A. , Hu, W., Litthauer, S., Lagarias, J. C. and Harmer, S. L. (2015) A constitutively active allele of phytochrome B maintains circadian robustness in the absence of light. Plant Physiology, 169, pp. 814-825. (doi: 10.1104/pp.15.00782) (PMID:26157113)

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The sensitivity of the circadian system to light allows entrainment of the clock, permitting coordination of plant metabolic function and flowering time across seasons. Light affects the circadian system via both photoreceptors, such as phytochromes and cryptochromes, and sugar production by photosynthesis. In the present study, we introduce a constitutively active version of phytochrome B-Y276H (YHB) into both wild-type and phytochrome null backgrounds of Arabidopsis (Arabidopsis thaliana) to distinguish the effects of photoreceptor signaling on clock function from those of photosynthesis. We find that the YHB mutation is sufficient to phenocopy red light input into the circadian mechanism and to sustain robust rhythms in steady-state mRNA levels even in plants grown without light or exogenous sugars. The pace of the clock is insensitive to light intensity in YHB plants, indicating that light input to the clock is constitutively activated by this allele. Mutation of YHB so that it is retained in the cytoplasm abrogates its effects on clock function, indicating that nuclear localization of phytochrome is necessary for its clock regulatory activity. We also demonstrate a role for phytochrome C as part of the red light sensing network that modulates phytochrome B signaling input into the circadian system. Our findings indicate that phytochrome signaling in the nucleus plays a critical role in sustaining robust clock function under red light, even in the absence of photosynthesis or exogenous sources of energy.

Item Type:Articles
Additional Information:This work was supported by the National Institutes of Health (grant nos. GM069418 to S.L.H. and GM068552 to J.C.L.), U.S. Department of Agriculture National Institute of Food and Agriculture (Hatch Project CA-D*–MCB–4126-H to J.C.L.), the Leverhulme Trust (grant no. ECF–2012–358 to M.A.J.), the Royal Society (grant no. RG130746 to M.A.J.), the Oppenheimer Memorial Trust (PhD studentship to S.L.), and the University of Essex (to M.A.J. and S.L.). M.A.J. is a Leverhulme Early Career Fellow.
Glasgow Author(s) Enlighten ID:Jones, Dr Matt
Authors: Jones, M. A., Hu, W., Litthauer, S., Lagarias, J. C., and Harmer, S. L.
College/School:College of Medical Veterinary and Life Sciences > Institute of Molecular Cell and Systems Biology
Journal Name:Plant Physiology
Publisher:American Society of Plant Biologists
ISSN (Online):1532-2548
Published Online:08 July 2015
Copyright Holders:Copyright © 2015 American Society of Plant Biologists
First Published:First published in Plant Physiology 169:814-825
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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