title: A Constitutively Active Allele of Phytochrome B Maintains Circadian Robustness in the Absence of Light.
abstract: 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.
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, United Kingdom (M.A.J., S.L.); andDepartment of Plant Biology, College of Biological Sciences (M.A.J., S.L.H.) and Department of Molecular and Cellular Biology (W.H., J.C.L.), University of California, Davis, California 95616.
authors.forename: Matthew Alan
authors.initials: MA
authors.lastname: Jones
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, United Kingdom (M.A.J., S.L.); andDepartment of Plant Biology, College of Biological Sciences (M.A.J., S.L.H.) and Department of Molecular and Cellular Biology (W.H., J.C.L.), University of California, Davis, California 95616.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, United Kingdom (M.A.J., S.L.); andDepartment of Plant Biology, College of Biological Sciences (M.A.J., S.L.H.) and Department of Molecular and Cellular Biology (W.H., J.C.L.), University of California, Davis, California 95616.
authors.forename: Suzanne
authors.initials: S
authors.lastname: Litthauer
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, United Kingdom (M.A.J., S.L.); andDepartment of Plant Biology, College of Biological Sciences (M.A.J., S.L.H.) and Department of Molecular and Cellular Biology (W.H., J.C.L.), University of California, Davis, California 95616.
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
authors.affiliation: School of Biological Sciences, University of Essex, Wivenhoe Park, Essex CO4 3SQ, United Kingdom (M.A.J., S.L.); andDepartment of Plant Biology, College of Biological Sciences (M.A.J., S.L.H.) and Department of Molecular and Cellular Biology (W.H., J.C.L.), University of California, Davis, California 95616 slharmer@ucdavis.edu.
authors.forename: Stacey Lynn
authors.initials: SL
authors.lastname: Harmer
mesh_terms: D000483:Alleles; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001683:Biological Clocks / Q000235:genetics / Q000528:radiation effects; D002940:Circadian Rhythm / Q000235:genetics* / Q000528:radiation effects; D003624:Darkness; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008027:Light; D010834:Phytochrome / Q000378:metabolism; D051939:Phytochrome B / Q000235:genetics* / Q000378:metabolism; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; C497952:PHYB protein, Arabidopsis; D012333:RNA, Messenger; C406683:phytochrome C, Arabidopsis; D010834:Phytochrome; D051939:Phytochrome B