title: Unanticipated regulatory roles for Arabidopsis phytochromes revealed by null mutant analysis.
abstract: In view of the extensive literature on phytochrome mutants in the Ler accession of Arabidopsis, we sought to secure a phytochrome-null line in the same genetic background for comparative studies. Here we report the isolation and phenotypic characterization of phyABCDE quintuple and phyABDE quadruple mutants in the Ler background. Unlike earlier studies, these lines possess a functional allele of FT permitting measurements of photoperiod-dependent flowering behavior. Comparative studies of both classes of mutants establish that phytochromes are dispensable for completion of the Arabidopsis life cycle under red light, despite the lack of a transcriptomic response, and also indicate that phyC is nonfunctional in the absence of other phytochromes. Phytochrome-less plants can produce chlorophyll for photosynthesis under continuous red light, yet require elevated fluence rates for survival. Unexpectedly, our analyses reveal both light-dependent and -independent roles for phytochromes to regulate the Arabidopsis circadian clock. The rapid transition of these mutants from vegetative to reproductive growth, as well as their insensitivity to photoperiod, establish a dual role for phytochromes to arrest and to promote progression of plant development in response to the prevailing light environment.
authors.affiliation: Department of Molecular and Cellular Biology and Plant Biology, University of California, Davis, CA 95616, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.forename: Keara A
authors.initials: KA
authors.lastname: Franklin
authors.forename: Robert A
authors.initials: RA
authors.lastname: Sharrock
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Jones
authors.forename: Stacey L
authors.initials: SL
authors.lastname: Harmer
authors.forename: J Clark
authors.initials: JC
authors.lastname: Lagarias
mesh_terms: D001059:Apoproteins / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D002734:Chlorophyll / Q000096:biosynthesis; D002940:Circadian Rhythm / Q000235:genetics; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D017343:Genes, Plant; D018525:Germination / Q000235:genetics; D018398:Homeodomain Proteins / Q000235:genetics; D008027:Light; D009154:Mutation; D017440:Photoperiod; D010834:Phytochrome / Q000235:genetics* / Q000378:metabolism*; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism; D051939:Phytochrome B / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D014157:Transcription Factors / Q000235:genetics
chemical_list: C080210:ATHB-2 protein, Arabidopsis; D001059:Apoproteins; D029681:Arabidopsis Proteins; D018398:Homeodomain Proteins; C497973:PHYA protein, Arabidopsis; C497952:PHYB protein, Arabidopsis; C088753:PHYE protein, Arabidopsis; D051942:Phytochrome A; D014157:Transcription Factors; C406683:phytochrome C, Arabidopsis; D010834:Phytochrome; D051939:Phytochrome B; D002734:Chlorophyll; C088754:PHYD protein, Arabidopsis