title: Organ specificity in the plant circadian system is explained by different light inputs to the shoot and root clocks.
abstract: Circadian clocks allow the temporal compartmentalization of biological processes. In Arabidopsis, circadian rhythms display organ specificity but the underlying molecular causes have not been identified. We investigated the mechanisms responsible for the similarities and differences between the clocks of mature shoots and roots in constant conditions and in light : dark cycles. We developed an imaging system to monitor clock gene expression in shoots and light- or dark-grown roots, modified a recent mathematical model of the Arabidopsis clock and used this to simulate our new data. We showed that the shoot and root circadian clocks have different rhythmic properties (period and amplitude) and respond differently to light quality. The root clock was entrained by direct exposure to low-intensity light, even in antiphase to the illumination of shoots. Differences between the clocks were more pronounced in conditions where light was present than in constant darkness, and persisted in the presence of sucrose. We simulated the data successfully by modifying those parameters of a clock model that are related to light inputs. We conclude that differences and similarities between the shoot and root clocks can largely be explained by organ-specific light inputs. This provides mechanistic insight into the developing field of organ-specific clocks.
authors.affiliation: Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Bordage
authors.affiliation: Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Stuart
authors.initials: S
authors.lastname: Sullivan
authors.affiliation: Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Janet
authors.initials: J
authors.lastname: Laird
authors.affiliation: SynthSys, University of Edinburgh, Edinburgh, EH9 3JD, UK.
authors.forename: Andrew J
authors.identifier: 0000-0003-1756-3654
authors.initials: AJ
authors.lastname: Millar
authors.affiliation: Institute of Molecular, Cell and Systems Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Hugh G
authors.initials: HG
authors.lastname: Nimmo
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D057906:Circadian Clocks / Q000528:radiation effects*; D002940:Circadian Rhythm / Q000528:radiation effects*; D003624:Darkness; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D009928:Organ Specificity / Q000235:genetics / Q000528:radiation effects; D017440:Photoperiod; D018517:Plant Roots / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D018520:Plant Shoots / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects
chemical_list: D029681:Arabidopsis Proteins
keywords: Arabidopsis thaliana; circadian rhythms; imaging; light sensitivity; organ specificity; systems biology