Molecular Genetics Analysis of Plant Circadian Rhythms

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McClung 9723482 The molecular basis by which time information is generated in plants will be investigated in the model plant, Arabidopsis thaliana. The molecular clock regulates overt rhythms in gas exchange, leaf movement and gene expression. Arabidopsis mutants affected in clock function have been isolated using the circadian rhythm in resistance/sensitivity to SO2 exposure that results from the circadian rhythms in stomatal aperture and gas exchange. If 65 mutants, 3 flower significantly earlier than wild type and 30 flower significantly later. Six of 21 tested also display a long hypocotyl phenotype. Efforts will be concentrated on one mutant, Circadian Timing Defective 1 (ctd1), which flowers later than wild type, but retains photoperiod sensitivity. The mutation is inherited as recessive nuclear gene. Ctd1 shows a short period in oscillations in mRNA abundance for four genes, the implication being that ctd1 affects a process common to expression of all four genes and thus defines a component of a common oscillator or of a common input or output pathway. Ctd1 will be characterized both phenotypically and genetically followed by cloning and characterization of the gene. Other ctd mutants with altered clock properties will continue to be characterized and the search for new mutants will also be continued. Rhythmic biological phenomena which recur at approximately 24 hour intervals in the absence of environmental time cues are termed circadian rhythms. Their timing is regulated by an endogenous biological clock. Such rhythms are ubiquitous and have been described in great detail at a phenomenological level. Plants provide excellent systems for study of circadian rhythmicity because plants are robustly rhythmic and exquisitely sensitive to environmental input, probably reflecting both their sessile growth form and their dependence on their immediate environment for nutrition and energy. Increased understanding of plant responses to environmental input and to endogenous temporal cues ha s agricultural importance, in particular, because both environmental cues and the circadian clock contribute to the photoperiodic decision to flower. A genetic and molecular biological analysis of mutants identified by a novel screen will be done in Arabidopsis thaliana, the model plant.