Molecular and Genetic Analysis of ZTL Function in the Arabidopsis Circadian Clock

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The circadian clock provides for both anticipation of coming changes and for a buffering against rapid variation in the environment. Despite its importance, little is known about the molecular components of the circadian clock in plants, though much phenomenology has shown that the basic properties of clocks are similar across the plant and animal kingdoms. The long-term objective of this study is to identify and integrate components of the circadian clock system of plants into a coherent framework of interaction. The specific means towards this end will be through using the mutant and wild-type gene products of the recently cloned locus in Arabidopsis, ZEITLUPE (ZTL). Mutations at this locus (ztl-1, -2) affect flowering time and greatly increase the period of the circadian clock in a light dependent way. These loci will be one of the primary tools used to understand how light input to the clock system interfaces with the oscillator itself. ZTL is comprised of a novel combination of a putative light-sensing domain (LOV domain), an F-box and 6 kelch motifs, identifying regions that are likely to play distinct roles in function of this protein. The specific goals of this project are: 1) to complete the genetic positioning of ZTL locus within the context of the known red light and blue light signal transduction pathways. 2) To identify physical interaction partners of the ZTL protein through yeast 2-hybrid interaction library screens and through targeted testing of candidate factors. 3) To identify genetic interaction partners of ZTL through suppressor and enhancer screens based on the ztl-1 phenotype. Given the strong effects these mutations have on flowering time, these studies should more clearly develop the link between the circadian clock, light signaling and plant development.