The circadian clock regulates many physiological and developmental processes in plants. The GIGANTEA (GI) protein plays a major role in the clock mechanism and controls important clock outputs including photoperiodic flowering. GI expression follows a circadian rhythm, with a peak in the evening, and changes in the timing of GI expression have dramatic effects on biological programs such as flowering. Natural-genetic variation in the timing of circadian-clock-controlled-gene expression is important in the adaptation of plants to growth at different latitudes both in nature and in agriculture. This project proposes to identify the molecular basis of natural-genetic variation that causes differences in the timing of GI expression between accessions of Arabidopsis. The three major objectives are (1) to map QTL implicated in the control of GI expression (2) to isolate the gene underlying at least one of these QTL and thereby identify a new gene, or natural allele of a known gene, that alters the timing of GI expression (3) to initiate the functional characterization of the identified GI regulator. To reach these objectives 85 Arabidopsis accessions were originally transformed with a GI::Luciferase transgene and several of them showed differences in the timing of GI expression compared to the reference accession Col. Two of these lines were crossed with Col and study of the F2 progeny demonstrated wide variation in the timing of GI expression. The results support the feasibility of the objectives, and these populations will be used in this program to identify QTL. Training on the study of natural variation will take place at the Max Planck Institute in Cologne and will complement the researchers existing skills in molecular biology. The technical expertise gained, the materials generated in the project and the expertise in project management that will be obtained will assist the applicant in reaching his goal of starting an independent research group in his home country.