Quantitative trait locus analysis of circadian phase in Arabidopsis thaliana

The plant clock is the least well characterized of circadian systems, although mutant screens have identified a number of putative components. Here, an approach using forward genetics is employed which takes advantage of natural allelic variation in Arabidopsis thaliana ecotypes to identify areas ofgenome responsible for variation in clock traits. This means that intact, viable systems are the basis of analysis. Circadian output in transgenic seedlings is monitored by measuring the activity of a cab2::1uc+ transgene. The circadian parameter studied here is 'phase', i.e., the timing of a point of the circadian cycle relative to a fixed point in the external light dark cycle. The timing of the peak of cab2::1uc+ expression after last dawn was used as a phase marker. Initially, a quantitative trait locus ('QTL') analysis attempted to identify QTL for phase. Phase was measured in transgenic Arabidopsis seedlings from a population of recombinant inbred lines (Rll-s), whose genomes are homozygous mosaics derived from two inbred parental genotypes (Ler xCvi). QTL analysis attempts to correlate phenotypic variation with genetic variation within this population; both types of variation arise from the natural allelic variation present in the parents. The analysis was repeated on phase data obtained after entrainment to different photoperiods. Loci were found where Cvi alleles either advanced or delayed the phase relative to Ler alleles in particular environments. The QTL were characterized in near isogenic lines (t\lJLs). The Nll..,s are lines which contain small regions of Cvi alleles in an otherwise homogeneous Ler background, and the lines were transformed with cab2::1uc+ in order to measure their circadian output. This allowed us to evaluate candidates for genes underlying the QTL found.EThOS - Electronic Theses Online ServiceGBUnited Kingdo