Detection and resolution of genetic loci affecting circadian period in Brassica oleracea

Circadian rhythms regulate many aspects of plant growth, Wtness and vigour. The components and detailed mechanism of circadian regulation to date have been dissected in the reference species Arabidopsis thaliana. To determine the genetic basis and range of natural allelic variation for intrinsic circadian period in the closest crop relatives, we used an accurate and high throughput data capture system to record rhythmic cotyledon movement in two immortal segregating populations of Brassica oleracea, derived from parent lines representing diVerent crop types. Periods varied between 24.4 and 26.1 h between the parent lines, with transgressive segregation between extreme recombinant lines in both populations of »3.5 h. The additive eVect of individual QTL identiWed in each population varied from 0.17 to 0.36 h. QTL detected in one doubled haploid population were veriWed and the mapping intervals further resolved by determining circadian period in genomic substitution lines derived from the parental lines. Comparative genomic analysis based on collinearity between Brassica and Arabidopsis also allowed identiWcation of candidate orthologous genes known to regulate period in Arabidopsis, that may account for the additive circadian eVects of speciWc QTL. The distinct QTL positions detected in the two populations, and the extent of transgressive segregation suggest that there is likely to be considerable scope for modulating the range of available circadian periods in natural populations and crop species of Brassica. This may provide adaptive advantage for optimising growth and development in diVerent latitudes, seasons or climate conditions.