Natural allelic variation identifies new genes in the Arabidopsis circadian system

We have analysed the circadian rhythm of Arabidopsis thaliana leaf movement s in the accession Cvi from the Cape Verde islands, and in the commonly use d laboratory strains Columbia (Col) and Landsberg (erecta) (Ler), which ori ginated in Northern Europe. The parental lines have similar rhythmic period s, but the progeny of crosses among them reveal extensive variation for thi s trait. An analysis of 48 Ler/Cvi recombinant inbred lines (RILs) and a fu rther 30 Ler/Col RILs allowed us to locate four putative quantitative trait loci (QTLs) that control the period of the circadian clock. Near-isogenic lines (NILs) that contain a QTL in a small, defined chromosomal region allo wed us to confirm the phenotypic effect and to map the positions of three p eriod QTLs, designated ESPRESSO, NON TROPPO and RALENTANDO. Quantitative tr ait loci at the locations of RALENTANDO and of a fourth QTL, ANDANTE, were identified in both Ler/Cvi and Ler/Col RIL populations. Some QTLs for circa dian period are closely linked to loci that control flowering time, includi ng FLC. We show that fle mutations shorten the circadian period such that t he known allelic variation in the MADS-box gene FLC can account for the AND ANTE QTL. The QTLs ESPRESSO and RALENTANDO identify new genes that regulate the Arabidopsis circadian system in nature, one of which may be the flower ing-time gene GIGANTEA.