A genetic and molecular analysis of flowering time in Arabidopsis thaliana using natural variation = Een genetische en moleculaire analyse van bloeitijd in Arabidopsis thaliana gebruikmakend van natuurlijke variatie

<strong></strong>The natural allelic variation at flowering time loci between two <em>Arabidopsis thaliana</em> accessions; Landsberg <em>erecta</em> (L <em>er</em> ) and the tropical Cape Verde Island (Cvi) has been analyzed. Quantitative trait locus (QTL) mapping in recombinant inbred lines (RILs) grown under three environments, differing in day-length and/or vernalization treatment, was used to detect and locate flowering loci on the genetic map of Arabidopsis. Four main QTLs were identified, designated <em>EDI</em> , <em>FLF</em> , <em>FLG</em> and <em>FLH</em> , to which most of the flowering time differences could be attributed. At the <em>EDI</em> and <em>FLH</em> loci, Cvi alleles resulted in earliness, whereas at <em>FLF</em> and <em>FLG</em> , Cvi alleles caused lateness. Among these QTL, <em>EDI</em> ( <em>EARLY, DAY-LENGTH INSENSITIVE</em> ) is the main locus responsible for day-length sensitivity. To determine the molecular basis of this natural genetic variation, we have isolated the <em>EDI</em> locus using a map-based cloning strategy. The positional cloning of the <em>EDI</em> QTL showed it to be a novel allele of <em>CRY2</em> , encoding the blue-light photoreceptor cryptochrome-2, that has previously been shown to promote flowering in long-day photoperiods. It was shown that the unique flowering phenotype in the <em>CRY2</em> -Cvi allele results from a single amino acid substitution that reduces the down-regulation of the CRY2 protein in plants grown under short photoperiods, leading to early flowering. The genetic interaction between <em>CRY2</em> and other loci involved in the different flowering promotion pathways was studied. The three different types of <em>CRY2</em> alleles ( <em>CRY2</em> -Cvi = <em>EDI</em> , <em>CRY2</em> -L <em>er</em> , and the <em>CRY2</em> null mutant <em>fha1-1</em> ) were combined with the mutants representing the different flowering pathways. This analysis indicated that the so called "vernalization and autonomous pathway" that control <em>FLC</em> ( <em>Flowering locus C</em> ) expression, repress the expression of <em>CRY2</em> .