A QTL for flowering time in Arabidopsis reveals a novel allele of CRY2

Variation of flowering time is found in the natural populations of many pla nt species. The underlying genetic variation, mostly of a quantitative natu re, is presumed to reflect adaptations to different environments contributi ng to reproductive success. Analysis of natural variation for flowering tim e in Arabidopsis thaliana has identified several quantitative trait loci (Q TL)(1), which have yet to be characterized at the molecular level. A major environmental factor that determines flowering time is photoperiod or day l ength, the length of the light period, which changes across the year differ ently with geographical latitude(2). We identified the EDI locus as a QTL p artly accounting for the difference in flowering response to the photoperio d between two Arabidopsis accessions: the laboratory strain Landsberg erect a (Ler), originating in Northern Europe, and Cvi, collected in the tropical Cape Verde Islands(3). Positional cloning of the EDI QTL showed it to be a novel allele of CRY2, encoding the blue-light photoreceptor cryptochrome-2 that has previously been shown to promote flowering in long-day (LD) photo periods(4). We show that the unique EDI flowering phenotype results from a single amino-acid substitution that reduces the light-induced downregulatio n of CRY2 in plants grown under Short photoperiods, leading to early flower ing.