CONSERVED STRUCTURE AND FUNCTION OF THE ARABIDOPSIS FLOWERING TIME GENE CONSTANS IN BRASSICA-NAPUS

The Arabidopsis thaliana CONSTANS (CO) gene which promotes flowering i n long days was recently isolated by chromosome walking. The mapping o f QTLs controlling flowering time in Brassica species has identified g enomic regions that contain homologues of the CO gene. Four genes homo logous to the Arabidopsis CO gene were isolated from a pair of homoeol ogous loci in each of two doubled-haploid Brassica napus lines display ing different flowering times, N-o-1 and N-o-9. The four genes, BnCOa1 , BnCOa9, BnCOb1 and BnCOb9, are located on linkage groups N10 and N19 , and are highly similar to each other and to the Arabidopsis CO gene. Two regions of the proteins are particularly well conserved, a N-term inal region with two putative zinc fingers and a C-terminal region whi ch may contain a nuclear localization signal. All four genes appear to be expressed in B. napus, The BnCOa1 allele was shown to complement t he co-2 mutation in Arabidopsis in a dosage-dependent manner causing e arlier flowering than in wild type under both long- and short-day cond itions.