The loss of vernalization requirement in narrow-leafed lupin is associated with a deletion in the promoter and de-repressed expression of a Flowering Locus T (FT) homologue

<li>Adaptation of <em>Lupinus angustifolius</em> (narrow-leafed lupin) to cropping in southern Australian and northern Europe was transformed by a dominant mutation (<em>Ku</em>) that removed vernalization requirement for flowering. The <em>Ku</em> mutation is now widely used in lupin breeding to confer early flowering and maturity. We report here the identity of the <em>Ku</em> mutation.</li> <li>We used a range of genetic, genomic and gene expression approaches to determine whether <em>Flowering Locus T</em> (<em>FT</em>) homologues are associated with the <em>Ku</em> locus.</li> <li>One of four <em>FT</em> homologues present in the narrow-leafed lupin genome, <em>LanFTc1</em>, perfectly co-segregated with the <em>Ku</em> locus in a reference mapping population. Expression of <em>LanFTc1</em> in the <em>ku</em> (late-flowering) parent was strongly induced by vernalization, in contrast to the <em>Ku</em> (early-flowering) parent, which showed constitutively high <em>LanFTc1</em> expression. Co-segregation of this expression phenotype with the <em>LanFTc1</em> genotype indicated that the <em>Ku</em> mutation impairs <em>cis</em>-regulation of <em>LanFTc1</em>. Sequencing of <em>LanFTc1</em> revealed a 1.4-kb deletion in the promoter region, which was perfectly predictive of vernalization response in 216 wild and domesticated accessions. Linkage disequilibrium rapidly decayed around <em>LanFTc1</em>, suggesting that this deletion caused the loss of vernalization response.</li> <li>This is the first time a legume <em>FTc</em> subclade gene has been implicated in the vernalization response.</li>