<i>FRIGIDA</i> -related genes are required for the winter-annual habit in <i>Arabidopsis</i>

<jats:p> In temperate climates, the prolonged cold temperature of winter serves as a seasonal landmark for winter-annual and biennial plants. In these plants, flowering is blocked before winter. In <jats:italic>Arabidopsis thaliana</jats:italic> , natural variation in the <jats:italic>FRIGIDA</jats:italic> ( <jats:italic>FRI</jats:italic> ) gene is a major determinate of the rapid-cycling vs. winter-annual flowering habits. In winter-annual accessions of <jats:italic>Arabidopsis, FRI</jats:italic> activity blocks flowering through the up-regulation of the floral inhibitor <jats:italic>FLOWERING LOCUS C</jats:italic> ( <jats:italic>FLC</jats:italic> ). Most rapid-flowering accessions, in contrast, contain null alleles of <jats:italic>FRI</jats:italic> . By performing a mutant screen in a winter-annual strain, we have identified a locus, <jats:italic>FRIGIDA LIKE 1</jats:italic> ( <jats:italic>FRL1</jats:italic> ), that is specifically required for the up-regulation of <jats:italic>FLC</jats:italic> by <jats:italic>FRI</jats:italic> . Cloning of <jats:italic>FRL1</jats:italic> revealed a gene with a predicted protein sequence that is 23% identical to <jats:italic>FRI</jats:italic> . Despite sequence similarity, <jats:italic>FRI</jats:italic> and <jats:italic>FRL1</jats:italic> do not have redundant functions. <jats:italic>FRI</jats:italic> and <jats:italic>FRL1</jats:italic> belong to a seven-member gene family in <jats:italic>Arabidopsis</jats:italic> , and <jats:italic>FRI, FRL1</jats:italic> , and at least one additional family member, <jats:italic>FRIGIDA LIKE 2</jats:italic> ( <jats:italic>FRL2</jats:italic> ), are in a clade of this family that is required for the winter-annual habit in <jats:italic>Arabidopsis</jats:italic> . </jats:p>