Vernalization-induced repression of FLOWERING LOCUS C stimulates flowering in Sinapis alba and enhances plant responsiveness to photoperiod.

* Of the Brassicaceae, Sinapis alba has been intensively studied as a physiological model of induction of flowering by a single long day (LD), while molecular-genetic analyses of Arabidopsis thaliana have disclosed complex interactions between pathways controlling flowering in response to different environmental cues, such as photoperiod and vernalization. The vernalization process in S. alba was therefore analysed here. * The coding sequence of S. alba SaFLC, which is orthologous to the A. thaliana floral repressor FLOWERING LOCUS C, was isolated and the transcript levels quantified in different conditions. * Two-week-old seedlings grown in noninductive short days (SDs) were vernalized for 1-6 wk. Down-regulation of SaFLC was already marked after 1 wk of cold but 2 wk was needed for a significant acceleration of flowering. Flower buds were initiated during vernalization. When vernalization was stopped after 1 wk, repression of SaFLC was not stable but a significant increase in plant responsiveness to 16-h LDs was observed when LDs followed immediately after the cold treatment. * These results suggest that vernalization does not only work when plants experience long exposure to cold during the winter: shorter cold periods might stimulate flowering of LD plants if they occur when photoperiod is increasing, such as in spring.