Characterization of a MADS FLOWERING LOCUS C-LIKE (MFL) sequence in Cichorium intybus: a comparative study of CiMFL and AtFLC reveals homologies and divergences in gene function.

In Arabidopsis thaliana, the ability to flower is mainly related to a floral repressor, FLOWERING LOCUS C (FLC), which is regulated through the vernalization pathway. The genes controlling the vernalization pathway seem to be only partially conserved in dicots other than the Brassicaceae. Cichorium intybus (chicory) is a biennial species belonging to the Asteraceae family, and it shows an obligate vernalization requirement for flowering. Cichorium intybus MADS (MCM1, Agamous, Deficiens, SRF) FLC-like (CiMFL) sequences were isolated in C. intybus by RT-PCR and their expression patterns characterized during plant development and in response to vernalization. The biological function of CiMFL was analysed by complementation of A. thaliana FRIGIDA (AtFRI);flc3. Resetting of MFL expression after vernalization was analysed during microsporogenesis. Before vernalization, CiMFL is mainly expressed in the axils of young leaves. Vernalization induced CiMFL down-regulation under a long-day photoperiod but not under a short-day photoperiod. Furthermore, together with a decrease in CiMFL transcripts, cold conditions induced changes in the morphology of the shoot apical meristem and in the transition to flowering. The biological function of CiMFL was found not to be conserved. Our results show that the regulation of CiMFL expression in time and space and in relation to environmental conditions is only partially conserved with respect to FLC isolated from A. thaliana. A model for flowering repression by CiMFL is proposed.