The AGAMOUS-LIKE 20 MADS domain protein integrates floral inductive pathways in Arabidopsis

The very late-flowering behavior of Arabidopsis winter-annual ecotypes is c onferred mainly by two genes, FRIGIDA (FRI) and FLOWERING LOCUS C (FLC). A MADS-domain gene, AGAMOUS-LIKE 20 (AGL20), was identified as a dominant FRI suppressor in activation tagging mutagenesis. Overexpression of AGL20 supp resses not only the late flowering of plants that have functional FRI and F LC alleles but also the delayed phase transitions during the vegetative sta ges of plant development. Interestingly, AGL20 expression is positively reg ulated not only by the redundant vernalization and autonomous pathways of f lowering but also by the photoperiod pathway. Our results indicate that AGL 20 is an important integrator of three pathways controlling flowering in Ar abidopsis.