The Synergistic Activation of FLOWERING LOCUS C by FRIGIDA and a New Flowering Gene AERIAL ROSETTE 1 Underlies a Novel Morphology in Arabidopsis

The genetic changes underlying the diversification of plant forms represent a key question in understanding plant macroevolution. To understand the mechanisms leading to novel plant morphologies we investigated the Sy-0 ecotype of Arabidopsis that forms an enlarged basal rosette of leaves, develops aerial rosettes in the axils of cauline leaves, and exhibits inflorescence and floral reversion. Here we show that this heterochronic shift in reproductive development of all shoot meristems requires interaction between dominant alleles at AERIAL ROSETTE 1 (ART1), FRIGIDA (FRI), and FLOWERING LOCUS C (FLC) loci. ART1 is a new flowering gene that maps 14 cM proximal to FLC on chromosome V. ART1 activates FLC expression through a novel flowering pathway that is independent of FRI and independent of the autonomous and vernalization pathways. Synergistic activation of the floral repressor FLC by ART1 and FRI is required for delayed onset of reproductive development of all shoot meristems, leading to the Sy-0 phenotype. These results demonstrate that modulation in flowering-time genes is one of the mechanisms leading to morphological novelties.