Genetic interactions of the Arabidopsis flowering time gene FCA, with genes regulating floral initiation

The genes controlling the timing of the transition from vegetative to repro ductive growth are likely candidates for regulators of genes initiating flo ral development. We have investigated the interaction of one particular gen e controlling flowering time, FCA, with the meristem identity-genes TERMINA L FLOWER I (TFL1), APETALA 1 (AP1) and LEAFY(LFY) and the floral repression gene EMBRYONIC FLOWER 1 (EMF1). Double mutant combinations were generated and the phenotypes characterized. The influence of strong and intermediate fca mutant alleles on the phenotype conferred by a 35S-LFY transgene was al so analysed. The results support a model where FCA function promotes flower ing in multiple pathways, one leading to activation of LFY and AP1, and ano ther acting in parallel with LFY and API. Only the latter pathway is predic ted to be non-functional in the intermediate fca-4 allele. The results are also consistent with AP1 and TFL1 negatively regulating FCA function. Combi nation of Columbia fca and emf1 mutant alleles confirmed that FCA is requir ed for the early flowering of emf1. EMF1 and FCA are therefore likely to op erate in different floral pathways.