FILAMENTOUS FLOWER controls the formation and development of Arabidopsis inflorescences and floral meristems

Phenotypic analysis of single and multiple mutants as well as in situ localization analysis of the expression patterns of floral genes have revealed that the FILAMENTOUS FLOWER (FIL) gene plays important roles in establishing the inflorescence in Arabidopsis. As previously reported, the fil mutant generates clusters of both filamentous structures and flowers with floral organs of altered number and shape. The structural resemblance of the filamentous structures to peduncles and the expression pattern of the APETALA1 (AP1) gene have shown that these filamentous structures are underdeveloped flowers that fail to form receptacles and floral organs, indicating that one of the roles of the FIL gene is to support the development of the floral meristem. That FIL also is involved in fate determination in the floral meristem is demonstrated by the homeotic conversion of flowers to inflorescences in fil ap1 double mutants and in fil ap1 cauliflower triple mutants. In double mutants with flowering-time loci (i.e., ft or fwa), leafy (lfy), and unusual floral organs (ufo), filamentous structures are formed, but very few or no flowers with floral organs develop. The enhanced phenotype in the fil apl and the fil lfy double mutants suggests that the FIL protein may work together with AP1 and LFY proteins. The FIL gene also may be involved in the cell fate determination of floral organ primordia, possibly by controlling the spatial expression patterns of the class A and C floral organ identity genes.