PLENA and FARINELLI: redundancy and regulatory interactions between two Antirrhinum MADS-box factors controlling flower development

We report the discovery of an Antirrhinum MADS-box gene, FARINELLI (FAR), a nd the isolation of far mutants by a reverse genetic screen. Despite striki ng similarities between FAR and the class C MADS-box gene PLENA (PLE), the phenotypes of their respective mutants are dramatically different. Unlike p le mutants, which show homeotic conversion of reproductive organs to perian th organs and a loss of floral determinacy, far mutants have normal flowers which are partially male-sterile. Expression studies of PLF and FAR, in wi ld-type and mutant backgrounds, show complex interactions between the two g enes. Double mutant analysis reveals an unexpected, redundant negative cont rol over the B-function MADS-box genes. This feature of the two Antirrhinum C-function-like genes is markedly different from the control of the inner boundary of the B-function expression domain in Ambidopsis, and we propose and discuss a model to account for these differences. The difference in phe notypes of mutants in two highly related genes illustrates the importance o f the position within the regulatory network in determining gene function.