MULTIPLE INTERACTIONS AMONGST FLORAL HOMEOTIC MADS BOX PROTEINS

Most known floral homeotic genes belong to the MADS box family and the ir products act in combination to specify floral organ identity by an unknown mechanism. We have used a yeast two-hybrid system to investiga te the network of interactions between the Antirrhinum organ identity gene products, Selective heterodimerization is observed between MADS b ox factors, Exclusive interactions are detected between two factors, D EFICIENS (DEF) and GLOBOSA (GLO), previously known to heterodimerize a nd control development of petals and stamens, In contrast, a third fat ter, PLENA (PLE), which is required for reproductive organ development , can interact with the products of MADS box genes ex-pressed at early , intermediate and late stages. We also demonstrate that heterodimeriz ation of DEF and GLO requires the K box, a domain not found in non-pla nt MADS box factors, indicating that the plant MADS box factors mag ha ve different criteria for interaction, The association of PLENA and th e temporally intermediate MADS box factors suggests that part of their function in mediating between the meristem and organ identity genes i s accomplished through direct interaction, These data reveal an unexpe ctedly complex network of interactions between the factors controlling flower development and have implications for the determination of org an identity.