A CHARACTERIZATION OF THE MADS-BOX GENE FAMILY IN MAIZE

Studies on distantly related dicot pla nt species have identified home otic genes that specify floral meristem identity and determine the fat e of floral organ primordia. Most of these genes belong to a family ch aracterized by the presence of a structural motif, the MADS-box, which encodes a protein domain with DNA-binding properties. As part of an e ffort to understand how such genes may have been recruited during the evolution of flowers with different organ types such as those found in maize, two members of this gene family in maize, ZAG? and ZAG2, have been characterized previously. Here, the isolation and characterizatio n of four new members of this gene family, designated ZAP1, ZAG3, ZAG4 and ZAG5, are described and the genetic map position of these and 28 additional maize MADS-box genes is determined. The first new member of this family appears to be the Zea mays ortholog of the floral homeoti c gene APETALA1 (API) and has been designated ZAP1. One of these genes , ZAG4, is unusual in that its deduced protein sequence includes the M ADS domain but lacks the K-domain characteristically present in this f amily of genes. In addition, its copy number and expression varies amo ng different inbreds. A large number of maize MADS-box genes map to du plicated regions of the genome, including one pair characterized here, ZAG3 and ZAG5. These data underscore the complexity of this gene fami ly in maize, and provide the basis for further studies into the regula tion of floral organ morphogenesis among the grasses.