Arabidopsis STERILE APETALA, a multifunctional gene regulating inflorescence, flower, and ovule development

A recessive mutation in the Arabidopsis STERILE APETALA (SAP) causes severe aberrations in inflorescence and flower and ovule development. In sap flow ers, sepals are carpelloid, petals are short and narrow or absent, gametoph yte formation, is arrested in sap ovules during or just after the first mei otic division. More severe aberrations were observed in double mutants betw een sap and mutant alleles of the floral homeotic gene APETALA2 (AP2) sugge sting that both genes are involved in the initiation of female gametophyte development. Together with the organ identity gene AGAMOUS (AG) SAP is requ ired for the maintenance of floral identity acting in a manner similar to A PETALA1. In contrast to the outer two floral organs in sap mutant flowers, normal sepals and petals develop in ag/sap double mutants, indicating that SAP negatively regulates AG expression in the perianth whorls. This suppose d cadastral function of SAP is supported by in situ hybridization experimen ts showing ectopic expression of AG in the sap mutant. We have cloned the S AP gene by transposon tagging and revealed that it encodes a novel protein with sequence motifs, that are also present in plant and animal transcripti on regulators. Consistent with the mutant phenotype, SAP is expressed in in florescence and floral meristems, floral organ primordia, and ovules. Taken together, we propose that SAP belongs to a new class of transcription regu lators essential for a number of processes in Arabidopsis flower developmen t.