Molecular characterization of the Arabidopsis floral homeotic gene APETALA1

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Abstract
THE first step in flower development is the transition of an inflorescence meristem into a floral meristem. Each floral meristem differentiates into a flower consisting of four organ types that occupy precisely defined positions within four concentric whorls. Genetic studies in Arabidopsis thaliana and Antirrhinum majus have identified early-acting genes that determine the identity of the floral meristem, and late-acting genes that determine floral organ identity1–5. In Arabidopsis, at least two genes, APETALA1 and LEAFY, are required for the transition of an inflorescence meristem into a floral meristem1. We have cloned the APETALA1 gene and here we show that it encodes a putative transcription factor that contains a MADS-domain2. APETALA1 RNA is uniformly expressed in young flower primordia, and later becomes localized to sepals and petals. Our results suggest that APETALA1 acts locally to specify the identity of the floral meristem, and to determine sepal and petal development.