TEMPERATURE-SENSITIVE SPLICING IN THE FLORAL HOMEOTIC MUTANT APETALA3-1

The floral homeotic gene APETALA3 (AP3) is required for stamen and pet al development in Arabidopsis. The previously described ap3-1 allele i s temperature sensitive and carries a missense mutation near a 5' spli ce site. The missense mutation lies within a domain of the AP3 protein that is thought to be important for protein-protein interactions, whi ch suggests that temperature sensitivity of ap3-1 could reflect an uns table interaction with cofactors. Here, we show instead that the ap3-1 mutation causes a temperature-dependent splicing defect and that temp erature sensitivity is not a property of the protein products of ap3-1 but of RNA processing, possibly because of unstable base pairing betw een the transcript and small nuclear RNAs. The unexpected defect of th e ap3-1 mutant offers unique opportunities for genetic and molecular s tudies of splice site recognition in plants.