Activation of the Arabidopsis B Class Homeotic Genes byAPETALA1

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Abstract
Proper development of petals and stamens in Arabidopsis flowers requires the activities of APETALA3AP3) and PISTILLATAPI), whose transcripts can be detected in the petal and stamen primordia. Localized expression of AP3andPI requires the activities of at least three genes: APETALA1AP1), LEAFYLFY), and UNUSUALFLORALORGANSUFO). It has been proposed that UFOprovides spatial cues and thatLFYspecifies competence forAP3andPIexpression in the developing flower. To understand the epistatic relationship amongAP1,LFY, andUFOin regulatingAP3andPIexpression, we generated two versions of AP1 that have strong transcriptional activation potential. Genetic and molecular analyses of transgenic plants expressing these activated AP1 proteins show that the endogenous AP1 protein acts largely as a transcriptional activator in vivo and thatAP1specifies petals by regulating the spatial domains ofAP3and PIexpression throughUFO.
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