DISCRETE SPATIAL AND TEMPORAL CIS-ACTING ELEMENTS REGULATE TRANSCRIPTION OF THE ARABIDOPSIS FLORAL HOMEOTIC GENE APETALA3

The APETALA3 floral homeotic gene is required for petal and stamen dev elopment in Arabidopsis. APETALA3 transcripts are first detected in a meristematic region that will give rise to the petal and stamen primor dia, and expression is maintained in this region during subsequent dev elopment of these organs. To dissect how the APETALA3 gene is expresse d in this spatially and temporally restricted domain, various APETALA3 promoter fragments were fused to the uidA reporter gene encoding beta -glucuronidase and assayed for the resulting patterns of expression in transgenic Arabidopsis plants. Based on these promoter analyses, we d efined cis-acting elements required for distinct phases of APETALA3 ex pression, as well as for petal-specific and stamen-specific expression . By crossing the petal-specific construct into different mutant backg rounds, we have shown that several floral genes, including APETALA3, P ISTILLATA, UNUSUAL FLORAL ORGANS, and APETALA1, encode traits-acting f actors required for second-whorl-specific APETALA3 expression. We have also shown that the products of the APETALA1, APETALA3, PISTILLATA an d AGAMOUS genes bind to several conserved sequence moths within the AP ETALA3 promoter. We present a model whereby spatially and temporally r estricted APETALA3 transcription is controlled via interactions betwee n proteins binding to different domains of the APETALA3 promoter.