ARABIDOPSIS HOMEOTIC GENE APETALA3 ECTOPIC EXPRESSION - TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL REGULATION DETERMINE FLORAL ORGAN IDENTITY

APETALA3 (AP3) specifies the development of petals and stamens in the Arabidopsis flower. We constructed a transgenic line, 35S-AP3, that ec topically expresses AP3 under the control of a constitutive promoter. The resulting flowers exhibit a replacement of carpels by stamens and resemble flowers homozygous for the previously described Arabidopsis m utation superman. Although AP3 RNA is detected at high levels througho ut the flower and stem in 35S-AP3, AP3 protein is detected at high lev els only in the second, third, and fourth floral whorls, demonstrating that AP3 is posttranscriptionally regulated. Ectopic expression of AP 3 causes a second floral homeotic gene, PISTILLATA (PI), to function i n the fourth whorl of 35S-AP3 flowers. AP3 and PI also activate an AP3 promoter-reporter gene fusion, demonstrating that AP3 positively auto regulates.