Minimal regions in the Arabidopsis PISTILLATA promoter responsive to the APETALA3/PISTILLATA feed back control do not contain a CArG box

PISTILLATA (PI) is a floral homeotic B function gene in Arabidopsis and tog ether with the other B function gene, APETALA3 (AP3), is involved in specif ying petal and stamen identities. The expression of PI and AP3 is under sim ilar developmental control. The initiation of AP3 and PI expression is at l east partly caused by the floral meristem identity gene LEAFY, but the main tenance of AP3 and PI expression involves an autoregulatory loop requiring the activity of both genes. PI and AP3 are MADS domain proteins that form, and appear to function as, a heterodimer. AP3/PI binds in vitro to a sequen ce motif, CC(A/T)(6)GG, a MADS domain protein consensus binding site also k nown as the CArG box. We identified a 481-bp PI promoter region that confer s both the initiation and the maintenance of PI expression patterns. We fur ther dissected the promoter and identified minimal regions responsible for the AP3/PI-dependent expression. No CArG box is present in these minimal re gions, suggesting that either AP3/PI does not bind directly to the PI promo ter for the maintenance control, or that it requires additional factors to bind to the PI promoter. Our results suggest that the mechanisms of regulat ion of the two B function genes, AP3 and PI, are different, because CArG bo xes are present in the AP3 promoter and are necessary for the AP3 feedback control.