A POTATO SUS3 SUCROSE SYNTHASE GENE CONTAINS A CONTEXT-DEPENDENT 3' ELEMENT AND A LEADER INTRON WITH BOTH POSITIVE AND NEGATIVE TISSUE-SPECIFIC EFFECTS

To examine which sequences are involved in regulating the potato sucro se synthase gene Sus3-65, we examined a series of deletion and substit ution constructs in transgenic potato and tobacco plants. In a constru ct containing 3.9 kb of 5' flanking region, substitution of the native 3' sequence with the nopaline synthase 3' sequence and deletion of th e leader intron did not significantly affect expression in vegetative tissues. However, in a construct containing only 320 bp of 5' flanking region, these changes had marked effects. Replacing the native 3' seq uences with nopaline synthase 3' sequences caused a six- to 20-fold in crease in expression in vascular tissue, and removing the leader intro n almost completely abolished expression in potato plants. Surprisingl y, removal of the leader intron from either the full-length construct or a construct containing only 320 bp of 5' flanking sequence reduced expression in vascular tissue of tobacco anthers at later stages of de velopment but increased expression in pollen by more than 100-fold.