EVALUATION IN TOBACCO OF THE ORGAN SPECIFICITY AND STRENGTH OF THE ROLD PROMOTER, DOMAIN-A OF THE 35S PROMOTER AND THE 35S(2) PROMOTER

In order to study the expression in plants of the rolD promoter of Agr obacterium rhizogenes, we have constructed chimaeric genes placing the coding region of the gusA (uidA) marker gene under control of two rol D promoter fragments of different length. Similar results were obtaine d with both genes. Expression studies were carried out in transformed R(1) progeny plants. In mature transformed tobacco plants, the rolD-gu s genes were expressed strongly in roots, and to much lower levels in stems and leaves. This pattern of expression was transmitted to progen y, though the ratio of the level of expression in roots relative to th at in leaves was much lower in young seedlings. The degree of root spe cificity in rolD-gus transformants was less than that of a gene constr ucted with domain A of the CaMV 35S promoter, domA-gus, but the level of root expression was much higher than with the latter gene. However, the level of expression of the rolD-gus genes was less than that of a gus gene with a 35S promoter with doubled domain B, 35S(2)-gus. The r olD-gus genes had a distinctive pattern of expression in roots, compar ed to that of the two other genes, with the strongest GUS activity obs erved in the root elongation zone and in vascular tissue, and much les s in the root apex.