Auxin regulates the promoter of the root-inducing rolB gene of Agrobacterium rhizogenes in transgenic tobacco.

The regulation in tobacco of the rolB and rolC promoters of Agrobacterium rhizogenes pRi 1855 TL-DNA was studied by using the beta-glucuronidase (GUS) reporter system in transgenic plants. A 20- to 100-fold increase of GUS activity was selectively induced by auxin in rolB-GUS transformed mesophyll protoplasts, whereas this auxin-dependent increase was only 5-fold in rolC-GUS protoplasts. Moreover, both gene fusions exhibited similar tissue-specific expression in aerial parts but different patterns in roots. The spatial pattern of rolB-GUS expression could be strongly modified by the addition of exogenous auxin, further suggesting that auxin plays a central role in the regulation of the rolB promoter in tobacco. The tissue-specific and auxin-dependent regulation of the rolB promoter is discussed in relation to the effects of the rolB gene on rhizogenesis and on cellular responses to auxin.