Anther-specific expression of the rolB gene of Agrobacterium rhizogenes increases IAA content in anthers and alters anther development and whole flower growth.

The promoter activity of a 2.2-kb DNA fragment from the 5' flanking sequence of the tap1 gene of snapdragon has been characterised in tobacco with the β-glucuronidase reporter gene. The tap1 promoter conferred to the reporter gene an expression that was limited to the early stages of anther development. Expression of the rolB gene of Agrobacterium rhizogenes under the control of the tap1 promoter impaired the development of tobacco flowers. Tobacco plants transgenic for the tap1-rolB chimeric gene showed altered anthers and a reduction in whole flower growth. Such growth alterations were correlated with an increase in free IAA content and a decrease in gibberellin activity present in anthers. Since the rolB gene codes for an indole β-glucosidase (Estruch et al. 1991), we interpret the phenotypic alterations to be a consequence of the increased content and activity of auxin in anthers. The perturbation of anther development would in turn affect gibberellin production and content, which is reflected in a reduced elongation of flowers.