Oligogalacturonides Prevent Rhizogenesis in rolB-Transformed Tobacco Explants by Inhibiting Auxin-Induced Expression of the rolB Gene.

Abstract

Oligogalacturonides elicit several defense responses and regulate different aspects of growth and development in plants. Many of the development-related effects of oligogaladuronides appear to be amenable to an auxin antagonist activity of these oligosaccharins. To clarify the role of oligogalacturonides in antagonizing auxin, we analyzed their effect on root formation in leaf explants of tobacco harboring the plant oncogene rolB We show here that oligogalacturonides are capable of inhibiting root morphogenesis driven by rol6 in transgenic leaf explants when this process requires exoge-nous auxin. Because rol6 expression is induced by auxin and dramatically altersthe response to this hormone in transformed plant cells, the inhibiting effect of oligogalacturonides could be exerted on the induction of rol6 and/or at some other auxin-requiring step(s) in rhizogenesis. We show that oligogalactumnides antagonize auxin primarily because they strongly inhibit auxin-regulated transcriptional activation of a rol6-B-glucuronidase gene fusion in both leaf explants and cul-tured leaf protoplasts. I n contrast, oligogalacturonides do not inhibit rhizogenesis when rol6 transcriptional activation is made independent of auxin, as shown by the lack of inhibition of root formation in leaf explants containing rol6 driven by a tetracycline-inducible promoter.