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Biological Activity of the Agrobacterium rhizogenes–Derived trolC Gene of Nicotiana tabacum and Its Functional Relation to Other plast Genes

¹Department of Molecular Mechanisms of Phenotypic Plasticity, Institut de Biologie Moléculaire des Plantes, Rue du Général Zimmer 12, 67084 Strasbourg, France, ²Département Architecture et Réactivité d'ARN, UPR9002, Institut de Biologie Moléculaire et Cellulaire, 15 Rue Descartes, 67084 Strasbourg, France

Agrobacterium rhizogenes induces hairy roots through the activity of three essential T-DNA genes, rolA, rolB, and rolC, whereas the orf13 gene acts as an accessory root-inducing gene. rolB, rolC, and orf13 belong to the highly diverged plast gene family with remotely related representatives in the endomycorrhizal basidiomycete Laccaria bicolor. Nicotiana glauca and N. tabacum contain A. rhizogenes–derived T-DNAs with active plast genes. Here, we report on the properties of a rolC homolog in N. tabacum, trolC. Dexamethasone-inducible trolC and A4-rolC genes from A. rhizogenes A4 induce comparable, strong growth effects affecting all parts of the plants. Several have not been described earlier and were found to be very similar to the effects of the distantly related plast gene 6b. They include leaf chlorosis and starch accumulation, enations, increase of sucrose-dependent leaf disk expansion, growth of isolated roots on low-sucrose media, and stimulation of sucrose uptake by small root fragments. Collectively, our findings indicate that enhancement of sucrose uptake plays an important role in generating the complex 6b and rolC phenotypes and might be an ancestral property of the plast genes.