The insertion of the Agrobacterium rhizogenes rolC gene in tomato (Solanum lycopersicum L.) affects plant architecture and endogenous auxin and abscisic acid levels

In the present paper we report on the effects of the insertion of the Agrobacterium rhizogenes rolC gene in the tomato (Solanum lycopersicum L., formerly Lycopersicon esculentum Mill.) cultivar Tondino. Several transgenic lines were successfully obtained, between which two clones, rolC1 and rolC3, were chosen for the analysis of morpho-productive traits as well as of the endogenous levels of auxin and abscisic acid. Consistent with the known phenotypic effect of this gene, the transformed tomato plants were significantly shorter than the corresponding controls. On the other hand, even if yield was not affected by the transformation in terms of average number of fruits produced, fruit weight was significantly lower in the transgenics with respect to the controls. Therefore, insertion of the rolC gene does not lead to an improvement in plant productivity. Furthermore, we have observed alterations in the hormonal levels in the shoot apices of the transgenic plants. In fact, quantifications of free and conjugated forms of indole-3-acetic acid (IAA) indicated a significant reduction of IAA levels in the shoot apical region of the transgenic clone rolC3, in comparison with both the control and the clone rolC1. Abscisic acid (ABA) concentration on the other hand was unchanged in the transgenics compared to the controls, but significantly lower in rolC3 with respect to rolC1 plants. The resulting ABA/IAA ratio was higher in both transgenic clones compared to the untransformed plants, indicating that the rolC gene affects the balance between these hormones in transformed tomato plants.