The rolC gene of agrobacteria: towards the understanding of its functions

Abstract

Agrobacterium rhizogenes Conn is a soil bacterium, which can transform plants by inserting a plasmid fragment into the plant genome. This fragment contains a “root locus”: four genes that cause root overgrowth of the transformed plant, the so-called “hairy root syndrome”. The most studied gene of the root locus is rolC. For more than 30 years of research on this gene, data have been obtained on its expression, protein localization and putative functions of the protein as well as on its effect on plant morphology and biochemistry. The rolC transformation leads to multiple morphological effects, most common among which are dwarfism, bushiness, and a change in the shape of the leaf blade. Such specific plant reactions are associated with changes in hormone balance under the influence of rolC. The levels of auxins, cytokinins, and abscisic acid do change in transformed plants, but no regularities have been revealed. Also, the signaling pathways of rolC affecting the hormonal system of plants are not established. Morphogenetic effects can occur in varying degrees depending on the promoter under which the rolC works. A constitutive promoter usually leads to a more pronounced effect when compared to a gene that operates under a native promoter. Secondary plant metabolism is also affected by rolC. The synthesis of various metabolites is amplified in transformants, and, in contrast to morphological effects, this biochemical effect does not depend on the promoter. Some secondary metabolites are associated with the plant defense system; thus, rolC is able to indirectly influence this aspect of plant physiology. This review summarizes the results of the rolC gene studies in plants. The authors formulate the main hypotheses regarding the mechanisms of the gene in order to promote our understanding of its function in plants.