Dicarboxylate Transporters of Sp7 Play an Important Role in the Colonization of Finger Millet () Roots.

is a plant growth-promoting bacterium that colonizes the roots of a large number of plants, including C3 and C4 grasses. Malate has been used as a preferred source of carbon for the enrichment and isolation spp., but the genes involved in their transport and utilization are not yet characterized. In this study, we investigated the role of the two types of dicarboxylate transporters (DctP and DctA) of in their ability to colonize and promote growth of the roots of a C4 grass. We found that DctP protein was distinctly upregulated in grown with malate as sole carbon source. Inactivation of in led to a drastic reduction in its ability to grow on dicarboxylates and form cell aggregates. Inactivation of , however, showed a marginal reduction in growth and flocculation. The growth and nitrogen fixation of a and double mutant of were severely compromised. We have shown here that DctPQM and DctA transporters play a major and a minor role in the transport of C-dicarboxylates in , respectively. Studies on inoculation of the seedlings of a C4 grass, , with and its dicarboxylate transport mutants revealed that dicarboxylate transporters are required by for an efficient colonization of plant roots and their growth.