Different strains and species of the soil phytopathogen Agrobacterium possess the ability to transfer and integrate a segment of DNA (T-DNA) into the genome of their eukaryotic hosts, which is mainly mediated by a set of virulence (vir) genes located on the bacterial Ti-plasmid that also contains the T-DNA. To date, Agrobacterium is considered to be unique in its capacity to mediate genetic transformation of eukaryotes. However, close homologs of the virgenes are encoded by the p42a plasmid of Rhizobium etli; this microorganism is related toAgrobacterium, but known only as a symbiotic bacterium that forms nitrogen-fixing nodules in several species of beans. Here, we show that R. etli can mediate functional DNA transfer and stable genetic transformation of plant cells, when provided with a plasmid containing a T-DNA segment. Thus, R. etli represents another bacterial species, besides Agrobacterium, that encodes a protein machinery for DNA transfer to eukaryotic cells and their subsequent genetic modification.
Since the discovery of gene transfer from Agrobacterium to host plants in the late 1970s, this bacterial pathogen has been widely used in research and biotechnology to generate transgenic plants. Agrobacterium’s infection process relies on a set of virulence proteins that mediate the transfer of a segment of its own DNA (T-DNA) into the host cell genome. To date,Agrobacterium is believed to be the only prokaryote with the capability of cross-kingdoms gene transfer. However, homologs of the Agrobacterium’s virulence proteins are found in some symbiotic plant-associated bacterial species, belonging to the Rhizobium genus. Here we show that one of these species, Rhizobium etli, encodes a complete set of virulence proteins and is able to mediate transfer and integration of DNA into host-plant cell genome, when provided with a T-DNA. This is the first time that a bacterium-to-plant DNA transfer machinery encoded by a non-Agrobacterium species is shown to be functional.
Lacroix, Benoît and Citovsky, Vitaly, "A Functional Bacterium-to-Plant DNA Transfer Machinery of Rhizobium etli" (2016). Biochemistry & Cell Biology Faculty Publications. 1.