Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 20, 2012
Publication Date: May 24, 2012
Citation: Vahling, C.M., Zhou, H., Benyon, L.S., Morgan, J.K., Duan, Y. 2012. Two plant bacteria, S. meliloti and Ca. Liberibacter asiaticus, share functional znuABC homologues that encode for a high affinity Zince uptake system. PLoS One. 7(5)e37340:1-12.
Interpretive Summary: The Znu system, encoded for by znuABC, is responsible for the import of zinc under low zinc conditions and is found in multiple genera of bacteria. Zinc is an essential trace element required by various enzymes and proteins in both eukaryotic and prokaryotic cells and must be procured from the host environment. Uptake of this element has been shown to be important for growth and/or pathogenesis in numerous bacteria but it has not been shown in a plant-associated bacterium. The plant endosymbiont, Sinorhizobium meliloti, contains one copy of the znuABC system while the citrus pathogen, Candidatus Liberibacter asiaticus, contains two copies. A complementation assay was devised allowing the individual genes in the znuABC system to be assayed independently for their ability to restore a partially-inactivated Znu system. While all of the genes from S. meliloti were able to re-establish activity, only one of the two Ca. L. asiaticus encoded gene clusters contained genes that could re-establish activity. Further analysis revealed that, despite their common intra-cellular plant environment, the two systems are regulated differently.
The Znu system, encoded for by znuABC, can be found in multiple genera of bacteria and has been shown to be responsible for the import of zinc under low zinc conditions. Although this high-affinity uptake system is known to be important for both growth and/or pathogenesis in bacteria, it has not been described in a plant-associated bacterium. A single homologue of this system has been identified in the plant endosymbiont, Sinorhizobium meliloti, while two homologous systems were found in the citrus pathogen, Candidatus Liberibacter asiaticus. To understand the role of these protein homologues, a complementation assay was devised allowing the individual genes that comprise the system to be assayed independently for their ability to reinstate a partially-inactivated Znu system. Results from the assays have demonstrated that although all of the genes from S. meliloti were able to restore activity, only one of the two Ca. L. asiaticus encoded gene clusters contained genes that were able to functionally complement the system. Additional analysis of the gene clusters reveals that distinctive modes of regulation may also exist between the Ca. L. asiaticus and S. meliloti import systems despite the intracellular-plant niche common to both of these bacteria.