United States Horticultural Research Laboratory, Plant Pathology, United States Department of Agriculture Agricultural Research Service, Fort Pierce, Florida, United States of America.
PLoS One. 2012;7(5):e37340. doi: 10.1371/journal.pone.0037340. Epub 2012 May 24.
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 functionally characterized 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 destructive 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. Liberibacter asiaticus encoded gene clusters contained genes that were able to functionally complement the system. Additional analysis of the gene clusters reveals that distinct modes of regulation may also exist between the Ca. Liberibacter asiaticus and S. meliloti import systems despite the intracellular-plant niche common to both of these bacteria.
Znu 系统由 znuABC 编码，存在于多种细菌属中，被证明负责在缺锌条件下导入锌。尽管这种高亲和力摄取系统已知对细菌的生长和/或发病机制很重要，但它在植物相关细菌中尚未得到功能表征。在植物内共生菌根瘤菌（Sinorhizobium meliloti）中鉴定出该系统的单个同源物，而在破坏性柑橘病原体亚洲韧皮杆菌（Candidatus Liberibacter asiaticus）中发现了两个同源系统。为了了解这些蛋白同源物的作用，设计了互补测定法，允许单独测定系统组成的各个基因，以评估它们恢复部分失活 Znu 系统的能力。测定结果表明，尽管根瘤菌中的所有基因都能够恢复活性，但亚洲韧皮杆菌的两个编码基因簇中只有一个包含能够使该系统功能互补的基因。对基因簇的进一步分析表明，尽管这两种细菌都存在于细胞内植物小生境中，但它们的导入系统之间可能存在不同的调控模式。
