Department of Biology, Indiana University, Bloomington, IN 47405-1847, USA.
J Bacteriol. 2011 Jul;193(14):3461-72. doi: 10.1128/JB.00317-11. Epub 2011 May 20.
The plant pathogen Agrobacterium tumefaciens encodes predicted iron-responsive regulators, Irr and RirA, that function in several other bacteria to control the response to environmental iron levels. Deletion mutations of irr and rirA, alone and in combination, were evaluated for their impact on cellular iron response. Growth was severely diminished in the Δirr mutant under iron-limiting conditions, but reversed to wild-type levels in an Δirr ΔrirA mutant. The level of uncomplexed iron in the Δirr mutant was decreased, whereas the ΔrirA mutant exhibited elevated iron levels. Sensitivity of the Δirr and ΔrirA mutants to iron-activated antimicrobial compounds generally reflected their uncomplexed-iron levels. Expression of genes that encode iron uptake systems was decreased in the Δirr mutant, whereas that of iron utilization genes was increased. Irr function required a trihistidine repeat likely to mediate interactions with heme. Iron uptake genes were derepressed in the ΔrirA mutant. In the Δirr ΔrirA mutant, iron uptake and utilization genes were derepressed, roughly combining the phenotypes of the single mutants. Siderophore production was elevated in the rirA mutant, but most strongly regulated by an RirA-controlled sigma factor. Expression of rirA itself was regulated by Irr, RirA, and iron availability, in contrast to irr expression, which was relatively stable in the different mutants. These studies suggest that in A. tumefaciens, the Irr protein is most active under low-iron conditions, inhibiting iron utilization and activating iron acquisition, while the RirA protein is active under high-iron conditions, repressing iron uptake.
植物病原体根癌农杆菌编码预测的铁反应调节剂 Irr 和 RirA，它们在其他几种细菌中发挥作用，以控制对环境铁水平的反应。单独和组合删除 irr 和 rirA 的突变体，评估其对细胞铁反应的影响。在缺铁条件下，irr 突变体的生长受到严重抑制，但在 irr ΔrirA 突变体中恢复到野生型水平。irr 突变体中的未复合铁水平降低，而 rirA 突变体则表现出升高的铁水平。Δirr 和 ΔrirA 突变体对铁激活的抗菌化合物的敏感性通常反映了它们的未复合铁水平。铁摄取系统的基因表达在 irr 突变体中降低，而铁利用基因的表达增加。Irr 功能需要一个三组氨酸重复序列，可能介导与血红素的相互作用。铁摄取基因在 rirA 突变体中被去阻遏。在 irr ΔrirA 突变体中，铁摄取和利用基因被去阻遏，大致结合了单个突变体的表型。在 rirA 突变体中，铁载体的产生升高，但受 RirA 控制的σ因子调节最强。rirA 自身的表达受 Irr、RirA 和铁可用性的调节，与 irr 表达相反，在不同的突变体中相对稳定。这些研究表明，在根癌农杆菌中，Irr 蛋白在低铁条件下最活跃，抑制铁利用并激活铁获取，而 RirA 蛋白在高铁条件下活跃，抑制铁摄取。
