The pha gene cluster of Rhizobium meliloti involved in pH adaptation and symbiosis encodes a novel type of K+ efflux system
The pha gene cluster of Rhizobium meliloti involved in pH adaptation and symbiosis encodes a novel type of K+ efflux system
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DOI：
10.1046/j.1365-2958.1998.00868.x
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发表时间：
1998-06
影响因子：
3.6
通讯作者：
P. Putnoky;A. Kereszt;Tatsunosuke Nakamura;G. Endré;E. Grosskopf;P. Kiss;A. Kondorosi
中科院分区：
文献类型：
--
作者：
P. Putnoky;A. Kereszt;Tatsunosuke Nakamura;G. Endré;E. Grosskopf;P. Kiss;A. Kondorosi
苜蓿根瘤菌的fix-2突变体（Inf-/Fix-）对K+敏感，在K+存在下不能适应碱性pH。使用定向Tn 5诱变，我们划定了一个6 kb的基因组区域，其中突变导致Inf-/Fix-和K+-敏感表型。在该DNA区域中，鉴定了7个开放阅读框（ORF），并将相应的基因命名为phaA、B、C、D、E、F和G。推定的PhaABC蛋白表现出同源性的Na+/H+反向转运蛋白的亚基从嗜碱芽孢杆菌菌株。此外，PhaA和PhaD还分别显示出与质子泵NADH：泛醌氧化还原酶的ND 5和ND 4亚基的相似性。计算机分析表明，所有七种蛋白质都是高度疏水的，具有几个可能的跨膜结构域。这些结构域中的一些通过产生活性碱性磷酸酶融合来证实。对phaA突变细胞的离子转运研究显示，在加入膜渗透性胺后，碱性pH下K+外流存在缺陷。这些结果表明，红曲霉的pha基因可能与其基因组中的一个或多个基因有关。苜蓿属植物编码一种新型的K+外排系统，该系统参与pH适应，并且是适应植物内部改变的环境所必需的。
The fix‐2 mutant of Rhizobium meliloti affected in the invasion of alfalfa root nodules (Inf−/Fix−) is K+ sensitive and unable to adapt to alkaline pH in the presence of K+. Using directed Tn5 mutagenesis, we delimited a 6 kb genomic region in which mutations resulted in both Inf−/Fix− and K+‐sensitive phenotypes. In this DNA region, seven open reading frames (ORFs) were identified and the corresponding genes were designated phaA, B, C, D, E, F and G. The putative PhaABC proteins exhibit homology to the subunits of a Na+/H+ antiporter from an alkalophilic Bacillus strain. Moreover, PhaA and PhaD also show similarity to the ND5 and ND4 subunits of the proton‐pumping NADH:ubiquinone oxidoreductase respectively. Computer analysis suggests that all seven proteins are highly hydrophobic with several possible transmembrane domains. Some of these domains were confirmed by generating active alkaline phosphatase fusions. Ion transport studies on phaA mutant cells revealed a defect in K+ efflux at alkaline pH after the addition of a membrane‐permeable amine. These results suggest that the pha genes of R. meliloti encode for a novel type of K+ efflux system that is involved in pH adaptation and is required for the adaptation to the altered environment inside the plant.