New NodW- or NifA-regulated Bradyrhizobium japonicum genes
New NodW- or NifA-regulated Bradyrhizobium japonicum genes
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DOI：
10.1094/mpmi.2003.16.4.342
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发表时间：
2003-04-01
影响因子：
3.5
通讯作者：
Hennecke, H
中科院分区：
文献类型：
--
作者：
Baumberger, IC;Fraefel, N;Hennecke, H
一组编码推定的植物细胞壁降解酶的基因（即，两种内切葡聚糖酶[gunA和gunA 2]、一种果胶甲酯酶[pme]和一种多聚半乳糖醛酸酶[pgl]的基因）通过慢生型大豆根瘤菌染色体的共生区中的序列相似性鉴定。此外，该区域的系统筛选揭示了几个可能由σ（54）-RNA聚合酶转录并由转录调节因子NifA激活的基因（即，与外膜蛋白相似的蛋白质的基因[id 117和id 525]和柠檬酸盐载体[id 331或citA]和一个与已知蛋白质不相似的开放阅读框[id 747]）。使用转录lacZ融合的表达研究表明，gunA 2和pgl强烈诱导的NodW依赖性的方式，表明的作用的基因产物在早期事件的paculation过程中，gunA和pme的表达是非常弱的测试条件。gunA 2基因产物经纯化后具有纤维素酶活性。在野生型和nifA和rpoN突变体背景中，从与id 117、0525和id 747的转录lacZ融合表达的β-半乳糖苷酶活性证实了它们的转录依赖于NifA和sigma（54）。尽管存在-24/-12型启动子和citA上游的NifA结合位点，但在这种情况下不能证明调控。在gunA、gunA 2、pgl、pme、citA、id 117、id 525和id 747中引入的突变不损害与宿主植物的共生关系。
A cluster of genes coding for putative plant cell-wall degrading enzymes (i.e., genes for two endoglucanases [gunA and gunA2], one pectinmethylesterase [pme], and one polygalacturonase [pgl]) was identified by sequence similarities in the symbiotic region of the Bradyrhizobium japonicum chromosome. In addition, a systematic screen of the region revealed several genes potentially transcribed by the sigma(54)-RNA polymerase and activated by the transcriptional regulator NifA (i.e., genes for proteins with similarity to outer membrane proteins [id117 and id525] and a citrate carrier [id331 or citA] and one open reading frame without similarity to known proteins [id747]). Expression studies using transcriptional lacZ fusions showed that gunA2 and pgl were strongly induced by the isoflavone genistein in a NodW-dependent manner, suggesting a role of the gene products in early events of the nodulation process; by contrast, gunA and pme expression was very weak in the conditions tested. The gunA2 gene product was purified and was shown to have cellulase activity. P-Galactosidase activity expressed from transcriptional lacZ fusions to id117, 0525, and id747 in the wild type and in nifA and rpoN mutant backgrounds confirmed that their transcription was dependent on NifA and sigma(54). Despite the presence of a -24/-12-type promoter and a NifA binding site upstream of citA, no regulation could be demonstrated in this case. Null mutations introduced in gunA, gunA2, pgl, pme, citA, id117, id525, and id747 did not impair the symbiosis with the host plants.