The Rhizobium meliloti putA gene: Its role in the establishment of the symbiotic interaction with alfalfa
The Rhizobium meliloti putA gene: Its role in the establishment of the symbiotic interaction with alfalfa
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DOI：
10.1046/j.1365-2958.1997.1861555.x
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发表时间：
1997-01-01
影响因子：
3.6
通讯作者：
Toro, N
中科院分区：
文献类型：
--
作者：
JimenezZurdo, JI;GarciaRodriguez, FM;Toro, N
根瘤菌在豆科植物的定植、入侵和根瘤形成过程中所利用的能量来源尚不清楚。我们最近报道了脯氨酸代谢受损导致紫花苜蓿根瘤菌结瘤效率和竞争力降低。在本研究中，我们鉴定了猪脯氨酸脱氢酶基因（putA），并对其在共生中的作用进行了探讨。该根瘤菌基因编码一个1224个氨基酸长的多肽，该多肽与肠道细菌、荚膜红杆菌和日本慢生根瘤菌PutA蛋白同源。与这些细菌的情况类似，序列分析发现了R. meliloti puta编码蛋白中的脯氨酸脱氢酶（PDH）和吡咯-5-羧酸脱氢酶（P5CDH）结构域。在携带putA- lacz转录融合的自由活细胞中进行的β -半乳糖苷酶分析表明，R. meliloti putA基因的表达是由脯氨酸诱导的，由其编码产物自动调节，独立于一般氮调节系统（Ntr）。此外，对putA在与苜蓿共生作用的不同阶段的表达分析表明，该基因的表达在根分泌物（RE）、根入侵和根瘤形成过程中开启，而在分化的固氮类细菌中不开启。此外，我们发现PutA（-）表型导致R. meliloti的苜蓿根定植显著减少。
Little is known about the energy sources used by rhizobia during colonization, invasion and root nodule formation on leguminous plants. We have recently reported that an impaired proline metabolism in Rhizobium meliloti leads to a reduced nodulation efficiency and competitiveness on alfalfa roots. In the present study we have characterized the R. meliloti proline dehydrogenase gene (putA) and addressed the question of its role in symbiosis. This rhizobial gene encodes a 1224-amino-acid-long polypeptide which is homologous to enteric bacteria, Rhodobacter capsulatus and Bradyrhizobium japonicum PutA proteins. Like the situation in these bacteria, sequence analysis identified the proline dehydrogenase (PDH) and pyrroline-5-carboxylate dehydrogenase (P5CDH) domains in the R. meliloti putA-encoded protein. Beta-galactosidase assays performed with free-living cells carrying a putA-lacZ transcriptional fusion revealed that R. meliloti putA gene expression is induced by proline, autoregulated by its encoded product, and independent of the general nitrogen regulatory system (Ntr). In addition, analysis of putA expression during the different steps of the symbiotic interaction with alfalfa showed that expression of this gene is turned on by the root exudates (RE), during root invasion and nodule formation, but not in differentiated nitrogen-fixing bacteroids. Furthermore, we show that the PutA(-) phenotype leads to a significant reduction of alfalfa root colonization by R. meliloti.