Ritsema T, Wijfjes A H, Lugtenberg B J, Spaink H P
Leiden University, Clusius Laboratory, The Netherlands.
Mol Gen Genet. 1996 Apr 24;251(1):44-51. doi: 10.1007/BF02174343.
In the biosynthesis of lipochitin oligosaccharides (LCOs) the Rhizobium nodulation protein NodA plays an essential role in the transfer of an acyl chain to the chitin oligosaccharide acceptor molecule. The presence of nodA in the nodABCIJ operon makes genetic studies difficult to interpret. In order to be able to investigate the biological and biochemical functions of NodA, we have constructed a test system in which the nodA, nodB and nodC genes are separately present on different plasmids. Efficient nodulation was only obtained if nodC was present on a low-copy-number vector. Our results confirm the notion that nodA of Rhizobium leguminosarum biovar viciae is essential for nodulation on Vicia. Surprisingly, replacement of R. l. by viciae nodA by that of Bradyrhizobium sp. ANU289 results in a nodulation-minus phenotype on Vicia. Further analysis revealed that the Bradyrhizobium sp. ANU289 NodA is active in the biosynthesis of LCOs, but is unable to direct the transfer of the R. l. by, viciae nodFE-dependent multi-unsaturated fatty acid to the chitin oligosaccharide acceptor. These results lead to the conclusion that the original notion that nodA is a common nod gene should be revised.
在脂壳寡糖（LCOs）的生物合成过程中，根瘤菌结瘤蛋白NodA在将酰基链转移至壳寡糖受体分子的过程中发挥着关键作用。nodABCIJ操纵子中nodA的存在使得遗传学研究难以解读。为了能够研究NodA的生物学和生化功能，我们构建了一个测试系统，其中nodA、nodB和nodC基因分别存在于不同的质粒上。只有当nodC存在于低拷贝数载体上时，才能实现高效结瘤。我们的结果证实了豌豆根瘤菌生物变种的nodA对蚕豆结瘤至关重要这一观点。令人惊讶的是，用慢生根瘤菌属的ANU289的nodA取代豌豆根瘤菌生物变种的nodA会导致蚕豆出现结瘤阴性表型。进一步分析表明，慢生根瘤菌属的ANU289 NodA在LCOs的生物合成中具有活性，但无法将豌豆根瘤菌生物变种依赖nodFE的多不饱和脂肪酸转移至壳寡糖受体上。这些结果得出结论，即nodA是一个通用结瘤基因这一最初观点应予以修正。
