Graduate School of Science and Engineering, Kagoshima University.
School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology.
Microbes Environ. 2019 Dec 27;34(4):393-401. doi: 10.1264/jsme2.ME19078. Epub 2019 Oct 8.
The nifV gene encodes homocitrate synthase, the enzyme that catalyzes the formation of homocitrate, which is essential for arranging the FeMo-cofactor in the catalytic center of nitrogenase. Some host plants, such as Lotus japonicus, supply homocitrate to their symbionts, in this case, Mesorhizobium loti, which lacks nifV. In contrast, Bradyrhizobium ORS285, a symbiont of Aeschynomene cross-inoculation (CI) groups 2 and 3, requires nifV for symbiosis with Aeschynomene species that belong to CI group 3, and some species belonging to CI group 2. However, it currently remains unclear whether rhizobial nifV is required for symbiosis with Aeschynomene species belonging to CI group 1 or with other legumes. We generated nifV-disruption (ΔnifV) mutants of two wide-host-range rhizobia, Bradyrhizobium SUTN9-2 and DOA9, to investigate whether they require nifV for symbiosis. Both ΔnifV mutant strains showed significantly less nitrogenase activity in a free-living state than the respective wild-type strains. The symbiotic phenotypes of SUTN9-2, DOA9, and their ΔnifV mutants were examined with four legumes, Aeschynomene americana, Stylosanthes hamata, Indigofera tinctoria, and Desmodium tortuosum. nifV was required for the efficient symbiosis of SUTN9-2 with A. americana (CI group 1), but not for that of DOA9. SUTN9-2 established symbiosis with all three other legumes; nifV was required for symbiosis with I. tinctoria and D. tortuosum. These results suggest that, in addition to Aeschynomene CI groups 2 and 3, CI group 1 and several other legumes require the rhizobial nifV for symbiosis.
nifV 基因编码同型柠檬酸合酶，该酶催化同型柠檬酸的形成，这对于氮酶催化中心的 FeMo 辅因子的排列至关重要。一些宿主植物，如百脉根，向其共生体提供同型柠檬酸，在这种情况下，根瘤菌 L. japonicus 缺乏 nifV。相比之下，Bradyrhizobium ORS285 是 Aeschynomene 交叉接种（CI）组 2 和 3 的共生体，需要 nifV 才能与属于 CI 组 3 的 Aeschynomene 物种共生，以及一些属于 CI 组 2 的物种。然而，目前尚不清楚根瘤菌 nifV 是否需要与属于 CI 组 1 的 Aeschynomene 物种或其他豆科植物共生。我们生成了两个广宿主范围根瘤菌 Bradyrhizobium SUTN9-2 和 DOA9 的 nifV 缺失（ΔnifV）突变体，以研究它们是否需要 nifV 进行共生。与各自的野生型菌株相比，两种ΔnifV 突变菌株在自由生活状态下的固氮酶活性均显著降低。用四种豆科植物（Aeschynomene americana、Stylosanthes hamata、Indigofera tinctoria 和 Desmodium tortuosum）研究了 SUTN9-2、DOA9 及其ΔnifV 突变体的共生表型。nifV 是 SUTN9-2 与 A. americana（CI 组 1）高效共生所必需的，但不是 DOA9 共生所必需的。SUTN9-2 与其他三种豆科植物建立了共生关系；nifV 是与 I. tinctoria 和 D. tortuosum 共生所必需的。这些结果表明，除了 Aeschynomene CI 组 2 和 3 之外，CI 组 1 和其他几种豆科植物也需要根瘤菌 nifV 进行共生。
