1 Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546-0312, USA; and.
2 Institute of Plant Biology, Biological Research Center, Szeged 6726, Hungary.
Mol Plant Microbe Interact. 2018 Feb;31(2):240-248. doi: 10.1094/MPMI-08-17-0207-R. Epub 2017 Dec 12.
Medicago truncatula shows a high level of specificity when interacting with its symbiotic partner Sinorhizobium meliloti. This specificity is mainly manifested at the nitrogen-fixing stage of nodule development, such that a particular bacterial strain forms nitrogen-fixing nodules (Nod/Fix) on one plant genotype but ineffective nodules (Nod/Fix) on another. Recent studies have just begun to reveal the underlying molecular mechanisms that control this specificity. The S. meliloti strain A145 induces the formation of Fix nodules on the accession DZA315.16 but Fix nodules on Jemalong A17. A previous study reported that the formation of Fix nodules on Jemalong A17 by S. meliloti A145 was conditioned by a single recessive allele named Mtsym6. Here we demonstrate that the specificity associated with S. meliloti A145 is controlled by multiple genes in M. truncatula, including NFS1 and NFS2 that encode nodule-specific cysteine-rich (NCR) peptides. The two NCR peptides acted dominantly to block rather than promote nitrogen fixation by S. meliloti A145. These two NCR peptides are the same ones that negatively regulate nitrogen-fixing symbiosis associated with S. meliloti Rm41.
蒺藜苜蓿与共生伙伴中华根瘤菌相互作用时表现出高度的特异性。这种特异性主要表现在根瘤发育的固氮阶段，例如，特定的细菌菌株在一个植物基因型上形成固氮根瘤（Nod/Fix），而在另一个植物基因型上则形成无效根瘤（Nod/Fix）。最近的研究才刚刚开始揭示控制这种特异性的潜在分子机制。中华根瘤菌 A145 菌株在 DZA315.16 品系上诱导形成 Fix 根瘤，但在 Jemalong A17 品系上则形成无效根瘤。先前的研究报告称，中华根瘤菌 A145 在 Jemalong A17 上形成 Fix 根瘤的条件是由一个名为 Mtsym6 的隐性等位基因决定的。在这里，我们证明与中华根瘤菌 A145 相关的特异性是由蒺藜苜蓿中的多个基因控制的，包括编码根瘤特异性半胱氨酸丰富（NCR）肽的 NFS1 和 NFS2。这两个 NCR 肽主要起阻止而不是促进中华根瘤菌 A145 的固氮作用。这两个 NCR 肽与中华根瘤菌 Rm41 相关的固氮共生关系的负调控相同。
