The Sinorhizobium meliloti ntrX gene is involved in succinoglycan production, motility, and symbiotic nodulation on alfalfa
The Sinorhizobium meliloti ntrX gene is involved in succinoglycan production, motility, and symbiotic nodulation on alfalfa
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苜蓿中华根瘤菌 ntrX 基因参与琥珀酸聚糖的产生、运动和苜蓿的共生结瘤
DOI：
10.1128/aem.02225-13
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发表时间：
2013
影响因子：
4.4
通讯作者：
Luo Li
中科院分区：
文献类型：
--
作者：
Wang Dong;Xue Haiying;Wang Yiwen;Yin Ruochun;Xie Fang;Luo Li
根瘤菌与寄主豆科植物建立共生关系，诱导形成固氮根瘤。这一过程受到许多根瘤菌调节剂的调控，包括一些双组分调控系统(TCSs)。Ntry/NtrX是在茎固氮瘤菌中首次发现的一种TCS，是田菁自由生活氮代谢和共生结瘤所必需的。然而，它在典型的根瘤菌如苜蓿中华根瘤菌中的功能仍不清楚。在这里，我们发现紫花苜蓿反应调节因子NtrX而不是组氨酸蛋白激酶参与调控胞外多糖的产生、运动和与紫花苜蓿的共生。NtrX的一个插入质粒的突变体形成了粘液菌落，通过上调其生物合成基因来过量生产胞外多糖琥珀多糖。该突变体还表现出运动性缺陷，原因是鞭毛减少，鞭毛蛋白和调控基因的表达减少。该法规独立于已知的Exor/EXOS/ChvI、EmmABC和Expr监管系统。接种thentrX突变体的紫花苜蓿植株体型较小，表现出氮素饥饿的症状。有趣的是，缺失突变体ntrY的表型与亲本菌株相似。这些发现表明，紫花苜蓿NtrX是一种新的琥珀酸聚糖生产和运动性调节器，它不是遗传上与Ntry偶联的。
Rhizobia establish a symbiotic relationship with their host legumes to induce the formation of nitrogen-fixing nodules. This process is regulated by many rhizobium regulators, including some two-component regulatory systems (TCSs). NtrY/NtrX, a TCS that was first identified in Azorhizobium caulinodans, is required for free-living nitrogen metabolism and symbiotic nodulation on Sesbania rostrata. However, its functions in a typical rhizobium such as Sinorhizobium meliloti remain unclear. Here we found that the S. meliloti response regulator NtrX but not the histidine kinase NtrY is involved in the regulation of exopolysaccharide production, motility, and symbiosis with alfalfa. A plasmid insertion mutant ofntrXformed mucous colonies, which overproduced succinoglycan, an exopolysaccharide, by upregulating its biosynthesis genes. This mutant also exhibited motility defects due to reduced flagella and decreased expression of flagellins and regulatory genes. The regulation is independent of the known regulatory systems of ExoR/ExoS/ChvI, EmmABC, and ExpR. Alfalfa plants inoculated with thentrXmutant were small and displayed symptoms of nitrogen starvation. Interestingly, the deletion mutant ofntrYshowed a phenotype similar to that of the parent strain. These findings demonstrate that the S. meliloti NtrX is a new regulator of succinoglycan production and motility that is not genetically coupled with NtrY.