Role of the Nod Factor Hydrolase MtNFH1 in Regulating Nod Factor Levels during Rhizobial Infection and in Mature Nodules of Medicago truncatula
Role of the Nod Factor Hydrolase MtNFH1 in Regulating Nod Factor Levels during Rhizobial Infection and in Mature Nodules of Medicago truncatula
复制标题
Nod因子水解酶MtNFH1在根瘤菌感染期间和蒺藜苜蓿成熟根瘤中调节Nod因子水平的作用
DOI：
10.1105/tpc.17.00420
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发表时间：
2018-02-01
期刊：
影响因子：
11.6
通讯作者：
Staehelin, Christian
中科院分区：
文献类型：
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作者：
Cai, Jie;Zhang, Lan-Yue;Staehelin, Christian
MtNFH1是一种切割固氮根瘤菌结瘤信号的紫花苜蓿水解酶，在根瘤共生中具有共生功能。豆科植物与固氮根瘤菌之间共生关系的建立依赖于细菌Nod因子（NFs），该因子在寄主植物中触发与共生相关的NF信号。NFs是几丁质具有脂肪酸部分的改性低聚糖。NFs可以被宿主酶（如MtNFH1 (MEDICAGO TRUNCATULA NOD FACTOR HYDROLASE1)）切割和灭活。与相关几丁质酶相比，MtNFH1既不水解几丁质，也不水解几丁质片段，表明对NFs具有高度的裂解偏好。在这里，我们提供了MtNFH1在与Sinorhizobium meliloti共生中的作用的证据。接种根瘤菌后，MtNFH1聚集在根毛卷曲的尖端，即所谓的感染室中。突变体分析显示，缺乏MtNFH1会延迟根瘤菌的根毛感染，这表明过量的NFs会对感染线的启动产生负面影响。MtNFH1缺乏导致小结节肥大和分枝异常。在CaMV 35S串联启动子驱动表达MtNFH1的植株和接种过高产nf的S. meliloti菌株的植株中，根瘤分支也受到刺激。我们认为，MtNFH1对NF水平的微调对于最佳的根毛感染以及成熟结节的NF调节生长是必要的。
MtNFH1, a Medicago truncatula hydrolase cleaving nodulation signals of nitrogen-fixing rhizobia, possesses a symbiotic function in the nodule symbiosis. Establishment of symbiosis between legumes and nitrogen-fixing rhizobia depends on bacterial Nod factors (NFs) that trigger symbiosis-related NF signaling in host plants. NFs are modified oligosaccharides of chitin with a fatty acid moiety. NFs can be cleaved and inactivated by host enzymes, such as MtNFH1 (MEDICAGO TRUNCATULA NOD FACTOR HYDROLASE1). In contrast to related chitinases, MtNFH1 hydrolyzes neither chitin nor chitin fragments, indicating a high cleavage preference for NFs. Here, we provide evidence for a role of MtNFH1 in the symbiosis with Sinorhizobium meliloti. Upon rhizobial inoculation, MtNFH1 accumulated at the curled tip of root hairs, in the so-called infection chamber. Mutant analysis revealed that lack of MtNFH1 delayed rhizobial root hair infection, suggesting that excess amounts of NFs negatively affect the initiation of infection threads. MtNFH1 deficiency resulted in nodule hypertrophy and abnormal nodule branching of young nodules. Nodule branching was also stimulated in plants expressing MtNFH1 driven by a tandem CaMV 35S promoter and plants inoculated by a NF-overproducing S. meliloti strain. We suggest that fine-tuning of NF levels by MtNFH1 is necessary for optimal root hair infection as well as for NF-regulated growth of mature nodules.