Callose-Regulated Symplastic Communication Coordinates Symbiotic Root Nodule Development
Callose-Regulated Symplastic Communication Coordinates Symbiotic Root Nodule Development
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DOI：
10.1016/j.cub.2018.09.031
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发表时间：
2018-11-19
期刊：
影响因子：
9.2
通讯作者：
de Carvalho-Niebel, Fernanda
中科院分区：
文献类型：
--
作者：
Gaudioso-Pedraza, Rocio;Beck, Martina;de Carvalho-Niebel, Fernanda
豆科植物固氮根瘤的形成涉及根表皮和皮层同步程序的启动，以允许根瘤菌感染和根瘤发育。在这项研究中，我们提供的证据表明，共质体通信，调节胼胝质营业额在胞间连丝（PD），是重要的协调结节的发展和感染在蒺藜苜蓿。在这里，我们表明，根瘤菌促进胼胝质水平的减少，在内部组织的结节开始。这种下调与M. Truncatula β-1，3-葡聚糖酶2（MtBG 2），编码一种新的PD相关胼胝质降解酶。时空分析表明，MtBG 2表达扩展从分裂结节的初始根瘤菌定植的皮层和表皮组织。如体内荧光分子的运输所示，共质体连接结构域在根瘤菌定植的组织中产生，并在组成型表达MtBG 2的根中增强。MtBG 2过表达的根还显示PD相关的胼胝质水平降低。总之，这些研究结果表明，在连续的结节发育阶段的胼胝质降解和共质体域的形成MtBG 2的积极作用。干扰共质体的连接导致剧烈的突变表型。异位表达β-1，3-葡聚糖酶（包括MtBG 2）的根表现出增加的根瘤数量，而那些表达MtBG 2 RNAi构建体或过度活跃的胼胝质合酶（在共生启动子下）的根表现出有缺陷的结瘤表型。阻碍共质体连接似乎阻断了脑皮层中的神经元摄取（NIN）及其靶核因子-YA 1（NF-YA 1）表达所需的信号通路。我们的结论是，共质体细胞间通讯积极增强根瘤菌，这是必要的细菌感染和根瘤发育的适当协调。
The formation of nitrogen-fixing nodules in legumes involves the initiation of synchronized programs in the root epidermis and cortex to allow rhizobial infection and nodule development. In this study, we provide evidence that symplastic communication, regulated by callose turnover at plasmodesmata (PD), is important for coordinating nodule development and infection in Medicago truncatula. Here, we show that rhizobia promote a reduction in callose levels in inner tissues where nodules initiate. This downregulation coincides with the localized expression of M. truncatula beta-1,3-glucanase 2 (MtBG2), encoding a novel PD-associated callose-degrading enzyme. Spatiotemporal analyses revealed that MtBG2 expression expands from dividing nodule initials to rhizobia-colonized cortical and epidermal tissues. As shown by the transport of fluorescent molecules in vivo, symplastic-connected domains are created in rhizobia-colonized tissues and enhanced in roots constitutively expressing MtBG2. MtBG2-overexpressing roots additionally displayed reduced levels of PD-associated callose. Together, these findings suggest an active role for MtBG2 in callose degradation and in the formation of symplastic domains during sequential nodule developmental stages. Interfering with symplastic connectivity led to drastic nodulation phenotypes. Roots ectopically expressing beta-1,3-glucanases (including MtBG2) exhibited increased nodule number, and those expressing MtBG2 RNAi constructs or a hyperactive callose synthase (under symbiotic promoters) showed defective nodulation phenotypes. Obstructing symplastic connectivity appears to block a signaling pathway required for the expression of NODULE INCEPTION (NIN) and its target NUCLEAR FACTOR-YA1 (NF-YA1) in the cortex. We conclude that symplastic intercellular communication is proactively enhanced by rhizobia, and this is necessary for appropriate coordination of bacterial infection and nodule development.