Spontaneous symbiotic reprogramming of plant roots triggered by receptor-like kinases.
Spontaneous symbiotic reprogramming of plant roots triggered by receptor-like kinases.
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DOI：
10.7554/elife.03891
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发表时间：
2014-11-25
期刊：
影响因子：
7.7
通讯作者：
Parniske M
中科院分区：
文献类型：
--
作者：
Ried MK;Antolín-Llovera M;Parniske M
共生受体样激酶（SYMRK）是获得磷的丛枝菌根（AM）和固氮根瘤共生体发育所必需的，但区分这两种不同共生体发育命运的机制一直是个谜。在这项研究中，我们表明，异位表达后，受体样激酶基因结瘤因子受体1（NFR 1），NFR 5，和SYMRK启动自发根瘤器官发生和结瘤相关基因的表达在根瘤菌的情况下。此外，在豆科植物百脉根中，过表达的NFR 1或NFR 5与内源SYMRK相关。上位性测试显示，显性活性SYMRK等位基因启动信号传导独立于NFR 1或NFR 5基因和一组基因的上游，所需的生成或解码的钙尖峰在两个共生体。只有SYMRK而非NFR的过表达触发了AM相关基因的表达，表明受体在AM或根瘤共生发育的决定中起关键作用。 http://dx.doi.org/10.7554/eLife.03891.001像所有的植物一样，农作物需要氮和磷等营养物质来生长。这些基本元素通常供应不足，因此每年有数百万吨化肥被施在农田上以维持作物产量。植物获得稀缺养分的另一种方式是与生活在土壤中的微生物形成共生关系。植物将含碳化合物（如糖）传递给微生物，作为回报，某些真菌为植物提供矿物质（如磷酸盐）。一些被称为豆类的植物（如豌豆，豆类和三叶草）也可以与细菌形成关系，将空气中的氮转化为氨，然后植物用氨来制造DNA和蛋白质等分子。为了与植物建立这些共生关系，固氮细菌释放化学信号，这些信号通过在植物根细胞表面发现的受体蛋白NFR 1和NFR 5识别。这些信号触发了一系列事件，最终导致植物形成一个名为“根瘤”的器官，以容纳和滋养固氮细菌。类似的信号机制被认为发生在植物和某些土壤真菌之间建立共生关系的过程中。一种被称为共生受体样激酶（Symbiosis Receptor-like Kinase，简称SYMRK）的植物蛋白也位于根细胞表面，是细菌-植物和真菌-植物发生关联所必需的。然而，这种蛋白在这些过程中的确切作用尚不清楚。Ried等人现在已经利用细胞表面受体蛋白的特性对此进行了研究：如果这些蛋白质中的一些蛋白质过量产生，即使初始信号不存在，它们也会激活它们的信号级联。Ried等人设计了一种名为Lotus的植物，以产生高水平的SYMRK，NFR 1或NFR 5。这些变化中的每一个都足以触发植物在没有微生物的情况下形成根瘤。当这三种蛋白质中的每一种都大量产生时，与涉及根瘤形成的信号级联激活相关的基因也被打开。相反，只有过量的SYMRK才能激活与真菌-植物相关的基因。Ried等人还发现，虽然SYMRK可以在没有NFR的情况下发挥作用，但NFR 1和NFR 5需要彼此才能发挥作用。这些数据表明，受体蛋白质在决定与细菌或真菌建立关联方面发挥关键作用。由于过量的共生受体导致植物形成共生结构，Ried等人提出，这种策略可以用来说服通常不与固氮细菌形成共生的植物这样做。如果这是可能的，它可能会引导我们设计农作物植物，使其与固氮细菌形成共生相互作用;这将有助于提高农作物产量，并使农作物能够在缺氮环境中种植，而无需添加额外的肥料。 DOI：http://dx.doi.org/10.7554/eLife.03891.002
Symbiosis Receptor-like Kinase (SYMRK) is indispensable for the development of phosphate-acquiring arbuscular mycorrhiza (AM) as well as nitrogen-fixing root nodule symbiosis, but the mechanisms that discriminate between the two distinct symbiotic developmental fates have been enigmatic. In this study, we show that upon ectopic expression, the receptor-like kinase genes Nod Factor Receptor 1 (NFR1), NFR5, and SYMRK initiate spontaneous nodule organogenesis and nodulation-related gene expression in the absence of rhizobia. Furthermore, overexpressed NFR1 or NFR5 associated with endogenous SYMRK in roots of the legume Lotus japonicus. Epistasis tests revealed that the dominant active SYMRK allele initiates signalling independently of either the NFR1 or NFR5 gene and upstream of a set of genes required for the generation or decoding of calcium-spiking in both symbioses. Only SYMRK but not NFR overexpression triggered the expression of AM-related genes, indicating that the receptors play a key role in the decision between AM- or root nodule symbiosis-development. DOI: http://dx.doi.org/10.7554/eLife.03891.001 Like all plants, crop plants need nutrients such as nitrogen and phosphate to grow. Often these essential elements are in short supply, and so millions of tons of fertiliser are applied to agricultural land each year to maintain crop yields. Another way for plants to gain access to scarce nutrients is to form symbiotic relationships with microorganisms that live in the soil. Plants pass on carbon-containing compounds—such as sugars—to the microbes and, in return, certain fungi provide minerals—such as phosphates—to the plants. Some plants called legumes (such as peas, beans, and clovers) can also form relationships with bacteria that convert nitrogen from the air into ammonia, which the plants then use to make molecules such as DNA and proteins. To establish these symbiotic relationships with plants, nitrogen-fixing bacteria release chemical signals that are recognized via receptor proteins, called NFR1 and NFR5, found on the surface of the plant root cells. These signals trigger a cascade of events that ultimately lead to the plant forming an organ called ‘root nodule’ to house and nourish the nitrogen-fixing bacteria. A similar signalling mechanism is thought to take place during the establishment of symbiotic relationships between plants and certain soil fungi. A plant protein called Symbiosis Receptor-like Kinase (or SYMRK for short) that is also located on the root cell surface is required for both bacteria–plant and fungi–plant associations to occur. However, the exact role of this protein in these processes was unclear. Ried et al. have now investigated this by taking advantage of a property of cell surface receptor proteins: if some of these proteins are made in excessive amounts they activate their signalling cascades even when the initial signal is not present. Ried et al. engineered plants called Lotus japonicus to produce high levels of SYMRK, NFR1, or NFR5. Each of these changes was sufficient to trigger the plants to develop root nodules in the absence of microbes. Genes associated with the activation of the signalling cascade involved the formation of root nodules were also switched on when each of the three proteins was produced in large amounts. In contrast, only an excess of SYMRK could activate genes related to fungi–plant associations. Ried et al. also found that, while SYMRK can function in the absence of the NFRs, NFR1 and NFR5 need each other to function. These data suggest that the receptor proteins play a key role in the decision between the establishment of an association with a bacterium or a fungus. As an excess of symbiotic receptors caused plants to form symbiotic structures, Ried et al. propose that this strategy could be used to persuade plants that usually do not form symbioses with nitrogen-fixing bacteria to do so. If this is possible, it might lead us to engineer crop plants to form symbiotic interactions with nitrogen-fixing bacteria; this would help increase crop yields and enable crops to be grown in nitrogen-poor environments without the addition of extra fertiliser. DOI: http://dx.doi.org/10.7554/eLife.03891.002