豆科植物根瘤茵结瘤因子的感知与信号转导

结瘤因子(脂壳寡糖,lipo-chito-oligosaccharides,LCOs)是根瘤菌在宿主植物根系分泌的类黄酮的作用下,合成并分泌的一类多糖信号分子,在根瘤菌与植物的共生结瘤过程中起重要作用。结瘤因子通过一定的机制感知,与某种特定受体(结瘤因子结合蛋白)结合,通过结瘤因子激活的信号转导途径如Ca2 介导的信号转导途径或磷酸类脂信号转导途径,诱导宿主植物的一系列反应,如根毛质膜去极化、皮层细胞分裂和结瘤素基因表达等。同时,结瘤因子的感知与信号转导也受一定基因和反馈机制调控。就豆科植物根瘤菌结瘤因子感知机制、信号转导途径及反馈调控等方面的研究进展进行了全面阐述。     

Legumes symbioses: absence of Nod genes in photosynthetic bradyrhizobia

Leguminous plants (such as peas and soybeans) and rhizobial soil bacteria are symbiotic partners that communicate through molecular signaling pathways, resulting in the formation of nodules on legume roots and occasionally stems that house nitrogen-fixing bacteria. Nodule formation has been assumed to be exclusively initiated by the binding of bacterial, host-specific lipochito-oligosaccharidic Nod factors, encoded by the nodABC genes, to kinase-like receptors of the plant. Here we show by complete genome sequencing of two symbiotic, photosynthetic, Bradyrhizobium strains, BTAi1 and ORS278, that canonical nodABC genes and typical lipochito-oligosaccharidic Nod factors are not required for symbiosis in some legumes. Mutational analyses indicated that these unique rhizobia use an alternative pathway to initiate symbioses, where a purine derivative may play a key role in triggering nodule formation.     

A cytokinin perception mutant colonized by Rhizobium in the absence of nodule organogenesis

In legumes, Nod-factor signaling by rhizobia initiates the development of the nitrogen-fixing nodule symbiosis, but the direct cell division stimulus that brings about nodule primordia inception in the root cortex remains obscure. We showed that Lotus japonicus plants homozygous for a mutation in the HYPERINFECTED 1 (HIT1) locus exhibit abundant infection-thread formation but fail to initiate timely cortical cell divisions in response to rhizobial signaling. We demonstrated that the corresponding gene encodes a cytokinin receptor that is required for the activation of the nodule inception regulator Nin and nodule organogenesis.     

Nodulation signaling in legumes requires NSP2, a member of the GRAS family of transcriptional regulators

Rhizobial bacteria enter a symbiotic interaction with legumes, activating diverse responses in roots through the lipochito oligosaccharide signaling molecule Nod factor. Here, we show that NSP2 from Medicago truncatula encodes a GRAS protein essential for Nod-factor signaling. NSP2 functions downstream of Nod-factor-induced calcium spiking and a calcium/calmodulin-dependent protein kinase. We show that NSP2-GFP expressed from a constitutive promoter is localized to the endoplasmic reticulum/nuclear envelope and relocalizes to the nucleus after Nod-factor elicitation. This work provides evidence that a GRAS protein transduces calcium signals in plants and provides a possible regulator of Nod-factor-inducible gene expression.     

LysM domain receptor kinases regulating rhizobial Nod factor-induced infection

The rhizobial infection of legumes has the most stringent demand toward Nod factor structure of all host responses, and therefore a specific Nod factor entry receptor has been proposed. The SYM2 gene identified in certain ecotypes of pea (Pisum sativum) is a good candidate for such an entry receptor. We exploited the close phylogenetic relationship of pea and the model legume Medicago truncatula to identify genes specifically involved in rhizobial infection. The SYM2 orthologous region of M. truncatula contains 15 putative receptor-like genes, of which 7 are LysM domain-containing receptor-like kinases (LYKs). Using reverse genetics in M. truncatula, we show that two LYK genes are specifically involved in infection thread formation. This, as well as the properties of the LysM domains, strongly suggests that they are Nod factor entry receptors.     

A putative Ca2+ and calmodulin-dependent protein kinase required for bacterial and fungal symbioses

Legumes can enter into symbiotic relationships with both nitrogen-fixing bacteria (rhizobia) and mycorrhizal fungi. Nodulation by rhizobia results from a signal transduction pathway induced in legume roots by rhizobial Nod factors. DMI3, a Medicago truncatula gene that acts immediately downstream of calcium spiking in this signaling pathway and is required for both nodulation and mycorrhizal infection, has high sequence similarity to genes encoding calcium and calmodulin-dependent protein kinases (CCaMKs). This indicates that calcium spiking is likely an essential component of the signaling cascade leading to nodule development and mycorrhizal infection, and sheds light on the biological role of plant CCaMKs.     

慢生根瘤菌及其与花生共生机制研究进展

氮是植物生长发育所必需的大量元素之一,豆科植物通过与根瘤菌的共生固氮获得氮素.这种共生关系的建立包括结瘤和固氮两个过程,涉及复杂的互作调控机理,并受环境因素的显著影响.花生与慢生根瘤菌的共生对花生生产尤为重要,具有较多特异和未知的共生机制.本文综述了慢生根瘤菌及其与花生共生的相关内容,具体包括:(1)花生的慢生根瘤菌多...     

A Legume Ethylene-Insensitive Mutant Hyperinfected by Its Rhizobial Symbiont

Development of the Rhizobium-legume symbiosis is controlled by the host plant, although the underlying mechanisms have remained obscure. A mutant in the annual legume Medicago truncatula exhibits an increase of more than an order of magnitude in the number of persistent rhizobial infections. Physiological and genetic analyses indicate that this same mutation confers insensitivity to the plant hormone ethylene for multiple aspects of plant development, including nodulation. These data support the hypothesis that ethylene is a component of the signaling pathway controlling rhizobial infection of legumes.     

紫花苜蓿根瘤菌及其共生系统耐酸性的研究

 土壤酸碱度是影响根瘤菌形成及固氮的一个主要因素,在南方酸性土壤地区,苜蓿生长的主要限制因素是固氮作用降低,筛选耐酸苜蓿根瘤菌用于接种具有十分重要的生产意义。本研究以9份根瘤菌株为研究对象,在不同的pH条件下培养研究其菌落直径,同时在不同的pH条件下分别与紫花苜蓿品种接种研究其结瘤数,结果表明：YNCY006菌株耐酸性最强而YNCY007菌株耐酸性最差,酸性土壤条件下GT13R紫花苜蓿分别与YNCY006或YNCY008接种是最佳结瘤的共生系统。     

豆科作物适应酸性土壤的养分高效根系遗传改良

世界上超过40%的耕作土壤为酸性,养分效率低是酸性土壤限制作物产量的主要因素。根系是植物吸收养分和水分的主要器官,也是植物与土壤微生物互作的主要界面。挖掘根系对土壤养分吸收和利用的遗传潜力、改善根际土壤微生物组成及活性是提高作物产量、减少环境污染和提升土壤健康的重要策略。此外,豆科作物与根瘤菌共生所固定的氮素是农业生态系统中不可替代的清洁氮源,也是影响根际土壤微生物组的重要因素。本文以大豆为代表,系统总结了酸性土壤中,豆科作物养分高效根系遗传改良、根系与根际微生物互作提高养分效率和土壤健康的研究进展。此外,本文还概述了应用养分高效大豆品种,通过接种高效根瘤菌剂并与玉米、茶树间套作的生态效益,为豆科作物养分高效遗传改良及推动其在可持续农业中的应用提供理论依据和应用案例。     

根瘤菌-豆科植物共生多样性与地理环境的关系

 根瘤菌与豆科植物形成的根瘤或茎瘤固氮共生体系在农、林、牧业的可持续发展中具有重要作用。 10 0多年前 ,在根瘤菌研究的起始阶段 ,人们提出的“宿主专一性”及“互接种族”2个概念一直流传至今。 2 0世纪 4 0年代 ,有学者根据实验室内豆科植物的交叉结瘤结果否定过“互接种族”的观念 ,70～ 80年代又发现某些根瘤菌在实验室条件下有广谱共生现象。但根瘤菌与豆科植物共生体与地理环境的关系却很少被涉及过。本文在对大量根瘤菌进行分类研究的基础上 ,结合宿主植物及其区域地理环境的综合分析 ,揭示出根瘤菌与豆科植物     

A gain-of-function mutation in a cytokinin receptor triggers spontaneous root nodule organogenesis

Legume root nodules originate from differentiated cortical cells that reenter the cell cycle and form organ primordia. We show that perception of the phytohormone cytokinin is a key element in this switch. Mutation of a Lotus japonicus cytokinin receptor gene leads to spontaneous development of root nodules in the absence of rhizobia or rhizobial signal molecules. The mutant histidine kinase receptor has cytokinin-independent activity and activates an Escherichia coli two-component phosphorelay system in vivo. Mutant analysis shows that cytokinin signaling is required for cell divisions that initiate nodule development and defines an autoregulated process where cytokinin induction of nodule stem cells is controlled by shoots.     

陕西豆科植物根瘤菌资源调查

在陕西关中、陕北地区,共采集到28属59种豆科植物根瘤样品930份,分离到710株根瘤菌,其中新发现地八角(Astragalus bhotanensis Baker)、硬毛棘豆(Oxytropis hirta Bunge)、塔落岩黄耆(Hedysarum fruticosum Pall)、毛掌锦鸡儿(Caragana leveillei kom)等10种豆科植物能够结瘤.在对豆科植物的结瘤特性比较研究后发现,豆科植物根瘤大小、数量、形状、颜色、着生部位除与寄主植物种有关系外,还与其所处的生态环境有很大的关系.该调查为根瘤菌在农业生产及生态环境建设中的应用提供宝贵的种质资源.     

Agglutinin from Alfalfa Necessary for Binding and Nodulation by Rhizobium meliloti

A protein that specifically agglutinates Rhizobium meliloti, the alfalfa root nodule endosymbiont, has been purified from alfalfa seed. Material cross-reactive to antiserum prepared against the purified agglutinin is present in all alfalfa varieties that were tested but is absent in corn and other legumes not nodulated by Rhizobium meliloti. Studies with nonnodulating mutants of this microorganism incapable of binding to alfalfa roots suggest that the agglutinin is responsible for specific recognition between Rhizobium meliloti and alfalfa and that this recognition is an essential step in nodule formation.     

Medicago truncatula DMI1 required for bacterial and fungal symbioses in legumes

Legumes form symbiotic associations with both mycorrhizal fungi and nitrogen-fixing soil bacteria called rhizobia. Several of the plant genes required for transduction of rhizobial signals, the Nod factors, are also necessary for mycorrhizal symbiosis. Here, we describe the cloning and characterization of one such gene from the legume Medicago truncatula. The DMI1 (does not make infections) gene encodes a novel protein with low global similarity to a ligand-gated cation channel domain of archaea. The protein is highly conserved in angiosperms and ancestral to land plants. We suggest that DMI1 represents an ancient plant-specific innovation, potentially enabling mycorrhizal associations.     

塔里木盆地豆科植物资源及其结瘤特性

2003年至2005年对塔里木盆地36个县(市)进行了豆科植物资源的调查及根瘤菌的采集工作,共采集到豆科植物30属66种,根瘤样品1160份;属内种间豆科植物根瘤的形状、大小、颜色及其在根上的着生位置相似,而属间植物根瘤特性差异明显。在调查采集到根瘤的豆科植物中,喀什黄华、矮沙冬青两种豆科植物在本研究之前未见到有结瘤固氮的报道。     

茶树丛枝菌根真菌的研究进展

丛枝菌根真菌是广泛存在于林地土壤中、与植物共生的重要的真菌类群,具有多种重要的有益功能。笔者综述了茶树丛枝菌根真菌的种类、形态结构、侵染率,及其对茶树在营养吸收、生长发育、矿质元素吸收、品质和抗逆性等方面的影响,并对其应用前景作了初步展望,以期为开展茶树AMF相关研究提供参考。