Aberrant nodulation response of Vigna umbellata to a Bradyrhizobium japonicum NodZ mutant and nodulation signals.

The (Brady)rhizobium nodulation gene products synthesize lipo-chitin oligosaccharide (LCO) signal molecules that induce nodule primordia on legume roots. In spot inoculation assays with roots of Vigna umbellata, Bradyrhizobium elkanii LCO and chemically synthesized LCO induced aberrant nodule structures, similar to the activity of these LCOs on Glycine soja (soybean). LCOs containing a pentameric chitin backbone and a reducing-end 2-O-methyl fucosyl moiety were active on V. umbellata. In contrast, the synthetic LCO-IV(C16:0), which has previously been shown to be active on G. soja, was inactive on V. umbellata. A B. japonicum NodZ mutant, which produces LCO without 2-O-methyl fucose at the reducing end, was able to induce nodule structures on both plants. Surprisingly, the individual, purified, LCO molecules produced by this mutant were incapable of inducing nodule formation on V. umbellata roots. However, when applied in combination, the LCOs produced by the NodZ mutant acted cooperatively to produce nodulelike structures on V. umbellata roots.     

Endogenous Nod-factor-like signal molecules promote early somatic embryo development in Norway spruce

Embryogenic cultures of Norway spruce (Picea abies) are composed of pro-embryogenic masses (PEMs) and somatic embryos of various developmental stages. Auxin is important for PEM formation and proliferation. In this report we show that depletion of auxin blocks PEM development and causes large-scale cell death. Extracts of the media conditioned by embryogenic cultures stimulate development of PEM aggregates in auxin-deficient cultures. Partial characterization of the conditioning factor shows that it is a lipophilic, low-molecular-weight molecule, which is sensitive to chitinase and contains GlcNAc residues. On the basis of this information, we propose that the factor is a lipophilic chitin oligosaccharide (LCO). The amount of LCO correlates to the developmental stages of PEMs and embryos, with the highest level in the media conditioned by developmentally blocked cultures. LCO is not present in nonembryogenic cultures. Cell death, induced by withdrawal of auxin, is suppressed by extra supply of endogenous LCO or Nod factor from Rhizobium sp. NGR234. The effect can be mimicked by a chitotetraose or chitinase from Streptomyces griseus. Taken together, our data suggest that endogenous LCO acts as a signal molecule stimulating PEM and early embryo development in Norway spruce.     

In vitro induction of lipo-chitooligosaccharide production in Bradyrhizobium japonicum cultures by root extracts from non-leguminous plants

Bradyrhizobium japonicum can form a N2-fixing symbiosis with compatible leguminous plants. It can also act as a plant-growth promoting rhizobacterium (PGPR) for non-legume plants, possibly through production of lipo-chitooligosaccharides (LCOs), which should have the ability to induce disease resistance responses in plants. The objective of this work was to determine whether non-leguminous crop plants can induce LCO formation by B. japonicum cultures. Cultures treated with root extracts of soybean, corn, cotton or winter wheat were assayed for presence and level of LCO. Root extracts of soybean, corn and winter wheat all induced LCO production, with extracts of corn inducing the greatest amounts. Root washings of corn also induced LCO production, but less than the root extract. These results indicated that the stimulation of non-legume plant growth by B. japonicum could be through the production of LCOs, induced by materials excreted by the roots of non-legume plants.     

Rhizobium NodI and NodJ proteins play a role in the efficiency of secretion of lipochitin oligosaccharides.

Thin-layer chromatographic analysis of extracts of D-[1-14C]glucosamine-labelled rhizobia was used to analyze the effects of nodI, nodJ, and nodT on secretion of lipochitin oligosaccharide (LCO) signal molecules. Secretion was analyzed by comparing quantities of radiolabelled LCOs present in the cellular and spent growth medium fractions. A second rapid and sensitive method was introduced to estimate the secreted LCO fractions by using D-[1-14C]glucosamine-labelled cells grown in medium supplemented with chitinase. At various times after induction of LCO synthesis, the quantity of degradation products of LCOs was compared with the amount of nondegraded LCOs. In wild-type strains of Rhizobium leguminosarum biovars viciae and trifolii the nodI and nodJ genes (but not the nodT gene) strongly enhance the secretion of LCOs during the first 5 h after the induction of LCO synthesis. In LCO-overproducing strains the enhancement of secretion was observed only during the first 3 h after induction. At times later than 5 h after induction, a significant influence of the presence of the nodI and nodJ genes on LCO secretion was detectable neither in the wild type nor in LCO-overproducing strains. By using plasmids in which the nodI and nodJ genes are cloned separately under control of a flavonoid-inducible promoter, it was shown that both genes are needed for a wild-type level of LCO secretion. Therefore, these results demonstrate that nodI and nodJ play a role in determining the efficiency of LCO secretion.     

Lipo-Chitin Oligosaccharides,Plant Symbiosis Signalling Molecules That Modulate Mammalian Angiogenesis In Vitro

Lipochitin oligosaccharides (LCOs) are signaling molecules required by ecologically and agronomically important bacteria and fungi to establish symbioses with diverse land plants. In plants, oligo-chitins and LCOs can differentially interact with different lysin motif (LysM) receptors and affect innate immunity responses or symbiosis-related pathways. In animals, oligo-chitins also induce innate immunity and other physiological responses but LCO recognition has not been demonstrated. Here LCO and LCO-like compounds are shown to be biologically active in mammals in a structure dependent way through the modulation of angiogenesis, a tightly-regulated process involving the induction and growth of new blood vessels from existing vessels. The testing of 24 LCO, LCO-like or oligo-chitin compounds resulted in structure-dependent effects on angiogenesis in vitro leading to promotion, or inhibition or nil effects. Like plants, the mammalian LCO biological activity depended upon the presence and type of terminal substitutions. Un-substituted oligo-chitins of similar chain lengths were unable to modulate angiogenesis indicating that mammalian cells, like plant cells, can distinguish between LCOs and un-substituted oligo-chitins. The cellular mode-of-action of the biologically active LCOs in mammals was determined. The stimulation or inhibition of endothelial cell adhesion to vitronectin or fibronectin correlated with their pro- or anti-angiogenic activity. Importantly, novel and more easily synthesised LCO-like disaccharide molecules were also biologically active and de-acetylated chitobiose was shown to be the primary structural basis of recognition. Given this, simpler chitin disaccharides derivatives based on the structure of biologically active LCOs were synthesised and purified and these showed biological activity in mammalian cells. Since important chronic disease states are linked to either insufficient or excessive angiogenesis, LCO and LCO-like molecules may have the potential to be a new, carbohydrate-based class of therapeutics for modulating angiogenesis.     

昆明西山滇青冈林内滇青冈种子库动态的研究

通过对昆明西山滇青冈林内滇青冈种子库的跟踪取样调查和种子埋藏试验,对滇青冈种子库的动态进行了研究。昆虫在种子成熟前侵入种子,经种子雨进入种子库时已有71.8%的种子失去萌发能力。种子雨输入种子库的绝大部分种子停留在表面种子库,其中48.55%的种子被虫害,25.36%被某些非生物或生物搬运,17.39%的腐烂,8.7%的被动物当场取食,没有种子萌发,影响种子库动态的各种因子的作用大小在时间上是变化。被搬运的种子中,有4.9%的由表面种子库转移到埋藏种子库。土层是滇青冈种子的安全生境,土壤种子库的存在时间超过250天。埋入土壤的试验种子一直处于静止状态,到6月雨季后有80%种子萌发,20%的腐烂。萌发种子数是当年产种子的0.26%。滇青冈林内的滇青冈种子库是季节性的,种子库对种群个体的补充作用是有限的。     

Jasmonates induce Nod factor production by Bradyrhizobium japonicum

Jasmonates are signaling molecules involved in induced systemic resistance, wounding and stress responses of plants. We have previously demonstrated that jasmonates can induce nod genes of Bradyrhizobium japonicum when measured by beta-galactosidase activity. In order to test whether jasmonates can effectively induce the production and secretion of Nod factors (lipo-chitooligosaccharides, LCOs) from B. japonicum, we induced two B. japonicum strains, 532C and USDA3, with jasmonic acid (JA), methyl jasmonate (MeJA) and genistein (Ge). As genistein is well characterized as an inducer of nod genes it was used a positive control. The high-performance liquid chromatography (HPLC) profile of LCOs isolated following treatment with jasmonates or genistein showed that both JA and MeJA effectively induced nod genes and caused production of LCOs from bacterial cultures. JA and MeJA are more efficacious inducers of LCO production than genistein. Genistein plus JA or MeJA resulted in greater LCO production than either alone. A soybean root hair deformation assay showed that jasmonate induced LCOs were as effective as those induced by genistein. This is the first report that jasmonates induce Nod factor production by B. japonicum. This report establishes the role of jasmonates as a new class of signaling molecules in the Bradyrhizobium-soybean symbiosis.     

结瘤因子的研究进展

结瘤因子是由根瘤菌产生的一类信号分子,它们在结瘤的起始阶段发挥着十分重要的作用。新近的研究结果证明结瘤因子大分子骨架上的不同侧链基团是决定细菌与宿主植物间相互识别的关键因素,根瘤菌细胞中一系列结瘤基因编码能够合成Lipo-chio-oligosaccharides(LCOs)的各种酶类,进而确定结瘤信号分子的特定结构。目前,一系列令人兴奋的实验结果表明：LCOs不仅可促进豆科作物的生物固氮作用,对一些非豆科作物的细胞分裂作用等同样具有刺激作用。对根瘤菌结瘤因子的研究显然有助于进一步了解细菌与植物的相互作用机理,并进而为农业生产为直接利益。本文在综述这方面的研究进展同时,还就瘤菌,豆科作用和结瘤信号分子之间的相互作用机理,以及根际促生细菌,水杨酸和结瘤信号分子之间的可能关系进行了理论分析。     

Molecular mechanisms of Nod factor diversity

The rhizobia–legume symbiosis is highly specific. Major host specificity determinants are the bacterial Nod factor signals that trigger the nodulation programme in a compatible host. Nod factors are lipo-chitooligosaccharides (LCOs) varying in the oligosaccharide chain length, the nature of the fatty acids and substitutions on the oligosaccharide. The nod genotype of rhizobia, which forms the genetic basis for this structural variety, includes a set of nodulation genes encoding the enzymes that synthesize LCOs. Allelic and non-allelic variation in these genes ensures the synthesis of different LCO structures by the different rhizobia. The nod genotypes co-evolved with host plant divergence in contrast to the rhizobia, which followed a different evolution. Horizontal gene transfer probably played an important role during evolution of symbiosis. The nod genotypes are particularly well equipped for horizontal gene transfer because of their location on transmissible plasmids and/or on 'symbiosis islands', which are symbiotic regions associated with movable elements.     

Nitric oxide elicitation for secondary metabolite production in cultured plant cells

Nitric oxide (NO) is an important signal molecule in stress responses. Accumulation of secondary metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. NO has been reported to play important roles in elicitor-induced secondary metabolite production in tissue and cell cultures of medicinal plants. Better understanding of NO role in the biosynthesis of such metabolites is very important for optimizing the commercial production of those pharmaceutically significant secondary metabolites. This paper summarizes progress made on several aspects of NO signal leading to the production of plant secondary metabolites, including various abiotic and biotic elicitors that induce NO production, elicitor-triggered NO generation cascades, the impact of NO on growth development and programmed cell death in medicinal plants, and NO-mediated regulation of the biosynthetic pathways of such metabolites. Cross-talks among NO signaling and reactive oxygen species, salicylic acid, and jasmonic acid are discussed. Some perspectives on the application of NO donors for induction of the secondary metabolite accumulation in plant cultures are also presented.     

Rhizobium sp. BR816 produces a complex mixture of known and novel lipochitooligosaccharide molecules

Rhizobial lipochitooligosaccharide (LCO) signal molecules induce various plant responses, leading to nodule development. We report here the LCO structures of the broadhost range strain Rhizobium sp. BR816. The LCOs produced are all pentamers, carrying common C18:1 or C18:0 fatty acyl chains, N-methylated and C-6 carbamoylated on the nonreducing terminal N-acetylglucosamine and sulfated on the reducing/terminal residue. A second acetyl group can be present on the penultimate N-acetylglucosamine from the nonreducing terminus. Two novel characteristics were observed: the reducing/terminal residue can be a glucosaminitol (open structure) and the degree of acetylation of this glucosaminitol or of the reducing residue can vary.     

Lipo-chitooligosaccharide signaling in endosymbiotic plant-microbe interactions

The arbuscular mycorrhizal (AM) and the rhizobia-legume (RL) root endosymbioses are established as a result of signal exchange in which there is mutual recognition of diffusible signals produced by plant and microbial partners. It was discovered 20 years ago that the key symbiotic signals produced by rhizobial bacteria are lipo-chitooligosaccharides (LCO), called Nod factors. These LCO are perceived via lysin-motif (LysM) receptors and activate a signaling pathway called the common symbiotic pathway (CSP), which controls both the RL and the AM symbioses. Recent work has established that an AM fungus, Glomus intraradices, also produces LCO that activate the CSP, leading to induction of gene expression and root branching in Medicago truncatula. These Myc-LCO also stimulate mycorrhization in diverse plants. In addition, work on the nonlegume Parasponia andersonii has shown that a LysM receptor is required for both successful mycorrhization and nodulation. Together these studies show that structurally related signals and the LysM receptor family are key components of both nodulation and mycorrhization. LysM receptors are also involved in the perception of chitooligosaccharides (CO), which are derived from fungal cell walls and elicit defense responses and resistance to pathogens in diverse plants. The discovery of Myc-LCO and a LysM receptor required for the AM symbiosis, therefore, not only raises questions of how legume plants discriminate fungal and bacterial endosymbionts but also, more generally, of how plants discriminate endosymbionts from pathogenic microorganisms using structurally related LCO and CO signals and of how these perception mechanisms have evolved.     

氧化甾醇结合蛋白相关蛋白家族的研究进展

膜脂是细胞膜的主要组分, 也是参与信号转导的重要信号分子。不同脂质分子在细胞膜上的不均等分布需要特殊类型的通道蛋白和运输蛋白来实现。氧化甾醇结合蛋白相关蛋白(ORPs)是一类非常保守的蛋白分子, 能够对磷脂酰肌醇和固醇等脂类分子进行识别并转运, 参与细胞中的许多生理过程, 包括信号转导、囊泡运输、脂类代谢和非囊泡运输等...     

Response of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> roots to lipo-chitooligosaccharide from <Emphasis Type="Italic">Bradyrhizobium japonicum</Emphasis> and other chitin-like compounds

Lipo-chitooligosaccharides (LCOs) are bacteria-to-plant signals required for the establishment of rhizobia–legume nitrogen fixing symbioses. The ability of LCO [Nod Bj V (C_18:1, MeFuc)] isolated from B. japonicum (strain 532C), and of oligomers of chitosan (tetramer, pentamer) and chitin (pentamer) to affect the developmental morphology of roots in Arabidopsis thaliana (L.) Heynh ecotype Columbia (Col-0) was assessed using an interactive scanner-based image analysis system. LCOs have been shown to play a role in plant organogenesis at nanomolar concentrations. LCO and the chitin pentamer promoted root growth and development in Arabidopsis at concentrations of 10 nM and 100 μM, respectively. The LCO treated Arabidopsis plants had about 35% longer roots than untreated control plants. Similarly, treatment with 100 μM chitin pentamer (CHIT5) resulted in 26% longer roots than the untreated plants; however, chitosan oligomer (CH4 or CH5) treated plants did not differ from the control plants at either concentration (100 or 1 μM). Both LCOs and the chitin pentamer at higher concentrations increased root surface area, mean root diameter and number of root tips. However, leaf area increase was observed only in plants treated with LCO at 10 nM.     

Alteration of plant growth and development by Rhizobium nodA and nodB genes involved in the synthesis of oligosaccharide signal molecules

The highly conserved Rhizobium nodulation genes nodABC are required to produce lipid-linked chitooligosaccharide signal molecules which elicit nodule organogenesis in roots of leguminous plants. Recently, it has been shown that NodB deacetylates chitooligosaccharides at the non-reducing terminus, so that the free amino group of the chitooligosaccharide backbone can then be acylated by a specific fatty acid. The Rhizobium NodA protein together with the nodB encoded chitooligosaccharide deacetylase are involved in generating small, heat-stable compounds that stimulate mitosis in protoplasts derived from either legumes or other plant species. To test whether these gene products could play a role in regulation of plant development, we introduced and expressed the Rhizobium meliloti nodA and nodB genes singly or in combination under the control of diverse promoters in tobacco. Altered phenotypes correlating with nodA and nodB gene expression in transgenic plants indicate that tobacco contains the necessary substrates for the NodA and NodB proteins to produce signal molecules modulating plant growth and organ development.     

Nod factors stimulate seed germination and promote growth and nodulation of pea and vetch under competitive conditions

Nod factors are lipochitooligosaccharide (LCO) produced by soil bacteria commonly known as rhizobia acting as signals for the legume plants to initiate symbiosis. Nod factors trigger early symbiotic responses in plant roots and initiate the development of specialized plant organs called nodules, where biological nitrogen fixation takes place. Here, the effect of specific LCO originating from flavonoid induced Rhizobium leguminosarum bv. viciae GR09 culture was studied on germination, plant growth and nodulation of pea and vetch. A crude preparation of GR09 LCO significantly enhanced symbiotic performance of pea and vetch grown under laboratory conditions and in the soil. Moreover, the effect of GR09 LCOs seed treatments on the genetic diversity of rhizobia recovered from vetch and pea nodules was presented.     

Source-sink regulation by sugar and stress.

The regulation of carbon partitioning between source and sink tissues in higher plants is not only important for plant growth and development, but insight into the underlying regulatory mechanism is also a prerequisite to modulating assimilate partitioning in transgenic plants. Hexoses, as well as sucrose, have been recognised as important signal molecules in source-sink regulation. Components of the underlying signal transduction pathways have been identified and parallels, as well as distinct differences, to known pathways in yeast and animals have become apparent. There is accumulating evidence for crosstalk, modulation and integration between signalling pathways responding to phytohormones, phosphate, light, sugars, and biotic and abiotic stress-related stimuli. These complex interactions at the signal transduction levels and co-ordinated regulation of gene expression seem to play a central role in source-sink regulation.     

细胞分裂素调控种子发育、休眠与萌发的研究进展

种子萌发是子代植株建立、生长和繁育的重要阶段,在种子植物生命周期中起重要作用。种子休眠是在发育过程中形成的,在生理成熟期达到峰值。种子休眠与萌发的植物激素调控可能是种子植物中一种高度保守的机制。细胞分裂素(CK)是植物体内的一种重要信号分子,调控植物生长发育的许多方面。生物活性CK的水平由其生物合成、活化、失活、再活化...     

Bacterial lipopolysaccharides induce defense responses associated with programmed cell death in rice cells

PAMP (pathogen-associated molecular pattern) recognition plays an important role during the innate immune response in both plants and animals. Lipopolysaccharides (LPS) derived from Gram-negative bacteria are representative of typical PAMP molecules and have been reported to induce defense-related responses, including the suppression of the hypersensitive response, the expression of defense genes and systemic resistance in plants. However, the details regarding the precise molecular mechanisms underlying these cellular responses, such as the molecular machinery involved in the perception and transduction of LPS molecules, remain largely unknown. Furthermore, the biological activities of LPS on plants have so far been reported only in dicots and no information is thus available regarding their functions in monocots. In our current study, we report that LPS preparations for various becteria, including plant pathogens and non-pathogens, can induce defense responses in rice cells, including reactive oxygen generation and defense gene expression. In addition, global analysis of gene expression induced by two PAMPs, LPS and chitin oligosaccharide, also reveals a close correlation between the gene responses induced by these factors. This indicates that there is a convergence of signaling cascades downstream of their corresponding receptors. Furthermore, we show that the defense responses induced by LPS in the rice cells are associated with programmed cell death (PCD), which is a finding that has not been previously reported for the functional role of these molecules in plant cells. Interestingly, PCD induction by the LPS was not detected in cultured Arabidopsis thaliana cells.