A multilocus sequence analysis of the genus Xanthomonas

A multilocus sequence analysis (MLSA) of strains representing all validly published Xanthomonas spp. (119 strains) was conducted using four genes; dnaK, fyuA, gyrB and rpoD, a total of 440 sequences. Xanthomonas spp. were divided into two groups similar to those indicated in earlier 16S rDNA comparative analyses, and they possibly represent distinct genera. The analysis clearly differentiated most species that have been established by DNA-DNA reassociation. A similarity matrix of the data indicated clear numerical differences that could form the basis for species differentiation in the future, as an alternative to DNA-DNA reassociation. Some species, X. cynarae, X. gardneri and X. hortorum, formed a single heterogeneous group that is in need of further investigation. X. gardneri appeared to be a synonym of X. cynarae. Recently proposed new species, X. alfalfae, X. citri, X. euvesicatoria, X. fuscans and X. perforans, were not clearly differentiated as species from X. axonopodis, and X. euvesicatoria and X. perforans are very probably synonyms. MLSA offers a powerful tool for further investigation of the classification of Xanthomonas. Based on the dataset produced, the method also offers a relatively simple way of identifying strains as members of known species, or of indicating their status as members of new species.     

Root Growth of Arabidopsis thaliana Is Regulated by Ethylene and Abscisic Acid Signaling Interaction in Response to HrpNEa, a Bacterial Protein of Harpin Group

HrpN_Ea is a harpin protein from Erwinia amylovora, a bacterial pathogen that causes fire blight in rosaceous plants. Treating plants with HrpN_Ea stimulates ethylene and abscisic acid (ABA) to induce plant growth and drought tolerance, respectively. Herein, we report that both growth hormones cooperate to mediate the role of HrpN_Ea in promoting root growth of Arabidopsis thaliana seedlings. Root growth is promoted coordinately with elevation in levels of ABA and ethylene subsequent to soaking of germinating seeds of wild-type (WT) Arabidopsis in a solution of HrpN_Ea. However, these responses are arrested by inhibiting WT roots from synthesizing ethylene as well as sensing of ABA and ethylene. The effects of HrpN_Ea on roots are also nullified in ethylene-insensitive etr1-1 and ein5-1 mutants and in the ABA-insensitive mutant abi2-1 of Arabidopsis. These results provide evidence for presence of a relationship between root growth enhancement and signaling by ABA and ethylene in response to HrpN_Ea. Nevertheless, when HrpN_Ea is applied to leaves, ethylene signaling is active in the absence of ABA signaling to promote plant growth. This suggests the presence of a different signaling mechanism in leaves from that in roots. X. Ren and F. Liu contributed equally to this study and are regarded as joint first authors     

Inducible antibacterial defence in the plant parasitic nematode Meloidogyne artiellia

Animals and plants both respond rapidly to pathogens by inducing the expression of defence-related genes. Within this context, a prominent role has been assigned to the lysozyme. In the present study we isolated and carried out detailed analysis of the lysozyme gene in the plant nematode Meloidogyne artiellia. The expression of lysozyme was up-regulated following exposure of M. artiellia juveniles to the Gram-negative bacterium Serratia marcescens. On the other hand, when isolated eggs containing embryos at various developmental stages were challenged with bacteria, no increase in lysozyme expression was detected. Evidence of lysozyme expression regulation was obtained in the case of adult male and females worms collected from soil. The lysozyme gene was expressed solely in the nematode intestine and, as it is predicted to be secreted, may protect the nematode from microbial infections originating in the intestinal lumen or in the pseudocoelom. This paper demonstrates, to our knowledge for the first time, the immune response to infection in a plant parasitic nematode.     

Application of silicon sources increases silicon accumulation in perennial ryegrass turf on two soil types

This study investigated the ability of perennial ryegrass to accumulate silicon and the factors that may influence plant silicon accumulation. Plants were grown in the greenhouse in two soil types, peat:sand mix and Hagerstown-silt-loam, amended with two commercially available sources of silicon, calcium silicate slag and wollastonite at 0, 0.5, 1, 2, 5 and 10 t/ha. Shoot tissue of nine-week-old perennial ryegrass plants was analyzed for silicon content (%) and found to reach a dry matter concentration of up to 4% in this study. Silicon accumulation in perennial ryegrass was influenced by the soil type and source, and was higher in plants grown in low-silicon peat:sand mix compared to Hagerstown-silt-loam. Silicon content (%) in the plants consistently increased with increasing rates of silicon in all four soil and source combinations. Acetic acid (HAc) extractable silicon and Ca increased in both soil types when amended with either of the silicon sources. Effects of silicon sources on soil pH varied with soil type. This study indicates that soil type, source of silicon, and rate of silicon application are important factors influencing the uptake of silicon by perennial ryegrass which is a widely used turfgrass species in golf courses, sports fields, and residential lawns in the United States.     

Hypericum perforatum plant cells reduce Agrobacterium viability during co-cultivation

Plant recalcitrance is the major barrier in developing Agrobacterium-mediated transformation protocols for several important plant species. Despite the substantial knowledge of T-DNA transfer process, very little is known about the factors leading to the plant recalcitrance. Here, we analyzed the basis of Hypericum perforatum L. (HP) recalcitrance to Agrobacterium-mediated transformation using cell suspension culture. When challenged with Agrobacterium, HP cells swiftly produced an intense oxidative burst, a typical reaction of plant defense. Agrobacterium viability started to decline and reached 99% mortality within 12 h, while the plant cells did not suffer apoptotic process. This is the first evidence showing that the reduction of Agrobacterium viability during co-cultivation with recalcitrant plant cells can affect transformation.     

The genome of the thermoacidophilic red microalga <Emphasis Type="Italic">Galdieria sulphuraria</Emphasis> encodes a small family of secreted class III peroxidases that might be involved in cell wall modification

We report the identification of a small family of secreted class III plant peroxidases (Prx) from the genome of the unicellular thermoacidophilic red alga Galdieria sulphuraria (Cyanidiaceae). Apart from two class I ascorbate peroxidases and one cytochrome c peroxidase, the red algal genome encodes four class III plant peroxidases, thus complementing the short list of algal cell wall peroxidases (Passardi et al. in Genomics 89:567–579, 2007). We have characterized the family gene structure, analyzed the extracellular space and cell wall fraction of G. sulphuraria for the presence of peroxidase activity and used shotgun proteomics to identify candidate extracellular peroxidases. For a detailed enzymatic characterization, we have purified a secreted peroxidase (GsPrx04) from the cell-free medium using hydrophobic interaction chromatography. The enzyme proved heat and acid-stable and exhibited an apparent molecular mass of 40 kDa. Comparative genomics between endolithically growing G. sulphuraria and a close relative, the obligatory aquatic, cell wall-less Cyanidioschyzon merolae, revealed that class III peroxidases only occur in the terrestrial microalga, thus supporting the key function of these enzymes in the process of land colonization. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Nucleotide sequence database accession numbers: GsuAPX01 (EF589723), GsuAPX02 (EF589721), GsuCcP01 (EF589722), GsPrx01 (EF589724), GsPrx02 (EF589725), GsPrx03 (EF589726), and GsPrx04 (EF589727). The nomenclature of peroxidases has been adapted to PeroxiBase ().     

木质素和氮含量对植物残体分解的影响

 在25 ℃和水分含量为400 g·kg-1（以风干土计）条件下对19种植物残体进行培养实验,同时进行田间填埋试验,研究残体的木质素和N含量对其在土壤中分解的影响。相关分析表明,不同植物残体的分解速率与其初始全N含量呈正相关,与初始木质素含量、木质素与N含量之比呈负相关。逐步回归分析进一步表明,植物残体的C分解与全N及木质素含量的数学关系可表达成：Y=B0+B1N+B2L。式中,B0、B1和B2为回归系数,N和L分别表示植物残体的初始全N含量及木质素含量。Y可分别表示为植物残体C分解的一级动力学常数、培     

植物化学通讯研究进展

 生物的信息传递是生命科学中引人入胜的研究领域之一,生物种间种内和个体内都存在着物理和化学等各种信息交流方式。植物种间种内是否通过物理信号进行通讯交流还是一个未知数,但邻近的同种或异种植物通过化学物质为媒介的通讯关系确是客观存在的。最近,愈来愈多的研究证明：许多陆生植物种可以合成并释放特定的次生物质,这些次生物质可以通过空气和土壤两种载体进行信息传递,尤其是在植物受到侵袭和寄生条件下。茉莉酮酸甲酯、水杨酸甲酯和乙烯等挥发性次生物质被确证为以空气为媒介进行植物种间和种内通讯的化学信号分子。植物根分泌的黄酮和氢醌等分子也可以经土壤媒介传递信息。由于在自然条件下植物根系分泌物的收集和活性信号分子的俘获及鉴定技术还未能突破,这增加了以土壤为媒介的植物种间和种内化学通讯关系研究的难度。但不论如何,植物的化学通讯是植物种间和种内交流的主要方式,植物间的化学通讯关系的研究还处于突破的前夜,这方面的任一研究成果都会引起世界性的关注。因此,破译植物种间和种内化学通讯密码具有重要的学术价值。     

三峡库区资源植物的现状与保护

据调查统计,三峡库区有资源植物2070种,其中药用植物1006种、纤维植物104种、油脂植物76种、观赏植物74种、野果植物54种、芳香植物54种、树脂树胶植物68种、淀粉及糖类植物52种,鞣科植物32种、珍稀植物49种、其它类型植物465种。论述了三峡库区资源植物的分类及保护现状。