Characterization of expressed genes in the establishment of arbuscular mycorrhiza between Amorpha fruticosa and Glomus mosseae

Arbuscular mycorrhiza （AM） formed between plant roots and fungi is one of the most widespread symbiotic associations in nature. To understand the molecular mechanisms of AM formation, we profiled 30 symbiosis-related genes expressed in Amorpha fruticosa roots colonized by Glomus mosseae and in non-mycorrhizal roots at different stages using differential-display RT-PCR （DDRT-PCR）. The expressed genes were confirmed by reverse Northern blotting. Eleven fragments were sequenced and putatively identified by homologous alignment. Of the eleven AM-related genes, five were obtained at the early-stage of plant-fungus interaction and six at the later stage. Three expressed se-quence tag （ESTs） sequences were found to originate from the fungi and eight from the host plant by use of PCR evaluation of gDNA of both plant and fungi. The target genes included an ATP-binding cassette sub-family transporter gene, a transposon-insertion display band, and a photosynthesis-related gene. The results provided information on the molecular mechanisms underlying the development of mycorrhizal sym-biosis between woody plants and AM fungi.

Transcriptome analysis of the symbiosis-related genes between Funneliformis mosseae and Amorpha fruticosa

Arbuscular mycorrhizal fungi(AMF) can colonize and form associations with the roots of Amorpha fruticosa L.(desert false indigo). Various genes are induced during the symbiotic process. In this study, de novo transcriptome sequencing using RNA-seq was conducted for the first time for a comprehensive analysis of AMF-A. fruticosa symbionts at the transcript level. We obtained 12 G of raw data from illumina sequencing and recovered 115,786 unigenes with an average length of547 bp, among them 41,848 of significance. A total of2460 diffexpression genes were identified, including 1579 down-regulated and 881 up-regulated genes. A threshold for false discovery rate of \ 0.001 and fold change of [ 1 determined significant differences in gene expression.Using these criteria, we screened 285 significant differentially expressed genes, of which 82 were up-regulated and203 down-regulated. The 82 up-regulated genes were classified according to their functions and assigned into seven categories: stress and defense, metabolism, signaling transduction, protein folding and degradation, energy,protein synthesis, and transcription. The 203 down-regulated genes were screened according to fold change [ 2,and 50 highly significant down-regulated genes were obtained related to stress and defense. The results of this study will provide a useful foundation for further investigation on the metabolic characteristics and molecular mechanisms of AMF associations with leguminous woody shrubs.

The eff ect of Rhizophagus irregularis on salt stress tolerance of Elaeagnus angustifolia roots

We assessed the eff ects of arbuscular mycorrhizal fungi(AMF)Rhizophagus irregularis inoculation on salt stress tolerance in roots of the drought-tolerant plant Elaeagnus angustifolia.We studied a plant growth index,spore density and hyphal length density of AMF,the Na+contents and ultrastructure of root cells,as well as rhizosphere soil enzyme activities of mycorrhizal and non-mycorrhizal E.angustifolia seedlings under diff erent salt stress.Under salt stress,growth of E.angustifolia with mycorrhizal inoculation was higher than that of non-inoculated treatments.The spore density and hyphal length density decreased signifi cantly under salt stress in rhizosphere soil of mycorrhizal E.angustifolia seedlings(p<0.05).The root cells of E.angustifolia seedlings inoculated with R.irregularis at 300 mmol L−1 salt had more organelles,greater integrity,and lower root Na+contents than those of non-inoculated seedlings.In addition,the results showed notably higher activities of catalase,phosphatase,urease and saccharase in rhizosphere soil of the mycorrhizal seedlings in response to salinity compared to those of the non-mycorrhizal seedlings.Therefore,AMF inoculation could enhance salt stress tolerance in roots of E.angustifolia.

复合菌系降解玉米秸秆过程中群落演替与秸秆降解的关系

【目的】为了获得木质素降解复合菌系LDC降解玉米秸秆的适宜条件,明确秸秆降解过程中可能发挥重要作用的功能微生物类群。【方法】以培养温度、pH、培养基装液量和接菌量等单因素试验结果为依据,采用响应面法优化复合菌系降解玉米秸秆的培养条件,利用Miseq高通量测序技术,分析不同降解时期复合菌系的群落结构变化规律。【结果】复合菌系对秸秆最佳降解条件为:培养温度32°C、初始pH为8.2、装液量为40%,接菌量为10%。此条件下木质素最大降解率为44.5%,相比未优化处理提高13.3%。在门水平上,变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)是复合菌系LDC的优势菌门。在玉米秸秆降解过程中,降解初期的优势菌属为Proteiniphilum(11.9%)、 Sphaerochaeta(8.4%)、 Ruminofilibacter(8.4%)、 Pannonibacter(6.7%)、Pseudomonas(6.1%)和Rhizobium(5.7%);在降解高峰期时,Anaerocolumna(24.0%)、Caenispirillum(9.2%)和Thauera(7.0%)的丰度显著上升,分别是其在降解初期的16.5倍、 3.0倍和5.9倍,而Ruminofilibacter(10.9%)的丰度仍然很高且排在第二位。在降解末期的优势菌属为Ruminofilibacter(25.4%)、Pseudomonas (9.7%)、Sphaerochaeta (8.8%)、Caenispirillum (8.4%)、Pannonibacter (4.3%)、Thauera (4.0%)以及Desulfomicrobium (3.4%)。【结论】明确了玉米秸秆降解复合菌系的最佳培养条件以及在不同降解时期微生物群落结构变化规律,在玉米秸秆降解过程中发挥重要作用的微生物类群为Pseudomonas、Pannonibacter、Thauera、Ruminofilibacter和Anaerocolumna。

芳香族化合物微生物代谢工程研究进展

代谢工程从20世纪90年代初期发展至今已有近30年历史,对微生物菌种改良和选育工作起到了极大的推动作用。芳香族化合物是一类可以通过微生物发酵生产的化学品,广泛应用于医药、食品、饲料和材料等领域。利用代谢工程手段对莽草酸和芳香族氨基酸合成途径进行理性改造,微生物细胞可以定向地大量积累人们需要的各种芳香族化合物。笔者对近30年来国内外代谢工程改造微生物合成各种芳香族化合物的研究策略和生物合成途径进行了梳理和总结,以期为开展相关研究提供参考。

异源表达多巴脱羧酶促进大肠杆菌从头合成多巴胺

多巴胺是多种天然抗氧化药物生物合成的前体物质,在人体内作为神经递质调控中枢神经系统的多种生理功能,常用于多种类型休克的临床治疗。目前,通过微生物合成技术已经实现了多巴胺的从头合成,但是合成效率很低。针对该问题,在左旋多巴(L-DOPA)大肠杆菌工程菌基础上,利用不同拷贝数质粒表达野猪Sus scrofa来源的多巴脱羧酶基因Ssddc,实现了葡萄糖到多巴胺的生产。为了进一步提高多巴胺合成效率,从100个候选基因中筛选出5个多巴脱羧酶基因进行测试,其中来源于人Homosapiens多巴脱羧酶基因Hsddc的工程菌摇瓶发酵的多巴胺产量最高,达到3.33 g/L;而来源于果蝇Drosophila melanogaster多巴脱羧酶基因Dmddc的工程菌摇瓶发酵的左旋多巴残余量最低,仅有0.02g/L;这两株工程菌分批补料发酵表明,多巴胺的产量可以分别达到13.3g/L和16.2g/L,左旋多巴残余量分别是0.45g/L和0.23g/L。将多巴脱羧酶基因Dmddc和Ssddc分别整合到基因组上,获得遗传稳定的工程菌,在分批补料发酵条件下,多巴胺产量最高达到17.7 g/L,是目前国内外报道的最高产量。