The origin and colonization history of the barley scald pathogen Rhynchosporium secalis

The origins of pathogens and their past and present migration patterns are often unknown. We used phylogenetic haplotype clustering in conjunction with model-based coalescent approaches to reconstruct the genetic history of the barley leaf pathogen Rhynchosporium secalis using the avirulence gene NIP1 and its flanking regions. Our results falsify the hypothesis that R. secalis emerged in association with its host during the domestication of barley 10,000 to 15,000 years ago in the Fertile Crescent and was introduced into Europe through the migration of Neolithic farmers. Estimates of time since most recent common ancestor (2500-5000 BP) placed the emergence of R. secalis clearly after the domestication of barley. We propose that modern populations of R. secalis originated in northern Europe following a host switch, most probably from a wild grass onto cultivated barley shortly after barley was introduced into northern Europe. R. secalis subsequently spread southwards into already established European barley-growing areas.     

Age‐related changes in the gut microbiota of wild House Sparrow nestlings

Here, we document the development of the House Sparrow Passer domesticus gut microbiota for the benefit of future ecological and evolutionary studies in this widely used avian system. We collected and inventoried luminal and mucosal samples from the distal guts of nestling House Sparrows between 3 and 12 days of age, and also collected similar samples from adult birds. Luminal bacterial community membership and structure differed significantly between nestlings and adults. The relative abundance of Proteobacteria in the lumen decreased around day 9, whereas the relative abundance of Firmicutes increased, demonstrating age‐related changes in the microbiota of House Sparrows.     

Loss of cytoplasmic incompatibility and minimal fecundity effects explain relatively low Wolbachia frequencies in Drosophila mauritiana

Maternally transmitted Wolbachia bacteria infect about half of all insect species. Many Wolbachia cause cytoplasmic incompatibility (CI) and reduced egg hatch when uninfected females mate with infected males. Although CI produces a frequency‐dependent fitness advantage that leads to high equilibrium Wolbachia frequencies, it does not aid Wolbachia spread from low frequencies. Indeed, the fitness advantages that produce initial Wolbachia spread and maintain non‐CI Wolbachia remain elusive. wMau Wolbachia infecting Drosophila mauritiana do not cause CI, despite being very similar to CI‐causing wNo from Drosophila simulans (0.068% sequence divergence over 682,494 bp), suggesting recent CI loss. Using draft wMau genomes, we identify a deletion in a CI‐associated gene, consistent with theory predicting that selection within host lineages does not act to increase or maintain CI. In the laboratory, wMau shows near‐perfect maternal transmission; but we find no significant effect on host fecundity, in contrast to published data. Intermediate wMau frequencies on the island of Mauritius are consistent with a balance between unidentified small, positive fitness effects and imperfect maternal transmission. Our phylogenomic analyses suggest that group‐B Wolbachia, including wMau and wPip, diverged from group‐A Wolbachia, such as wMel and wRi, 6–46 million years ago, more recently than previously estimated.     

Seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence on desert sand dunes

Seedling emergence is a critical stage in the establishment of desert plants. Soil microbes participate in plant growth and development, but information is lacking with regard to the role of microbes on seedling emergence. We applied the biocides (captan and streptomycin) to assess how seed mucilage interacts with soil microbial community and physiochemical processes to affect seedling emergence of Artemisia sphaerocephala on the desert sand dune. Fungal and bacterial community composition and diversity and fungal–bacterial interactions were changed by both captan and streptomycin. Mucilage increased soil enzyme activities and fungal–bacterial interactions. Highest seedling emergence occurred under streptomycin and mucilage treatment. Members of the phyla Firmicutes and Glomeromycota were the keystone species that improved A. sphaerocephala seedling emergence, by increasing resistance of young seedlings to drought and pathogen. Seed mucilage directly improved seedling emergence and indirectly interacted with the soil microbial community through strengthening fungal–bacterial interactions and providing favourable environment for soil enzymes to affect seedling emergence. Our study provides a comprehensive understanding of the regulatory mechanisms by which soil microbial community and seed mucilage interactively promote successful establishment of populations of desert plants on the barren and stressful sand dune.     

Plant responses to fungal volatiles involve global posttranslational thiol redox proteome changes that affect photosynthesis

Microorganisms produce volatile compounds (VCs) that promote plant growth and photosynthesis through complex mechanisms involving cytokinin (CK) and abscisic acid (ABA). We hypothesized that plants' responses to microbial VCs involve posttranslational modifications of the thiol redox proteome through action of plastidial NADPH‐dependent thioredoxin reductase C (NTRC), which regulates chloroplast redox status via its functional relationship with 2‐Cys peroxiredoxins. To test this hypothesis, we analysed developmental, metabolic, hormonal, genetic, and redox proteomic responses of wild‐type (WT) plants and a NTRC knockout mutant (ntrc) to VCs emitted by the phytopathogen Alternaria alternata. Fungal VC‐promoted growth, changes in root architecture, shifts in expression of VC‐responsive CK‐ and ABA‐regulated genes, and increases in photosynthetic capacity were substantially weaker in ntrc plants than in WT plants. As in WT plants, fungal VCs strongly promoted growth, chlorophyll accumulation, and photosynthesis in ntrc–Δ2cp plants with reduced 2‐Cys peroxiredoxin expression. OxiTRAQ‐based quantitative and site‐specific redox proteomic analyses revealed that VCs promote global reduction of the thiol redox proteome (especially of photosynthesis‐related proteins) of WT leaves but its oxidation in ntrc leaves. Our findings show that NTRC is an important mediator of plant responses to microbial VCs through mechanisms involving global thiol redox proteome changes that affect photosynthesis.     

新型隐球菌临床菌株中CNAG_01032基因的鉴定和功能研究

新型隐球菌是一种具有荚膜的重要临床致病真菌。本课题组在前期工作中发现CNAG_01032基因可能引起不同来源菌株的表型差异,本研究在此基础上以新型隐球菌临床来源菌株IFM56800（C1）、IFM56769（C2）为背景构建CNAG_01032基因敲除突变体,并检测突变株和野生型菌株经典毒力因子变化情况;使用API 20C AUX测试系统测试突变株和野生型菌株对19种糖的利用情况;使用尾静脉注射法感染BALB/c雌性小鼠进行致病性检测。结果显示：成功构建以临床株C1、C2为背景的CNAG-01032基因敲除突变株;突变株在37℃生长、黑色素产生与野生型菌株无显著差异,但荚膜厚度分别比C1、C2减少16.4%、18.2%;两基因敲除菌株均不能分解利用纤维二糖;致病性与野生型菌株无显著差异。新型隐球菌CNAG_01032基因可能参与临床来源菌株IFM56800、IFM56769的荚膜合成和纤维二糖的代谢。     

禽致病性大肠杆菌gspL基因缺失株构建及生物学特性

【目的】研究gsp L基因缺失对禽致病性大肠杆菌(Avian pathogenic Escherichia coli,APEC)生物学特性的影响。【方法】利用Red重组方法构建禽致病性大肠杆菌DE17株的gsp L缺失株;分析野生株与缺失株的生长特性、黏附和入侵DF1细胞的差异;采用荧光定量PCR的方法比较野生株和缺失株毒力基因转录水平的变化;比较野生株与缺失株的半数致死量(LD50)差异。【结果】gsp L缺失不影响DE17的生长特性,但其黏附和入侵DF1细胞能力显著下调。荧光定量PCR检测结果表明,缺失株毒力基因lux S,pfs,fyu A和iss转录水平明显上调,tsh的转录水平明显下调,而vat,ibe A,stx2f和omp A的转录水平无显著变化;LD50检测结果表明,缺失株比野生株毒力增强了12倍。【结论】gsp L基因的缺失不影响禽致病性大肠杆菌的生长特性,但能减弱其黏附和入侵能力,且可以正调控禽致病性大肠杆菌部分毒力基因的转录水平,推测gsp L基因可能与APEC对宿主的致病性有关。