Submillisecond Elastic Recoil Reveals Molecular Origins of Fibrin Fiber Mechanics

Fibrin fibers form the structural scaffold of blood clots. Thus, their mechanical properties are of central importance to understanding hemostasis and thrombotic disease. Recent studies have revealed that fibrin fibers are elastomeric despite their high degree of molecular ordering. These results have inspired a variety of molecular models for fibrin’s elasticity, ranging from reversible protein unfolding to rubber-like elasticity. An important property that has not been explored is the timescale of elastic recoil, a parameter that is critical for fibrin’s mechanical function and places a temporal constraint on molecular models of fiber elasticity. Using high-frame-rate imaging and atomic force microscopy-based nanomanipulation, we measured the recoil dynamics of individual fibrin fibers and found that the recoil was orders of magnitude faster than anticipated from models involving protein refolding. We also performed steered discrete molecular-dynamics simulations to investigate the molecular origins of the observed recoil. Our results point to the unstructured αC regions of the otherwise structured fibrin molecule as being responsible for the elastic recoil of the fibers.     

ZmGA3ox2, a candidate gene for a major QTL,qPH3.1, for plant height in maize

Maize plant height is closely associated with biomass, lodging resistance and grain yield. Determining the genetic basis of plant height by characterizing and cloning plant height genes will guide the genetic improvement of crops. In this study, a quantitative trait locus (QTL) for plant height, qPH3.1, was identified on chromosome 3 using populations derived from a cross between Zong3 and its chromosome segment substitution line, SL15. The plant height of the two lines was obviously different, and application of exogenous gibberellin A₃ removed this difference. QTL mapping placed qPH3.1 within a 4.0 cM interval, explaining 32.3% of the phenotypic variance. Furthermore, eight homozygous segmental isolines (SILs) developed from two larger F₂ populations further narrowed down qPH3.1 to within a 12.6 kb interval. ZmGA3ox2, an ortholog of OsGA3ox2, which encodes a GA3 β‐hydroxylase, was positionally cloned. Association mapping identified two polymorphisms in ZmGA3ox2 that were significantly associated with plant height across two experiments. Quantitative RT‐PCR showed that SL15 had higher ZmGA3ox2 expression relative to Zong3. The resultant higher GA₁ accumulation led to longer internodes in SL15 because of increased cell lengths. Moreover, a large deletion in the coding region of ZmGA3ox2 is responsible for the dwarf mutant d1‐6016. The successfully isolated qPH3.1 enriches our knowledge on the genetic basis of plant height in maize, and provides an opportunity for improvement of plant architecture in maize breeding.     

New antifungal scaffold derived from a natural pharmacophore: Synthesis of α-methylene-γ-butyrolactone derivatives and their antifungal activity against Colletotrichum lagenarium

Thirty new and thirty-four known analogues were designed and synthesized to improve the potential use of the α-methylene-γ-butyrolactone ring, a natural pharmacophore. All structures were confirmed by ¹H and ¹³C NMR, MS, and single-crystal X-ray diffraction analyses. The results of antifungal and cytotoxic activity indicated that the synthesized analogues showed significant inhibitory activity and limited selectivity. Compound 45 exhibited the highest antifungal activity with IC₅₀ = 22.8 μM but moderate cytotoxic activity with IC₅₀ = 28.5 μM (against BGC823 cell line) and 7.7 μM (against HeLa cell line). Analysis of structure–activity relationships revealed that the incorporation of an aromatic ring into the β, γ positions of the lactone ring improved antifungal activity, and that the introduction of electron-withdrawing groups into the aromatic rings increased the activity compared with electron-donating groups. The above results identified 4-phenyl-3-phenyl-2-methylenebutyrolactone (33) as a lead scaffold for discovering and developing novel and improved crop-protection agents.     

Impact of GC content on gene expression pattern in chicken

Background

GC content varies greatly between different genomic regions in many eukaryotes. In order to determine whether this organization named isochore organization influences gene expression patterns, the relationship between GC content and gene expression has been investigated in man and mouse. However, to date, this question is still a matter for debate. Among the avian species, chicken (Gallus gallus) is the best studied representative with a complete genome sequence. The distinctive features and organization of its sequence make it a good model to explore important issues in genome structure and evolution.

Methods

Only nuclear genes with complete information on protein-coding sequence with no evidence of multiple-splicing forms were included in this study. Chicken protein coding sequences, complete mRNA sequences (or full length cDNA sequences), and 5^′ untranslated region sequences (5^′ UTR) were downloaded from Ensembl and chicken expression data originated from a previous work. Three indices i.e. expression level, expression breadth and maximum expression level were used to measure the expression pattern of a given gene. CpG islands were identified using hgTables of the UCSC Genome Browser. Correlation analysis between variables was performed by SAS Proprietary Software Release 8.1.

Results

In chicken, the GC content of 5^′ UTR is significantly and positively correlated with expression level, expression breadth, and maximum expression level, whereas that of coding sequences and introns and at the third coding position are negatively correlated with expression level and expression breadth, and not correlated with maximum expression level. These significant trends are independent of recombination rate, chromosome size and gene density. Furthermore, multiple linear regression analysis indicated that GC content in genes could explain approximately 10% of the variation in gene expression.

Conclusions

GC content is significantly associated with gene expression pattern and could be one of the important regulation factors in the chicken genome.     

10种棘豆属植物的trnL-F序列及其分子系统学研究

选择内蒙古27个样地采集的10种棘豆属植物54个单株,提取样品的基因组DNA,对其叶绿体trnL-F序列进行扩增、测序,所得序列利用ClustalX软件进行对位排列,并用MEGA5.0软件采用最大似然法构建系统发育树,以探讨棘豆属的种间关系与系统进化.结果显示:(1)10种棘豆属trnL-F的变异位点54个,信息位点46个,种间碱基差异百分率为1.9％,GC含量变化范围在30.69％～31.50％之间.(2)棘豆属与黄芪属各为一支,自展支持率达99％,支持棘豆属植物为单系起源.(3)系统树中小花棘豆的样本自成一支,为相对独立进化;多叶棘豆、砂珍棘豆和黄毛棘豆的样本相互混杂,表明亲缘关系很近,从而支持《内蒙古植物志》将三者归入真棘豆亚属轮叶棘豆组的观点.(4)刺叶柄棘豆的样本不同样地形成2个分支,对其亚属水平上的分类需进一步探讨.(5)缘毛棘豆与阴山棘豆的样本聚成一支,支持将二者归入矮生棘豆组.研究表明,trnL-F序列可为棘豆属下种间系统发育关系研究提供分子证据.     

Molecular and pathogenic characterization of new Xanthomonas oryzae pv. oryzae strains from the coastline region of Fangchenggang city in China

Virulence assays and DNA polymorphism analyses were used to characterize 33 Xanthomonas oryzae pv. oryzae (Xoo) strains collected from the coastline region of Fangchenggang city in China. Two new pathogenic races (FXP1 and FXP2), were determined by leaf-clipping inoculation of 12 near-isogenic International Rice-Bacterial Blight (IRBB) rice lines, each containing a single resistance gene. Race FXP1 consisted of twenty-eight strains that were incompatible on IRBB5 and IRBB7, while race FXP2 included five strains that were incompatible on IRBB5 and IRBB7 and moderately virulent on IRBB8 containing the xa8 gene. Restriction fragment length polymorphism (RFLP) analysis revealed that each probe of avrXa10 and IS1112 resolved two haplotypes. In a dendrogram generated from the combined RFLP data, the 33 Xoo strains were resolved into two clusters. There was a weak correlation (r = 0.53) between race and haplotype. All of the rice cultivars planted in the coastline region of Fangchenggang city were susceptible to the representative Xoo strains tested above. However, we found that four rice cultivars used as breeding materials in the laboratory could fully resist infection by the Xoo strains, suggesting that the isolated Xoo strains could be used to detect resistant rice cultivars suitable for planting in the local rice field.