谷氨酸棒杆菌生产异亮氨酸辅因子策略及其基因组整合研究进展

L?异亮氨酸属于三大支链氨基酸,是人体8种必需氨基酸之一,广泛应用于食品、药品、保健品、化妆品等领域。目前,微生物发酵法是工业生产L?异亮氨酸的主要方法,其中谷氨酸棒杆菌（Corynebacterium glutamicum）是发酵生产L?异亮氨酸的优势菌株,然而随机诱变会使产量的提高能力达到饱和,难以得到更加高产的菌株,因此针对诱变菌株进行理性改造已成为进一步提高产量的主要方式;且随着遗传操作技术在谷氨酸棒杆菌中的应用与优化,代谢工程育种已逐渐取代传统的诱变育种。综述了谷氨酸棒杆菌中L?异亮氨酸的生物合成途径、代谢调控机制和理性改造L?异亮氨酸生产菌株的策略,并对辅助因子工程应用于理性改造及对谷氨酸棒杆菌基因组整合策略进行了系统阐述,以期为工业水平稳定生产L?异亮氨酸高产菌株的基因组整合策略提供参考依据。     

Regulation of germination by targeted mutagenesis of grain dormancy genes in barley

High humidity during harvest season often causes pre-harvest sprouting in barley (Hordeum vulgare). Prolonged grain dormancy prevents pre-harvest sprouting; however, extended dormancy can interfere with malt production and uniform germination upon sowing. In this study, we used Cas9-induced targeted mutagenesis to create single and double mutants in QTL FOR SEED DORMANCY 1 (Qsd1) and Qsd2 in the same genetic background. We performed germination assays in independent qsd1 and qsd2 single mutants, as well as in two double mutants, which revealed a strong repression of germination in the mutants. These results demonstrated that normal early grain germination requires both Qsd1 and Qsd2 function. However, germination of qsd1 was promoted by treatment with 3% hydrogen peroxide, supporting the notion that the mutants exhibit delayed germination. Likewise, exposure to cold temperatures largely alleviated the block of germination in the single and double mutants. Notably, qsd1 mutants partially suppress the long dormancy phenotype of qsd2, while qsd2 mutant grains failed to germinate in the light, but not in the dark. Consistent with the delay in germination, abscisic acid accumulated in all mutants relative to the wild type, but abscisic acid levels cannot maintain long-term dormancy and only delay germination. Elucidation of mutant allele interactions, such as those shown in this study, are important for fine-tuning traits that will lead to the design of grain dormancy through combinations of mutant alleles. Thus, these mutants will provide the necessary germplasm to study grain dormancy and germination in barley.     

基于分子模拟的河鲀毒素核酸适配体的连续优化*

河鲀毒素(tetrodotoxin, TTX)是一种生物碱类神经毒素,其中毒事件在世界范围内广泛发生,严重危害到人类健康,但尚无特效解毒剂,因此TTX的检测对食品安全领域有重大意义。为了得到更高效的TTX识别元件,在分子模拟指导下对SELEX筛选所得的核酸适配体TTX-27进行了连续优化。首先,使用Mini-hairpin结构替换阻碍TTX结合的茎环结构,使TTX更易与截短型适配体结合,然后将T39、C40碱基突变为C39、T40碱基,并对C39进行了2'-OH修饰,以增强结合区域碱基与TTX的氢键作用和范德瓦耳斯相互作用。微量热泳动(microscale thermophoresis, MST)实验证实,经截短、碱基突变和化学修饰的各适配体变体的亲和力均有提高,其中化学修饰变体TTX-D2-X-R结合TTX的解离平衡常数K_d为1.08 nmol/L,相较于TTX-27的亲和力提高了75.5倍。表明基于分子模拟的截短-突变-化学修饰是核酸适配体post-SELEX优化的有效途径,所得的适配体变体TTX-D2-X-R在TTX检测领域有着潜在的应用价值。     

Comparing membrane and spacer biofouling by Gram-negative Pseudomonas aeruginosa and Gram-positive Anoxybacillus sp. in forward osmosis

Bacteria of different Gram-types have inherently different outer cell structures, influencing cell surface properties and bacterial attachment. Dynamic biofouling experiments were conducted over four days in a bench-scale forward osmosis (FO) system with Gram-negative Pseudomonas aeruginosa or Gram-positive Anoxybacillus sp. Biofouling resulted in ～10% decline in FO permeate water flux and was found to be significant for Anoxybacillus sp. but not for P. aeruginosa. Additionally, a stronger permeate water flux decline for P. aeruginosa in experiments with a superhydrophilic feed spacer demonstrated that mitigation methods require testing with different bacterial Gram-types. It was found that although permeate water flux decline can be affected by bacterial Gram-type the stable performance under enhanced biofouling conditions highlights the potential of FO for wastewater reclamation.     

PPR蛋白在植物生长发育中的作用

PPR蛋白在陆生植物中属于最大的蛋白家族之一,其成员种类和数量均十分庞大。PPR蛋白主要的功能是通过在多种细胞器中进行定位从而参与细胞核和细胞器中特异单链RNA的转录后修饰和编辑,在植物生长发育的多个阶段均发挥着重要的作用。多数PPR蛋白编码基因的突变体呈现异常的发育表型,如胚胎致死、发育迟缓及绿化延迟等。对近年来植物PPR蛋白的分类、定位、RNA修饰的机制及其对植物生长发育影响进行了综述,并展望了植物PPR发挥功能区域和参与的调控网络研究。     

Methionine in proteins: The Cinderella of the proteinogenic amino acids

Methionine in proteins, apart from its role in the initiation of translation, is assumed to play a simple structural role in the hydrophobic core, in a similar way to other hydrophobic amino acids such as leucine, isoleucine, and valine. However, research from a number of laboratories supports the concept that methionine serves as an important cellular antioxidant, stabilizes the structure of proteins, participates in the sequence‐independent recognition of protein surfaces, and can act as a regulatory switch through reversible oxidation and reduction. Despite all these evidences, the role of methionine in protein structure and function is largely overlooked by most biochemists. Thus, the main aim of the current article is not so much to carry out an exhaustive review of the many and diverse processes in which methionine residues are involved, but to review some illustrative examples that may help the nonspecialized reader to form a richer and more precise insight regarding the role‐played by methionine residues in such processes.     

肠浒苔多糖的羧甲基化修饰及其抗氧化活性研究

该研究采用氢氧化钠-氯乙酸的化学反应体系制备羧甲基化肠浒苔多糖,以获得不同取代度的羧甲基化肠浒苔多糖,取代度的大小受氢氧化钠浓度、反应温度和反应时间的影响。结果表明:(1)当氢氧化钠浓度20%、反应温度60℃、反应时间3 h时,得到羧甲基化的最大取代度为0.781。(2)通过体外抗氧化来评价不同羧甲基化肠浒苔多糖的抗氧化活性。(3)当羧甲基化肠浒苔多糖的浓度为1.6 mg·mL~(-1)时,羧甲基化肠浒苔多糖清除羟基自由基、超氧阴离子自由基的能力分别为44.45%、51.98%,其清除DPPH自由基清除率和还原能力分别为16.75%、0.457 6。(4)与修饰前的相比,羟基自由基、超氧阴离子的清除能力均有较大幅度提高,羧甲基化修饰对肠浒苔多糖的DPPH自由基和还原力有减弱作用。以上结果表明,羧甲基化修饰引起的肠浒苔多糖的结构变化可以提高其抗氧化活性。     

Extensive allele‐level remodeling of histone methylation modification in reciprocal F1 hybrids of rice subspecies

Epigenetic mechanisms play a major role in heterosis, partly as a result of the remodeling of epigenetic modifications in F₁ hybrids. Based on chromatin immunoprecipitation‐sequencing (ChIP‐Seq) analyses, we show that at the allele level extensive histone methylation remodeling occurred for a subset of genomic loci in reciprocal F₁ hybrids of Oryza sativa (rice) cultivars Nipponbare and 93‐11, representing the two subspecies japonica and indica. Globally, the allele modification‐altered loci in leaf or root of the reciprocal F₁ hybrids involved ?12–43% or more of the genomic regions carrying either of two typical histone methylation markers, H3K4me3 (>21 000 genomic regions) and H3K27me3 (>11 000 genomic regions). Nevertheless, at the total modification level, the majority (from ?43 to >90%) of the modification‐altered alleles lay within the range of parental additivity in the hybrids because of concerted alteration in opposite directions, consistent with an overall attenuation of allelic differences in the modifications. Importantly, of the genomic regions that did show non‐additivity in total modification level by either marker in the two tissues of hybrids, >80% manifested transgressivity, which involved genes enriched in specific functional categories. Extensive allele‐level alteration of H3K4me3 alone was positively correlated with genome‐wide changes in allele‐level gene expression, whereas at the total level, both H3K4me3 and H3K27me3 remodeling, although affecting just a small number of genes, contributes to the overall non‐additive gene expression to variable extents, depending on tissue/marker combinations. Our results emphasize the importance of allele‐level analysis in hybrids to assess the remodeling of epigenetic modifications and their relation to changes in gene expression.