青贮乳酸菌类型和乳酸合成途径的研究进展

青贮是乳酸菌在厌氧环境下,分解可溶性糖,生成乳酸,降低环境pH,同时抑制有害菌和霉菌生长的一种储存方法,其中乳酸发酵途径主要包括同型乳酸发酵和异型乳酸发酵两种,乳酸菌在发酵过程中起关键作用。已有的研究结果表明,乳酸杆菌属、片球菌菌属和魏斯氏菌属等是青贮过程中的主要优势菌属,是发酵中后期的优势功能微生物类群。目前对青贮过程的研究处于基础阶段,相关的研究主要集中在青贮中微生物群落结构、开发外源添加剂以及评价发酵品质等方面。文章从乳酸发酵途径、优良菌株的筛选和改造、关键基因以及乳酸合成调控等方面进行综述,为从菌株水平和分子水平调控青贮乳酸发酵途径、改善发酵品质,提供一定的参考价值。

Regulation of Anthocyanin during Storage Root Development Stage in Sweet Potato(Ipomoea batatas(L.) Lam.)

Anthocyanin accumulation during storage root development in purple-fleshed sweet potato was analyzed by detection of anthocyanin concentration, accumulation rate and the expression pattern of anthocyanin biosynthetic genes by semi-quantitative RT-PCR. Anthocyanin concentration in sweet potato cvs Jishu 18 and Ayamurasaki increased steadily during storage root development stage. The accumulation rate in two genotypes peaked at 50 to 65 d after transplanting, and then declined rapidly. During storage root development of Ayamurasaki, the anthocyanin biosynthesis gene, IbCHS, was constitutively expressed, the genes IbF3H, IbDFR, IbANS were induced steadily, reaching a maximum at the later stage of root thickening, and IbPAL steadily decreased. Therefore, the mechanism of anthocyanin accumulation differed between the two cultivars, and anthocyanin biosynthesis was regulated through regulation of its synthetic enzymes.

Atg5 regulates late endosome and lysosome biogenesis

Autophagy is an evolutionarily conserved lysosome-based degradation process.Atg5 plays a very important role in autophagosome formation.Here we show that Atg5 is required for biogenesis of late endosomes and lysosomes in an autophagy-independent manner.In Atg5 cells,but not in other essential autophagy genes defecting cells,recycling and retrieval of late endosomal components from hybrid organelles are impaired,causing persistent hybrid organelles and defective formation of late endosomes and lysosomes.Defective retrieval of late endosomal components from hybrid organelles resulting from impaired recruitment of a component of V1-ATPase to acidic organelles blocks the pH-dependent retrieval of late endosomal components from hybrid organelles.Lowering the intracellular pH restores late endosome/lysosome biogenesis in Atg5 cells.Our data demonstrate an unexpected role of Atg5 and shed new light on late endosome and lysosome biogenesis.

JA-mediated transcriptional regulation of secondary metabolism in medicinal plants

Plants produce a wide spectrum of secondary metabolites that play critical roles in plant-environment interactions and against biotic and abiotic stresses. Moreover, many secondary metabolites have pharmaceu- tical efficacy for a wide range of diseases （cancer, malaria, etc.）. Controlled transcription of biosynthetic genes is one of the major mechanisms regulating sec- ondary metabolism in plants. Several transcription factor families such as MYC, MYB, WRKY and AP2/ERF have been found to be involved in the regulation of secondary metabolism in different medicinal plants. In addition, the biosynthesis and proper accumulation of secondary metabolites are also induced by signaling molecule jasmonic acid （JA）. This review provides an insight into JA signaling pathway and JA-mediated transcriptional regu- lation of secondary metabolism （vinblastine, nicotine, artemisinin, taxol and ginsenoside） in a range of medicinal plant species.

Cotton GhMYB7 is predominantly expressed in developing fibers and regulates secondary cell wall biosynthesis in transgenic Arabidopsis

The secondary cell wall in mature cotton fibers contains over 90%cellulose with low quantities of xylan and lignin.However,little is known regarding the regulation of secondary cell wall biosynthesis in cotton fibers.In this study,we characterized an R2R3-MYB transcription factor,Gh MYB7,in cotton.Gh MYB7 is expressed at a high level in developing fibers and encodes a MYB protein that is targeted to the cell nucleus and has transcriptional activation activity.Ectopic expression of Gh MYB7 in Arabidopsis resulted in small,curled,dark green leaves and also led to shorter inflorescence stems.A cross-sectional assay of basal stems revealed that cell wall thickness of vessels and interfascicular fibers was higher in transgenic lines overexpressing Gh MYB7 than in the wild type.Constitutive expression of Gh MYB7 in Arabidopsis activated the expression of a suite of secondary cell wall biosynthesis-related genes(including some secondary cell wall-associated transcription factors),leading to the ectopic deposition of cellulose and lignin.The ectopic deposition of secondary cell walls may have been initiated before the cessation of cell expansion.Moreover,Gh MYB7 was capable of binding to the promoter regions of At SND1 and At Ces A4,suggesting that Gh MYB7 may function upstream of NAC transcription factors.Collectively,these findings suggest that Gh MYB7 is a potential transcriptional activator,which may participate in regulating secondary cell wall biosynthesis of cotton fibers.

Neomycin biosynthesis is regulated positively by AfsA-g and NeoR in Streptomyces fradiae CGMCC 4.7387

Neomycins are a group of aminoglycoside antibiotics with both clinical and agricultural applications.To elucidate the regulatory mechanism of neomycin biosynthesis,we completed draft genome sequencing of a neomycin producer Streptomyces fradiae CGMCC 4.7387 from marine sediments,and the neomycin biosynthesis gene cluster was identified.Inactivation of the afsA-g gene encoding a γ-butyrolactone(GBL) synthase in S.fradiae CGMCC 4.7387 resulted in a significant decrease of neomycin production.Quantitative RT-PCR analysis revealed that the transcriptional level of neoR and the aphA-neoGH operon were reduced in the afsA-g::aac(3)Ⅳ mutant.Interestingly,a conserved binding site of AdpA,a key activator in the GBL regulatory cascade,was discovered upstream of neoR,a putative regulatory gene encoding a protein with an ATPase domain and a tetratricopeptide repeat domain.When neoR was inactivated,the neomycin production was reduced about 40%in comparison with the WT strain.Quantitative RT-PCR analysis revealed that the transcriptional levels of genes in the aphA-neoGH operon were reduced clearly in the neoR::aac(3)Ⅳ mutant.Finally,the titers of neomycin were improved considerably by overexpression of qfsA-gand neoR in S.fradiae CGMCC 4.7387.