Essentials of Tritium Planigraphy

The method is based on labeling organic compounds, including peptides and proteins, by bombarding the target (usually prepared by spray freezing the protein solution on the reactor wall chilled with liquid nitrogen) in a vacuum chamber with a beam of “hot” tritium atoms (generated through catalytic dissociation of molecular tritium at the surface of a tungsten filament heated to 2,000 K) (1). The resulting preparations are labeled to high specific activity and retain their structure and bioactivity (2、3). Labeling takes place by single collisions of tritium atoms with the target, and the intramolecular label distribution among amino acid residues is governed by their steric accessibility in the macromolecule (4). This crucial point has been verified with a quite broad range of objects (5) including complex supramolecular structures such as viruses (6、7) and ribosomes (8).

1、Shishkov A V, Filatov E S, Simonov E F, Gol’danskii V I, Nesmejanov A N. Dokl Akad Nauk SSSR.1976;228:1237–1239. [PubMed]

2、Ulmasov Ch A, Nesterova M V, Poletaev A I, Severin E S. Biochemistry (Moskow) 1981;46:1609–1612.

3、Yusupov M M, Spirin A S. Methods Enzymol. 1988;164:426–439. [PubMed]

4、Gol’danskii V I, Rumyantsev Yu M, Shishkov A V, Baratova L A, Belyanova L P. Mol Biol.1982;16:528–534.

5、Shishkov A V, Baratova L A. Russian Chem Rev. 1994;9:781–796.

6、Gol’danskii V I, Kashirin I A, Shishkov A V, Baratova L A, Grebenshchikov N I. J Mol Biol.1988;201:567–574. [PubMed]

7、Baratova L A, Grebenshchikov N I, Dobrov E N, Gedrovich A V, Kashirin I A, Shishkov A V, Efimov A V, Jarvekulg L, Radavsky Yu L, Saarma M. Virology. 1992;188:175–180. [PubMed]

8、Agafonov D E, Kolb V A, Spirin A S. Proc Natl Acad Sci USA. 1997;94:12892–12897.[PMC free article] [PubMed]

Fear of Fungi.

Research pubished by Matthew Fisher and colleges indicates that more fungi have been emerged as infectious diseases, and are threatening diversity of ecosystems and agricultural productivity.

more detail can be found here:
http://fungalgenomes.org/blog/2012/04/fear-of-fungi/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+fungalcompgenomics+%28The+Hyphal+Tip%29

Figures from http://www.nature.com/nature/journal/v484/n7393/full/nature10947.html

植物抵御DNA病毒体系

中国科学院遗传与发育生物学研究所利用新近在细菌中发现的适应性免疫系统特异识别病毒和外源DNA特性，将该成果引入植物，在植物中建立一套DNA病毒防御体系。

双生病毒是存在于植物中惟一一类具有孪生颗粒形态的单链DNA病毒，也是目前已知的最大单链DNA病毒家族，该病毒在单子叶和双子叶植物中具有广泛的宿主。目前已报道双生病毒能够感染玉米、棉花、番茄、木薯、甜菜等重要农作物，对农业生产危害极大。传统抗病机理的研究主要基于对病毒基因功能的分析及宿主病毒互作机理的解析，但目前在育种中的应用还比较有限。

中科院遗传与发育生物学研究所此次以甜菜严重曲顶病毒为模式病毒，通过实验证明：向植物中引入高效的适应性免疫系统，能有效地抑制甜菜严重曲顶病毒在寄主植物中的积累。此外，靶位点的突变分析表明该系统能特异性切割病毒DNA，利用此方法培育抗病毒植物，不必基于病毒基因功能的深入了解，简单易行，通用性强。因此，该研究对培育抗DNA病毒作物具有指导意义。

来源：北京日报

植物基因沉默抵抗双生病毒新机制

植物转录后基因沉默(PTGS)和转录水平基因沉默(TGS)是其抵抗病毒以及其它外源基因的入侵的一套基于核酸的免疫系统。该系统能够监测、发现并及时清除病毒或外源基因的表达产物，产生对病毒等多种病原的抗性。近几年来，生物体如何在利用该机制抵抗病毒等病原入侵的同时，保持内源基因表达的稳定性是一个热点科学问题。

　　在最近20年内，由烟粉虱传播的双生病毒(Geminivirus)引起的病害已经从由局部发生衍变成为最重要的全球性植物病害之一，严重危害玉米、小麦、棉花、木薯、番茄等重要作物和观赏植物。例如仅木薯花叶病毒病一项，每年在非洲撒哈拉地区造成的经济损失就高达12-23亿美元之巨。由于缺乏有效抗病基因及种质资源，目前对双生病毒病害尚无环保高效的防治方法， 仍主要依赖通过对介体昆虫的化学防治来实现病毒的预防与控制。中国科学院微生物研究所叶健青年研究组于2014年双生病毒与寄主植物、传毒介体昆虫烟粉虱三者互作取得重要进展的基础上（Li et al., Plant Cell 2014），同美国洛克菲勒大学蔡南海教授实验室合作，从植物对木薯花叶病毒的感病基因入手，在植物如何抵御双生病毒感染和病毒与植物基因沉默互作研究中，又鉴定了两类植物对木薯花叶病毒的易感基因，揭示了高等植物中保守的抵抗双生病毒病害的新机制，相关的工作已经发表在PLoS Pathogens 和Scientific Reports 上。这两类双生病毒的植物感病基因的发现，为发展广谱高效的植物抗双生病毒病害策略奠定了理论基础，并为通过基因组编辑技术获得增强作物抗病性提供了有效的分子靶标。

　　该团队研究人员利用遗传学、细胞学、分子生物学和病毒学等研究手段，首次发现叶型发育干细胞决定因子AS2是双生病毒易感基因，并且在负调控植物细胞质PTGS中发挥重要功能。他们发现AS2参与了植物细胞质mRNA decapping途径，抑制PTGS和植物对双生病毒的抗性。植物内源基因转录具有发生PTGS的潜在的风险，细胞质mRNA decapping途径在真核生物中非常保守，是重要的RNA降解途径，具有抑制PTGS的功能。而双生病毒通过促进AS2转录激活、AS2核质穿梭和增强decapping等策略，抑制植物PTGS的发生，增强其致病性。研究成果为发展高效防治双生病毒病害提供了新的靶点（PLoS Pathogens 2015, 11:e1005196），叶健为该文的第一作者和共同通讯作者，微生物所方荣祥研究员、叶健课题组的孙艳伟、赵平芝为共同作者。

　　 除PTGS外，TGS也对双生病毒抗性起到重要作用。该团队研究人员发现本生烟草(Nicotiana benthamiana)组蛋白甲基转移酶NbKYP和DNA甲基转移酶NbCMT3是TGS途径的重要因子，通过对双生病毒基因组进行甲基化修饰，限制病毒复制和转录等事件的发生。在NbKYP低表达的本生烟草中，植物和双生病毒基因组的CG和CHG甲基化均大幅度的降低，揭示了NbKYP在TGS中的新特点。研究发现本生烟草也存在负调控TGS的机制，而木薯花叶病毒可以通过激活负调控因子NbRAV2抑制NbKYP转录，从而抑制了本生烟草TGS的发生，进而促进了病毒的复制。相关论文已经被Scientific Reports 接收，叶健为该文的通讯作者，叶健课题组的孙艳伟和马永焕为共同第一作者，姚香梅为共同作者。

　　这两项研究工作得到了中国科学院战略性先导科技专项（B类）-“作物病虫害的导向性防控项目（XDB11040300）”、国家自然基金委优秀青年项目（31522046）和植物基因组学国家重点实验室经费的资助。

病毒复制复合体与磷脂酰乙醇胺

Plants, animals, and humans are threatened by positive-stranded RNA viruses, which are one of the major groups of intracellular pathogens. To support robust virus replication, these viruses subvert intracellular membranes and co-opt host proteins into virus-induced replication compartments. Tomato bushy stunt virus (TBSV) is a model virus used in yeast to dissect the roles of lipids and proteins in virus replication. In this work, the authors show that one of the two TBSV replication proteins interacts with the guanosine triphosphate (GTP)-bound Rab5 small GTPase, which allows the virus to take advantage of phosphatidylethanolamine (PE)-rich endosomes to build viral replication compartments consisting of peroxisomes. Peak level of TBSV replication depends on the co-opted abundant PE-rich Rab5-positive membranes in plants, too.
威胁人类、动物和植物的正单链RNA病毒是一类重要的细胞内病原物。为保证自身的复制，病毒必须需要同寄主互作，利用病毒的寄主来形成病毒诱导的复制复合体。下面的文章结果表明Tomato bushy stunt virus 复制蛋白通过与寄主TRab5 小GTPase互作来利用寄主富集磷脂酰乙醇胺的内体来构建病毒复制复合体。



Abstract

Positive-strand RNA viruses build extensive membranous replication compartments to support replication and protect the virus from antiviral responses by the host. These viruses require host factors and various lipids to form viral replication complexes (VRCs). The VRCs built by Tomato bushy stunt virus (TBSV) are enriched with phosphatidylethanolamine (PE) through a previously unknown pathway. To unravel the mechanism of PE enrichment within the TBSV replication compartment, in this paper, the authors demonstrate that TBSV co-opts the guanosine triphosphate (GTP)-bound active form of the endosomal Rab5 small GTPase via direct interaction with the viral replication protein. Deletion of Rab5 orthologs in a yeast model host or expression of dominant negative mutants of plant Rab5 greatly decreases TBSV replication and prevents the redistribution of PE to the sites of viral replication. We also show that enrichment of PE in the viral replication compartment is assisted by actin filaments. Interestingly, the closely related Carnation Italian ringspot virus, which replicates on the boundary membrane of mitochondria, uses a similar strategy to the peroxisomal TBSV to hijack the Rab5-positive endosomes into the viral replication compartments. Altogether, usurping the GTP-Rab5–positive endosomes allows TBSV to build a PE-enriched viral replication compartment, which is needed to support peak-level replication. Thus, the Rab family of small GTPases includes critical host factors assisting VRC assembly and genesis of the viral replication compartment.

老文章新讨论-系统性坏死与过敏性坏死（HR）

Komatsu等2010年在MPMI上面发表了题为Viral-Induced Systemic Necrosis in Plants Involves  Both Programmed Cell Death and the Inhibition  of Viral Multiplication, Which Are Regulated  by Independent Pathways 的文章，
文中在系统性坏死植物中发现类似于过敏性坏死反应的一些特性，例如PR1a, SGT1，RAR1等基因表达及其作用。但最终结论是系统性坏死和过敏性坏死反应都有PCD和抑制病毒繁殖的特点，但HR拥有自己特殊的途径。
怎么来看系统性坏死和过敏性坏死反应。

原文摘要：
Resistant plants respond rapidly to invading avirulent plant viruses by triggering a hypersensitive response (HR). An HR is accompanied by a restraint of virus multiplication and programmed cell death (PCD), both of which have been observed in systemic necrosis triggered by a successful viral infection. Here, we analyzed signaling pathways underlying the HR in resistance genotype plants and those leading to systemic necrosis. We show that systemic necrosis in Nicotiana benthamiana, induced by Plantago asiatica mosaic virus (PlAMV) infection, was associated with PCD, biochemical features, and gene expression patterns that are characteristic of HR. The induction of necrosis caused by PlAMV infection was dependent on SGT1, RAR1, and the downstream mitogen-activated protein kinase (MAPK) cascade involving MAPKKKα and MEK2. However, although SGT1 and RAR1 silencing led to an increased accumulation of PlAMV, silencing of the MAPKKKα-MEK2 cascade did not. This observation indicates that viral multiplication is partly restrained even in systemic necrosis induced by viral infection, and that this restraint requires SGT1 and RAR1 but not the MAPKKKα-MEK2 cascade. Similarly, although both SGT1 and MAPKKKα were essential for the Rx-mediated HR to Potato virus X (PVX), SGT1 but not MAPKKKα was involved in the restraint of PVX multiplication. These results suggest that systemic necrosis and HR consist of PCD and a restraint of virus multiplication, and that the latter is induced through unknown pathways independent from the former.