鞘脂在植物-真菌互作中的分子调控机制研究进展

鞘脂是细胞生物膜结构的重要组分, 鞘脂及其代谢产物参与许多重要的信号转导过程。在植物-真菌互作中, 植物鞘脂的主要作用是诱导细胞发生程序性死亡; 真菌鞘脂既能引起植物死亡, 也能诱导植物产生抗病性。该文总结了植物和真菌鞘脂的结构及代谢特点, 综述了鞘脂参与调控植物-真菌互作的分子机制研究进展, 并展望了植物-真菌共生关系中鞘脂作用的研究方向。     

植物鞘脂的结构、代谢途径及其功能

众所周知,鞘脂是生物膜结构的重要组成成分,随着鞘脂在动物和酵母中的深入研究发现,鞘脂及其代谢产物是一类很重要的活性分子,它们参与调节细胞的生长、分化、衰老和细胞程序性死亡等许多重要的信号转导过程。鞘脂在植物中的研究最近几年才开始,植物鞘脂的功能还不十分清楚。最近的研究发现,鞘脂及其代谢产物在植物中也起着很重要的信号分子作用。该文详细总结了鞘脂在植物中的结构、代谢途径和主要生物学功能,并结合实验室的工作对植物鞘脂的功能研究进行了展望。     

植物鞘脂的结构、代谢途径及其功能

众所周知, 鞘脂是生物膜结构的重要组成成分, 随着鞘脂在动物和酵母中的深入研究发现, 鞘脂及其代谢产物是一类很重要的活性分子, 它们参与调节细胞的生长、分化、衰老和细胞程序性死亡等许多重要的信号转导过程。鞘脂在植物中的研究最近几年才开始, 植物鞘脂的功能还不十分清楚。最近的研究发现, 鞘脂及其代谢产物在植物中也起着很重要的信号分子作用。该文详细总结了鞘脂在植物中的结构、代谢途径和主要生物学功能, 并结合实验室的工作对植物鞘脂的功能研究进行了展望。     

鞘脂代谢及其相关疾病研究进展

近年对鞘脂代谢及其产物的研究越来越多.鞘脂及其代谢产物不仅是构成细胞膜的重要结构分子,而且参与调节细胞的生长、分化、衰老和细胞程序性死亡等许多重要的信号转导过程,使细胞产生各种不同的生物学功能.该文综述了鞘脂代谢途径的重要酶,鞘脂及其代谢产物的功能,以及它们与相关疾病的研究进展,并就其存在的问题和今后可能的研究方向做出展望.为鞘脂代谢的过程和鞘脂相关疾病的生理病理学研究提供重要的理论依据.     

植物防御素结构与功能及其抗真菌机制研究进展

植物防御素是一类分子量约为5 kD的阳离子肽,是植物内免疫系统的主要成分之一,参与了多种植物生理生化活动。植物防御素含8个保守半胱氨酸,形成4对链内二硫键来稳定其3条反向平行的β折叠片和1个α螺旋,构成所谓的Csαβ模体结构。植物防御素具有抑制真菌和细菌生长、抑制酶的活性、抑制癌细胞增殖和作为离子通道阻断剂等功能。植物防御素抗真菌机制比较复杂,但它可能首先必须和真菌细胞质膜外侧的鞘脂等复杂脂类结合,引起真菌细胞发生一系列的反应,包括细胞膜通透性增强、胞内活性氧水平增高和诱导真菌细胞凋亡等。但是植物防御素详细的抗真菌机制及其在真菌细胞内作用靶点等有待于深入研究。综述了近年来植物防御素结构、功能及其抗真菌机制等方面的最新研究进展。     

miRNA介导植物-微生物互作中的调控作用及其研究进展北大核心CSCD

微生物与植物之间存在错综复杂的双向交流和串扰,植物与病原微生物互作直接影响寄主植物的生存状况,而植物和益生微生物互作则有利于宿主的生长和健康,共生微生物也会从中受益。不管是病原微生物还是有益微生物进入植物体内,植物miRNA都会迅速做出响应,同时微生物也可以产生miRNA样RNA(miRNA-likeRNA,milRNA)影响植物健康,可见miRNA(或milRNA)是植物与微生物互作过程中迅速响应的重要媒介分子,其内在机制研究近年来取得了许多进展。文中概述了植物-病原微生物、植物-益生微生物互作中miRNA的调控作用,重点阐述了植物miRNA在植物-病原微生物互作过程中对寄主植物抗病性的调控作用和植物-益生微生物互作过程中对宿主植物生长发育及代谢的调控,以及真菌milRNA对寄主植物的跨界调控作用。     

神经酰胺与细胞凋亡

细胞凋亡 (apoptosis) 又称细胞的程序性死亡,参与机体许多生理和病理过程.近年来的研究表明细胞凋亡与鞘脂质代谢有密切的关系,鞘磷脂的水解产物神经酰胺作为脂质第二信使在诱导和抑制细胞凋亡中起着重要的作用.     

真菌草酸的代谢和作用研究进展

草酸(oxalic acid)是一种重要的生物代谢产物,广泛分布于植物、动物和微生物中,在不同的生命体中发挥重要功能。本文回顾了国内外关于真菌草酸的相关研究进展。许多真菌能够分泌草酸,包括植物病原真菌、食药用真菌及工业真菌等。草酸作为一种简单的二元羧酸,在真菌中主要通过三羧酸循环途径、乙醛酸循环途径和草酰乙酸途径合成。草酸是真菌产生的一种重要的生物因子,能够影响真菌的生长与发育,还能够通过毒素作用、酸化寄主组织环境、参与细胞壁降解和诱导活性氧产生等作用方式,在真菌与寄主植物的互作中发挥作用,也在真菌的生活史和侵染循环中发挥重要的生物学和病理学作用。本文从草酸的理化特性、代谢途径、产草酸的真菌种类、草酸的作用和草酸相关基因功能等方面进行综述,并对未来真菌草酸研究应关注的问题提出了建议。     

植物-内生真菌共生体对昆虫种群的影响

植物内生真菌与植食性昆虫共用寄主植物作为食物、能量来源及栖息场所,三者之间的互作关系复杂多变,在生物种群控制、生物进化和植物生产中发挥重要作用.从植物-内生真菌共生体、内生真菌对植食性昆虫与多级营养层的影响,及内生真菌抗虫代谢产物等方面概括了内生真菌-植物-昆虫相互关系的研究进展,建议将植物内生真菌纳入植物生态学、昆虫生态学和作物病虫害控制的范畴内.     

真菌鞘脂代谢及其与抗真菌药物关系研究进展

鞘脂是真核细胞中普遍存在的成分,它在真核细胞的胞吞、胞饮、信号转导、细胞的生长、凋亡、分化、衰老等过程中起着非常重要的作用.该文论述了真菌鞘脂代谢的途径及参与其合成的相关酶和基因,并比较了真菌与哺乳动物鞘脂代谢途径的不同,旨在为研究新型无公害抗真菌药物提供理论依据.     

Translocation of cytoplasm and nucleus to fungal penetration sites is associated with depolymerization of microtubules and defence gene activation in infected, cultured parsley cells.

We describe a novel system of reduced complexity for analysing molecular plant-fungus interactions. The system consists of suspension-cultured parsley (Petroselinum crispum) cells infected with a phytopathogenic fungus (Phytophthora infestans) which adheres to a coated glass plate and thus immobilizes the plant cells for live microscopy. Conventional light and electron microscopy as well as time-lapse video microscopy confirmed the virtual identity of fungal infection structures and of several characteristic early plant defence reactions in the cultured cells and whole-plant tissue. Using this new system to approach previously unresolved questions, we made four major discoveries: (i) rapid translocation of plant cell cytoplasm and nucleus to the fungal penetration site was associated with local depolymerization of the microtubular network; (ii) the directed translocation was dependent on intact actin filaments; (iii) a typical plant defence-related gene was activated in the fungus-invaded cell; and (iv) simultaneous activation of this gene in adjacent, non-invaded cells did not require hypersensitive death of the directly affected cell.     

Building a mycorrhizal cell: How to reach compatibility between plants and arbuscular mycorrhizal fungi

Abstract

Arbuscular mycorrhizal fungi occur throughout the majority of ecosystems supporting host plant nutrition. Recent findings describe the accommodation of the fungus by the root cell as a crucial step for compatibility between the partners. We discuss here the novel aspects of cellular plant-fungus interactions, with a particular attention to the interface compartment, the unique apoplastic space hosting intracellular fungal structures. The main features of arbuscular mycorrhizal colonization are examined and recent information in the field of plant and fungal cell responses during the establishment of the symbiosis is discussed. Differences between the colonization of root epidermal and cortical tissues are discussed, highlighting the growing interest in the role of epidermal cells during the first and decisive steps of the symbiosis. New approaches such as root organ cultures, in vivo observations, GFP tagging and mutant plant analysis are commented on and information from these is compared with that gained from more traditional methods. In particular, the use of plant mutants is depicted as a powerful tool for dissecting and understanding the genetic and cellular aspects of plant/fungus compatibility. Finally, perspectives in this field are outlined through the application of these approaches to the currently unanswered questions.     

Very long chain fatty acid and lipid signaling in the response of plants to pathogens

Recent findings indicate that lipid signaling is essential for plant resistance to pathogens. Besides oxylipins and unsaturated fatty acids known to play important signaling functions during plant-pathogen interactions, the very long chain fatty acid (VLCFA) biosynthesis pathway has been recently associated to plant defense through different aspects. VLCFAs are indeed required for the biosynthesis of the plant cuticle and the generation of sphingolipids. Elucidation of the roles of these lipids in biotic stress responses is the result of the use of genetic approaches together with the identification of the genes/proteins involved in their biosynthesis. This review focuses on recent observations which revealed the complex function of the cuticle and cuticle-derived signals, and the key role of sphingolipids as bioactive molecules involved in signal transduction and cell death regulation during plant-pathogen interactions.Key words: very long chain fatty acids (VLCFAs), plant-pathogen interactions, lipid signaling, sphingolipids, epicuticular waxes, lipid rafts, cuticle, plant defense     

Sphingolipids in inflammation: roles and implications

Sphingolipids, historically described as potential reservoirs for bioactive lipids, presently define a new family of cellular mediators, joining the well-established glycerolipid-derived mediators of signal transduction such as diacylglycerol, phosphatidylinositides, and eicosanoids. Sphingolipid metabolism is clearly involved in the regulation of cell growth, differentiation, and programmed cell death. Indeed, a majority of the greater than four thousand studies conducted on sphingolipids during the past five years were investigations of the role of sphingolipids as cellular bioregulators. Studies spanning more than a decade have shown multiple interactions and intersections of the sphingolipid-mediated pathways and the eicosanoid pathway. This review will discuss the emerging mechanisms by which sphingolipids induce inflammatory responses via the eicosanoid pathway in addition to linking previous literature on sphingolipids and inflammation with newer findings of distinct roles for sphingosine-1-phosphate in regulating cyclooygenase-2 and ceramide-1-phosphate in the regulation of cytosolic phospholipase A2alpha. Finally, the relationship between bioactive sphingolipids and inflammation is discussed.     

Cell Death Control: The Interplay of Apoptosis and Autophagy in the Pathogenicity of Sclerotinia sclerotiorum

Programmed cell death is characterized by a cascade of tightly controlled events that culminate in the orchestrated death of the cell. In multicellular organisms autophagy and apoptosis are recognized as two principal means by which these genetically determined cell deaths occur. During plant-microbe interactions cell death programs can mediate both resistant and susceptible events. Via oxalic acid (OA), the necrotrophic phytopathogen Sclerotinia sclerotiorum hijacks host pathways and induces cell death in host plant tissue resulting in hallmark apoptotic features in a time and dose dependent manner. OA-deficient mutants are non-pathogenic and trigger a restricted cell death phenotype in the host that unexpectedly exhibits markers associated with the plant hypersensitive response including callose deposition and a pronounced oxidative burst, suggesting the plant can recognize and in this case respond, defensively. The details of this plant directed restrictive cell death associated with OA deficient mutants is the focus of this work. Using a combination of electron and fluorescence microscopy, chemical effectors and reverse genetics, we show that this restricted cell death is autophagic. Inhibition of autophagy rescued the non-pathogenic mutant phenotype. These findings indicate that autophagy is a defense response in this necrotrophic fungus/plant interaction and suggest a novel function associated with OA; namely, the suppression of autophagy. These data suggest that not all cell deaths are equivalent, and though programmed cell death occurs in both situations, the outcome is predicated on who is in control of the cell death machinery. Based on our data, we suggest that it is not cell death per se that dictates the outcome of certain plant-microbe interactions, but the manner by which cell death occurs that is crucial.     

Sphingolipid long-chain base hydroxylation is important for growth and regulation of sphingolipid content and composition in Arabidopsis

Sphingolipids are structural components of endomembranes and function through their metabolites as bioactive regulators of cellular processes such as programmed cell death. A characteristic feature of plant sphingolipids is their high content of trihydroxy long-chain bases (LCBs) that are produced by the LCB C-4 hydroxylase. To determine the functional significance of trihydroxy LCBs in plants, T-DNA double mutants and RNA interference suppression lines were generated for the two Arabidopsis thaliana LCB C-4 hydroxylase genes Sphingoid Base Hydroxylase1 (SBH1) and SBH2. These plants displayed reductions in growth that were dependent on the content of trihydroxy LCBs in sphingolipids. Double sbh1 sbh2 mutants, which completely lacked trihydroxy LCBs, were severely dwarfed, did not progress from vegetative to reproductive growth, and had enhanced expression of programmed cell death associated-genes. Furthermore, the total content of sphingolipids on a dry weight basis increased as the relative amounts of trihydroxy LCBs decreased. In trihydroxy LCB-null mutants, sphingolipid content was approximately 2.5-fold higher than that in wild-type plants. Increases in sphingolipid content resulted from the accumulation of molecular species with C16 fatty acids rather than with very-long-chain fatty acids, which are more commonly enriched in plant sphingolipids, and were accompanied by decreases in amounts of C16-containing species of chloroplast lipids. Overall, these results indicate that trihydroxy LCB synthesis plays a central role in maintaining growth and mediating the total content and fatty acid composition of sphingolipids in plants.     

Diversity and classification of mycorrhizal associations

Most mycorrhizas are 'balanced' mutualistic associations in which the fungus and plant exchange commodities required for their growth and survival. Myco-heterotrophic plants have 'exploitative' mycorrhizas where transfer processes apparently benefit only plants. Exploitative associations are symbiotic (in the broad sense), but are not mutualistic. A new definition of mycorrhizas that encompasses all types of these associations while excluding other plant-fungus interactions is provided. This definition recognises the importance of nutrient transfer at an interface resulting from synchronised plant-fungus development. The diversity of interactions between mycorrhizal fungi and plants is considered. Mycorrhizal fungi also function as endophytes, necrotrophs and antagonists of host or non-host plants, with roles that vary during the lifespan of their associations. It is recommended that mycorrhizal associations are defined and classified primarily by anatomical criteria regulated by the host plant. A revised classification scheme for types and categories of mycorrhizal associations defined by these criteria is proposed. The main categories of vesicular-arbuscular mycorrhizal associations (VAM) are 'linear' or 'coiling', and of ectomycorrhizal associations (ECM) are 'epidermal' or 'cortical'. Subcategories of coiling VAM and epidermal ECM occur in certain host plants. Fungus-controlled features result in 'morphotypes' within categories of VAM and ECM. Arbutoid and monotropoid associations should be considered subcategories of epidermal ECM and ectendomycorrhizas should be relegated to an ECM morphotype. Both arbuscules and vesicles define mycorrhizas formed by glomeromycotan fungi. A new classification scheme for categories, subcategories and morphotypes of mycorrhizal associations is provided.     

Plasma membrane-cell wall adhesion is required for expression of plant defense responses during fungal penetration

Fungal pathogens almost invariably trigger cell wall-associated defense responses, such as extracellular hydrogen peroxide generation and callose deposition, when they attempt to penetrate either resistant or susceptible plant cells. In the current study, we provide evidence that the expression of these defenses is dependent on adhesion between the plant cell wall and the plasma membrane. Peptides containing an Arg-Gly-Asp (RGD) motif, which interfered with plasma membrane-cell wall adhesion as shown by the loss of the thin plasma membrane-cell wall connections known as Hechtian strands, reduced the expression of cell wall-associated defense responses during the penetration of nonhost plants by biotrophic fungal pathogens. This reduction was associated with increased fungal penetration efficiency. Neither of these effects was seen after treatment with similar peptides lacking the RGD motif. Disruption of plant microfilaments had no effect on Hechtian strands but mimicked the effect of RGD peptides on wall defenses, suggesting that the expression of cell wall-associated defenses involves communication between the plant cell wall and the cytosol across the plasma membrane. To visualize the state of the plasma membrane-cell wall interaction during fungal penetration, we observed living cells during sucrose-induced plasmolysis. In interactions that were characterized by the early expression of cell wall-associated defenses, there was no change, or an increase, in plasma membrane-cell wall adhesion under the penetration point as the fungus grew through the plant cell wall. In contrast, for rust fungus interactions with host plants, there was a strong correlation between a lack of cell wall-associated defenses and a localized decrease in plasma membrane-cell wall adhesion under the penetration point. Abolition of this localized decreased adhesion by previous inoculation with a fungus that increased plasma membrane-cell wall adhesion resulted in reduced penetration by the rust fungus and induction of cell wall-associated defenses. These results suggest that rust fungi may induce a decrease in plasma membrane-cell wall adhesion as a means of disrupting the expression of nonspecific defense responses during penetration of host cells.