磷脂酸在植物中的第二信使功能

磷脂酸(phosphatidic acid, PA)是植物中重要的细胞内信号分子,被称为“脂质第二信使”,特别是几个PA的作用靶点已被克隆和鉴定.植物体内PA的产生可以通过磷脂酶C和D两条信号通路,前者与甘油二酯激酶协同作用.PA主要由各种生物和非生物胁迫诱导产生,磷脂酸的水平在各种胁迫处理后的几分钟内增强.增强的信号水平通过PA的磷酸化形成甘油二酯焦磷酸而被迅速减弱.本文就PA产生的磷脂酶信号通路,PA在各种胁迫诱导下的产生,PA的作用靶点和作用机理及在植物中的功能等几个方面进行综述.     

植物PLC-DGK/PA途径介导的渗透胁迫应答反应

肌醇磷脂依赖的磷脂酶C(PLC)是经典肌醇磷脂信号系统的重要组分,它分解二磷酸磷脂酰肌醇分子(PIP2)产生双信使IP3和DAG分子。动物细胞中DAG激活蛋白激酶C(PKC)参与调节多种细胞功能。植物基因组中缺乏PKC的同源序列,DAG被二酰甘油激酶(DGK)进一步磷酸化形成磷脂酸(PA),形成新的植物特有的第二信使分子。酶蛋白PLC和DGK及其作用的底物和产物形成植物特色的信号途径,该信号途径在植物对非生物和生物胁迫的反应中发挥重要作用。该文从蛋白信号分子的表达特征和脂质信号分子的含量变化等两个方面综述了植物特色的肌醇信号途径PLC-DGK/PA在应答渗透胁迫反应中的作用。除了PLC-DG活性外,PA也可由磷脂酶D(PLD)产生。该文还对两种途径产生的PA进行了讨论。     

植物甘油二酯激酶(DGK)信号转导作用

甘油二酯激酶(DGK)是产生信号分子磷脂酸(PA)途径中的一个磷酸激酶,它与磷脂酶C(PLC)协同作用产生PA,磷脂酶D(PLD)途径也是PA产生的一个来源。PA是脂质信号分子,参与调节植物各种细胞生物学过程。文章介绍植物中DGK的信号转导作用、分子生物学反应、DGK的抑制剂以及与底物的亲和力的研究进展。     

植物磷脂酸的特性及其在ABA诱导气孔运动中的作用

磷脂酸(PA)是应答多种生理过程的第二信使, 其作为一个脂质信号快速积累从而响应多种环境。PA主要通过磷脂酶D (PLD)和磷脂酶C/甘油二酯激酶(PLC/DGK)途径产生。基于PLDs的生化特性、激活机制以及在不同类型胁迫下被激活的特定同种型的差异, 不同类型胁迫下会产生特定分子种组成的PA。PA在多种环境下起信号转导作用, 在调节气孔运动中, PA的作用模式主要是通过与多种蛋白结合, 激活或抑制这些蛋白的活性, 进而执行其信使功能。该文主要综述PA的生化特性以及信号途径中PA互作蛋白的研究进展, 并提出PA研究中亟待解决的问题及今后的重点研究方向。     

植物甾醇在植物逆境胁迫中的研究进展

植物甾醇是一类重要的生理活性物质,对植物的生长发育具有重要作用,对响应植物逆境胁迫也具有重要功能.植物甾醇是细胞膜和脂质筏的重要组分,与膜的稳定性密切相关,主要通过甾醇含量的相对变化维持膜的稳定性及影响脂质筏的生物功能响应逆境胁迫.植物甾醇作为信号分子参与逆境胁迫中的信号传导,油菜素内酯类(BRs)是植物甾醇合成途径的重要产物,作为一种重要的信号分子调控植物甾醇合成酶基因的表达以响应逆境胁迫.     

磷脂酶D信号转导与植物耐盐研究进展

土壤盐害是一个全球性的生态问题,对生态环境和农业生产带来了巨大的负面影响。研究发现,植物磷脂酶D(Phospholipase D,PLD)是磷脂代谢和应答非生物胁迫的重要酶类;PLD具有不同的结构、生化和调节特性,产生信号分子磷脂酸(Phosphatidic acid,PA)并参与多种胁迫反应。总结了PLD及其产物PA调控植物耐盐的相关报道,探讨其感受、应答盐信号的分子机制,为研究植物应答高盐胁迫和农作物分子遗传改良提供相关参考。     

磷脂酸和溶血磷脂酸的生理功能

磷脂酸(phosphatidic acid, PA)和溶血磷脂酸(lysophosphatidic acid,LPA)是细胞内和细胞外信号转导的重要磷脂信号分子.它们主要通过磷脂酶D和磷脂酶C两条途径产生,并且PA在磷脂酶A2的催化下可水解生成LPA.越来越多证据表明,PA和LPA在细胞诸多生理功能中起重要作用.本文主要介绍PA和LPA的生理功能及作用机制的研究进展.     

磷脂酸和溶血磷脂酸的生理功能

磷脂酸（phosphatidic acid,PA)和溶血磷脂酸（lysophosphatidic acid,LPA)是细胞内和细胞外信号转导的重要磷脂信号分子。它们主要通过磷脂酶D和磷脂酶C两条途径产生,并且PA在磷脂酶A2的催化下可水解生成LPA。越来越多证据表明,PA和LPA在细胞诸多生理功能中起重要作用。本文主要介绍PA和LPA的生理功能及作用机制的研究进展。     

ABF转录因子在植物响应非生物胁迫中的作用

非生物胁迫严重影响植物的生长发育及农作物的产量.植物激素脱落酸(ABA,abscisic acid)是植物响应非生物胁迫的重要信号分子,其介导的ABA信号途径在植物应答非生物胁迫过程中发挥关键作用,其中ABF(ABA-responsive element binding factors)转录因子在ABA信号途径中扮演着...     

大麦幼苗多胺合成比脯氨酸合成对盐胁迫更敏感

NaCl 2 0 0mmol/L处理结合14 C Glu叶面饲喂 6天龄大麦幼苗 ,结果证明盐胁迫下Pro主要积累在叶片中 ,在根系中PA的积累占优势。PA合成途径对盐胁迫的响应早于Pro。盐处理 8h以后PA与Pro的合成竞争共同前体Arg。盐胁迫激活了Pro两条合成途径 ,胁迫 8h以前Pro积累主要受Glu途径控制 ,随后Orn途径对Pro积累的贡献占主导地位。盐胁迫促进了PA合成的Arg途径 ,对Orn途径没有影响     

Substrate preference of stress-activated phospholipase D in Chlamydomonas and its contribution to PA formation

In response to various environmental stress conditions, plants rapidly form the intracellular lipid second messenger phosphatidic acid (PA). It can be generated by two independent signalling pathways via phospholipase D (PLD) and via phospholipase C (PLC) in combination with diacylglycerol kinase (DGK). In the green alga Chlamydomonas, the phospholipid substrates for these pathways are characterized by specific fatty acid compositions. This allowed us to establish: (i) PLD's in vivo substrate preference; and (ii) PLD's contribution to PA formation during stress signalling. Accordingly, G-protein activation (1 micro m mastoparan), hyperosmotic stress (150 mm NaCl) and membrane depolarization (50 mm KCl) were used to stimulate PLD, as monitored by the accumulation in 5 min of its unique transphosphatidylation product phosphatidylbutanol (PBut). In each case, PBut's fatty acid composition specifically matched that of phosphatidylethanolamine (PE), identifying this lipid as PLD's favoured substrate. This conclusion was substantiated by analysing the molecular species by electrospray ionization-mass spectrometry (ESI-MS/MS), which revealed that PE and NaCl-induced PBut share a unique (18 : 1)2-structure. The fatty acid composition of PA was much more complex, reflecting the different contributions from the PLC/DGK and PLD pathways. During KCl-induced stress, the PA rise was largely accounted for by PLD activity. In contrast, PLD's contribution to hyperosmotic stress-induced PA was less, being approximately 63% of the total increase. This was because the PLC/DGK pathway was activated as well, resulting in phosphoinositide-specific fatty acids and molecular species in PA.     

Nitric oxide-induced phosphatidic acid accumulation: a role for phospholipases C and D in stomatal closure

Stomatal closure is regulated by a complex network of signalling events involving numerous intermediates, among them nitric oxide (NO). Little is known about the signalling events occurring downstream of NO. Previous studies have shown that NO modulates cytosolic calcium concentration and the activation of plasma membrane ion channels. Here we provide evidence that supports the involvement of the lipid second messenger phosphatidic acid (PA) in NO signalling during stomatal closure. PA levels in Vicia faba epidermal peels increased upon NO treatment to maximum levels within 30 min, subsequently decreasing to control levels at 60 min. PA can be generated via phospholipase D (PLD) or via phospholipase C (PLC) in concerted action with diacylglycerol kinase (DGK). Our results showed that NO-induced PA is produced via the activation of both pathways. NO-induced stomatal closure was blocked either when PLC or PLD activity was inhibited. We have shown that PLC- and PLD-derived PA represents a downstream component of NO signalling cascade during stomatal closure.     

Phosphatidic acid production in chitosan-elicited tomato cells, via both phospholipase D and phospholipase C/diacylglycerol kinase, requires nitric oxide

Nitric oxide (NO) and the lipid second messenger phosphatidic acid (PA) are involved in plant defense responses during plant-pathogen interactions. NO has been shown to be involved in the induction of PA production in response to the pathogen associated molecular pattern (PAMP) xylanase in tomato cells. It was shown that NO is critical for PA production induced via phospholipase C (PLC) in concerted action with diacylglycerol kinase (DGK) but not for the xylanase-induced PA via phospholipase D (PLD). In order to study whether this is a general phenomenon during PAMP perception or if it is particular for xylanase, we studied the effect of the PAMP chitosan in tomato cell suspensions. We observed a rapid NO production in tomato cells treated with chitosan. Chitosan induced the formation of PA by activating both PLD and PLC/DGK. The activation of either phospholipase-mediated signaling pathway was inhibited in cells treated with the NO scavenger cPTIO. This indicates that NO is required for PA generation via both the PLD and PLC/DGK pathway during plant defense response in chitosan elicited cells. Responses downstream PA were studied. PLC inhibitors neomycin and U73122 inhibited chitosan-induced ROS production. Differences between xylanase and chitosan-induced phospholipid signaling pathways are discussed.     

Phospholipase D and the Maintenance of Phosphatidic Acid Levels for Regulation of Mammalian Target of Rapamycin (mTOR)

Phosphatidic acid (PA) is a critical metabolite at the heart of membrane phospholipid biosynthesis. However, PA also serves as a critical lipid second messenger that regulates several proteins implicated in the control of cell cycle progression and cell growth. Three major metabolic pathways generate PA: phospholipase D (PLD), diacylglycerol kinase (DGK), and lysophosphatidic acid acyltransferase (LPAAT). The LPAAT pathway is integral to de novo membrane phospholipid biosynthesis, whereas the PLD and DGK pathways are activated in response to growth factors and stress. The PLD pathway is also responsive to nutrients. A key target for the lipid second messenger function of PA is mTOR, the mammalian/mechanistic target of rapamycin, which integrates both nutrient and growth factor signals to control cell growth and proliferation. Although PLD has been widely implicated in the generation of PA needed for mTOR activation, it is becoming clear that PA generated via the LPAAT and DGK pathways is also involved in the regulation of mTOR. In this minireview, we highlight the coordinated maintenance of intracellular PA levels that regulate mTOR signals stimulated by growth factors and nutrients, including amino acids, lipids, glucose, and Gln. Emerging evidence indicates compensatory increases in one source of PA when another source is compromised, highlighting the importance of being able to adapt to stressful conditions that interfere with PA production. The regulation of PA levels has important implications for cancer cells that depend on PA and mTOR activity for survival.     

Phospholipase Dalpha3 is involved in the hyperosmotic response in Arabidopsis

Rapid activation of phospholipase D (PLD), which hydrolyzes membrane lipids to generate phosphatidic acid (PA), occurs under various hyperosmotic conditions, including salinity and water deficiency. The Arabidopsis thaliana PLD family has 12 members, and the function of PLD activation in hyperosmotic stress responses has remained elusive. Here, we show that knockout (KO) and overexpression (OE) of previously uncharacterized PLDalpha3 alter plant response to salinity and water deficit. PLDalpha3 uses multiple phospholipids as substrates with distinguishable preferences, and alterations of PLDalpha3 result in changes in PA level and membrane lipid composition. PLDalpha3-KO plants display increased sensitivities to salinity and water deficiency and also tend to induce abscisic acid-responsive genes more readily than wild-type plants, whereas PLDalpha3-OE plants have decreased sensitivities. In addition, PLDalpha3-KO plants flower later than wild-type plants in slightly dry conditions, whereas PLDalpha3-OE plants flower earlier. These data suggest that PLDalpha3 positively mediates plant responses to hyperosmotic stresses and that increased PLDalpha3 expression and associated lipid changes promote root growth, flowering, and stress avoidance.     

Interleukin-1 rapidly stimulates lysophosphatidate acyltransferase and phosphatidate phosphohydrolase activities in human mesangial cells.

Phosphatidic acid (PA) is a cytokine in a variety of cell types, and an intermediary in cell activation. It is produced from membrane phospholipids by either lysophosphatidate acyl-CoA:acyltransferase (lyso-PA AT) or phospholipase D. Interleukin-1 (IL-1) stimulation of human mesangial cells (HMC) induced activation of lyso-PA AT, and synthesis of new PA species with significant increase in PA mass. These PA species were enriched in long-chain unsaturated acyl side chains (C18:1, C18:2, C20:5, and C22:6) in both the sn-2 and sn-1 positions, and stimulated the action of the lyso-PA AT as a positive feedback mechanism. Gas-liquid chromatography and mass spectrometry demonstrate that the acyl composition of phosphatidic acid does not resemble that of the major phospholipid fractions of this preparation and therefore is not the product of phospholipase D. The PA species were rapidly converted to 1,2-sn-diacylglycerols by phosphatidate phosphohydrolase, which also was activated by IL-1 via a separate mechanism involving a pertussis-sensitive G-protein. The activities of lyso-PA AT and phosphatidate phosphohydrolase were associated with plasma membrane enriched and refined microsomal fractions. IL-1 stimulation of a murine T cell (thymoma) line, EL-4, also caused stimulation of lyso-PA AT, resulting in PA formation. EL-4 mutants with defective IL-1 receptors did not demonstrate stimulation of lyso-PA AT, showing the necessity of intact IL-1 receptors for activation of this enzyme. We conclude that PA is a significant signaling intermediary for IL-1 via activation of lyso-PA AT and a G-protein, which activates phosphatidate phosphohydrolase. This system suggests a novel mechanism whereby a low intensity signal may be translated into cellular activation.     

Nitric oxide is critical for inducing phosphatidic acid accumulation in xylanase-elicited tomato cells

Nitric Oxide (NO) is a second messenger related to development and (a)biotic stress responses in plants. We have studied the role of NO in signaling during plant defense responses upon xylanase elicitation. Treatment of tomato cell cultures with the fungal elicitor xylanase resulted in a rapid and dose-dependent NO accumulation. We have demonstrated that NO is required for the production of the lipid second messenger phosphatidic acid (PA) via the activation of the phospholipase C (PLC) and diacylglycerol kinase (DGK) pathway. Defense-related responses downstream of PA were studied. PA and, correspondingly, xylanase were shown to induce reactive oxygen species production. Scavenging of NO or inhibition of either the PLC or the DGK enzyme diminished xylanase-induced reactive oxygen species production. Xylanase-induced PLDbeta1 and PR1 mRNA levels decreased when NO or PA production were compromised. Finally, we have shown that NO and PA are involved in the induction of cell death by xylanase. Treatment with NO scavenger cPTIO, PLC inhibitor U73122, or DGK inhibitor R59022 diminished xylanase-induced cell death. On the basis of biochemical and pharmacological experimental results, we have shown that PLC/DGK-derived PA represents a novel downstream component of NO signaling cascade during plant defense.     

Rapid activation of phosphatidate phosphohydrolase in mesangial cells by lipid A

Knowledge of rapid events in cell signaling initiated by lipid A, the core moiety of bacterial lipopolysaccharide, is limited. In the present study we have demonstrated that cis-parinaric acid (cis-PnA) rapidly labels 1,2-sn-diacylglycerol (DAG) subsequent to labeling of phosphatidic acid (PA). Stimulation of microsomal membranes with lipid A decreased the level of PA labeled with cis-PnA within 5 s and increased the proportion of fluorescent label in DAG. Lipid A stimulation of DAG synthesis at 5-15 s was inhibited by incubation of mesangial cells with pertussis toxin prior to isolation of microsomal membranes. Inhibition of DAG formation was accompanied by an accumulation of the mass and fluorescent label in the cis-PnA-labeled phosphatidic acid pool. GTP gamma S caused a decrease in labeled PA and an increase in labeled 1,2-DAG. We conclude that the PA pool was enlarged via the lipid A sensitive lyso-PA acyl transferase (lyso-PA-AT) and was decreased by a phosphatidate phosphohydrolase to form DAG. The phosphatidate phosphohydrolase was at least partly regulated by a pertussis-sensitive G-protein. Lipid A or 1,2-dilinoleyl-PA, a product of lyso-PA-AT, induced cell activation as monitored by actin reorganization and cellular shape changes. Pretreatment of cells with pertussis toxin prevented the morphological changes normally induced by lipid A or 1,2-dilinoleyl-PA. In contrast, 1-oleoyl-2-acetylglycerol induced rapid actin reorganization and shape change, presumably bypassing the pertussis blockade. We propose that specific pools of PA and PA-derived DAG are key elements in rapid signaling in mesangial cells and are independent of the PI cycle and phospholipase C.