植物细胞程序性死亡中的类caspases 蛋白酶

细胞程序性死亡对于植物的正常生长发育及病理过程具有十分重要的生物学意义。现有的实验证据表明, 细胞程序性死亡在动物和植物中有许多相似之处, 但也各有特点。在植物中, VPEs、metacaspases和saspases 等酶类在细胞程序 性死亡过程中发挥了关键性作用。该文详细比较了动、植物细胞程序性死亡的差异, 并阐述了VPEs 、metacas pases 和saspases三种类caspases蛋白酶在植物程序性细胞死亡中所起的作用。     

Classes of programmed cell death in plants, compared to those in animals

Relatively little is known about programmed cell death (PCD) in plants. It is nonetheless suggested here that tonoplast rupture and the subsequent rapid destruction of the cytoplasm can distinguish two large PCD classes. One class, which is here called 'autolytic', shows this feature, whilst the second class (called 'non-autolytic') can include tonoplast rupture but does not show the rapid cytoplasm clearance. Examples of the 'autolytic' PCD class mainly occur during normal plant development and after mild abiotic stress. The 'non-autolytic' PCD class is mainly found during PCD that is due to plant-pathogen interactions. Three categories of PCD are currently recognized in animals: apoptosis, autophagy, and necrosis. An attempt is made to reconcile the recognized plant PCD classes with these groups. Apoptosis is apparently absent in plants. Autophagic PCD in animals is defined as being accompanied by an increase in the number of autophagosomes, autolysosomes, and small lytic vacuoles produced by autolysosomes. When very strictly adhering to this definition, there is no (proof for) autophagic PCD in plants. Upon a slightly more lenient definition, however, the 'autolytic' class of plant PCD can be merged with the autophagic PCD type in animal cells. The 'non-autolytic' class of plant PCD, as defined here, can be merged with necrotic PCD in animals.     

植物细胞程序死亡的机理及其与发育的关系

细胞程序死亡（PCD）是在植物体发育过程中普遍存在的,在发育的特定阶段发生的自然的细胞死亡过程,这一死亡过程是由某些特定基因编码的“死亡程序”控制的。PCD是细胞分化的最后阶段。细胞分化的临界期就处于死亡程序执行中的某个阶段。PCD包含启动期、效应期和清除期三个阶段,其间caspase家族起着重要作用。PCD在细胞和组织的平衡、特化,以及组织分化、器官建成和对病原体的反应等植物发育过程中起着重要作用。PCD中的形态学变化和生物化学变化都有着严格的时序性。植物的PCD和动物的PCD有许多共性,包括细胞形态和DNA降解等变化。也有一些不同,植物PCD的产物既可被其它细胞吸收利用;也可用于构建自身的次生细胞壁。     

植物细胞程序死亡的机理及其与发育的关系

细胞程序死亡（ＰＣＤ）是在植物体发育过程中普遍存在的,在发育的特定阶段发生的自然的细胞死亡过程,这一死亡过程是由某些特定基因编码的“死亡程序”控制的。ＰＣＤ的细胞分化的最后阶段。细胞分化的临界期就牌死亡程序执行中的某个阶段。ＰＣＤ包含启动期和清除期三个阶段,其间ＣＡＳＰＡＳＥ家族起着重要作用。ＰＣＤ在细胞和组织的平衡、特化,以及组织分化、器官建成和对病原体的反应等植物发育过程中起着重要作用。ＰＣＤ     

植物细胞程序性死亡(PCD)的研究进展

细胞死亡是动、植物生长发育过程中常见的一种生命现象 ,而细胞程序性死亡 (PCD)是细胞遵循自身生命活动程序 ,并受多种因子调控的一种积极的死亡方式。近年来随着动物中PCD研究的深入 ,植物PCD亦得到相应的研究。植物细胞程序性死亡研究不仅可揭示植物衰老、死亡的内部变化规律 ,而且可为其生长发育的调控提供依据和技术。该文试对有关PCD的特点、研究意义及近年来的研究概况与方法进行简述与评价。     

ABCA1-dependent but apoA-I-independent cholesterol efflux mediated by fatty acid-bile acid conjugates (FABACs)

PCD (programmed cell death) in plants presents important morphological and biochemical differences compared with apoptosis in animal cells. This raises the question of whether PCD arose independently or from a common ancestor in plants and animals. In the present study we describe a cell-free system, using wheat grain nucellar cells undergoing PCD, to analyse nucleus dismantling, the final stage of PCD. We have identified a Ca2+/Mg2+ nuclease and a serine protease localized to the nucleus of dying nucellar cells. Nuclear extracts from nucellar cells undergoing PCD triggered DNA fragmentation and other apoptotic morphology in nuclei from different plant tissues. Inhibition of the serine protease did not affect DNA laddering. Furthermore, we show that the nuclear extracts from plant cells triggered DNA fragmentation and apoptotic morphology in nuclei from human cells. The inhibition of the nucleolytic activity with Zn2+ or EDTA blocked the morphological changes of the nucleus. Moreover, nuclear extracts from apoptotic human cells triggered DNA fragmentation and apoptotic morphology in nuclei from plant cells. These results show that degradation of the nucleus is morphologically and biochemically similar in plant and animal cells. The implication of this finding on the origin of PCD in plants and animals is discussed.     

Deficient plastidic fatty acid synthesis triggers cell death by modulating mitochondrial reactive oxygen species

Programmed cell death (PCD) is of fundamental importance to development and defense in animals and plants. In plants, a well-recognized form of PCD is hypersensitive response (HR) triggered by pathogens, which involves the generation of reactive oxygen species (ROS) and other signaling molecules. While the mitochondrion is a master regulator of PCD in animals, the chloroplast is known to regulate PCD in plants. Arabidopsis Mosaic Death 1 (MOD1), an enoyl-acyl carrier protein (ACP) reductase essential for fatty acid biosynthesis in chloroplasts, negatively regulates PCD in Arabidopsis. Here we report that PCD in mod1 results from accumulated ROS and can be suppressed by mutations in mitochondrial complex I components, and that the suppression is confirmed by pharmaceutical inhibition of the complex I-generated ROS. We further show that intact mitochondria are required for full HR and optimum disease resistance to the Pseudomonas syringae bacteria. These findings strongly indicate that the ROS generated in the electron transport chain in mitochondria plays a key role in triggering plant PCD and highlight an important role of the communication between chloroplast and mitochondrion in the control of PCD in plants.     

A programmed cell death pathway activated in carrot cells cultured at low cell density

Programmed cell death (PCD) occurs in plants during development and defense, but the processes and mechanisms are not yet defined. Culture of carrot single cells at a cell density of <10⁴ cells ml⁻¹ activates a cell death process involving condensation and shrinkage of the cytoplasm and nucleus and fragmentation of the DNA. Modest abiotic stress treatments also cause cell condensation and shrinkage and the formation of DNA fragments, but the same abiotic stresses at high levels cause rapid necrosis with cell swelling and lysis. The common morphological features of cells dying at low cell density and following modest abiotic stress treatments suggest that these features reveal a PCD pathway in carrot. The addition of a cell-conditioned growth medium allows cells at low cell density to remain alive, demonstrating that cell-derived signal molecules suppress a pathway that is otherwise induced by default. Differences in the morphology of the dead cells suggest that proteolysis during PCD differs in detail in plants and animals; however, these findings show that plants, like animals, can control PCD by social signaling, and imply that the mechanism of PCD in plants and animals may be similar. Consistent with this, manipulation of signal pathway intermediates that regulate PCD in animals shows that Ca²⁺ and protein phosphorylation events are PCD pathway intermediates in carrot.     

Multiple mediators of plant programmed cell death: interplay of conserved cell death mechanisms and plant-specific regulators

Programmed cell death (PCD) is a process aimed at the removal of redundant, misplaced, or damaged cells and it is essential to the development and maintenance of multicellular organisms. In contrast to the relatively well-described cell death pathway in animals, often referred to as apoptosis, mechanisms and regulation of plant PCD are still ill-defined. Several morphological and biochemical similarities between apoptosis and plant PCD have been described, including DNA laddering, caspase-like proteolytic activity, and cytochrome c release from mitochondria. Reactive oxygen species (ROS) have emerged as important signals in the activation of plant PCD. In addition, several plant hormones may exert their respective effects on plant PCD through the regulation of ROS accumulation. The possible plant PCD regulators discussed in this review are integrated in a model that combines plant-specific regulators with mechanisms functionally conserved between animals and plants.     

植物细胞程序性死亡中的类caspases蛋白酶

细胞程序性死亡对于植物的正常生长发育及病理过程具有十分重要的生物学意义。现有的实验证据表明,细胞程序性死亡在动物和植物中有许多相似之处,但也各有特点。在植物中,VPEs、metacaspases和saspases等酶类在细胞程序性死亡过程中发挥了关键性作用。该文详细比较了动、植物细胞程序性死亡的差异,并阐述TVPEs、metacaspases和saspases三种类caspases蛋白酶在植物程序性细胞死亡中所起的作用。     

A cellular suicide strategy of plants: vacuole-mediated cell death

Programmed cell death (PCD) occurs in animals and plants under various stresses and during development. Recently, vacuolar processing enzyme (VPE) was identified as an executioner of plant PCD. VPE is a cysteine protease that cleaves a peptide bond at the C-terminal side of asparagine and aspartic acid. VPE exhibited enzymatic properties similar to that of a caspase, which is a cysteine protease that mediates the PCD pathway in animals, although there is limited sequence identity between the two enzymes. VPE and caspase-1 share several structural properties: the catalytic dyads and three amino acids forming the substrate pockets (Asp pocket) are conserved between VPE and caspase-1. In contrast to such similarities, subcellular localizations of these proteases are completely different from each other. VPE is localized in the vacuoles, while caspases are localized in the cytosol. VPE functions as a key molecule of plant PCD through disrupting the vacuole in pathogenesis and development. Cell death triggered by vacuolar collapse is unique to plants and has not been seen in animals. Plants might have evolved a VPE-mediated vacuolar system as a cellular suicide strategy.     

植物Metacaspase研究进展

过敏性坏死反应是植物的一种重要的抗病机制, 类似于动物细胞凋亡, 它是一种程序性细胞死亡(programmed cell death, PCD)过程。目前, 已经确定半胱天冬蛋白酶(caspase)在动物PCD过程中起核心作用。在植物中, 尚未发现其直系同源蛋白, 但是有一类与其结构相似的蛋白酶, 称为metacaspase。在植物不同的PCD过程中, 有的依赖于metacaspase, 而有的则不依赖于该类蛋白酶。目前对metacaspase的结构和功能已有了初步的研究, 对其深入的研究则进展缓慢, 其具体的生物学功能和在PCD信号路径中的定位有待进一步探索。     

环境胁迫诱导的植物细胞程序性死亡

在最近的10年中,兴起了对植物细胞程序性死亡的研究。大量的证据表明,在各种环境胁迫因子诱导植物细胞PCD过程中,活性氧、乙烯、Ca2+、水杨酸、NO等成为重要的信号分子。像动物细胞凋亡一样,在植物PCD中也存在一条依赖于天冬氨酸特异性半胱氨酸蛋白酶(Caspases)活性的信号传导途径,其中,线粒体处于PCD调控的中心位置。 Abstract:Programmed cell death (PCD) research in higher plants has blossomed in the past ten years.Many evidences suggested that reactive oxygen species,ethylene,Ca2+,salicylic acid,nitric oxide etc.are important signal molecules during environmental stress-induced PCD in plants.Like apoptosis in animals,there also exists a Caspase-dependent PCD signal transduction pathway,in which mitochondrion plays a role of central depot.     

Induction of cell death in arabidopsis by superoxide in combination with salicylic acid or with protein synthesis inhibitors

Induction of programmed cell death (PCD) by oxidative stress is a widespread phenomenon in all living organisms. The degree of cell death depends on the concentration of oxidants and on environmental and physiological conditions. In plants, generation of reactive oxygen intermediates (ROI) occurs during many biotic and abiotic stresses. Recently, a number of spontaneous cell death mutants have been isolated in Arabidopsis. In one of the mutants (lsd1) induction of PCD has been attributed to superoxide (O(2)(*)(-)). Here we show that while in wild type plants generation of superoxide is symptomless, combination of O(2)(*)(-) with salicylic acid or with inhibitors of protein synthesis induced PCD. Cell death induced by these treatments was suppressed by protease inhibitors, indicating an active response. PCD induced by both treatments was preceded by nuclear condensation, which is a hallmark of apoptosis in plants and animals. These results may explain increased sensitivity to oxidative stress under certain physiological conditions, associated with high levels of salicylic acid or decrease in protein synthesis.     

Programmed cell death correlates with virus transmission in a filamentous fungus

Programmed cell death (PCD) is an essential part of the defence response in plants and animals against pathogens. Here, we report that PCD is also involved in defence against pathogens of fungi. Vegetative incompatibility is a self/non-self recognition system in fungi that results in PCD when cells of incompatible strains fuse. We quantified the frequency of cell death associated with six vegetative incompatibility (vic) genes in the filamentous ascomycete fungus Cryphonectria parasitica. Cell death frequencies were compared with the effects of vic genes on transmission of viruses between the same strains. We found a significant negative correlation between cell death and virus transmission. We also show that asymmetry in cell death correlates with asymmetry in virus transmission; greater transmission occurs into vic genotypes that exhibit delayed or infrequent PCD after fusion with an incompatible strain. Furthermore, we found that virus infection can have a significant, strain-specific, positive or negative effect on PCD. Specific interactions between vic gene function and viruses, along with correlations between cell death and transmission, strongly implicate PCD as a host-mediated pathogen defence strategy in fungi.     

Programmed cell death in plants: distinguishing between different modes

Programmed cell death (PCD) in plants is a crucial componentof development and defence mechanisms. In animals, differenttypes of cell death (apoptosis, autophagy, and necrosis) havebeen distinguished morphologically and discussed in these morphologicalterms. PCD is largely used to describe the processes of apoptosisand autophagy (although some use PCD and apoptosis interchangeably)while necrosis is generally described as a chaotic and uncontrolledmode of death. In plants, the term PCD is widely used to describemost instances of death observed. At present, there is a vastarray of plant cell culture models and developmental systemsbeing studied by different research groups and it is clear fromwhat is described in this mass of literature that, as with animals,there does not appear to be just one type of PCD in plants.It is fundamentally important to be able to distinguish betweendifferent types of cell death for several reasons. For example,it is clear that, in cell culture systems, the window of timein which ‘PCD’ is studied by different groups varieshugely and this can have profound effects on the interpretationof data and complicates attempts to compare different researcher'sdata. In addition, different types of PCD will probably havedifferent regulators and modes of death. For this reason, inplant cell cultures an apoptotic-like PCD (AL-PCD) has beenidentified that is fairly rapid and results in a distinct corpsemorphology which is visible 4–6 h after release of cytochromec and other apoptogenic proteins. This type of morphology, distinctfrom autophagy and from necrosis, has also been observed inexamples of plant development. In this review, our model systemand how it is used to distinguish specifically between AL-PCDand necrosis will be discussed. The different types of PCD observedin plants will also be discussed and the importance of distinguishingbetween different forms of cell death will be highlighted. Key words: Apoptosis, apoptosis-like programmed cell death (AL-PCD), Arabidopsis, autophagy, mitochondria, necrosis, programmed cell death (PCD) Received 5 June 2007; Revised 13 September 2007 Accepted 20 September 2007