Roles for the extracellular matrix in plant development and pollination: a special case of cell movement in plants.

Pattern formation in plants is now thought to be primarily dependent on positional information during development. We discuss the prevalent theories on how position is deciphered by cells in an organism and highlight the recent advances implicating molecules of the cell wall or extracellular matrix (ECM) in this process. We compare the functions of the ECM in plants and animals and describe the various cell and substrate adhesion molecules of the animal ECM which play a role in morphogenesis and cell movement. We propose that analogous molecules may occur in plants and provide evidence for the presence of a substrate adhesion molecule like vitronectin in plants and algae. We provide a model for how substrate adhesion molecules may be involved in a special case of cell movement in plants, pollination.     

Structure and function of heterotrimeric G proteins in plants

Heterotrimeric G proteins are mediators that transmit the external signals via receptor molecules to effector molecules. The G proteins consist of three different subunits: alpha, beta, and gamma subunits. The cDNAs or genes for all the alpha, beta, and gamma subunits have been isolated from many plant species, which has contributed to great progress in the study of the structure and function of the G proteins in plants. In addition, rice plants lacking the alpha subunit were generated by the antisense method and a rice mutant, Daikoku d1, was found to have mutation in the alpha-subunit gene. Both plants show abnormal morphology such as dwarfism, dark green leaf, and small round seed. The findings revealed that the G proteins are functional molecules regulating some body plans in plants. There is evidence that the plant G proteins participate at least in signaling of gibberellin at low concentrations. In this review, we summarize the currently known information on the structure of plant heterotrimeric G proteins and discuss the possible functions of the G proteins in plants.     

植物与病原菌互作的分子机制研究进展

植物的先天免疫主要包括模式识别受体对保守的微生物病原相关分子模式的识别和抗病蛋白对效应蛋白的识别。植物与病原体互作过程中存在广泛的信号交流,信号分子在植物与病原体的互作攻防中发挥了重要的调控作用,决定了二者的竞争关系。当前,大量植物与病原体互作中的信号分子被定位和克隆,其作用方式被揭示。本文总结了这些信号分子及其在植物免疫过程中的作用机制,主要包括植物细胞表面的模式识别受体分子对病原相关分子模式的识别与应答,植物抗病蛋白对病原体效应蛋白的识别与应答,以及免疫反应下游相关信号分子及其在植物抗病中的作用。此外,本文对未来相关研究提出了展望。     

Safe and acceptable strategies for producing foreign molecules in plants

The ability to express foreign genes using transgenic technologies has opened up options for producing large quantities of commercially important industrial or pharmaceutical products in plants. These technologies have made it possible to use well-developed systems of commercial agriculture that were developed principally to produce raw material for large-scale food, feed or processing applications for the production of foreign molecules. The possibility of the novel industrial or pharmaceutical molecules produced in such plants, or components derived from them, contaminating the environment and food chains has become especially controversial. This potential contamination has prompted detailed consideration of how such crops and the molecules that they produce can be effectively isolated and contained. First, the crop can be completely isolated physically from its food or feed counterpart during every aspect of its development and commercialization. Second, genetic isolation systems or genetic barriers that prevent normal reproduction can be used to reduce the likelihood of the industrial or pharmaceutical crop entering the food chain.     

寄生植物对寄主植物的化学识别

植物间寄生关系的研究近年来受到了广泛的重视。大量的研究表明,寄主释放的次生物质对植物间寄生关系的建立和维持起了重要的调节作用。寄主植物的次生物质对寄生植物的化学防御和昆虫授粉等生态功能起重要的作用,寄主植物次生物质对寄生植物生理与生态的调节作用是受寄生植物基因调节的。更为重要的是寄主植物释放的次生物质成为寄生植物的种子萌发和吸器发生的异源识别物质。能够刺激寄生植物种子萌发的次生物质主要是倍半萜和氢醌类物质,而诱导吸器发生的物质则是酚酸、醌和黄酮类化合物,诱导吸器发生的核心结构是对苯醌。这些异源识别物质大多是寄主植物释放的化感抑制物质,显示寄生植物在化学防御方面要比寄主植物高级。异源识别化合物的活性与其氧化潜力显著相关。由于寄生植物中存在一抑制异源识别物质诱导吸器发生的调节过程,因此吸器的产生与寄生植物根部接触异源识别物质的浓度与时间呈正相关关系,这一调节过程对寄生植物准确识别寄主并寄生其上是十分重要的。对寄生植物和寄主植物间的化学识别关系的揭示有助于人们防治有害寄生植物和开发利用有价值的寄生植物资源。     

Zoospore interspecific signaling promotes plant infection by <Emphasis Type="Italic">Phytophthora</Emphasis>

Background  

Oomycetes attack a huge variety of economically and ecologically important plants. These pathogens release, detect and respond to signal molecules to coordinate their communal behaviors including the infection process. When signal molecules are present at or above threshold level, single zoospores can infect plants. However, at the beginning of a growing season population densities of individual species are likely below those required to reach a quorum and produce threshold levels of signal molecules to trigger infection. It is unclear whether these molecules are shared among related species and what their chemistries are.     

Mitochondrial DNA recombination in Brassica campestris

The structure of the mitochondrial genome in plants is unclear, but appears to consist of mostly linear DNA with some other structures, including branched molecules and subgenomic circles. Mitochondrial DNA (mtDNA) recombination was analyzed in Brassica campestris, which has one of the smallest mitochondrial genomes (218 kb) in higher plants. Field-inversion gel electrophoresis (FIGE) separated mtDNA into discrete populations that each represents the entire genome. Electron microscopy revealed large, mostly linear molecules trapped in the wells, slower migrating populations with mostly linear DNA and a low level of circular and networked mtDNA molecules of 10–140 kbp, and a fast migrating population of 10–50 kbp linear mtDNA. Some smaller than genome size circular molecules and circles with tails were observed, and may represent recombination or rolling circle replication intermediates. Hybridization of end-labeled mtDNA suggests there may be specific ends (or recombination hotspots) for some linear molecules. Analysis of mtDNA enriched by BND-cellulose and separated by two-dimensional agarose gel electrophoresis shows the presence of complex recombination structures and the presence of significant single-stranded regions in mtDNA. These findings provide further evidence that DNA recombination contributes to the complex structure of mtDNA in plants.     

植物胞外钙调素与信号转导

植物体需要构建复杂的信号转导体系以调节自身的生长发育过程并适应外界环境的变化,这种功能的实现需要胞内和胞外诸多信号分子的参与,胞外钙调素的发现使人们开始相信植物细胞外多肽信使的存在。胞外钙调素的生物学功能极其广泛,几乎涉及到植物生长发育的各个阶段,其信号转导途径是目前研究得最多也是最为清楚的方面,异三聚体G蛋白、磷脂酶C(PLC)-肌醇三磷酸(IP3)-肌醇三磷酸受体(IP3R)信号通路、活性氧和Ca2 通道之间直接或间接的相互作用是胞外钙调素信号转导的核心。     

Replicating satellite RNA induces sequence-specific DNA methylation and truncated transcripts in plants

Tobacco plants were transformed with a chimeric transgene comprising sequences encoding beta-glucuronidase (GUS) and the satellite RNA (satRNA) of cereal yellow dwarf luteovirus. When transgenic plants were infected with potato leafroll luteovirus (PLRV), which replicated the transgene-derived satRNA to a high level, the satellite sequence of the GUS:Sat transgene became densely methylated. Within the satellite region, all 86 cytosines in the upper strand and 73 of the 75 cytosines in the lower strand were either partially or fully methylated. In contrast, very low levels of DNA methylation were detected in the satellite sequence of the transgene in uninfected plants and in the flanking nonsatellite sequences in both infected and uninfected plants. Substantial amounts of truncated GUS:Sat RNA accumulated in the satRNA-replicating plants, and most of the molecules terminated at nucleotides within the first 60 bp of the satellite sequence. Whereas this RNA truncation was associated with high levels of satRNA replication, it appeared to be independent of the levels of DNA methylation in the satellite sequence, suggesting that it is not caused by methylation. All the sequenced GUS:Sat DNA molecules were hypermethylated in plants with replicating satRNA despite the phloem restriction of the helper PLRV. Also, small, sense and antisense approximately 22 nt RNAs, derived from the satRNA, were associated with the replicating satellite. These results suggest that the sequence-specific DNA methylation spread into cells in which no satRNA replication occurred and that this was mediated by the spread of unamplified satRNA and/or its associated 22 nt RNA molecules.     

Involvement of phospholipid signaling in plant growth and hormone effects

Biochemical and genetics studies demonstrated the critical roles of phospholipid signaling and relevant molecules in regulating multiple processes of plant growth and development, signal transduction, mediating hormone effects and cell responses to environmental stimuli, through modulating protein subcellular localization, cross-talking with other signaling or metabolic pathways, or interacting with signaling molecules. The updated achievements of physiological effects and functional mechanism of phospholipid signaling in higher plants were reviewed.     

MAMPs and MIMPs: proposed classifications for inducers of innate immunity

Plants encode a sophisticated innate immune system. Resistance against potential pathogens often relies on active responses. Prerequisite to the induction of defences is recognition of the pathogenic threat. Significant advances have been made in our understanding of the non-self molecules that are recognized by plants and the means by which plants perceive them. Established terms describing these recognition events, including microbe-associated molecular pattern (MAMP), MAMP-receptor, effector, and resistance (R) protein, need clarification to represent our current knowledge adequately. In this review we propose criteria to classify inducers of plant defence as either MAMPs or microbe-induced molecular patterns (MIMPs). We refine the definition of MAMP to mean a molecular sequence or structure in ANY pathogen-derived molecule that is perceived via direct interaction with a host defence receptor. MIMPs are modifications of host-derived molecules that are induced by an intrinsic activity of a pathogen-derived effector and are perceived by a host defence receptor. MAMP-receptors have previously been classified separately from R-proteins as a discrete class of surveillance molecules. However, MAMP-receptors and R-proteins cannot be distinguished on the basis of their protein structures or their induced responses. We propose that MAMP-receptors and MIMP-receptors are each a subset of R-proteins. Although our review is based on examples from plant pathogens and plants, the principles discussed might prove applicable to other organisms.     

Cucumber mosaic virus coat protein-mediated protection

Transgenic tobacco plants (CP +) that express the coat protein gene of cucumber mosaic virus (CMV)-Y strain were highly protected from infection with either CMV virions or CMV RNA, while transgenic protoplasts were also protected from infection with CMV virions but not with CMV RNA. CP + plants showed greater susceptibility to infection with satellite RNA-free CMV-Y than CMV-Y containing satellite RNA. At temperatures above 30°C, CP + plants did not or poorly resist infection with CMV. Elevated temperature affected the accumulation of CP rather than its mRNA, suggesting that CP molecules are mainly involved in virus resistance in CP + plants.     

Antimicrobial Phytoprotectants and Fungal Pathogens: A Commentary

Many plants produce antifungal secondary metabolites. These may be preformed compounds which are found in healthy plants and which may represent in-built chemical barriers to infection by potential pathogens (preformed antimicrobial compounds or phytoanticipins). Alternatively they may be synthesized in response to pathogen attack as part of the plant defence response (phytoalexins). If these molecules do play a role in protecting plants against pathogen attack, then successful pathogens are presumably able to circumvent or tolerate these defences. Strategies may include avoidance, enzymatic degradation, and/or nondegradative mechanisms. This review outlines the different ways in which fungal pathogens may counter the antifungal compounds produced by their host plants and summarizes the evidence for and against these compounds as antimicrobial phytoprotectants.     

Regulation of physiological aspects in plants by hydrogen sulfide and nitric oxide under challenging environment

Plants are exposed to a plethora of abiotic stresses such as drought, salinity, heavy metal and temperature stresses at different stages of their life cycle, from germination to seedling till the reproductive phase. As protective mechanisms, plants release signaling molecules that initiate a cascade of stress-signaling events, leading either to programmed cell death or plant acclimation. Hydrogen sulfide (H₂S) and nitric oxide (NO) are considered as new ‘gasotransmitter’ molecules that play key roles in regulating gene expression, posttranslational modification (PTM), as well as cross-talk with other hormones. Although the exact role of NO in plants remains unclear and is species dependent, various studies have suggested a positive correlation between NO accumulation and environmental stress in plants. These molecules are also involved in a large array of stress responses and act synergistically or antagonistically as signaling components, depending on their respective concentration. This study provides a comprehensive update on the signaling interplay between H₂S and NO in the regulation of various physiological processes under multiple abiotic stresses, modes of action and effects of exogenous application of these two molecules under drought, salt, heat and heavy metal stresses. However, the complete picture of the signaling cascades mediated by H₂S and NO is still elusive. Recent researches indicate that during certain plant processes, such as stomatal closure, H₂S could act upstream of NO signaling or downstream of NO in response to abiotic stresses by improving antioxidant activity in most plant species. In addition, PTMs of antioxidative pathways by these two molecules are also discussed.     

一氧化氮与激发子诱导的植物抗病防卫反应

来源于真菌或植物细胞壁的激发子可以诱导植物的抗性反应。一系列的信号分子,如一氧化氮、活性氧、茉莉酸、水杨酸、乙烯等都参与了激发子诱导的植物抗性反应。它们在介导激发子刺激诱发胞内抗性反应的过程中起着重要的作用。本文介绍了激发子的种类,并简述了激发了受体以及植物细胞对激发子刺激的感受与传递;重点介绍了一氧化氮在激发子诱导植物抗性反应过程中的作用,以及它与其他信号分子之间相互关系的研究进展。     

Pigment shuffling in antenna systems achieved by expressing prokaryotic chlorophyllide a oxygenase in Arabidopsis

The organization of pigment molecules in photosystems is strictly determined. The peripheral antennae have both chlorophyll a and b, but the core antennae consist of only chlorophyll a in green plants. Furthermore, according to the recent model obtained from the crystal structure of light-harvesting chlorophyll a/b-protein complexes II (LHCII), individual chlorophyll-binding sites are occupied by either chlorophyll a or chlorophyll b. In this study, we succeeded in altering these pigment organizations by introducing a prokaryotic chlorophyll b synthesis gene (chlorophyllide a oxygenase (CAO)) into Arabidopsis. In these transgenic plants (Prochlirothrix hollandica CAO plants), approximately 40% of chlorophyll a of the core antenna complexes was replaced by chlorophyll b in both photosystems. Chlorophyll a/b ratios of LHCII also decreased from 1.3 to 0.8 in PhCAO plants. Surprisingly, these transgenic plants were capable of photosynthetic growth similar to wild type under low light conditions. These results indicate that chlorophyll organizations are not solely determined by the binding affinities, but they are also controlled by CAO. These data also suggest that strict organizations of chlorophyll molecules are not essential for photosynthesis under low light conditions.     

Green leaf volatiles: hydroperoxide lyase pathway of oxylipin metabolism

Green leaf volatiles (GLVs) are C(6) aldehydes, alcohols, and their esters formed through the hydroperoxide lyase pathway of oxylipin metabolism. Plants start to form GLVs after disruption of their tissues and after suffering biotic or abiotic stresses. GLV formation is thought to be regulated at the step of lipid-hydrolysis, which provides free fatty acids to the pathway. Recently, studies dissecting the physiological significance of GLVs in plants have emerged, and it has been postulated that GLVs are important molecules both for signaling within and between plants and for allowing plants and other organisms surrounding them to recognize or compete with each other.