Brassinosteroid-Mediated Stress Responses

Brassinosteroids (BRs) are a group of naturally occurring plant steroidal compounds with wide-ranging biological activity that offer the unique possibility of increasing crop yields through both changing plant metabolism and protecting plants from environmental stresses. In recent years, genetic and biochemical studies have established an essential role for BRs in plant development, and on this basis BRs have been given the stature of a phytohormone. A remarkable feature of BRs is their potential to increase resistance in plants to a wide spectrum of stresses, such as low and high temperatures, drought, high salt, and pathogen attack. Despite this, only a few studies aimed at understanding the mechanism by which BRs promote stress resistance have been undertaken. Studies of the BR signaling pathway and BR gene-regulating properties indicate that there is cross-talk between BRs and other hormones, including those with established roles in plant defense responses such as abscisic acid, jasmonic acid, and ethylene. Recent studies aimed at understanding how BRs modulate stress responses suggest that complex molecular changes underlie BR-induced stress tolerance in plants. Analyses of these changes should generate exciting results in the future and clarify whether the ability of BRs to increase plant resistance to a range of stresses lies in the complex interactions of BRs with other hormones. Future studies should also elucidate if BRI1, an essential component of the BR receptor, directly participates in stress response signaling through interactions with ligands and proteins involved in plant defense responses.     

Priming for stress resistance: from the lab to the field

Upon treatment with necrotizing pathogens, many plants develop an enhanced capacity for activating defense responses to biotic and abiotic stress--a process called priming. The primed state can also be induced by colonization of plant roots with beneficial micro-organisms or by treatment of plants with various natural and synthetic compounds. Priming is thought to be the mechanism by which plants can show induced resistance against ostensibly virulent pathogens after a conditioning treatment. Although the phenomenon has been known for years, it has been appreciated just recently that priming for enhanced defense responses can result from plant-plant communication in nature and that priming can also boost the resistance of crops to biotic and abiotic stresses in the field.     

The Plant-Stress Metabolites,Hexanoic Aacid and Melatonin,Are Potential “Vaccines” for Plant Health Promotion

A plethora of compounds stimulate protective mechanisms in plants against microbial pathogens and abiotic stresses. Some defense activators are synthetic compounds and trigger responses only in certain protective pathways, such as activation of defenses under regulation by the plant regulator, salicylic acid (SA). This review discusses the potential of naturally occurring plant metabolites as primers for defense responses in the plant. The production of the metabolites, hexanoic acid and melatonin, in plants means they are consumed when plants are eaten as foods. Both metabolites prime stronger and more rapid activation of plant defense upon subsequent stress. Because these metabolites trigger protective measures in the plant they can be considered as “vaccines” to promote plant vigor. Hexanoic acid and melatonin instigate systemic changes in plant metabolism associated with both of the major defense pathways, those regulated by SA- and jasmonic acid (JA). These two pathways are well studied because of their induction by different microbial triggers: necrosis-causing microbial pathogens induce the SA pathway whereas colonization by beneficial microbes stimulates the JA pathway. The plant’s responses to the two metabolites, however, are not identical with a major difference being a characterized growth response with melatonin but not hexanoic acid. As primers for plant defense, hexanoic acid and melatonin have the potential to be successfully integrated into vaccination-like strategies to protect plants against diseases and abiotic stresses that do not involve man-made chemicals.     

Seed priming for abiotic stress tolerance: an overview

Plants are exposed to any number of potentially adverse environmental conditions such as water deficit, high salinity, extreme temperature, submergence, etc. These abiotic stresses adversely affect the plant growth and productivity. Nowadays various strategies are employed to generate plants that can withstand these stresses. In recent years, seed priming has been developed as an indispensable method to produce tolerant plants against various stresses. Seed priming is the induction of a particular physiological state in plants by the treatment of natural and synthetic compounds to the seeds before germination. In plant defense, priming is defined as a physiological process by which a plant prepares to respond to imminent abiotic stress more quickly or aggressively. Moreover, plants raised from primed seeds showed sturdy and quick cellular defense response against abiotic stresses. Priming for enhanced resistance to abiotic stress obviously is operating via various pathways involved in different metabolic processes. The seedlings emerging from primed seeds showed early and uniform germination. Moreover, the overall growth of plants is enhanced due to the seed-priming treatments. The main objective of this review is to provide an overview of various crops in which seed priming is practiced and about various seed-priming methods and its effects.     

一氧化氮在植物体内的来源和功能

一氧化氮(nitric oxide,NO)是生物体内重要的活性分子。NO参与了动物体内血管松弛、神经传递及免疫防御反应等一系列生理功能而被认为是可扩散的多功能第二信使。在植物体内NO也是一种广泛存在的信号分子,参与调节了许多重要的生理过程如生长、发育、抗病防御反应、细胞程序性死亡和抗逆反应。对NO在植物体内的来源、信号转导、调节植物生长发育和对胁迫的响应方面所发挥的作用进行了综述,并讨论了其潜在的一些功能。     

拟南芥AtWRKY25、AtWRKY26和AtWRKY33在非生物胁迫条件下的表达分析

WRKY 转录因子家族在调控植物逆境诱导反应、生长发育及其信号转导等方面起着重要的分子生物学功能。文章采用Northern 杂交的方法, 对拟南芥3个WRKY基因进行表达谱分析。结果表明: AtWRKY25、AtWRKY26和AtWRKY33受多种非生物逆境因子(温度因子、高盐、渗透胁迫和激素脱落酸)的影响, 其中低温和高盐对AtWRKY25、AtWRKY26和AtWRKY33的诱导尤为明显, 表明这3个AtWRKY基因可能在响应环境信号方面起着一定的作用。作为序列相似性较高的AtWRKY25、AtWRKY26和AtWRKY33对一些胁迫因子的表达模式呈现一定的相似性; 但AtWRKY33受高温的抑制和低温的快速诱导, 与另外两个基因的表达模式不同, 推测它们对温度胁迫因子的反应存在差异。此外, 对启动子序列的生物信息学分析发现, 3个基因的启动子包含多个与非生物逆境反应相关的顺式作用元件。     

Molecular epigenetic mechanisms for the memory of temperature stresses in plants

The sessile plants encounter various stresses; some are prolonged, whereas some others are recurrent. Temperature is crucial for plant growth and development, and plants often encounter adverse high temperature fluctuations (heat stresses) as well as prolonged cold exposure such as seasonal temperature drops in winter when grown in temperate regions. Many plants can remember past temperature stresses to get adapted to adverse local temperature changes to ensure survival and/or reproductive success. Here, we summarize chromatin-based mechanisms underlying acquired thermotolerance or thermomemory in plants and review recent progresses on molecular epigenetic understanding of ‘remembering of prolonged cold in winter’ or vernalization, a process critical for various over-wintering plants to acquire competence to flower in the coming spring. In addition, perspectives on future study in temperature stress memories of economically-important crops are discussed.     

Signaling through MAP kinase networks in plants

Protein phosphorylation is the most important mechanism for controlling many fundamental cellular processes in all living organisms including plants. A specific class of serine/threonine protein kinases, the mitogen-activated protein kinases (MAP kinases) play a central role in the transduction of various extra- and intracellular signals and are conserved throughout eukaryotes. These generally function via a cascade of networks, where MAP kinase (MAPK) is phosphorylated and activated by MAPK kinase (MAPKK), which itself is activated by MAPKK kinase (MAPKKK). Signaling through MAP kinase cascade can lead to cellular responses including cell division, differentiation as well as response to various stresses. In plants, MAP kinases are represented by multigene families and are organized into a complex network for efficient transmission of specific stimuli. Putative plant MAP kinase cascades have been postulated based on experimental analysis of in vitro interactions between specific MAP kinase components. These cascades have been tested in planta following expression of epitope-tagged kinases in protoplasts. It is known that signaling for cell division and stress responses in plants are mediated through MAP kinases and even auxin, ABA and possibly ethylene and cytokinin also utilize a MAP kinase pathway. Most of the biotic (pathogens and pathogen-derived elicitors) including wounding and abiotic stresses (salinity, cold, drought, and oxidative) can induce defense responses in plants through MAP kinase pathways. In this article we have covered the historical background, biochemical assay, activation/inactivation, and targets of MAP kinases with emphasis on plant MAP kinases and the responses regulated by them. The cross-talk between plant MAP kinases is also discussed to bring out the complexity within this three-component module.     

The pepper extracellular peroxidase CaPO2 is required for salt, drought and oxidative stress tolerance as well as resistance to fungal pathogens

In plants, biotic and abiotic stresses regulate the expression and activity of various peroxidase isoforms. Capsicum annuum EXTRACELLULAR PEROXIDASE 2 (CaPO2) was previously shown to play a role in local and systemic reactive oxygen species bursts and disease resistance during bacterial pathogen infection. Here, we report CaPO2 expression patterns and functions during conditions of biotic and abiotic stress. In pepper plants, CaPO2 expression was strongly induced by abscisic acid, but not by defense-related plant hormones such as salicylic acid, ethylene and jasmonic acid. CaPO2 was also strongly induced by abiotic and biotic stress treatments, including drought, cold, high salinity and infection by the hemibiotrophic fungal pathogen Colletotrichum coccodes. Loss-of-function of CaPO2 in virus-induced gene silenced pepper plants led to increased susceptibility to salt- and osmotic-induced stress. In contrast, CaPO2 overexpression in transgenic Arabidopsis thaliana plants conferred enhanced tolerance to high salt, drought, and oxidative stress, while also enhancing resistance to infection by the necrotrophic fungal pathogen Alternaria brassicicola. Taken together, these results provide evidence for the involvement of pepper extracellular peroxidase CaPO2 in plant defense responses to various abiotic stresses and plant fungal pathogens.     

植物光合系统对高温胁迫的响应机制

温度变化是影响植物生长和发育的一个非常重要的因素,而光合作用是植物对温度变化最为敏感的生理过程.高温胁迫给植物光合器官造成了严重的危害,但在高温胁迫下,植物并不是消极被动的,并且能够在生理生化及分子水平上发生各种变化来渡过逆境.本文结合当今国内外研究进展,从光合系统热量耗散与光合修复的相关因素,如类囊体膜上相关蛋白,热激蛋白,水杨酸,抗过氧化物酶及抗坏血酸等几个方面展开分析,阐述了植物光合系统对高温胁迫的防御机制,并对今后的研究方向进行了探讨和展望.     

Strigolactones in plant adaptation to abiotic stresses: An emerging avenue of plant research

Phytohormones play central roles in boosting plant tolerance to environmental stresses, which negatively affect plant productivity and threaten future food security. Strigolactones (SLs), a class of carotenoid‐derived phytohormones, were initially discovered as an “ecological signal” for parasitic seed germination and establishment of symbiotic relationship between plants and beneficial microbes. Subsequent characterizations have described their functional roles in various developmental processes, including root development, shoot branching, reproductive development, and leaf senescence. SLs have recently drawn much attention due to their essential roles in the regulation of various physiological and molecular processes during the adaptation of plants to abiotic stresses. Reports suggest that the production of SLs in plants is strictly regulated and dependent on the type of stresses that plants confront at various stages of development. Recently, evidence for crosstalk between SLs and other phytohormones, such as abscisic acid, in responses to abiotic stresses suggests that SLs actively participate within regulatory networks of plant stress adaptation that are governed by phytohormones. Moreover, the prospective roles of SLs in the management of plant growth and development under adverse environmental conditions have been suggested. In this review, we provide a comprehensive discussion pertaining to SL‐mediated plant responses and adaptation to abiotic stresses.     

植物逆境驯化作用的生理与分子机制研究进展

植物在生长发育过程中要面对各种生物和非生物胁迫,目前对于植物应对胁迫的研究较为充分。在自然界中,各种逆境胁迫因子对植物的影响更多的是渐变的,逐渐积累的,在此过程中植物会通过驯化的方式适应这种形式的胁迫。尽管有关驯化作用提高植物耐逆性的研究有些报道,但其生理与分子机制现在还不十分清楚。本文主要介绍了植物应对病虫,冷,热,高盐4种环境因子的驯化过程的研究进展,同时总结了驯化过程的生理与分子机制,包括非激活状态的信号分子的积累以及表观遗传学修饰等。     

Riboflavin-induced Priming for Pathogen Defense in Arabidopsis thaliana

Riboflavin (vitamin B2) participates in a variety of redox processes that affect plant defense responses. Previously we have shown that riboflavin induces pathogen resistance in the absence of hypersensitive cell death (HCD) in plants. Herein, we report that riboflavin induces priming of defense responses in Arabidopsis thaliana toward infection by virulent Pseudomonas syringae pv. Tomato DC3000 (Pst). Induced resistance was mechanistically connected with the expression of defense response genes and cellular defense events, including H2O2 burst, HCD, and callose deposition in the plant. Riboflavin treatment and inoculation of plants with Pst were neither active but both synergized to induce defense responses. The priming process needed NPR1 (essential regulator of systemic acquired resistance) and maintenance of H2O2 burst but was independent of salicylic acid, jasmonic acid, ethylene, and abscisic acid. Our results suggest that the role of riboflavin in priming defenses is subject to a signaling process distinct from the known pathways of hormone signal transduction.     

Mitogen-activated protein kinase signaling in plants under abiotic stress

Mitogen-activated protein kinase cascade is evolutionarily conserved signal transduction module involved in transducing extracellular signals to the nucleus for appropriate cellular adjustment. This cascade consists essentially of three components, a MAPK kinase kinase (MAPKKK), a MAPK kinase (MAPKK) and a MAPK connected to each other by the event of phosphorylation. These kinases play various roles in intra- and extra-cellular signaling in plants by transferring the information from sensors to responses. Signaling through MAP kinase cascade can lead to cellular responses including cell division, differentiation as well as responses to various stresses. MAPK signaling has also been associated with hormonal responses. In plants, MAP kinases are represented by multigene families and are involved in efficient transmission of specific stimuli and also involved in the regulation of the antioxidant defense system in response to stress signaling. In the current review we summarize and investigate the participation of MAPKs as possible mediators of various abiotic stresses in plants.Key words: abiotic stress, cross talk, mitogen-activated protein kinases, heat map, MAPK signaling, signal transduction, stress signaling     

Unraveling the role of mitochondria during oxidative stress in plants

The sedentary habit of plants means that they must stand and fight environmental stresses that their mobile animal cousins can avoid. A range of these abiotic stresses initiate the production in plant cells of reactive oxygen and nitrogen species that ultimately lead to oxidative damage affecting the yield and quality of plant products. A complex network of enzyme systems, producing and quenching these reactive species operate in different organelles. It is the integration of these compartmented defense systems that coordinates an effective response to the various stresses. Future attempts to improve plant growth or yield must consider the complexity of inter-organelle signaling and protein targeting if they are to be successful in producing plants with resistance to a broad range of stresses. Here we highlight the role of pre-oxidant, antioxidant, and post-oxidant defense systems in plant mitochondria and the potential role of proteins targeted to both mitochondria and chloroplasts, in an integrated defense against oxidative damage in plants.     

Jasmonate-dependent defense signaling in plant tissues

Depending on the stress type, plants activate various signal transduction pathways inducing the optimum defense process. This review is devoted to jasmonate (JA) dependent signaling involved in plant defense against biotic and abiotic stresses, including those determined by wounding, necrotrophic pathogens, pests, and herbivores. The sequence of major events of JA signaling is discussed. It is noted that JA signaling in plants is incorporated into a complex signaling network.     

Signals Regulating Multiple Responses to Wounding and Herbivores

Damage inflicted by herbivore feeding necessitates multiple defense strategies in plants. The wound site must be sealed and defense responses mounted against the herbivore itself and against invading opportunistic pathogens. These defenses are controlled both in time and space by highly complex regulatory networks that themselves are modulated by interactions with other signaling pathways. In this review, we describe the signaling events that occur in individual wounded leaves, in systemic unwounded regions of the plant, and between the plant, and other organisms, and attempt to place these events in the context of a coordinated system. Key signals that are discussed include ion fluxes, active oxygen species, protein phosphorylation cascades, the plant hormones jasmonic acid, ethylene, abscisic acid and salicylic acid, peptide signals, glycans, volatile chemicals, and physical signals such as hydraulic and electrical signals. Themes that emerge after consideration of the published data are that glycans and peptide elicitors are likely primary triggers of wound-induced defense responses and that they function through the action of jasmonic acid, a central mediator of defense gene expression, whose effect is modulated by ethylene. In the field, wound signaling pathways are significantly impacted on by other stress response pathways, including pathogen responses that often operate through potentially antagonistic signals such as salicylic acid. However, gross generalisations are not possible because some wound and pathogen responses operate through common jasmonate- and ethylene-dependent pathways. Understanding the ways in which local and systemic wound signaling pathways are coordinated individually and in the context of the plants wider environment is a key challenge in the application of this science to crop-protection strategies.