Plant chitinases--regulation and function

The aim of this review is to present the current state of knowledge on plant chitinases and their regulation and function. Chitinases are up-regulated by a variety of stress conditions, both biotic and abiotic, and by such phytohormones as ethylene, jasmonic acid, and salicylic acid. Like other PR proteins, chitinases play a role in plant resistance against distinct pathogens. Moreover, by reducing the defence reaction of the plant, chitinases allow symbiotic interaction with nitrogen-fixing bacteria or mycorrhizal fungi. However, recent investigations have shown that these enzymes are also involved in numerous physiological events. The involvement of chitinases in development and growth processes is also described.     

The CRE1 Cytokinin Pathway Is Differentially Recruited Depending on Medicago truncatula Root Environments and Negatively Regulates Resistance to a Pathogen

Cytokinins are phytohormones that regulate many developmental and environmental responses. The Medicago truncatula cytokinin receptor MtCRE1 (Cytokinin Response 1) is required for the nitrogen-fixing symbiosis with rhizobia. As several cytokinin signaling genes are modulated in roots depending on different biotic and abiotic conditions, we assessed potential involvement of this pathway in various root environmental responses. Phenotyping of cre1 mutant roots infected by the Gigaspora margarita arbuscular mycorrhizal (AM) symbiotic fungus, the Aphanomyces euteiches root oomycete, or subjected to an abiotic stress (salt), were carried out. Detailed histological analysis and quantification of cre1 mycorrhized roots did not reveal any detrimental phenotype, suggesting that MtCRE1 does not belong to the ancestral common symbiotic pathway shared by rhizobial and AM symbioses. cre1 mutants formed an increased number of emerged lateral roots compared to wild-type plants, a phenotype which was also observed under non-stressed conditions. In response to A. euteiches, cre1 mutants showed reduced disease symptoms and an increased plant survival rate, correlated to an enhanced formation of lateral roots, a feature previously linked to Aphanomyces resistance. Overall, we showed that the cytokinin CRE1 pathway is not only required for symbiotic nodule organogenesis but also affects both root development and resistance to abiotic and biotic environmental stresses.     

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.     

Linking plant functional genes to rhizosphere microbes: a review

The importance of rhizomicrobiome in plant development, nutrition acquisition and stress tolerance is unquestionable. Relevant plant genes corresponding to the above functions also regulate rhizomicrobiome construction. Deciphering the molecular regulatory network of plant-microbe interactions could substantially contribute to improving crop yield and quality. Here, the plant gene-related nutrient uptake, biotic and abiotic stress resistance, which may influence the composition and function of microbial communities, are discussed in this review. In turn, the influence of microbes on the expression of functional plant genes, and thereby plant growth and immunity, is also reviewed. Moreover, we have specifically paid attention to techniques and methods used to link plant functional genes and rhizomicrobiome. Finally, we propose to further explore the molecular mechanisms and signalling pathways of microbe-host gene interactions, which could potentially be used for managing plant health in agricultural systems.     

BRs在植物响应非生物胁迫中的作用

油菜素甾体(brassinosteroids,BRs)是植物界普遍存在的一类多羟基化的植物甾体激素,不仅调节植物的生长发育过程,还参与植物对生物和非生物胁迫的响应.概述了BRs的生物合成途径以及信号转导途径,重点阐述了BRs参与非生物胁迫应答的分子机制,展望了BRs未来的研究方向,为深入理解BRs介导的非生物胁迫调控网...     

The role of mycorrhizae and plant growth promoting rhizobacteria (PGPR) in improving crop productivity under stressful environments

Both biotic and abiotic stresses are major constrains to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, producing plant growth regulators, solubilizing nutrients and inducing resistance against plant pathogens. In addition to their interactions with plants, these microbes also show synergistic as well as antagonistic interactions with other microbes in the soil environment. These interactions may be vital for sustainable agriculture because they mainly depend on biological processes rather than on agrochemicals to maintain plant growth and development as well as proper soil health under stress conditions. A number of research articles can be deciphered from the literature, which shows the role of rhizobacteria and mycorrhizae alone and/or in combination in enhancing plant growth under stress conditions. However, in contrast, a few review papers are available which discuss the synergistic interactions between rhizobacteria and mycorrhizae for enhancing plant growth under normal (non-stress) or stressful environments. Biological interactions between PGPR and mycorrhizal fungi are believed to cause a cumulative effect on all rhizosphere components, and these interactions are also affected by environmental factors such as soil type, nutrition, moisture and temperature. The present review comprehensively discusses recent developments on the effectiveness of PGPR and mycorrhizal fungi for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review. Growth promotion by single and dual inoculation of PGPR and mycorrhizal fungi under stress conditions have also been discussed and reviewed comprehensively.     

微生物帮助烟草抗旱的机理及其应用

干旱是中国烟草种植业面临的较为严重的非生物胁迫.很多与植物共生或联合的根际微生物能帮助植物避旱和耐旱.微生物能通过菌丝吸水并转运到植物,通过产生植物激素或改变植物内源激素的平衡来促进根发育和伸长,或诱导叶片关闭气孔,促进根吸水和减少叶片散失水分来避旱.微生物能通过调整不同激素介导的信号通路,诱导植物产生系统抗逆性,促进植物细胞产生渗透保护剂、抗氧化物和活性氧清除剂而耐旱.微生物还能帮助植物吸收营养,以支持植物在干旱胁迫下的代谢和生长.本文关注丛枝菌根真菌、模式内生真菌印度梨形孢和根际促植物生长细菌帮助烟草和番茄等植物抗旱的机理,探讨如何在烟草育苗和栽培中应用有益微生物来帮助烟草抗旱.     

丛枝菌根对植物根际逆境的生态学意义

近年来,我国在菌根分子生物学、菌根营养学、菌根分类学和菌根生态学等方面取得了令人瞩目的研究成果,其中对丛枝菌根真菌(AMF)的研究居多。AMF能与大部分陆地植物根系形成共生关系,促进植物生长发育,提高植物抗逆性,在保持生态平衡、保护生态环境等方面发挥重要作用。本文主要从非生物胁迫(干旱胁迫、重金属污染、盐碱胁迫)和生物胁迫(致病菌和线虫侵染)方面介绍了AMF在植物根际逆境中发挥的生态功能及作用机制,提出了该研究领域尚存的不足之处和研究前景,为AMF后续研究提供参考。     

Is —— the rhizosphere a source of applicable multi-beneficial microorganisms for plant enhancement?

The plant faces different pedological and climatic challenges that influence its growth and enhancement. While, plant-microbes interactions throught the rhizosphere offer several privileges to this hotspot in the service of plant, by attracting multi-beneficial mutualistic and symbiotic microorganisms as plant growth-promoting bacteria (PGPB), archaea, mycorrhizal fungi, endophytic fungi, and others…). Currently, numerous investigations showed the beneficial effects of these microbes on growth and plant health. Indeed, rhizospheric microorganisms offer to host plants the essential assimilable nutrients, stimulate the growth and development of host plants, and induce antibiotics production. They also attributed to host plants numerous phenotypes involved in the increase the resistance to abiotic and biotic stresses. The investigations and the studies on the rhizosphere can offer a way to find a biological and sustainable solution to confront these environmental problems. Therefore, the interactions between microbes and plants may lead to interesting biotechnological applications on plant improvement and the adaptation in different climates to obtain a biological sustainable agricultures without the use of chemical fertilizers.     

Plant symbionts: keys to the phytosphere

The exterior and interior of plants, aboveground and belowground, comprise a complex plant micro-ecosystem, known in recent years as the phytosphere. There are three components: the phyllosphere, endosphere, and rhizosphere. Although in comparison with other ecosystems the phytosphere is small, it similarly includes a great variety of functional microbes. Among these are certain microbes that live in symbiotic relationships with plants; these microbes are known as plant symbionts. Recent research has shown that these symbionts have tremendous effects on plant growth, confer resistance to abiotic stresses and pathogens, aid in the accumulation of metabolites, and have crucial relationships with other plant-associated microbes in the phytosphere. We review the ecological effects of plant symbionts on other microbes, and interactions between plant symbionts in the phytosphere. In addition, we discuss internal mechanisms and suggest future hot spots for research.     

Bacillus subtilis: A plant-growth promoting rhizobacterium that also impacts biotic stress

Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.     

环境胁迫下内生菌与宿主代谢相互作用研究进展

植物体内成分是实时反映其生理状态的最直接指标,是其遭受生物或非生物胁迫应激状态的体现,微生物与植物的共生抗逆亦由代谢的重置与调控得以实现.内生菌可以自身细胞功能或代谢产物调控宿主代谢,其自身可产生独特的、显著区别于宿主的代谢成分参与抗逆;而宿主内环境的长期“驯化”亦可改变内生菌的表型和代谢.较全面地分析了植物与微生物共...     

Role of Pathogen-Related Protein 10 (PR 10) under Abiotic and Biotic Stresses in Plants

Members of the Pathogenesis Related (PR) 10 protein family have been identified in a variety of plant species and a wide range of functions ranging from defense to growth and development has been attributed to them. PR10 protein possesses ribonuclease (RNase) activity, interacts with phytohormones, involved in hormone-mediated signalling, afforded protection against various phytopathogenic fungi, bacteria, and viruses particularly in response to biotic and abiotic stresses. The resistance mechanism of PR10 protein may include activation of defense signalling pathways through possible interacting proteins involved in mediating responses to pathogens, degradation of RNA of the invading pathogens. Moreover, several morphological changes have been shown to accompany the enhanced abiotic stress tolerance. In this review, the possible mechanism of action of PR10 protein against biotic and abiotic stress has been discussed. Furthermore, our findings also confirmed that the in vivo Nitric oxide (NO) is essential for most of environmental abiotic stresses and disease resistance against pathogen infection. The proper level of NO may be necessary and beneficial, not only in plant response to the environmental abiotic stress, but also to biotic stress. The updated information on this interesting group of proteins will be useful in future research to develop multiple stress tolerance in plants.     

Kinase-dead mutation: A novel strategy for improving soybean resistance to soybean cyst nematode Heterodera glycines

Protein kinases phosphorylate proteins for functional changes and are involved in nearly all cellular processes, thereby regulating almost all aspects of plant growth and development, and responses to biotic and abiotic stresses. We generated two independent co-expression networks of soybean genes using control and stress response gene expression data and identified 392 differentially highly interconnected kinase hub genes among the two networks. Of these 392 kinases, 90 genes were identified as “syncytium highly connected hubs”, potentially essential for activating kinase signalling pathways in the nematode feeding site. Overexpression of wild-type coding sequences of five syncytium highly connected kinase hub genes using transgenic soybean hairy roots enhanced plant susceptibility to soybean cyst nematode (SCN; Heterodera glycines) Hg Type 0 (race 3). In contrast, overexpression of kinase-dead variants of these five syncytium kinase hub genes significantly enhanced soybean resistance to SCN. Additionally, three of the five tested kinase hub genes enhanced soybean resistance to SCN Hg Type 1.2.5.7 (race 2), highlighting the potential of the kinase-dead approach to generate effective and durable resistance against a wide range of SCN Hg types. Subcellular localization analysis revealed that kinase-dead mutations do not alter protein cellular localization, confirming the structure–function of the kinase-inactive variants in producing loss-of-function phenotypes causing significant decrease in nematode susceptibility. Because many protein kinases are highly conserved and are involved in plant responses to various biotic and abiotic stresses, our approach of identifying kinase hub genes and their inactivation using kinase-dead mutation could be translated for biotic and abiotic stress tolerance.     

The biosynthetic potential of plant roots

The contribution of roots to the biology of the whole plant is being reevaluated in the light of classical and recent findings. In addition to their role in water and nutrient uptake and in symbiotic associations, plant roots also synthesize a remarkable variety of secondary metabolites. These chemicals, many of which are used as pharmaceuticals, agrichemicals, flavors, dyes, or fragrances, may help the plant cope with biotic and abiotic stress. Root cultures are being used as experimental systems to explore both root-specific secondary metabolites and their biological significance. They may also provide future systems for commercial production of plant specialty chemicals.     

Plant protein kinases stimulated by calcium

Calcium signals play an important role in many aspects of plant growth and development, including plant response to biotic and abiotic stress. The stimulus characteristic intracellular Ca2+ signals are generated in plant cells by a variety of stimuli, including changes in environmental conditions, interaction with microbes and growth and development processes. Cytoplasmatic calcium brings about responses by interacting with target proteins, like calcium-dependent kinases. In plant there are at least five classes of protein kinases (CDPK, CRK, CCaMK, CaMK and SnRK3), which activity is regulated by calcium ions. In this article the structure, regulation and function of calcium stimulated protein kinases are briefly reviewed.     

Unraveling the role of fungal symbionts in plant abiotic stress tolerance

Fungal symbionts have been found to be associated with every plant studied in the natural ecosystem, where they colonize and reside entirely or partially in the internal tissues of their host plant. Fungal endophytes can express/form a range of different lifestyle/relationships with different host including symbiotic, mutualistic, commensalistic and parasitic in response to host genotype and environmental factors. In mutualistic association fungal endophyte can enhance growth, increase reproductive success and confer biotic and abiotic stress tolerance to its host plant. Since abiotic stress such as, drought, high soil salinity, heat, cold, oxidative stress and heavy metal toxicity is the common adverse environmental conditions that affect and limit crop productivity worldwide. It may be a promising alternative strategy to exploit fungal endophytes to overcome the limitations to crop production brought by abiotic stress. There is an increasing interest in developing the potential biotechnological applications of fungal endophytes for improving plant stress tolerance and sustainable production of food crops. Here we have described the fungal symbioses, fungal symbionts and their role in abiotic stress tolerance. A putative mechanism of stress tolerance by symbionts has also been covered.Key words: abiotic stress, endophytes, fungal symbiont, mycorrhizal fungus, Piriformospora indica, stress tolerance, symbiosis     

多胺与环境胁迫关系研究进展

多胺是植物对胁迫响应的重要物质,可以抵消胁迫引起的负效应.多胺预处理可缓解胁迫引起的伤害,通过转基因技术过量表达多胺可提高植物胁迫耐性.本文综述了生物胁迫和非生物胁迫条件下,多胺的合成、代谢、功能及其作为抗氧化剂减少胁迫诱导氧化损伤的研究现状.重点综述了病虫胁迫、盐胁迫、重金属胁迫、渗透胁迫,也简要的综述了其它胁迫如低氧胁迫、冷胁迫、酸胁迫、辐射胁迫等条件下植物体内多胺合成的变化及功能.