植物-土壤反馈与草地群落演替:菌根真菌和土壤病原菌的调控作用

由植物引起的根际土壤生物或非生物环境的改变能够反馈影响群落中不同植物的生长,直接改变共存植物的相对竞争关系,推动群落结构的动态变化。作为土壤生物群落的重要组成部分,土壤微生物在植物-土壤反馈关系中起到重要的调控作用,对解释植物群落的演替进程和方向有着重要的意义。在草地植物群落演替的早期阶段和外来物种入侵的过程中,宿主植物对丛枝菌根真菌（AMF）的依赖性较低,受本地病原菌的影响较小,一般不存在负反馈。在演替后期,植物对AMF更具依赖性,而积累的病原菌则产生较强的负反馈效应,从而促进群落物种共存和植物多样性,提高草地生产力和稳定性。研究微生物-植物反馈机制不仅有助于完善草地退化与恢复理论,还对退化草地恢复治理的实践有着指导意义。未来关于根际微生物-植物反馈在草地群落演替中的作用应该加强以下几方面的研究：（1）在实验方法上,开展专性微生物-植物反馈研究;（2）在测定指标上,进一步量化不同微生物在反馈关系中的功能差异;（3）在研究对象上,加强土壤微生物在植物群落水平的反馈研究;（4）在应用上,明晰植物-土壤反馈在退化草地恢复过程中的作用,指导草地管理实践。     

Symbiotic microorganisms, a key for ecological success and protection of plants

Plant-associated microbial diversity encompasses symbionts, protecting their host against various aggressions. Mycorrhizal and rhizospheric microorganisms buffer effects of soil toxic compounds and soil-borne pathogens. Endophytic bacteria and fungi, some of which are vertically inherited through seeds, take part in plant protection by acting directly on aggressive factors (mainly pathogens and herbivores) or by enhancing plant responses. Plant protective microbial symbionts determine the ecological success of plants; they drastically modify plant communities and related trophic webs. This review suggests approaches to improve the inventory of diversity and functions of in situ plant-associated microorganisms.     

植物微生物组的功能及应用研究进展

健康的植物中生活着多种多样但分类学结构不同的微生物群落,它们在所有可接触到的植物组织中定殖。这些微生物群落赋予植物宿主健康优势,包括促进宿主植物生长、营养吸收、抗逆性和对病原菌的抵抗力等。植物菌群及其相互作用具有高度的多样性,多种因素决定着群落的组成和功能。虽然从19世纪开始植物菌群就被人们所认识,但对其功能及应用的相关研究却从20世纪80年代才开始蓬勃发展。综述了植物及相关微生物群落和环境之间遗传、生化、物理和代谢相互作用的复杂网络及其研究方法与应用的研究进展,以期为绿色农业、环境生态保护等提供新的思路。     

The BRI1-associated kinase 1, BAK1, has a brassinolide-independent role in plant cell-death control

Programmed cell death (PCD) is a common host response to microbial infection [1-3]. In plants, PCD is associated with immunity to biotrophic pathogens, but it can also promote disease upon infection by necrotrophic pathogens [4]. Therefore, plant cell-suicide programs must be strictly controlled. Here we demonstrate that the Arabidopsis thaliana Brassinosteroid Insensitive 1 (BRI1)-associated receptor Kinase 1 (BAK1), which operates as a coreceptor of BRI1 in brassinolide (BL)-dependent plant development, also regulates the containment of microbial infection-induced cell death. BAK1-deficient plants develop spreading necrosis upon infection. This is accompanied by production of reactive oxygen intermediates and results in enhanced susceptibility to necrotrophic fungal pathogens. The exogenous application of BL rescues growth defects of bak1 mutants but fails to restore immunity to fungal infection. Moreover, BL-insensitive and -deficient mutants do not exhibit spreading necrosis or enhanced susceptibility to fungal infections. Together, these findings suggest that plant steroid-hormone signaling is dispensable for the containment of infection-induced PCD. We propose a novel, BL-independent function of BAK1 in plant cell-death control that is distinct from its BL-dependent role in plant development.     

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。     

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.     

Plant Surface Receptors Recognizing Microbe-Associated Molecular Patterns

As sessile, plants are inevitably exposed to environmental threats including pathogens. Due to the lack of mobile immune cells, plants solely depend on the innate immune system to defend against pathogens. The first layer of pathogen detection in plant immunity is to recognize microbe-associated molecular patterns (MAMPs) that compose structural or functional units in microbial pathogens. For this, plants utilize pattern-recognition receptors (PRRs). Continuous attack by pathogens resulting from immotility likely contributes to the extension of PRR numbers in plants, although genomeencoded. Recent findings revealed that plant PRRs as a complex dynamically switch between inactive and active forms at the plasma membrane depending on a cognate MAMP. In addition, by regulating the activity and stability of a downstream signal-relaying receptor-like cytoplasmic kinase (RLCK), plants can control the immune homeostasis. Therefore, we in this review discuss on how plants detect a pathogen and how they control immune responses at the level of PRRs in a correct and delicate way. We additionally provide a possible balancing mechanism between growth and responses to biotic and abiotic stresses in plants, which is required for survival in nature.     

Plant recognition of microbial patterns

Animals express an innate immune system against pathogens through receptor-mediated recognition of conserved microbial structures called pathogen-associated molecular patterns (PAMPs). In plants, resistance to invading microorganisms is often governed by specific recognition between plant and pathogen proteins. Perception of more broadly conserved 'general' pathogen elicitors constitutes another layer of plant resistance and prompts questions of where, mechanistically and evolutionarily, this mode of non-self discrimination fits within known systems of microbial surveillance in animals and plants.     

The rhizosphere microbiome and plant health

The diversity of microbes associated with plant roots is enormous, in the order of tens of thousands of species. This complex plant-associated microbial community, also referred to as the second genome of the plant, is crucial for plant health. Recent advances in plant-microbe interactions research revealed that plants are able to shape their rhizosphere microbiome, as evidenced by the fact that different plant species host specific microbial communities when grown on the same soil. In this review, we discuss evidence that upon pathogen or insect attack, plants are able to recruit protective microorganisms, and enhance microbial activity to suppress pathogens in the rhizosphere. A comprehensive understanding of the mechanisms that govern selection and activity of microbial communities by plant roots will provide new opportunities to increase crop production.     

细菌铁载体拮抗植物病原真菌及促生作用研究进展

铁载体是微生物在缺铁条件下分泌的小分子有机化合物,以获取铁元素维持其生长。细菌分泌的铁载体在拮抗植物病原菌和促进植物生长方面具有重要作用。本文总结了细菌铁载体拮抗植物病原真菌的营养和生态位竞争、诱导植物诱导性系统抗性、扰乱病原菌铁稳态的机制,以及促进植物生长的作用,以解释细菌分泌的铁载体在多功能微生物菌剂研制中的重要作用。     

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.     

Plasmodesmata: the battleground against intruders

Plasmodesmata are intercellular channels that establish a symplastic communication pathway between neighboring cells in plants. Owing to this role, opportunistic microbial pathogens have evolved to exploit plasmodesmata as gateways to spread infection from cell to cell within the plant. However, although these pathogens have acquired the capacity to breach the plasmodesmal trafficking pathway, plants are unlikely to relinquish control over a structure essential for their survival so easily. In this review, we examine evidence that suggests plasmodesmata play an active role in plant immunity against viral, fungal and bacterial pathogens. We discuss how these pathogens differ in their lifestyles and infection modes, and present the defense strategies that plants have adopted to prevent the intercellular spread of an infection.     

喀斯特区不同退化程度植被群落植物-凋落物-土壤-微生物生态化学计量特征

为摸清喀斯特植被退化对群落各组分C、N、P生态化学计量特征及内稳态特征的影响，为喀斯特退化生态系统植被恢复与重建提供科学依据，以桂西北喀斯特地区5种退化程度植被群落为研究对象，测定了不同退化程度植被群落植物叶片、凋落物、土壤和微生物生物量的C、N、P含量，分析其化学计量比特征、相互关系及植物内稳性特征。结果表明：(1)随着退化程度加剧，叶片C、N、P含量、N∶P和凋落物N∶P、微生物量C显著下降，而叶片C∶N、C∶P则显著增加，且植物叶片N∶P<14;随退化程度加剧，凋落物N、P含量、土壤C、N、P含量、微生物量N、P呈先略有增后显著降低的趋势，且不同退化程度群落土壤N∶P和微生物量C∶N无显著差异。(2)叶片N、P含量与土壤N、P含量，叶片C∶P与土壤C∶N、C∶P、N∶P,叶片N∶P与凋落物N、N∶P,叶片C、N、P含量与微生物量C呈显著或极显著正相关关系；叶片C∶N与土壤C、N,叶片C∶P与土壤N、P,叶片N∶P与土壤P呈显著或极显著负相关关系。(3)喀斯特地区植物叶片N、P元素的内稳性指数(H)平均值分别为2.74和2.31,属于弱稳态型，叶片N∶P的H值为5.14,为稳...     

Recent advances in plant immunity: recognition, signaling, response, and evolution

Innate immune system is employed by plants to defend against phytopathogenic microbes through specific perception of non-self molecules and subsequent initiation of resistance responses. Current researches elucidate that plants mostly rely on cell surface-located pattern recognition receptors (PRRs) and intracellular nucleotide-binding leucine-rich repeat proteins (NB-LRRs) to recognize pathogen-associated molecular patterns (PAMPs) and effector proteins from microbial pathogens, initiating PAMP- and effector-triggered immunity (PTI and ETI), respectively. Some pathogenic bacterial effector proteins are usually secreted into plant cells and play a virulence function by suppressing plant PTI, implying an evolutionary process of plant immunity from PTI to ETI. In the past several years, a great progress has been achieved to reveal fascinating molecular mechanisms underlying the pathogenic recognition, resistance signaling transduction, and plant immunity evolution. Here, we summarized the latest breakthroughs about these topics, and offered an integral understanding of plant molecular immunity.     

Spatio-temporal variation of rhizosphere soil microbial abundance and enzyme activities under different vegetation types in the coastal zone,Shandong, China

In coastal sandy soils, the establishment of a plant cover is fundamental to avoid degradation and desertification processes. A better understanding of the ability of plants to promote soil microbial process in these conditions is necessary for successful soil reclamation. The current study was to investigate the ability of four different plant species to regenerate the microbiological processes in the rhizosphere soil and to discuss which species were the most effective for the reclamation of the coastal zone. The rhizosphere soils were studied by measuring microbial abundance (bacteria, fungi, actinomycetes, and ammonifiers), enzyme activities (invertase, catalase, urease, and phosphatase) and their relationship. Microbial abundance greatly varied among rhizospheres of different plant species (p < 0.05). Phragmites australis supported the highest amount of bacterial, actinomycetes, and ammonifiers abundance, and Echinochloa crusgalli supported the highest fungi abundance. In addition, the significant differences in rhizosphere enzyme activities of different plant species were also observed. There was a significant linear correlation between rhizosphere soil microbial abundances and enzyme activities between bacteria and urease and between fungi and catalase, but no such significant relationship was found between all rhizosphere soil microbial abundance and phosphatases. It was concluded that different plant species in coastal areas have different rhizosphere soils due to the impact of the different root exudates and plant residues of the microbial properties. In addition, natural grasslands (P. australis and E. crusgalli) are the most effective for revegetating coastal sandy soils.     

Protein acetylation and deacetylation in plant-pathogen interactions

Protein acetylation and deacetylation catalysed by lysine acetyltransferases (KATs) and deacetylases (KDACs), respectively, are major mechanisms regulating various cellular processes. During the fight between microbial pathogens and host plants, both apply a set of measures, including acetylation interference, to strengthen themselves while suppressing the other. In this review, we first summarize KATs and KDACs in plants and their pathogens. Next, we introduce diverse acetylation and deacetylation mechanisms affecting protein functions, including the regulation of enzyme activity and specificity, protein–protein or protein-DNA interactions, subcellular localization and protein stability. We then focus on the current understanding of acetylation and deacetylation in plant–pathogen interactions. Additionally, we also discuss potential acetylation-related approaches for controlling plant diseases.     

DCD – a novel plant specific domain in proteins involved in development and programmed cell death

Background  

Recognition of microbial pathogens by plants triggers the hypersensitive reaction, a common form of programmed cell death in plants. These dying cells generate signals that activate the plant immune system and alarm the neighboring cells as well as the whole plant to activate defense responses to limit the spread of the pathogen. The molecular mechanisms behind the hypersensitive reaction are largely unknown except for the recognition process of pathogens. We delineate the NRP-gene in soybean, which is specifically induced during this programmed cell death and contains a novel protein domain, which is commonly found in different plant proteins.     

Host-microbe interactions: shaping the evolution of the plant immune response

The evolution of the plant immune response has culminated in a highly effective defense system that is able to resist potential attack by microbial pathogens. The primary immune response is referred to as PAMP-triggered immunity (PTI) and has evolved to recognize common features of microbial pathogens. In the coevolution of host-microbe interactions, pathogens acquired the ability to deliver effector proteins to the plant cell to suppress PTI, allowing pathogen growth and disease. In response to the delivery of pathogen effector proteins, plants acquired surveillance proteins (R proteins) to either directly or indirectly monitor the presence of the pathogen effector proteins. In this review, taking an evolutionary perspective, we highlight important discoveries over the last decade about the plant immune response.     

Mycorrhizosphere interactions to improve plant fitness and soil quality

Arbuscular mycorrhizal fungi are key components of soil microbiota and obviously interact with other microorganisms in the rhizosphere, i.e. the zone of influence of plant roots on microbial populations and other soil constituents. Mycorrhiza formation changes several aspects of plant physiology and some nutritional and physical properties of the rhizospheric soil. These effects modify the colonization patterns of the root or mycorrhizas (mycorrhizosphere) by soil microorganisms. The rhizosphere of mycorrhizal plants, in practice a mycorrhizosphere, harbors a great array of microbial activities responsible for several key ecosystem processes. This paper summarizes the main conceptual principles and accepted statements on the microbial interactions between mycorrhizal fungi and other members of rhizosphere microbiota and discusses current developments and future trends concerning the following topics: (i) effect of soil microorganisms on mycorrhiza formation; (ii) mycorrhizosphere establishment; (iii) interactions involved in nutrient cycling and plant growth; (iv) interactions involved in the biological control of plant pathogens; and (v) interactions to improve soil quality. The main conclusion is that microbial interactions in the rhizosphere of mycorrhizal plants improve plant fitness and soil quality, critical issues for a sustainable agricultural development and ecosystem functioning. This revised version was published online in August 2006 with corrections to the Cover Date.