Mechanisms of plant defense against insect herbivores

Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.     

硅对植物抗虫性的影响及其机制

硅不是植物必需营养元素,但硅在提高植物对一系列非生物和生物胁迫的抗性方面都具有重要作用。综述了硅对植物抗虫性的影响及其机制。在多数植物中,增施硅肥可增强其抗虫性;所增强的抗性与硅肥种类和施用方式之间存在关系。植物组织中沉积的硅可增加其硬度和耐磨度,降低植物可消化性,从而增强植物组成性防御,包括延缓昆虫生长发育、降低繁殖力、减轻植物受害程度;植物体内的硅含量以及硅沉积的位点和排列方式影响组成性防御作用的强度。此外,硅可以调节植物诱导性防御,包括直接防御和间接防御,直接防御涉及增加有毒物质含量、产生局部过敏反应或系统获得抗性、产生有毒化合物和防御蛋白,从而延缓昆虫发育;间接防御主要通过释放挥发性化合物吸引植食性昆虫的捕食性和寄生性天敌而导致植食性昆虫种群下降。     

植食性昆虫唾液效应子和激发子的研究进展

植食性昆虫与寄主植物通过协同进化形成了复杂的防御和反防御机制.本文系统综述了昆虫唾液效应子和激发子在植物与昆虫互作中的作用及机理.昆虫取食中释放的唾液激发子被植物识别而激活植物早期免疫反应,昆虫也能从口腔分泌效应子到植物体内抑制免疫;抗性植物则利用抗性(R)蛋白识别昆虫无毒效应子,启动效应子诱导的免疫反应,而昆虫又进化...     

Rice–gall midge interactions: Battle for survival

Gall midges are insects specialized in maneuvering plant growth, metabolic and defense pathways for their benefit. The Asian rice gall midge and rice share such an intimate relationship that there is a constant battle for survival by either partner. Diverse responses by the rice host against the midge include necrotic hypersensitive resistance reaction, non-hypersensitive resistance reaction and gall-forming compatible interaction. Genetic studies have revealed that major R (resistance) genes confer resistance to gall midge in rice. Eleven gall midge R genes have been characterized so far in different rice varieties in India. In addition, no single R gene confers resistance against all the seven biotypes of the Asian rice gall midge, and none of the biotypes is virulent against all the resistance genes. Further, the interaction of the plant resistance gene with the insect avirulence gene is on a gene-for-gene basis. Our recent investigations involving suppressive subtraction hybridization cDNA libraries, microarray analyses, gene expression assays and metabolic profiling have revealed several molecular mechanisms, metabolite markers and pathways that are induced, down-regulated or altered in the rice host during incompatible or compatible interactions with the pest. This is also true for some of the pathways studied in the gall midge. Next generation sequencing technology, gene expression studies and conventional screening of gall midge cDNA libraries highlighted molecular approaches adopted by the insect to feed, survive and reproduce. This constant struggle by the midge to overcome the host defenses and the host to resist the pest has provided us with an opportunity to observe this battle for survival at the molecular level.     

Silicon‐mediated multiple interactions: Simultaneous induction of rice defense and inhibition of larval performance and insecticide tolerance of Chilo suppressalis by sodium silicate

The rice striped stem borer (SSB, Chilo suppressalis) is one of the most destructive pests of rice plants. Si‐mediated rice defense against various pests has been widely reported, and sodium silicate (SS) has been used as an effective source of silicon for application to plants. However, there is quite limited information about the direct effects of Si application on herbivorous insects. SSB larval performance and their insecticide tolerance were examined after they had been reared either on rice plants cultivated in nutrient solution containing 0.5 and 2.0 mM SS or on artificial diets with 0.1% and 0.5% SS. SS amendment in either rice culture medium or artificial diets significantly suppressed the enzymatic activities of acetylcholinesterase, glutathione S‐transferases, and levels of cytochrome P450 protein in the midgut of C. suppressalis larvae. Larvae fed on diets containing SS showed lower insecticide tolerance. Additionally, RNA‐seq analysis showed that SS‐mediated larval insecticide tolerance was closely associated with fatty acid biosynthesis and pyruvate metabolism pathways. Our results suggest that Si not only enhances plant resistance against insect herbivore, but also impairs the insect's capacity to detoxify the insecticides. This should be considered as another important aspect in Si‐mediated plant–insect interaction and may provide a novel approach of pest management.     

Ecological and Evolutionary Interactions between Wild Crucifers and Their Herbivorous Insects

Abstract Insects feeding on ten species of wild crucifer were investigated. Differences in host plant range and insect community structure were examined with regard to anti-herbivore defense mechanisms. Most of the crucifer species deterred insect herbivory by disappearing in the summer or by lowering their intrinsic quality as food for insects. Species with these defense mechanisms were exploited by only a few specialized herbivorous insects that seemed to have counter defenses. The plants without these defense mechanisms were used by many herbivorous insect species. Rorippa indica lacked direct defenses, but supported a low total density of herbivore individuals. This crucifer has an indirect defense mechanism: ants attracted to floral nectar defended the plant from deleterious herbivores. Crucifers that disappeared seasonally lacked other anti-herbivore defense mechanisms. This suggests that the phonological response is an alternative other responses to herbivore attack.     

Molecular strategies of plant defense and insect counter-defense

The prediction of human population growth worldwide indicates there will be a need to substantially increase food production in order to meet the demand on food supply.This can be achieved in part by the effective management of insect pests. Since plants have co-evolved with herbivorous insects for millions of years, they have developed an array of defense genes to protect themselves against a wide variety of chewing and sucking insects.Using these naturally-occurring genes via genetic engineering represents an environmentally friendly insect pest-control measure. Insects, however, have been actively evolving adaptive mechanisms to evade natural plant defenses. Such evolved adaptability undoubtedly has helped insects during the last century to rapidly overcome a great many humanimposed management practices and agents, including chemical insecticides and genetically engineered plants. Thus, better understanding of the molecular and genetic basis of plant defense and insect counter-defense mechanisms is imperative, not only from a basic science perspective, but also for biotechnology-based pest control practice. In this review, we emphasize the recent advance and understanding of molecular strategies of attack-counterattack and defense-counter-defense between plants and their herbivores.     

茶树诱导抗虫性的研究进展

为了抵御植食性昆虫的为害,植物在进化过程中形成了包括组成抗性和诱导抗性在内的复杂防御体系.在通过受体识别茶树害虫为害后,茶树会启动早期信号事件,继而激活茉莉酸、水杨酸、乙烯和赤霉素等植物激素信号通路,从而引起次生代谢物的积累,最终对害虫产生直接和间接抗性.基于近年来茶树害虫为害诱导的茶树防御反应及其相关调控机理的研究进...     

Nonglandular silicified trichomes are essential for rice defense against chewing herbivores

Interspecific New Rice for Africa (NERICA) varieties have been recently developed and used in Sub-Saharan Africa but herbivore resistance properties of these plants remain poorly understood. Here we report that, compared to a local Japanese cultivar Nipponbare, NERICA 1, 4 and 10 are significantly more damaged by insect herbivores in the paddy fields. In contrast to high levels of leaf damage from rice skippers and grasshoppers, constitutive and induced volatile organic compounds for indirect plant defense were higher or similar in NERICAs and Nipponbare. Accumulation of direct defense secondary metabolites, momilactones A and B, and p-coumaroylputrescine (CoP) was reduced in NERICAs, while feruloylputrescine accumulated at similar levels in all varieties. Finally, we found that Nipponbare leaves were covered with sharp nonglandular trichomes impregnated with silicon but comparable defense structures were virtually absent in herbivory-prone NERICA plants. As damage to the larval gut membranes by Nipponbare silicified trichomes that pass intact through the insect digestive system, occurs, and larval performance is enhanced by trichome removal from otherwise chemically defended Nipponbare plants, we propose that silicified trichomes work as an important defense mechanism of rice against chewing insect herbivores.     

外源茉莉酸和茉莉酸甲酯诱导植物抗虫作用及其机理

综述了茉莉酸(jasmonic acid, JA)和茉莉酸甲酯(methyl jasmo nate, MJA)的分子结构和应用其诱导的植物抗虫作用及其机制。植物受外源茉莉酸或茉莉酸甲酯刺激后,一条反应途径是由硬脂酸途径激活防御基因,另一条途径是直接激活防御基因。防御基因激活后导致代谢途径重新配置,并可能诱导植物产生下列4种效应：（1）直接防御,即植物产生对害虫有毒的物质、抗营养和抗消化的酶类,或具驱避性和妨碍行为作用的化合物;（2）间接防御,即产生吸引天敌的挥发物;（3）不防御,即无防御反应;（4）负防御,即产生吸引害虫的挥发物。     

Defense strategies used by two sympatric vineyard moth pests

Natural enemies including parasitoids are the major biological cause of mortality among phytophagous insects. In response to parasitism, these insects have evolved a set of defenses to protect themselves, including behavioral, morphological, physiological and immunological barriers. According to life history theory, resources are partitioned to various functions including defense, implying trade-offs among defense mechanisms. In this study we characterized the relative investment in behavioral, physical and immunological defense systems in two sympatric species of Tortricidae (Eupoecilia ambiguella, Lobesia botrana) which are important grapevine moth pests. We also estimated the parasitism by parasitoids in natural populations of both species, to infer the relative success of the investment strategies used by each moth. We demonstrated that larvae invest differently in defense systems according to the species. Relative to L. botrana, E. ambiguella larvae invested more into morphological defenses and less into behavioral defenses, and exhibited lower basal levels of immune defense but strongly responded to immune challenge. L. botrana larvae in a natural population were more heavily parasitized by various parasitoid species than E. ambiguella, suggesting that the efficacy of defense strategies against parasitoids is not equal among species. These results have implications for understanding of regulation in communities, and in the development of biological control strategies for these two grapevine pests.     

虫害诱导植物间接防御反应的激发与信号转导途径

植物通过产生和释放挥发性物质增加植食性昆虫的天敌对其寄主或猎物的定位,减少植食性昆虫对植物的取食,从而达到间接防御的目的。植物对植食性昆虫所做出间接防御反应激发因子和信号转导途径的研究,对应用虫害诱导植物挥发物引诱害虫天敌,并进一步从植物、植食性昆虫及其天敌间三级营养关系,研究动植物协同进化机理和病虫害防治具有深远意义。本文根据国内外最新研究进展,对虫害诱导植物间接防御反应的激发因子,昆虫取食信号的转导途径及对植物间接防御相关基因的激活等方面进行了系统地综述。     

植食性昆虫对植物的反防御机制

本文综述了植食性昆虫对植物的反防御机制.一方面,植食性昆虫可通过其快速进化的寄主选择适应性,改变取食策略,调节生长发育的节律,以及规避自然天敌等抑制、逃避或改变植物的防御,即行为防御机制;另一方面,植食性昆虫可适应植物蛋白酶抑制剂、逃避植物防御伤信号、解毒植物次生物质,以及抑制植物阻塞反应来对植物防御进行反防御,即生理和生化防御机制.其中,昆虫抑制植物伤信号,防止植物阻塞反应是反防御机制的研究热点.昆虫反防御的研究有助于提高对昆虫-植物间协同进化关系的认识,并为害虫治理和抗虫植物的培育提供新的思路.     

细胞核质转运及其受体在植物抗病防御反应中的调控作用

植物病害严重威胁全球粮食生产,研究植物对病原菌防御机制和病原菌对寄主作物的侵染过程和分子机制,有助于改良植物种源使其获得持久抗性。近年来, 日渐增多的研究表明, 一些抗病蛋白需要转移到细胞核内才能启动免疫反应,进而发挥抗病防御作用,而细胞核质转运受体是实现这些抗病蛋白核质转运必不可少的“载体”。因此,细胞核质转运及转运...     

The function of small RNAs in plant biotic stress response

Small RNAs(s RNAs) play essential roles in plants upon biotic stress. Plants utilize RNA silencing machinery to facilitate pathogen-associated molecular pattern-triggered immunity and effector-triggered immunity to defend against pathogen attack or to facilitate defense against insect herbivores. Pathogens, on the other hand, are also able to generate effectors and s RNAs to counter the host immune response. The arms race between plants and pathogens/insect herbivores has triggered the evolution of s RNAs,RNA silencing machinery and pathogen effectors. A great number of studies have been performed to investigate the roles of s RNAs in plant defense, bringing in the opportunity to utilize s RNAs in plant protection. Transgenic plants with pathogen-derived resistance ability or transgenerational defense have been generated, which show promising potential as solutions for pathogen/insect herbivore problems in the field. Here we summarize the recent progress on the function of s RNAs in response to biotic stress, mainly in plant-pathogen/insect herbivore interaction,and the application of s RNAs in disease and insect herbivore control.     

Induced resistance in rice against insects

Vaccinations are the mainstay of western preventive medicine, and they have been used to protect some crops against disease and insect pests. We consider rice as a model for protection using induced resistance since it is one of the most important staple crops and there have been significant new developments in: cross-resistance among rice insects, chemical pathways involved in induced resistance, sequencing the rice genome and expression of genes conferring resistance against rice insect pests. Insect attack has been found to cause lesions that kill planthopper eggs and early stages of gall midges. Damaged plants released volatiles that made them less likely to be chosen by planthoppers and more attractive to parasitoids. Chemical elicitors have been developed for dicotyledonous plants and these can induce resistance in rice, although rice does not fit models developed to explain signalling in dicots. For example, salicylic acid did not increase in rice after infection by pathogens and did not appear to be the mobile signal for induced resistance against pathogens although it was involved in induced responses to phloem-feeding insects. Jasmonic acid acted as a signal in some induced responses to pathogens as well as chewing insects. Many of the genes associated with induced resistance in rice have recently been mapped, and techniques are being developed to incorporate them into the genome of cultivated varieties. Attempts to control insect pests of rice will affect interactions with pathogens, predators and parasites, and other organisms in this agroecosystem.     

植物与植食性昆虫相互作用的分子机制

在长期的协同进化中,植物建立起应对昆虫取食为害的精密而又复杂的防御机制,植物转录组调控中防御应答基因的表达及防御物质的合成因不同的昆虫取食方式而异。一般来说,咀嚼式口器昆虫取食时造成大面积组织伤害,可诱导植物产生伤害反应;而刺吸式口器昆虫因其特殊的口针取食,诱导植物激活病原体相关的防御途径。不同的防御途径激活不同的识别机制和信号途径。本文从信号识别和转导上综述了不同食性的昆虫取食植物时所引发的防御反应,分析了昆虫-植物相互作用关系的分子机制。     

昆虫共生细菌研究进展

昆虫体内定殖着大量微生物,经过漫长协同进化,昆虫与这些微生物构建了共生体系,这些昆虫共生微生物参与整个生态过程,对于生态系统中物质转化与交换、能量流动与利用、信息传递与调控等均发挥着重要作用。昆虫共生细菌具有丰富的物种多样性;昆虫与其共生细菌之间通过化学机制、生理机制、生态学机制和遗传学机制构建复杂的共生体系;昆虫为细菌提供稳定的生境并共享特定的代谢途径,共生细菌则协助宿主营养代谢,提供食物中缺乏的养分,促进昆虫生长和繁殖;通过分泌抗菌肽、毒素等,细菌能增强昆虫对寄生物的防御能力和抗病性,并通过调节昆虫对非生物因子的抗逆性和耐药性,扩大昆虫的生态位。昆虫共生细菌在农林牧渔业可持续安全生产与医药研发等领域具有应用潜力和广阔的发展前景。