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.     

昆虫对植物蛋白酶抑制素的诱导及适应机制

植物蛋白酶抑制素是植物重要的防御物质之一,一般是分子量较小的多肽或蛋白质,能够与昆虫消化道内的蛋白酶形成复合物,阻断或削弱蛋白酶对食物中蛋白的水解,使昆虫厌食或消化不良而致死。植物蛋白酶抑制素在植物体内一般是诱导表达的,昆虫取食危害后,导致某些植物在伤口产生一种寡聚糖信息素-蛋白酶抑制素诱导因子,蛋白酶抑制素诱导因子诱导叶片局部产生植物蛋白酶抑制素,并刺激产生信号物质系统肽,通过十八烷酸途径在一系列酶的作用下产生茉莉酸,茉莉酸与受体结合,活化植物蛋白酶抑制素基因。昆虫在长期取食植物蛋白酶抑制素后会在生理及行为上产生适应性而导致不敏感,适应方式主要包括：(1)改变肠道蛋白酶对蛋白酶抑制素的敏感性;(2) 水解蛋白酶抑制素;(3)过量取食及干扰产生蛋白酶抑制素的信号通道。由于昆虫能够对植物蛋白酶抑制素产生适应,因此合理利用植物蛋白酶抑制素的抗虫作用显得十分重要。     

植物、植食性昆虫及捕食者种间化学信息物质

昆虫与植物、昆虫与昆虫之间的联系,存在一个极为复杂的信息化学网络（alleloch。micalwe）,这些信息化学物质（semiochemica）引起昆虫行为和生理上的许多反应,从而形成一个多层次、巨大的生物群落网络,并协调三级营养（tritronhic）即植食性昆虫取食植物,而肉食昆虫又捕食或寄生植食性昆虫,或更多营养层次之间的关系。本文拟概述化学生态学在这方面取得的一些新进展。种内信息化学物质叫做信息素（pheromone）研究的较早,例如多种昆虫的性息素。而另一类属于种间的信息化学物质（allelochemics）则研究的较少。在任何三级营养水平…     

昆虫对植物次生物质的代谢适应机制及其对昆虫抗药性的意义

植物次生物质(plant secondary metabolites)对昆虫的取食行为、生长发育及繁殖可以产生不利影响,甚至对昆虫可以产生毒杀作用。为了应对植物次生物质的不利影响,昆虫通过对植物次生物质忌避取食、解毒代谢等多种机制,而对寄主植物产生适应性。其中,昆虫的解毒代谢酶包括昆虫细胞色素P450酶系（P450s）及谷胱甘肽硫转移酶（GSTs）等,在昆虫对植物次生物质的解毒代谢及对寄主植物的适应性中发挥了重要作用。昆虫的解毒酶系统不仅可以代谢植物次生物质,还可能代谢化学杀虫剂,因而昆虫对寄主植物的适应性与其对杀虫剂的耐药性甚至抗药性密切相关。昆虫细胞色素P450s和GSTs等代谢解毒酶活性及相关基因的表达可以被植物次生物质影响,这不仅使昆虫对寄主植物的防御产生了适应性,还影响了昆虫对杀虫剂的解毒代谢,因而改变昆虫的耐药性或抗药性。掌握昆虫对植物次生物质的代谢适应机制及其在昆虫抗药性中的作用,对于明确昆虫的抗药性机制具有重要的参考意义。本文综述了植物次生物质对昆虫的影响、昆虫对寄主植物次生物质的代谢机制、昆虫对植物次生物质的代谢适应性对昆虫耐药性及抗药性的影响等方面的研究进展。     

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。     

电子取食监测仪在植物抗虫性研究中的应用

主要综述了电子取食监测仪在植物对同翅目昆虫抗虫性研究中的应用情况.利用电子取食监测仪可监测同翅目昆虫（蚜虫、飞虱、叶蝉、蓟马、粉虱等）在不同抗、感虫品种上的取食行为,并根据取食行为参数如刺探频率、唾液分泌时间、韧皮部取食时间等在不同抗、感品种上的差异来区别品种的抗、感虫特性和确定抗虫因子存在的部位.     

植物抗虫“防御警备”:概念、机理与应用

植物抗虫"防御警备"是指受到某些生物或者非生物因子刺激警备后,植物会提前做好抗虫防御准备,之后当再次受到害虫袭击时,植物会产生更加快速和强烈的抗虫防御反应,从而使自身抗虫性显著提高.这是近年来新发现的植物防御害虫的一种策略,是一种特殊的诱导抗虫机制.植食性昆虫的取食、分泌物、产卵、为害诱导的植物挥发物(HIPVs)以及某些有益微生物、植物营养元素、重金属和一些化学物质均可以引起植物产生抗虫防御警备.防御警备具有抗性高效、持久、环境友好,甚至可以遗传到子代等优点.本文综述了近年来有关植物抗虫防御警备的研究,主要概括了植物抗虫防御警备的一般特征、刺激警备因子和形成机制,并对其在生产实践中的应用前景进行了简要分析,提出了这一领域尚未解决的问题和亟待深入的研究方向.通过合适的方法使植物产生抗虫防御警备可以大大减少杀虫剂的使用,成为害虫综合防治的重要手段.     

韧皮部取食昆虫诱导的植物防御反应

刺吸式昆虫与寄主植物之间具有特殊的生物互作关系。本文对刺吸式昆虫取食韧皮部诱导的植物防御反应类型、 防御物质变化、 信号途径以及植物反应转录组学研究等方面进行综述。韧皮部取食昆虫取食诱导的植物防御反应机制主要包括： (1)改变自身的营养状况; (2)产生有毒的次生化合物; (3)产生防御蛋白。防御反应与植物水杨酸、 茉莉酸、 乙烯等信号分子密切相关。研究表明, 刺吸式昆虫取食诱导的植物防御反应主要引发以水杨酸为主的信号途径, 但相关分子互作机制还有待明确。日益丰富的基因组资源和不断发展的分子生物学技术为揭示植物防御反应中信号分子的作用机制、 找出植物内生抗性的特异因子以及阐明诱导防御机制奠定了基础。了解刺吸式昆虫取食诱导的植物防御反应, 为深入理解植物-昆虫间协同进化关系提供了依据, 为害虫治理和抗虫植物的培育提供了新的思路。     

植物的诱导抗虫性

植物对植食性昆虫的抗性可包括两个方面,即植物的组成抗性（constitutiveresistance）和诱导抗性（inducedresistance）。组成抗性是指植物在遭受植食性昆虫进攻前就已存在的抗虫特性;而诱导抗性是指植物在遭受植食性昆虫进攻后所表现出来的一种抗虫特性[1,2]。根据作用世代的不同,诱导抗性又分为迅速的诱导抗性（rapidlyinducedre－sistance,RIR）和滞后的诱导抗性（delayedinducedresistance,DIR）。前者是指对当前世代的植食性昆虫的影响,而后者是指对后续的1～几个世代的植食性昆虫的影响[2]。研究植物的诱导抗虫性,不仅能在…     

植物抗虫“防御警备”: 概念、机理与应用

植物抗虫“防御警备”是指受到某些生物或者非生物因子刺激警备后,植物会提前做好抗虫防御准备,之后当再次受到害虫袭击时,植物会产生更加快速和强烈的抗虫防御反应,从而使自身抗虫性显著提高.这是近年来新发现的植物防御害虫的一种策略,是一种特殊的诱导抗虫机制.植食性昆虫的取食、分泌物、产卵、为害诱导的植物挥发物(HIPVs)以及某些有益微生物、植物营养元素、重金属和一些化学物质均可以引起植物产生抗虫防御警备.防御警备具有抗性高效、持久、环境友好,甚至可以遗传到子代等优点.本文综述了近年来有关植物抗虫防御警备的研究,主要概括了植物抗虫防御警备的一般特征、刺激警备因子和形成机制,并对其在生产实践中的应用前景进行了简要分析,提出了这一领域尚未解决的问题和亟待深入的研究方向.通过合适的方法使植物产生抗虫防御警备可以大大减少杀虫剂的使用,成为害虫综合防治的重要手段.     

Identification and characterization of protease inhibitors in Diplotaxis species

PCR analysis of the genomes of two wild Brassicaceae plants, Diplotaxis muralis and Diplotaxis tenuifolia, demonstrated the presence of several genes coding for potential protease inhibitors, classifiable within the mustard inhibitor family (MSI). This is a small family of plant protease inhibitors named after the mustard trypsin inhibitor MTI-2, the first protease inhibitor characterized in Brassicaceae. From identified sequences two recombinant inhibitors were expressed in Pichia pastoris. In comparison with MTI-2, they show a reduced activity against bovine trypsin. However, when tested against trypsin-like proteases present in the guts of Helicoverpa zea larvae, the Diplotaxis inhibitors and MTI-2 show similar activities, indicating that the usually adopted procedure of reporting activity of plant protease inhibitors against bovine trypsin may lead to wrong estimation of their effect on insect proteases. This issue is of particular relevance when planning the use of PI genes for developing insect resistant plants.     

Protease inhibitors of pigeonpea (Cajanus cajan) and its wild relatives

Plant protease inhibitors have been implicated in defense against insect pests. Podborer and pod fly are major pests of developing seeds of pigeonpea ( Cajanus cajan L. Millsp.). Therefore, we studied the presence of protease inhibitors in seeds of pigeonpea and its wild relatives. Seed extracts were analyzed for protease inhibitor activities by caseinolytic assay, and the number of protease inhibitors determined by polyacrylamide gel electrophoresis. Besides trypsin and chymotrypsin inhibitors, seed extracts contained weak papain inhibitor(s) but no bromelain inhibitor. Treatment of seed extract with bromelain generated new active forms of trypsin inhibitors. The relative amounts of different trypsin inhibitors and the total trypsin inhibitor activity varied with different extraction media. Trypsin inhibitors were not detectable in pigeonpea leaves. The profiles of trypsin and chymotrypsin inhibitors in almost all the cultivars of pigeonpea analyzed were similar; however, those in wild relatives were quite variable.     

Colorado potato beetle larvae on potato plants expressing a locust proteinase inhibitor

The natural defence system of plants often involves inhibitors of digestive enzymes of their pests. Modem and environmental-friendly methods try to increase this plant resistance by expressing heterologous protease inhibitors in crops. Here we report the effects of expressing a gene from desert locust (Schistocerca gregaria) encoding two serine protease inhibitors in potato on Colorado potato beetle (Leptinotarsa decemlineata) larvae. The gene encoding both peptides on a single chain was used for Agrobacterium-mediated transformation of potato plants. The presence of the active inhibitor protein in the leaves was verified. The feeding bioassays in the laboratory showed that despite the low level of the peptide in leaves, CPB larvae on transgenic plants have grown slightly but significantly more slowly than those on control potato plants. The results support the notion that expression of multifunctional proteinase inhibitors of insect origin in plants might be a good strategy to improve insect resistance.     

Transgenic Plants for Insect Pest Control: A Forward Looking Scientific Perspective

One of the first successes of plant biotechnology has been the creation and commercialisation of transgenic crops exhibiting resistance to major insect pests. First generation products encompassed plants with single insecticidal Bt genes with resistance against major pests of corn and cotton. Modelling studies predicted that usefulness of these resistant plants would be short-lived, as a result of the ability of insects to develop resistance against single insecticidal gene products. However, despite such dire predictions no such collapse has taken place and the acreage of transgenic insect resistance crops has been increasing at a steady rate over the 9 years since the deployment of the first transgenic insect resistant plant. However, in order to assure durability and sustainability of resistance, novel strategies have been contemplated and are being developed. This perspective addresses a number of potentially useful strategies to assure the longevity of second and third generation insect resistant plants.     

Serine protease inhibitors in plants: nature’s arsenal crafted for insect predators

Plant serine protease inhibitors are defense proteins crafted by nature for inhibiting serine proteases. Use of eco-friendly, sustainable and effective protein molecules which could halt or slow down metabolism of nutrients in pest would be a pragmatic approach in insect pest management of crops. The host-pest complexes that we observe in nature are evolutionary dynamic and inter-depend on other defense mechanisms and interactions of other pests or more generally speaking symbionts with the same host. Insects have co-evolved and adapted simultaneously, which makes it necessary to investigate serine protease inhibitors in non-host plants. Such novel serine protease inhibitors are versatile candidates with vast potential to overcome the host inhibitor-insensitive proteases. In a nutshell exploring and crafting plant serine proteinase inhibitors (PIs) for controlling pests effectively must go on. Non-host PI seems to be a better choice for coevolved insensitive proteases. Transgenic plants expressing wound inducible chimaeric PIs may be an outstanding approach to check wide spectrum of gut proteinases and overcome the phenomenon of resistance development. Thus, this article focuses on an entire array of plant serine protease inhibitors that have been explored in the past decade, their mode of action and biological implications as well as applications.     

Differential inhibition of Helicoverpa armigera gut proteinases by proteinase inhibitors of pigeonpea (Cajanus cajan) and its wild relatives

The seeds of 36 pigeonpea [Cajanus cajan (L) Millsp.] cultivars, resistant and susceptible to pests and pathogens and 17 of its wild relatives were analysed for inhibitors of trypsin, chymotrypsin, and insect gut proteinases to identify potential inhibitors of insect (Helicoverpa armigera) gut enzymes. Proteinase inhibitors (PIs) of pigeonpea cultivars showed total inhibition of trypsin and chymotrypsin, and moderate inhibition potential towards H. armigera proteinases (HGP). PIs of wild relatives exhibited stronger inhibition of HGP, which was up to 87% by Rhynchosia PIs. Electrophoretic detection of HGPI proteins and inhibition of HGP isoforms by few pigeonpea wild relative PIs supported our enzyme inhibitor assay results. Present results indicate that PIs exhibit wide range of genetic diversity in the wild relatives of pigeonpea whereas pigeonpea cultivars (resistant as well as susceptible to pests and pathogens) are homogeneous. The potent HGPIs identified in this study need further exploration for their use in strengthening pigeonpea defence against H. armigera.     

Use of cowpea trypsin inhibitor (CpTI) to protect plants against insect predation

Transgenic tobacco plants expressing a cowpea trypsin inhibitor gene have enhanced levels of insect resistance to a variety of insect pests. Furthermore, insect bioassay has shown the cowpea trypsin inhibitor to have anti-metabolic activity to insect pests of the orders Lepidoptera, Coleoptera and Orthoptera. The advantages and disadvantages of this approach to developing insect resistant crops is discussed in relationship to other methods, including conventional plant breeding and chemical control. Eventually it is hoped that African farmers will benefit from this industrially sponsored research.     

Regulation of expression of genes encoding digestive proteases in the gut of a polyphagous lepidopteran larva in response to dietary protease inhibitors

Abstract. Larvae of Helicoverpa armigera (Hübner), a polyphagous lepidopteran crop pest, adapt to the presence of protease inhibitors in their diet by differential regulation of multiple genes encoding digestive proteases. The time‐course of their response to dietary soybean Kunitz trypsin inhibitor (SKTI) involves several stages; an initial up‐regulation of all protease genes assayed (up to 12 h after exposure to inhibitor) is succeeded by a longer‐term down‐regulation of expression of specific genes that encode proteases most sensitive to the inhibitor, whereas genes encoding putative inhibitor‐insensitive proteases continue to be up‐regulated (after 24 h of exposure). Consequently, insect protease activity changes from being sensitive to the inhibitor, to being largely insensitive. The insect response is comparable in its timescale with that of the synthesis of protease inhibitors in the plant wounding response. SKTl causes similar effects on protease gene expression and gut protease activity when fed in diets containing casein or hydrolysed casein as sources of amino acid, suggesting that the insect response is not mediated through inhibition of digestive proteolysis. Soybean Bowman–Birk inhibitor, which has a broader range of inhibitory activity against gut proteases in H. armigera, but is a less effective inhibitor on an I₅₀ basis, proves to be a more effective antimetabolite than SKTI, but does not induce inhibitor‐insensitive protease activity because it causes a general up‐regulation of protease‐encoding genes. A possible mechanism to account for these different responses is discussed.     

Diamondback moth compensatory consumption of protease inhibitor-transformed plants

Prior study of the effect of protease inhibitors (PIs) on diamondback moths suggests that moths are resistant to them, so PIs represent an ineffective defence against moths. However, our data suggest that diamondback moths do suffer lower growth rates when they consume plants transformed with potato protease inhibitor (PI2), but that effect is hidden by compensatory consumption. Plants, instead of gaining an advantage by lowering the insect growth rate, suffer a disadvantage as moths consume more tissue to mitigate the effect. Furthermore, PI2, when used in conjunction with another transgenic pesticidal protein, Bt (from Bacillus thuringiensis) counteracts the effectiveness of Bt at protecting plant tissue. Thus, transgenic PIs are not only less effective than previously thought in protecting Brassica plants from diamondback moths, they may actually lead to increased plant damage by the moths.     

A potato carboxypeptidase inhibitor gene provides pathogen resistance in transgenic rice

A defensive role against insect attack has been traditionally attributed to plant protease inhibitors. Here, evidence is described of the potential of a plant protease inhibitor, the potato carboxypeptidase inhibitor (PCI), to provide resistance to fungal pathogens when expressed in rice as a heterologous protein. It is shown that rice plants constitutively expressing the pci gene exhibit resistance against the economically important pathogens Magnaporthe oryzae and Fusarium verticillioides . A M. oryzae carboxypeptidase was purified by affinity chromatography and further characterized by mass spectrometry. This fungal carboxypeptidase was found to be a novel carboxypeptidase B which was fully inhibited by PCI. Overall, the results indicate that PCI exerts its antifungal activity through the inhibition of this particular fungal carboxypeptidase B. Although pci confers protection against fungal pathogens in transgenic rice, a significant cost in insect resistance is observed. Thus, the weight gain of larvae of the specialist insect Chilo suppressalis (striped stem borer) and the polyphagous insect Spodoptera littoralis (Egyptian cotton worm) fed on pci rice is significantly larger than that of insects fed on wild-type plants. Homology-based modelling revealed structural similarities between the predicted structure of the M. oryzae carboxypeptidase B and the crystal structure of insect carboxypeptidases, indicating that PCI may function not only as an inhibitor of fungal carboxypeptidases, but also as an inhibitor of insect carboxypeptidases. The potential impact of the pci gene in terms of protection against fungal and insect diseases is discussed.