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。     

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。     

植物与植食性昆虫防御与反防御的三个层次

在植物与植食性昆虫长期的进化过程中,双方形成了一系列的防御与反防御策略。本文将这些策略归为3个层次:第一层次起始于植物对植食性昆虫相关分子模式的识别,并由此激活植食性昆虫分子模式相关的免疫反应。这种免疫反应对于不能产生效应子的植食性昆虫种群是有效的;第二层次是一些植食性昆虫种群可以通过释放特异性效应子抑制植物产生的植食性昆虫分子模式相关的免疫反应,从而在植物上正常生长与繁衍;第三层次是一些植物基因型可以通过特异抗性基因识别植食性昆虫的效应子,进而激活效应子诱导的免疫反应,表现出特异的抗虫性。深入揭示植物与植食性昆虫间的这种分子互作机制,不仅在理论上有助于理解昆虫与植物的协同进化机制,而且在实践上可为作物抗性品种的培育提供重要的技术指导。     

Molecular and genomic basis of volatile-mediated indirect defense against insects in rice

Rice plants fed on by fall armyworm ( Spodoptera frugiperda , FAW) caterpillars emit a blend of volatiles dominated by terpenoids. These volatiles were highly attractive to females of the parasitoid Cotesia marginiventris . Microarray analysis identified 196 rice genes whose expression was significantly upregulated by FAW feeding, 18 of which encode metabolic enzymes potentially involved in volatile biosynthesis. Significant induction of expression of seven of the 11 terpene synthase ( TPS ) genes identified through the microarray experiments was confirmd using real-time RT-PCR. Enzymes encoded by three TPS genes, Os02g02930, Os08g07100 and Os08g04500, were biochemically characterized. Os02g02930 was found to encode a monoterpene synthase producing the single product S- linalool, which is the most abundant volatile emitted from FAW-damaged rice plants. Both Os08g07100 and Os08g04500 were found to encode sesquiterpene synthases, each producing multiple products. These three enzymes are responsible for production of the majority of the terpenes released from FAW-damaged rice plants. In addition to TPS genes, several key genes in the upstream terpenoid pathways were also found to be upregulated by FAW feeding. This paper provides a comprehensive analysis of FAW-induced volatiles and the corresponding volatile biosynthetic genes potentially involved in indirect defense in rice. Evolution of the genetic basis governing volatile terpenoid biosynthesis for indirect defense is discussed.     

Induced production of extrafloral nectar in intact lima bean plants in response to volatiles from spider mite-infested conspecific plants as a possible indirect defense against spider mites

We found that intact lima bean plants increased the secretion of extrafloral nectar (EFN) after exposure to Tetranychus urticae-induced plant volatiles. Predatory mites, Phytoseiulus persimilis, dispersed more slowly from an exposed intact plant than from a control plant (plant exposed to volatiles from intact conspecific). The predators also dispersed more slowly from those plants that were provided with extra EFN than from untreated plants. We further show that EFN was a potential alternative food source for P. persimilis. From these results, we concluded that increased EFN was involved in the slow dispersal of P. persimilis from the plants exposed to herbivore-induced plant volatiles. Our data suggest that the increase of EFN in an HIPV-exposed intact plant could be an induced indirect defense against spider mites.     

The phenology and intrinsic quality of wild crucifers that determine the community structure of their herbivorous insects

This report examines the plant traits that effect the community structure of herbivorous insects on wild crucifers. Wild crucifers were classified into 4 types (A, B, C, D) according to their phenology. Type A and B plants had a pausing phenology, disappearing in the middle of the insects' active season, while type C and D plants had a continual phenology, existing all year long. The intrinsic quality of the plants as food, which was assessed by measuring the performance of herbivores, was superior in type A, B and D plants, while it was inferior in type C. The phenology and intrinsic quality were the alternative means of direct defense mechanisms against herbivorous insects: The plants with a pausing phenology were intrinsically superior (A, B), while the plants with a continual phenology were intrinsically inferior (C). However, there were a few plants with continual phenology and superior intrinsic quality (D, the type B plants that remained in the summer). Within the community of the herbivorous insects on the plants with direct defense mechanisms, the number of species and individuals was small and most of the community members were specialists of the plants. On the other hand, within the community on plants without direct defense mechanisms, the number of species was large and the proportion of generalists was high. In addition, the number of individuals was very large on the remaining type B plants, but it was small on type D plants, which were inferred to have indirect defense mechanisms.     

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...     

Antinutritive and toxic components of plant defense against insects

Chemical defense of the tomato plant against noctuid larvae is argued to result from suites of interactive chemical traits that simultaneously impair the acquisition of nutrients and toxify the insect. Defense results from tomatine, catecholic phenolics and phenol oxidases, proteinase inhibitors, and lipoxygenase. The catalytic role of plant oxidative enzymes in activating a variety of defense mechanisms is discussed. It is argued that the terms “digestibility reducer,” “toxin,” and “nutrient” signify ecological outcomes, not properties of molecules. Current views on the roles and the modes of activity of plant natural products against herbivorous insects are challenged. It is proposed that chemical context and mixture are critical determinants of biological activity, and that viewing natural products as isolated defensive factors is often misleading. © 1996 Wiley-Liss, Inc.     

Sugar and amino acid composition of ant‐attended nectar and honeydew sources from an Australian rainforest

Abstract Ants (Hymenoptera: Formicidae) consume a broad spectrum of liquid food sources including nectar and honeydew, which play a key role in their diet especially in tropical forests. This study compares carbohydrates and amino acids from a representative spectrum of liquid sources used by ants in the canopy and understorey of a tropical rainforest in northern Queensland, Australia. Eighteen floral nectars, 16 extrafloral nectars, two wound sap and four homopteran honeydew sources were analysed using high performance liquid chromatography. Wounds comprised flower abscission scars on Normanbya normanbyi L. H. Bailey and bitemarks on Cardwellia sublimis F. Muell. where ants were actively involved in wounding. Discriminant analysis was performed to model differences between food sources in sugar and amino acid concentration and composition. All characteristics varied significantly among plant species. Honeydew contained a broader spectrum of sugars (including melezitose, raffinose, melibiose, lactose and maltose) than nectar (sucrose, glucose, fructose), but certain extrafloral nectars had similar amino acid profiles and, like honeydew sources, were often monopolized by ants. Most common amino acids across the sources were proline, alanine and threonine among 17 α‐amino acids identified. Interspecific variability concealed characteristic differences in sugar and amino acid parameters between nectar, honeydew and wound sap across all plants, but these types differed significantly when found on the same plant. Among all sources studied, only a few flower nectars were naturally not consumed by ants and they were significantly less attended than sugar controls in feeding trials. These nectars did not differ in sugars and amino acids from ant‐attended flower nectars, suggesting the activity of repellents. Apart from these exceptions, variability in amino acids and carbohydrates is proposed to play a key role in ant preferences and nutrition.     

Deer browsing reduces leaf damage by herbivorous insects through an induced response of the host plant

We aimed to demonstrate an indirect relationship between a mammalian herbivore (sika deer) and herbivorous insects on the induced responses of a shared host plant, Viburnum dilatatum. Field studies were conducted at three sites (i.e. two islands and one mainland) and within a deer exclusion area. One island, Kinkazan (Kz) Island, harbored a high density of deer while the other sites (controls) had no deer or very low densities of deer. The deer exclusion area had been established approximately 10years earlier on Kz. We collected leaves above the browsing line of the deer and measured leaf hardness and tannin concentration. Leaf damage by insects was used as a measure of insect abundance. Leaves collected at Kz were harder than those from one of the control sites and from inside the deer exclusion area, while no difference was detected among the other controls and inside the exclusion area. In contrast, the tannin concentration of leaves from Kz was lower than in leaves from the control site. Leaf damage by herbivorous insects was lower in Kz than the other study sites. In addition, hole-type leaf damage tended to be higher inside, rather than outside, the exclusion area. These results suggest the possibility that deer browsing increased leaf hardness, which exerted an indirect negative effect on the herbivorous insects utilizing the common host plant. To our knowledge, this is the first study to provide evidence of indirect negative effects between mammalian herbivores and herbivorous insects sharing a host plant.     

A major function of the tobacco floral nectary is defense against microbial attack

 We have characterized the major nectar protein (Nectarin I) from ornamental tobacco as a superoxide dismutase that functions to generate high levels of hydrogen peroxide in nectar. Other nectar functions include an anti-polygalacturonase activity that may be due to a polygalacturonase inhibiting protein (PGIP). We also examined the expression of defense related genes in the nectary gland by two independent methods. We isolated a sample of nectary-expressed cDNAs and found that 21% of these cDNAs were defense related clones. Finally, we examined the expression of a number of specific defense-related genes by hybridization to specific cDNAs. These results demonstrated that a number of specific defense genes were more strongly expressed in the floral nectary than in the foliage. Taken together these results indicate that the floral nectary gland can have specific functions in plant defense. Received August 8, 2002; accepted January 7, 2003 Published online: June 2, 2003     

Aboveground herbivory affects indirect defences of brassicaceous plants against the root feeder Delia radicum Linnaeus: laboratory and field evidence

1. Belowground herbivory has recently been shown to disrupt the host location behaviour of aboveground parasitoids and thereby impact plants indirect defences. Reverse interactions, on the other hand, have received little attention so far. 2. Lab and field studies were conducted to examine whether the presence of the leaf herbivore Pieris brassicae Linnaeus on brassicaceous plants influences the response of Trybliographa rapae Westwood, a specialist parasitoid of the root feeder Delia radicum Linnaeus. 3. The present results show that the attraction of the parasitoid towards host‐infested plants disappeared when these plants were also infested by P. brassicae. This absence of attraction was observed both when the complete odour blend or only undamaged leaves from damaged plants were offered, emphasising the role of systemically induced volatiles for host location in T. rapae. 4. Furthermore, the field study revealed that parasitism levels dropped from 30% on root‐infested plants to 4% on double‐infested plants. 5. The present study is the first to confirm that reduced attraction to host‐infested plants as a result of simultaneous attack by below‐ and aboveground herbivores translates into lower levels of parasitism in the field.     

Silique burst ofCardamine scutata (Cruciferae) as a physical inducible defense against seed predatory caterpillars

Matured seeds of bitter cress,Cardamine scutata Thumb, are scattered by the bursting of siliques. They also burst in response to chewing by seed predatory caterpillars even when seeds are immature. In this case, the caterpillars are frequently expelled, or killed when their bodies become enswathed by the released pericarps. Consequently, many seeds escape from the attack. The plant trait is explained as an immediate induction of a physical defense against seed predators. The germination rate of scattered immature seeds was significantly lower than that of mature ones, which is a direct demonstration of trade-off between anti-herbivore defense and reproduction of the plant.     

The spitting image of plant defenses: Effects of plant secondary chemistry on the efficacy of caterpillar regurgitant as an anti‐predator defense

In the arms race between plants, herbivores, and their natural enemies, specialized herbivores may use plant defenses for their own benefit, and variation in plant traits may affect the benefits that herbivores derive from these defenses. Pieris brassicae is a specialist herbivore of plants containing glucosinolates, a specific class of defensive secondary metabolites. Caterpillars of P. brassicae are known to actively spit on attacking natural enemies, including their main parasitoid, the braconid wasp Cotesia glomerata. Here, we tested the hypothesis that variation in the secondary metabolites of host plants affects the efficacy of caterpillar regurgitant as an anti‐predator defense. Using a total of 10 host plants with different glucosinolate profiles, we first studied natural regurgitation events of caterpillars on parasitoids. We then studied manual applications of water or regurgitant on parasitoids during parasitization events. Results from natural regurgitation events revealed that parasitoids spent more time grooming after attack when foraging on radish and nasturtium than on Brassica spp., and when the regurgitant came in contact with the wings rather than any other body part. Results from manual applications of regurgitant showed that all parameters of parasitoid behavior (initial attack duration, attack interruption, grooming time, and likelihood of a second attack) were more affected when regurgitant was applied rather than water. The proportion of parasitoids re‐attacking a caterpillar within 15 min was the lowest when regurgitant originated from radish‐fed caterpillars. However, we found no correlation between glucosinolate content and regurgitant effects, and parasitoid behavior was equally affected when regurgitant originated from a glucosinolate‐deficient Arabidopsis thaliana mutant line. In conclusion, host plant affects to a certain extent the efficacy of spit from P. brassicae caterpillars as a defense against parasitoids, but this is not due to glucosinolate content. The nature of the defensive compounds present in the spit remains to be determined, and the ecological relevance of this anti‐predator defense needs to be further evaluated in the field.     

Slippery flowers as a mechanism of defence against nectar-thieving ants

Background and AimsThe great diversity of floral characteristics among animal-pollinated plants is commonly understood to be the result of coevolutionary interactions between plants and pollinators. Floral antagonists, such as nectar thieves, also have the potential to exert an influence upon the selection of floral characteristics, but adaptation against floral antagonists has attracted comparatively little attention. We found that the corollas of hornet-pollinated Codonopsis lanceolata (Campanulaceae) and the tepals of bee-pollinated Fritillaria koidzumiana (Liliaceae) are slippery to nectar-thieving ants living in the plant’s habitat; because the flowers of both species have exposed nectaries, slippery perianths may function as a defence against nectar-thieving ants.MethodsWe conducted a behavioural experiment and observed perianth surface microstructure by scanning electron microscopy to investigate the mechanism of slipperiness. Field experiments were conducted to test whether slippery perianths prevent floral entry by ants, and whether ant presence inside flowers affects pollination.Key ResultsScanning electron microscopy observations indicated that the slippery surfaces were coated with epicuticular wax crystals. The perianths lost their slipperiness when wiped with hexane. Artificial bridging of the slippery surfaces using non-slippery materials allowed ants to enter flowers more frequently. Experimental introduction of live ants to the Codonopsis flowers evicted hornet pollinators and shortened the duration of pollinator visits. However, no statistical differences were found in the fruit or seed sets of flowers with and without ants.ConclusionsSlippery perianths, most probably based on epicuticular wax crystals, prevent floral entry by ants that negatively affect pollinator behaviour. Experimental evidence of floral defence based on slippery surfaces is rare, but such a mode of defence may be widespread amongst flowering plants.     

入侵植物乌桕防御策略的适应性进化研究

生长于不同昆虫群落胁迫下的植物地理种群可能进化出不同的防御策略。入侵植物在原产地同时受到专食性昆虫和广食性昆虫的取食危害, 而在入侵地“逃逸”了专食性昆虫的取食危害。入侵植物对不同类型昆虫防御策略的演化可能在其成功入侵的过程中起着至关重要的作用。该文主要以原产中国入侵北美的木本植物乌桕(Triadica sebifera)为例, 并结合其他入侵植物防御策略演化的研究, 从抗性和耐受性、直接抗性和间接抗性、组成抗性和诱导抗性三个方面系统分析不同昆虫选择压力下入侵植物防御策略的演化, 同时探讨入侵植物防御策略演化对生物防治效果的影响, 指出未来的重点研究方向。