Protease inhibitors: use to increase plant tolerance to insects and pathogens

The review deals with analysis of the possibility of the use of genes of inhibitors of proteolytic enzymes of plants to increase plant tolerance to insect pests and phytopathogens. The idea of using protease inhibitors for plant defense is strongly supported, first, by their wide distribution in plant tissues and high activity towards various proteolytic enzymes of insects, bacteria and fungi. The results obtained for the last years indicate that the genetic engineering approach is perspective for solving of this kind of problems. The main losses and advantages of the discussed approach are also considered. The described approach for increase of plant tolerance to insects and pathogens has few advantages as compared to traditional ones and belongs to ecologically pure technologies.     

植物蛋白酶抑制剂在植物抗虫与抗病中的作用

综述了植物蛋白酶抑制剂抗虫与抗病作用的研究进展.蛋白酶抑制剂广泛存在于植物体内,与植物抗虫抗病密切相关.植物蛋白酶抑制剂能抑制昆虫肠道蛋白酶,使昆虫生长发育缓慢,甚至死亡.但取食蛋白酶抑制剂后,昆虫能迅速分泌对抑制剂不敏感的蛋白酶,而使蛋白酶抑制剂无效.食物蛋白的含量和质量也影响植物蛋白酶抑制剂的抗虫效果.病原菌的感染能诱导植物产生蛋白酶抑制剂,诱导产生的蛋白酶抑制剂能抑制病原菌的生长.     

The influence of host and non‐host companion plants on the behaviour of pest insects in field crops

Companion plants grown as ‘trap crops’ or ‘intercrops’ can be used to reduce insect infestations in field crops. The ways in which such reductions are achieved are being described currently using either a chemical approach, based on the ‘push‐pull strategy’, or a biological approach, based on the ‘appropriate/inappropriate landing theory’. The chemical approach suggests that insect numbers are reduced by chemicals from the intercrop ‘repelling’ insects from the main crop, and by chemicals from the trap‐crop ‘attracting’ insects away from the main crop. This approach is based on the assumptions that (1) plants release detectable amounts of volatile chemicals, and (2) insects ‘respond’ while still some distance away from the emitting plant. We discuss whether the above assumptions can be justified using the ‘appropriate/inappropriate landing theory’. Our tenet is that specialist insects respond only to the volatile chemicals released by their host plants and that these are released in such small quantities that, even with a heightened response to such chemicals, specialist insects can only detect them when a few metres from the emitting plant. We can find no robust evidence in the literature that plant chemicals ‘attract’ insects from more than 5 m and believe that ‘trap crops’ function simply as ‘interception barriers’. We can also find no evidence that insects are ‘repelled’ from landing on non‐host plants. Instead, we believe that ‘intercrops’ disrupt host‐plant finding by providing insects with a choice of host (appropriate) and non‐host (inappropriate) plant leaves on which to land, as our research has shown that, for intercropping to be effective, insects must land on the non‐host plants. Work is needed to determine whether non‐host plants are repellent (chemical approach) or ‘non‐stimulating’ (biological approach) to insects.     

Phytochemical feeding deterrents for stored product insect pests

This review summarises information on compounds of plant origin and plant products as feeding inhibitors for stored product insects. More than 200 compounds (mostly sesquiterpenes) and over 160 plant extracts have been tested to date. Indeed, we did not consider substances stimulating olfactory receptors (repellents) or compounds just toxic to insects. The main scope of the review is to enable best choice for the most active, as well as biorationally suitable substances, for evolving further rational experiments in future. Feeding inhibitors may be used along with food or sex attractants in biorational control of the stored food pests. However, each semiochemical should be submitted to a formal registration process before its use in practice.     

Proteinase Inhibitors as Antistress Proteins in Higher Plants

Physicochemical and functional characteristics of plant protein proteinase inhibitors as antistress biopolymers were studied to determine the mechanisms for plant resistance to phytopathogens and to obtain disease-resistant cereal and leguminous cultures. The activity of trypsin, chymotrypsin, and subtilisin inhibitors varied in monocotyledonous and dicotyledonous cultures. Study varieties of leguminous and cereal cultures were shown to contain endogenous inhibitors specific to proteinases of phytopathogenic fungi Fusarium, Colletotrichum, Helminthosporium, and Botrytis. These inhibitors were characterized by species specificity and variety specificity. Protease inhibitors from buckwheat seeds inhibited proteases of fungal pathogens and suppressed germination of spores and growth of the fungal mycelium. Our results suggest that proteinaceous inhibitors of proteinases are involved in the protective reaction of plants under stress conditions.__________Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 4, 2005, pp. 392–396.Original Russian Text Copyright © 2005 by Dunaevskii, Tsybina, Belyakova, Domash, Sharpio, Zabreiko, Belozerskii.     

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.     

Proteinase inhibitors and their function in plants: A review

The spread, classification, and properties of plant proteins capable of inhibiting proteinases have been reviewed. Data from the literature on the likely physiological functions of these inhibitors in plants are analyzed.__________Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 3, 2005, pp. 261–282.Original Russian Text Copyright © 2005 by Mosolov, Valueva.     

Plants as green phones: Novel insights into plant-mediated communication between below- and above-ground insects

Plants can act as vertical communication channels or ‘green phones’ linking soil-dwelling insects and insects in the aboveground ecosystem. When root-feeding insects attack a plant, the direct defense system of the shoot is activated, leading to an accumulation of phytotoxins in the leaves. The protection of the plant shoot elicited by root damage can impair the survival, growth and development of aboveground insect herbivores, thereby creating plant-based functional links between soil-dwelling insects and insects that develop in the aboveground ecosystem. The interactions between spatially separated insects below- and aboveground are not restricted to root and foliar plant-feeding insects, but can be extended to higher trophic levels such as insect parasitoids. Here we discuss some implications of plants acting as communication channels or ‘green phones’ between root and foliar-feeding insects and their parasitoids, focusing on recent findings that plants attacked by root-feeding insects are significantly less attractive for the parasitoids of foliar-feeding insects.Key words: above-belowground interactions, green phones, multitrophic plant-insect interactions, plant defense, plant volatiles, parasitoids     

Relationship between plant development, tannin concentration and insects associated with Copaifera langsdorffii (Fabaceae)

Plant development is the main factor that determines the insect-ontogeny interaction, since it leads to variations in resource quality and availability. The aim of this study was to test the hypothesis that plant development and varying tannin concentration leads to changes in species richness, abundance and composition of ants, free-feeding herbivores and galling insects associated with Copaifera langsdorffii (Fabaceae). The plant ontogeny and tannin concentration effects on insects were tested on 60 individuals with height varying from 0.9 to 11.0 m. A positive correlation was observed for tree height and species richness and abundance of ants, free-feeding and galling insects. In contrast, we did not find a significant relation between leaf tannin concentration and plant height, or richness and abundance of the different insect guilds. The assemblage of ants (composition of species) did not change between saplings and adults of C. langsdorffii. However, the assemblage of free-feeding herbivores and galling insects varied between the two development stages studied. The present study reveals an ontogenetic succession pattern for herbivore insects along the C. langsdorffii growth, probably due to both indirect and direct benefits from the host plant architecture and quality. Those plants with more complex architectures should support a wider diversity of insects, since they present higher number of sites for egg laying, housing, feeding and better environmental conditions. This is the first work to investigate the host plant ontogeny effect on insects in Cerrado “Savanna” vegetation. The pattern described, along with other previous studies, suggests a vast occurrence of ontogenetic succession in tropical areas.     

Identification and characterization of digestive serine proteases from inhibitor-resistant Helicoverpa zea larval midgut

Protease inhibitors mediate a natural form of plant defence against insects, by interfering with the digestive system of the insect. In this paper, affinity chromatography was used to isolate trypsins and chymotrypsins from Helicoverpa zea larvae, which had been raised on inhibitor-containing diet. Sensitivity of the fractions to inhibition by plant proteinase inhibitors was tested, and compared to the sensitivity of proteinases found in insects raised on diet to which no inhibitor had been added. The isolated chymotrypsin activity was found to be less sensitive to plant protease inhibitors. The sensitivity of the isolated trypsin activity was found to be intermediate between completely sensitive trypsins and completely insensitive forms that have been previously described. Mass spectrometry was used to identify one trypsin and two chymotrypsins in the partially purified protease fraction. The sequence features of these proteases are discussed in relation to their sensitivity to inhibitors. The results provide insight in the enzymes deployed by Helicoverpa larvae to overcome plant defence.     

Generalist insects behave in a jasmonate-dependent manner on their host plants,leaving induced areas quickly and staying longer on distant parts

Plants are sessile, so have evolved sensitive ways to detect attacking herbivores and sophisticated strategies to effectively defend themselves. Insect herbivory induces synthesis of the phytohormone jasmonic acid which activates downstream metabolic pathways for various chemical defences such as toxins and digestion inhibitors. Insects are also sophisticated animals, and many have coevolved physiological adaptations that negate this induced plant defence. Insect behaviour has rarely been studied in the context of induced plant defence, although behavioural adaptation to induced plant chemistry may allow insects to bypass the host''s defence system. By visualizing jasmonate-responsive gene expression within whole plants, we uncovered spatial and temporal limits to the systemic spread of plant chemical defence following herbivory. By carefully tracking insect movement, we found induced changes in plant chemistry were detected by generalist Helicoverpa armigera insects which then modified their behaviour in response, moving away from induced parts and staying longer on uninduced parts of the same plant. This study reveals that there are plant-wide signals rapidly generated following herbivory that allow insects to detect the heterogeneity of plant chemical defences. Some insects use these signals to move around the plant, avoiding localized sites of induction and staying ahead of induced toxic metabolites.     

Plant species from Brazilian Caatinga: a control alternative for Aedes aegypti

The mosquito Aedes aegypti is the main vector for the virus dengue, chikungunya and Zika. For its control, it is essential to search for natural products with insecticidal effects. The climatic singularity of Caatinga, an exclusive Brazilian biome, aids the survival of plants that produce secondary metabolites, which could be toxic to insects. Therefore, this review discusses the insecticidal potential of Caatinga plants on Aedes aegypti mosquitoes. The meta-analysis was performed using Review Manager Software 5.4.1®. Several studies have demonstrated the insecticidal efficacy of Caatinga plants on the egg, larvae, pupae and adult phases of Ae. aegypti, with a predominance of the plant activity in the larval stage. The leaves were the most utilized part of the plant. The essential oils from Caatinga plants were significantly active against Ae. aegypti (RR = 0.21, 95 % CI = 0.07 – 0.68, p = 0.009). The most promising botanical genera as an insecticide are: Abarema, Myracrodruon, Croton, Lippia and Syagrus. Among chemical compounds from these insecticidal plants has been identified and isolated flavonoids and fatty acids. Therefore, the Caatinga plant is a promising plant that contain bioactive compounds that are useful in the control of vector insects. This could contribute to the characterisation and valorisation of flora of this biome, as well as the production of environmentally friendly insecticides with specific action on target insects.     

Carnivorous pitcher plant uses free radicals in the digestion of prey

Abstract

A study of the involvement of free oxygen radicals in trapping and digestion of insects by carnivorous plants was the main goal of the present investigation. We showed that the generation of oxygen free radicals by pitcher fluid of Nepenthes is the first step of the digestion process, as seen by EPR spin trapping assay and gel-electrophoresis. The EPR spectrum of N. gracilis fluid in the presence of DMPO spin trap showed the superposition of the hydroxyl radical spin adduct signal and of the ascorbyl radical signal. Catalase addition decreased the generation of hydroxyl radicals showing that hydroxyl radicals are generated from hydrogen peroxide, which can be derived from superoxide radicals. Gel-electrophoresis data showed that myosin, an abundant protein component of insects, can be rapidly broken down by free radicals and protease inhibitors do not inhibit this process. Addition of myoglobin to the pitcher plant fluid decreased the concentration of detectable radicals. Based on these observations, we conclude that oxygen free radicals produced by the pitcher plant aid in the digestion of the insect prey.     

Volatiles that encode host-plant quality in the grapevine moth

Plant volatiles are signals used by herbivorous insects to locate host plants and select oviposition sites. Whether such volatiles are used as indicators of plant quality by adult insects in search of host plants has been rarely tested. We tested whether volatiles indicate plant quality by studying the oviposition of the grapevine moth Lobesia botrana on the grapevine plant Vitis vinifera. Host plants were infected with a variety of microorganisms, and larval fitness was correlated to the infected state of the substrate. Our results show an oviposition preference for volatiles that is significantly correlated with the fitness of the substrate. The chemical profiles of the bouquets from each V. vinifera–microorganism system are clearly differentiated in a PCA analysis. Both the volatile signal and the quality of the plant as larval food were affected by the introduction of microorganisms. Our study represents a broad approach to the study of plant–insect interactions by considering not only the direct effect of the plant but also the effect of plant–microorganism interactions on insect population dynamics.     

植物蛋白酶抑制剂基因结构、调控及其控制害虫的策略

各种不同类型的植物蛋白酶抑制剂基因已被分离,它们的特异产物(单基因或多基因组合),对昆虫体内各种生化和生理过程会产生不同程度的影响,在对昆虫和病原体防御体系中起重要作用。多种蛋白酶抑制剂重组,协同保护植物的方法,已成为害虫综合防治计划的一部分。尽管它们近期内尚不能代替化学杀虫剂,但可作为有效的替补。目前,大多数抑制剂的作用和机理正在详尽地研究中,该文综述了植物蛋白酶抑制剂的基因结构、调控与表达并讨论了培育转基因作物控制害虫的策略。     

To be or not to be: postcubital vein in insects revealed by microtomography

To better understand insect evolution, fossils – mainly known by their wings – must be used as terminals in phylogenetic analyses. Such analyses are, however, rarely performed because of a lack of consensus on the homology of venation in insects. Researchers do not agree with the current concept on the exact number and identity of the main veins. Here, we confirm the presence, which has been in question since the early 20th century, of an independent main postcubital vein (PCu vein) between the cubital and anal veins (29 fossil and extant examined orders; > 85% of observed insects). The PCu vein corresponds to the so-called vein 1A or first anal vein. It is easily identified by the unique shape of its bulla. It may have several branches and be partially fused with the cubital and anal veins. Once the PCu vein was identified, we reconsidered as an example the particular case of the Phasmatodea, showing that extant stick insects have a unique venation among insects, with a reduced median vein and a simple cubital vein adjacent or fused to the PCu vein. This study is a new approach towards resolving wing vein homology issues, crucial for future large-scale phylogenetic analyses in insects combining extant and extinct taxa.     

The adaptation of insects to plant protease inhibitors

Plants and herbivores have been co-evolving for thousands of years, and as a result, plants have defence mechanisms that offer protection against many herbivores such as nematodes, insects, birds and mammals. Only when a herbivore has managed to adapt to these defence mechanisms does it have the potential to become a pest. One such method of plant defence involves the production of protease inhibitors (PIs). These inhibitors are proteins that may be found constitutively in various parts of the plant, or may be induced in response to herbivore attack. PIs work at the gut level, by inhibiting the digestion of plant protein. This review focuses on insect herbivores and looks at the mechanisms involved in the role and function of PIs in plant defense against insects, as well as at the ability of well adapted species to overcome the effects of these plant PIs.     

Structure and activity of NO synthase inhibitors specific to the L-arginine binding site

Synthesis of compounds containing a fragment similar to the guanidine group of L-arginine, which is a substrate of nitric oxide synthase (NOS), is the main direction in creating NOS inhibitors. The inhibitory effect of such compounds is caused not only by their competition with the substrate for the L-arginine-binding site and/or oxidizing center of the enzyme (heme) but also by interaction with peptide motifs of the enzyme that influence its dimerization, affinity for cofactors, and interaction with associated proteins. Structures, activities, and relative in vitro and in vivo specificities of various NOS inhibitors (amino acid and non-amino acid) with linear or cyclic structure and containing guanidine, amidine, or isothiuronium group are considered. These properties are mainly analyzed by comparison with effects of the inhibitors on the inducible NOS.Translated from Biokhimiya, Vol. 70, No. 1, 2005, pp. 14–32.Original Russian Text Copyright © 2005 by Proskuryakov, Konoplyannikov, Skvortsov, Mandrugin, Fedoseev.     

Dietary proteinase inhibitors alter complement of midgut proteases

Plant serine proteinase inhibitors (Pls) have the potential to restrict the growth and/or development of herbivorous insects. However, there are limitations to the efficacy of these Pls. An insect's susceptibility to a Pl is determined, at least in part, by the relative proportion of proteolytic enzyme activity in the midgut that is suppressed by that inhibitor. Insects adapt to dietary trypsin inhibitor in their host plant by secreting “inhibitor-resistant” trypsin(s). These “inhibitor-resistant” enzyme(s) may be the standard proteinase(s) secreted into the midgut (e.g., Pieris rapae), or may be enhanced following ingestion of proteinase inhibitor (e.g., Helicoverpa zea). In addition, insects may be pre-adapted to specific Pl(s), following adaptation to a Pl from the same family. For example, Pieris rapae is a crucifer specialist that is resistant to cabbage Pl, but is also resistant to Kunitz soybean trypsin inhibitor, a Pl in the same family as cabbage Pl, but from a non-host plant. The ultimate value of this pre-adaptation to herbivory by a species of insect will be determined by the number of different families of Pl in host plant(s) to which the species has adapted, and the distribution of those families among other species of plants. Thus, it is possible that the presence of a plant Pl limits herbivory by insect(s). However, multiple inhibitors, matched to the complement of enzymes in the insect's midgut, may be required to enhance this resistance of plants to herbivorous insects. © 1996 Wiley-Liss, Inc.     

An omics evolutionary perspective on phytophagous insect–host plant interactions in Anastrepha obliqua: a review

Phytophagous insects have a close relationship with their host plants. For this reason, their interactions can lead to important changes in insect population dynamics and evolutionary trajectories. Next generation sequencing (NGS) has provided an opportunity to analyze omics data on a large scale, facilitating the change from a classical genetics approach to a more holistic understanding of the underlying molecular mechanisms of host plant use by insects. Most studies have been carried out on model species in Holarctic and temperate zones. In tropical zones, however, the effects of use of various host plants on evolutionary insect history is less understood. In the current review, we describe how omics methodologies help us to understand phytophagous insect–host plant interactions from an evolutionary perspective, using as example the Neotropical phytophagous insect West Indian fruit fly, Anastrepha obliqua (Macquart) (Diptera: Tephritidae), an economically important fruit crop pest in the Americas. Anastrepha obliqua could adopt a generalist or a specialist lifestyle. We first review the adaptive molecular mechanisms of phytophagous insects to host plants, and then describe the main tools to study phytophagous insect–host plant interactions in the era of omics sciences. The omics approaches will advance the understanding of insect molecular mechanisms and their influence on diversification and evolution. Finally, we discuss the importance of a multidisciplinary approach that integrates the use of omics tools and other, more classical methodologies in evolutionary studies.