An overview of antifungal peptides derived from insect

Fungi are not classified as plants or animals. They resemble plants in many ways but do not produce chlorophyll or make their own food photosynthetically like plants. Fungi are useful for the production of beer, bread, medicine, etc. More complex than viruses or bacteria; fungi can be destructive human pathogens responsible for various diseases in humans. Most people have a strong natural immunity against fungal infection. However, fungi can cause diseases when this immunity breaks down. In the last few years, fungal infection has increased strikingly and has been accompanied by a rise in the number of deaths of cancer patients, transplant recipients, and acquired immunodeficiency syndrome (AIDS) patients owing to fungal infections. The growth rate of fungi is very slow and quite difficult to identify. A series of molecules with antifungal activity against different strains of fungi have been found in insects, which can be of great importance to tackle human diseases. Insects secrete such compounds, which can be peptides, as a part of their immune defense reactions. Active antifungal peptides developed by insects to rapidly eliminate infectious pathogens are considered a component of the defense munitions. This review focuses on naturally occurring antifungal peptides from insects and their challenges to be used as armaments against human diseases.     

Entomopathogenic fungi and insect behaviour: from unsuspecting hosts to targeted vectors

The behavioural response of an insect to a fungal pathogen will have a direct effect on the efficacy of the fungus as a biological control agent. In this paper we describe two processes that have a significant effect on the interactions between insects and entomopathogenic fungi: (a) the ability of target insects to detect and avoid fungal pathogens and (b) the transmission of fungal pathogens between host insects. The behavioural interactions between insects and entomopathogenic fungi are described for a variety of fungal pathogens ranging from commercially available bio-pesticides to non-formulated naturally occurring pathogens. The artificial manipulation of insect behaviour using dissemination devices to contaminate insects with entomopathogenic fungi is then described. The implications of insect behaviour on the use of fungal pathogens as biological control agents are discussed.     

Indirect plant-mediated effects on insect immunity and disease resistance in a tritrophic system

Host plant quality can significantly influence the growth and condition of phytophagous insects, and consequently their susceptibility to pathogens. This study examined the relationship between host plant quality, insect condition, immune responsiveness and resistance to pathogens in the cabbage looper, Trichoplusia ni. Two baseline and induced immune parameters were estimated, haemocyte numbers and haemolymph phenoloxidase (PO) activity, for larvae on two host plants, broccoli and cucumber. Haemolymph protein concentration was assessed as an indication of insect condition, and the susceptibility of larvae to T. ni single nucleopolyhedrovirus (SNPV) was used as a measure of disease resistance. T. ni growth, survival and condition was much higher on broccoli than cucumber. Haemocyte numbers were significantly higher in broccoli-reared larvae, whereas PO activity was not. An immune challenge induced significantly elevated numbers of haemocytes for larvae reared on both host plants, but did not affect PO activity or protein concentrations. Susceptibility to T. ni SNPV was markedly higher in larvae reared on cucumber than on broccoli. These results clearly indicate that host plant quality can affect both immune response and disease resistance of T. ni larvae and that bottom-up effects could be important in interactions between insects and entomopathogens.     

The relationships of plant and insect diversities in succession

The basic features of an intensive study on the various stages of a secondary succession, from fallow Held to birch woodland, are described. The α-β diversities of the green plants, and two orders of insects, Hetcroptera and adult Coleoptera, are described. For the vegetation, in addition to taxonotnic diversity, structural diversity, with both spatial and architectural components, was recognized. It was found that up to a successional age of 16 months, the taxonomic diversities of plants and insects rose; thereafter the diversity of the plant species declined far more than the insect species diversity. It was concluded that in the later successional stages the maintenance of a high level of taxonomic diversity of these orders of insects is correlated with the rising structural diversity of the green plants, which virtually compensates for their falling taxonomic diversity. The larger fungi appear to show a similar trend to the insects.     

Interspecific hybridization in plant-associated fungi and oomycetes: a review

Fungi (kingdom Mycota) and oomycetes (kingdom Stramenopila, phylum Oomycota) are crucially important in the nutrient cycles of the world. Their interactions with plants sometimes benefit and sometimes act to the detriment of humans. Many fungi establish ecologically vital mutualisms, such as in mycorrhizal fungi that enhance nutrient acquisition, and endophytes that combat insects and other herbivores. Other fungi and many oomycetes are plant pathogens that devastate natural and agricultural populations of plant species. Studies of fungal and oomycete evolution were extraordinarily difficult until the advent of molecular phylogenetics. Over the past decade, researchers applying these new tools to fungi and oomycetes have made astounding new discoveries, among which is the potential for interspecific hybridization. Consequences of hybridization among pathogens include adaptation to new niches such as new host species, and increased or decreased virulence. Hybrid mutualists may also be better adapted to new hosts and can provide greater or more diverse benefits to host plants.     

Differential effects of foliar endophytic fungi on insect herbivores attacking a herbaceous plant

Foliar endophytic fungi appear to be ubiquitous in nature, occurring in a very wide range of herbaceous plants. However, their ecological role within forbs is very poorly known and interactions with foliar-feeding insects virtually unexplored. In this study, leaves of Cirsium arvense were infected with different combinations of endophyte fungi that had been previously isolated from this plant species. Two months later, leaf material was fed to larvae of a generalist insect, Mamestra brassicae, and adults of a specialist feeder, Cassida rubiginosa. Endophytes had different effects on the two insects; one species, Chaetomium cochliodes, reduced growth of M. brassicae but increased feeding by C. rubiginosa. Another species, Cladosporium cladosporioides, increased beetle feeding also, but had no effect on M. brassicae. Interactions were also seen between fungal species and dual infection with C. cladosporioides and Trichoderma viride greatly reduced beetle feeding. It is concluded that endophytes have significant effects on foliar feeding insects that differ with degree of specialism of the herbivore. We suggest that these effects are due to chemical changes in the host, brought about by fungal infection. These fungi have received remarkably little attention in the study of insect–plant interactions and yet could be important determinants of insect growth and even population dynamics.     

Arbuscular mycorrhizal fungi affect phytophagous insect specialism

The majority of phytophagous insects eat very few plant species, yet the ecological and evolutionary forces that have driven such specialism are not entirely understood. The hypothesis that arbuscular mycorrhizal (AM) fungi can determine phytophagous insect specialism, through differential effects on insect growth, was tested using examples from the British flora. In the UK, plant families and species in the family Lamiaceae that are strongly mycorrhizal have higher proportions of specialist insects feeding on them than those that are weakly mycorrhizal. We suggest that AM fungi can affect the composition of insect assemblages on plants and are a hitherto unconsidered factor in the evolution of insect specialism.     

Are green islands red herrings? Significance of green islands in plant interactions with pathogens and pests

The term green island was first used to describe an area of living, green tissue surrounding a site of infection by an obligately biotrophic fungal pathogen, differentiated from neighbouring yellowing, senescent tissue. However, it has now been used to describe symptoms formed in response to necrotrophic fungal pathogens, virus infection and infestation by certain insects. In leaves infected by obligate biotrophs such as rust and powdery mildew pathogens, green islands are areas where senescence is retarded, photosynthetic activity is maintained and polyamines accumulate. We propose such areas, in which both host and pathogen cells are alive, be termed green bionissia. By contrast, we propose that green areas associated with leaf damage caused by toxins produced by necrotrophic fungal pathogens be termed green necronissia. A range of biotrophic/hemibiotrophic fungi and leaf-mining insects produce cytokinins and it has been suggested that this cytokinin secretion may be responsible for the green island formation. Indeed, localised cytokinin accumulation may be a common mechanism responsible for green island formation in interactions of plants with biotrophic fungi, viruses and insects. Models have been developed to study if green island formation is pathogen-mediated or host-mediated. They suggest that green bionissia on leaves infected by biotrophic fungal pathogens represent zones of host tissue, altered physiologically to allow the pathogen maximum access to nutrients early in the interaction, thus supporting early sporulation and increasing pathogen fitness. They lead to the suggestion that green islands are 'red herrings', representing no more than the consequence of the infection process and discrete changes in leaf senescence.     

植物耐虫性研究进展

本文简要介绍了植物耐虫性的含义、发生范围、耐虫性的进化过程和遗传特性、耐虫性机理以及影响植物耐虫性表达的非生物和生物因子。植物耐虫性机理的研究涉及光合作用能力变化、同化产物的再分配、内源激素的变化、休眠分生组织的激活和补偿生长、储藏器官的利用、植物物候学和植株株型结构的变化等。研究表明,植物受害后光合作用强度的变化与其耐虫性没有相关性,有些耐虫植物受害后光合作用能力增加,有些植物光合作用强度无明显影响或者下降较少; 害虫取食为害可促进耐虫植物的同化产物得到最大程度利用,能激活耐虫植物的休眠分生组织,产生超补偿作用; 耐虫植物受害部位细胞分裂素含量显著升高; 虫害引起物候学变化小的植物具有较强的耐虫性; 植物的冠层结构、叶形态、根茎比、茎蘖数等植株株型变化与耐虫性有关。影响植物耐虫性表达的因子主要有温度、大气CO₂浓度、土壤营养水平、农用化学物质、植株年龄、害虫分布类型和取食方式、植物共生物等。不同植物在相同温度下对同一种害虫的耐害性差异大,其主要原因可能是由于温度的变化引起同化产物的分配和再分配以及气孔关闭对气体交换和光合作用能力的影响; 生长在高CO₂含量大气中的植物,对害虫的为害有较强耐受性。土壤营养水平对植物耐虫性表达的影响大于温度,增施磷、钾肥可增加植物的耐虫性。聚集分布型害虫为害对植物造成的损失大于随机分布型和均匀分布型害虫,害虫的取食方式、传粉昆虫的活动、植物内生真菌和菌根真菌的感染均影响到植物耐虫性的表达水平。文中最后讨论了植物耐虫性在害虫综合治理中的重要性及应用前景。     

昆虫唾液成分在昆虫与植物关系中的作用

近年来,人们对于植食性昆虫唾液的深入研究,揭示出其在昆虫与植物的相互关系和协同进化中起到非常重要的作用。植食性昆虫唾液中含有的酶类和各种有机成分,能诱导植物的一系列生化反应,而且这些反应有很强的特异性,与为害的昆虫种类甚至龄期有关。鳞翅目幼虫口腔分泌物（或反吐液）中含有的β-葡糖苷酶、葡萄糖氧化酶等酶类和挥发物诱导素等有机成分,已经证明可以诱导植物的反应; 刺吸式昆虫的取食也可以刺激植物产生反应,但其唾液内的酶类,如烟粉虱的碱性磷酸酶, 蚜虫的酚氧化酶、果胶酶和多聚半乳糖醛酸酶, 蝽类的寡聚半乳糖醛酸酶等是否发挥作用,目前还没有直接的证据。寄主植物对昆虫的唾液成分也有很大的影响,可能是昆虫对不同植物营养成分和毒性成分的适应方式。对昆虫唾液蛋白的分析表明,具有同样类型口器、食物类型接近的昆虫,唾液成分有更多的相似性。研究植食性昆虫的唾液成分,对于阐明昆虫和植物的协同进化关系、昆虫生物型的形成机理、害虫的致害机理,以及指导害虫防治等,有着一定的理论和实际意义。     

Aspergillus oryzae NRRL 35191 from coffee, a non-toxigenic endophyte with the ability to synthesize kojic acid

Aspergillus oryzae NRRL 35191 was isolated as an endophyte from coffee leaves and found to produce kojic acid (KA) in culture. When inoculated into cacao seedlings (Theobroma cacao), A. oryzae grew endophytically and synthesized KA in planta. Cacao seedlings inoculated with A. oryzae produced higher levels of caffeine than non-inoculated ones. Aspergillus oryzae may be a useful endophyte to introduce to cacao since it grows non-pathogenically and induces the caffeine defense response that may make the plant more tolerant to insects and pathogens.     

Testing assumptions of the enemy release hypothesis: generalist versus specialist enemies of the grass Brachypodium sylvaticum

The enemy release hypothesis (ERH) suggests greater success of species in an invaded range due to release from natural enemies. The ERH assumes there will be more specialist enemies in the native range and that generalists will have an equal effect in both ranges. We tested these assumptions with the grass Brachypodium sylvaticum in the native range (Switzerland) and invaded range (Oregon, USA). We assessed all the kinds of damage present (caused by fungi, insects, mollusk and deer) on both leaves and seeds at 10 sites in each range and correlated damage with host fitness. Only two of the 20 fungi found on leaves were specialist pathogens, and these were more frequent in the native range. Conversely there was more insect herbivory on leaves in the invaded range. All fungi and insects found on seeds were generalists. More species of fungi were found on seeds in the native range, and a higher proportion of them were pathogenic than in the invaded range. There were more kinds of enemies in the native range, where the plants had lower fitness, in accordance with the ERH. However, contrary to assumptions of the ERH, generalists appear to be equally or more important than specialists in reducing host fitness.     

Arbuscular mycorrhizal fungi influence visitation rates of pollinating insects

Abstract.  1. Arbuscular mycorrhizal (AM) fungi can increase a number of plant traits to which pollinating insects are known to respond. These include total plant size, flower number, flower size, and amount of pollen produced.
2. It was hypothesised that these effects would lead to a different visitation rate of pollinating insects on mycorrhizal and non-mycorrhizal plants. To test this idea, three species of annual plants ( Centaurea cyanus , Tagetes erecta , and Tagetes patula ) were grown with and without AM fungi and the visits by pollinating insects were recorded over a 2-month period.
3. In all three species, mycorrhizal plants experienced a greater number of pollinator visits per flower per unit time. Diptera and Hymenoptera were the predominant insects and the latter order showed the strongest response.
4. Here, it is suggested that mycorrhizal fungi increase floral visitation rates by insects, but that the mechanism varies from one plant species to another. In C. cyanus , it appears to be due to flower number per plant, in T. patula it is individual inflorescence size, and in T. patula it is nectar standing crop per inflorescence.     

Effects of non-native plants on the native insect community of Delaware

Due to the lack of a co-evolutionary history, the novel defenses presented by introduced plants may be insurmountable to many native insects. Accordingly, non-native plants are expected to support less insect biomass than native plants. Further, native insect specialists may be more affected by introduced plants than native generalist herbivores, resulting in decreased insect diversity on non-native plants due to the loss of specialists. To test these hypotheses, we used a common garden experiment to compare native insect biomass, species richness, and the proportion of native specialist to native generalist insects supported by 45 species of woody plants. Plants were classified into three groupings, with 10 replicates of each species: 15 species native to Delaware (Natives), 15 non-native species that were congeneric with a member of the Native group (Non-native Congeners), and 15 non-native species that did not have a congener present in the United States (Aliens). Native herbivorous insects were sampled in May, June, and July of 2004 and 2005. Overall, insect biomass was greater on Natives than Non-native Congeners and Aliens, but insect biomass varied unpredictably between congeneric pair members. Counter to expectations, Aliens held more insect biomass than did Non-native Congeners. There was no difference in species richness or the number of specialist and generalist species collected among the three plant groupings in either year, although our protocol was biased against sampling specialists. If these results generalize to other studies, loss of native insect biomass due to introduced plants may negatively affect higher trophic levels of the ecosystem.     

甘油对粒毛盘菌DP5胞外多酚积累的影响

【目的】探明以甘油为碳源促进粒毛盘菌DP5积累多酚的可能原因。【方法】对碳源种类、甘油浓度、曲酸、抑制剂和前体等对多酚产量和生物量的影响进行分析。【结果】以甘油为碳源,能显著提高粒毛盘菌胞外多酚产量。甘油浓度为20 g/L时,胞外多酚产量最高,达到0.664 g GAE/L,并在发酵液中检测到曲酸,其含量为0.25 g/L。向以蔗糖为碳源的发酵液添加曲酸,胞外多酚含量从0.209 g GAE/L提高至0.376 g GAE/L。以甘油为碳源的发酵液中,酚氧化酶活性较低。粒毛盘菌DP5通过莽草酸途径和聚酮途径合成多酚,甘油有利于莽草酸途径和聚酮途径前体物质的合成。【结论】粒毛盘菌以甘油为碳源合成出曲酸,曲酸抑制多酚向黑色素的转化;甘油促进多酚前体的合成,从而提高了粒毛盘菌胞外多酚的积累量。     

Kinetic properties of catecholoxidase activity of tarantula hemocyanin

Phenoloxidases occur in almost all organisms, being essentially involved in various processes such as the immune response, wound healing, pigmentation and sclerotization in arthropods. Many hemocyanins are also capable of phenoloxidase activity after activation. Notably, in chelicerates, a phenoloxidase has not been identified in the hemolymph, and thus hemocyanin is assumed to be the physiological phenoloxidase in these animals. Although phenoloxidase activity has been shown for hemocyanin from several chelicerate species, a characterization of the enzymatic properties is still lacking. In this article, the enzymatic properties of activated hemocyanin from the tarantula Eurypelma californicum are reported, which was activated by SDS at concentrations above the critical micellar concentration. The activated state of Eurypelma hemocyanin is stable for several hours. Dopamine is a preferred substrate of activated hemocyanin. For dopamine, a K(M) value of 1.45 +/- 0.16 mm and strong substrate inhibition at high substrate concentrations were observed. Typical inhibitors of catecholoxidase, such as l-mimosine, kojic acid, tyramine, phenylthiourea and azide, also inhibit the phenoloxidase activity of activated hemocyanin. This indicates that the activated hemocyanin behaves as a normal phenoloxidase.     

Molecular dialogues between Trichoderma and roots: Role of the fungal secretome

Trichoderma species are opportunistic fungi residing primarily in soil, tree bark and on wild mushrooms. Trichoderma is capable of killing other fungi and penetrating plant roots, and is commonly used as both a biofungicide and inducer of plant defence against pathogens. These fungi also exert other beneficial effects on plants including growth promotion and tolerance to abiotic stresses, primarily mediated by their intimate interactions with roots. In root–microbe interactions (both beneficial and harmful), fungal secreted proteins play a crucial role in establishing contact with the roots, fungal attachment, root penetration and triggering of plant responses. In Trichoderma–root interactions, the sucrose present in root exudates has been demonstrated to be important in fungal attraction. Attachment to roots is mediated by hydrophobin-like proteins, and secreted swollenins and plant cell wall degrading enzymes facilitate internalization of the fungal hyphae. During the early stage of penetration, suppression of plant defence is vital to successful initial root colonisation; this is mediated by small soluble cysteine-rich secreted proteins (effector-like proteins). Up to this stage, Trichoderma's behaviour is similar to that of a plant pathogen invading root structures. However, subsequent events like oxidative bursts, the synthesis of salicylic acid by the plants, and secretion of elicitor-like proteins by Trichoderma spp. differentiate this fungus from pathogens. These processes induce immunity in plants that help counter subsequent invasion by plant pathogens and insects. In this review, we present an inventory of soluble secreted proteins from Trichoderma that might play an active role in beneficial Trichoderma–plant interactions, and review the function of such proteins where known.     

Minor effects of two elicitors of insect and pathogen resistance on volatile emissions and parasitism of Spodoptera frugiperda in Mexican maize fields

Synthetic elicitors can be used to induce resistance in plants against pathogens and arthropod herbivores. Such compounds may also change the emission of herbivore-induced plant volatiles, which serve as important cues for parasitic wasps to locate their hosts. Therefore, the use of elicitors in the field may affect biological control of insect pests. To test this, we treated maize seedlings growing in a subtropical field in Mexico with methyl jasmonate (MeJA), an elicitor of defense responses against many insects, and benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), an elicitor of resistance against certain pathogens. Volatile emission, herbivore infestation, pathogen infection, and plant performance (growth and grain yield) of treated and untreated maize plants were measured. Application of BTH slightly reduced volatile emission in maize, while MeJA increased the emission compared to control treatments. Despite the apparent changes in volatile emissions, the elicitor application did not consistently affect infestation by Spodoptera frugiperda larvae, the main insect pest found on the maize seedlings, and had only marginal effects on parasitism rates. Similarly, there were no treatment effects on infestation by other herbivores and pathogens. Results for the six replications that stretched over one summer and one winter season were highly variable, with parasitism rates and the species composition of the parasitoids differing significantly between seasons. This variability, as well as the severe biotic and abiotic stresses on young seedlings might explain why we measured only slight effects of elicitor application on pest incidence and biological control in this specific field study. Indeed, an additional field experiment under milder and more standardized conditions revealed that BTH induced significant resistance against Bipolaris maydis, a major pathogen in the experimental maize fields. Similar affects can be expected for herbivory and parasitism rates.     

Introduction of Non-Native Pollinators Can Lead to Trans-Continental Movement of Bee-Associated Fungi

Bees are essential pollinators for many flowering plants, including agriculturally important crops such as apple. As geographic ranges of bees or their host plants change as a result of human activities, we need to identify pathogens that could be transmitted among newly sympatric species to evaluate and anticipate their effects on bee communities. We used PCR screening and DNA sequencing to evaluate exposure to potentially disease-causing microorganisms in a pollinator of apple, the horned mason bee (Osmia cornifrons). We did not detect microsporidia, Wolbachia, or trypanosomes, which are common pathogens of bees, in any of the hundreds of mason bees screened. We did detect both pathogenic and apathogenic (saprophytic) fungal species in the genus Ascosphaera (chalkbrood), an unidentified species of Aspergillus fungus, and a strain of bacteria in the genus Paenibacillus that is probably apathogenic. We detected pathogenic fungal strains in asymptomatic adult bees that therefore may be carriers of disease. We demonstrate that fungi from the genus Ascosphaera have been transported to North America along with the bee from its native range in Japan, and that O. cornifrons is exposed to fungi previously only identified from nests of other related bee species. Further study will be required to quantify pathogenicity and health effects of these different microbial species on O. cornifrons and on closely-related native North American mason bees that may now be exposed to novel pathogens. A global perspective is required for pathogen research as geographic ranges of insects and microorganisms shift due to intentional or accidental introductions.