Evidence that the caterpillar salivary enzyme glucose oxidase provides herbivore offense in solanaceous plants

The insect salivary enzyme glucose oxidase (GOX) can inhibit wound-inducible nicotine production in tobacco, Nicotiana tabacum. We examined whether salivary gland extracts of Helicoverpa zea lacking active GOX could still suppress nicotine in tobacco, Nicotiana tabacum, and whether GOX could suppress wound-inducible defenses of another Solanaceous plant, tomato Lycopersicon esculentum. Tobacco leaves were wounded with a cork borer and treated with water, salivary gland extracts with active GOX (SxG), or salivary gland extracts with inactive GOX (SxI). After three days, leaves treated with SxG had significantly less nicotine than all other wounded treatments. Neonates that fed on the terminal leaves of tobacco plants treated with SxG had significantly higher survival than neonates that fed on leaves treated with either SxI or water. This evidence supports the assertion that GOX is the salivary factor responsible for the suppression of tobacco plant nicotine production by H. zea saliva. Results for the NahG tobacco plants, which lack salicylic acid (SA) due to a transgene for bacterial SA hydroxylase, indicate that suppression of nicotine by GOX does not require SA. However, tobacco leaves that were wounded and treated with SxG had significantly higher levels of the SA-mediated PR-1a protein than leaves treated with SxI or water. Leaves of tomato plants wounded with scissors and then treated with SxG had trypsin inhibitor levels that were moderately lower than plants wounded and treated with purified GOX, water, or SxI. However, all the wounded tomato leaves irrespective of treatment resulted in lower caterpillar growth rates than the non-wounded tomato leaves. Glucose oxidase is the first insect salivary enzyme shown to suppress wound-inducible herbivore defenses of plants.     

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,而昆虫又进化出多种方式来躲避植物R蛋白的识别。总之,在这场军备竞赛中,昆虫的唾液成分决定着昆虫能否取食成功。取食过程中,咀嚼式口器害虫分泌大量酶类到植物体内,而刺吸式害虫则分泌胶状和水样唾液到植物中,它们都利用激发子和效应子去调控植物的免疫防御反应。分析现已报道的昆虫效应子发现其作用机制各有不同,具体表现为影响植物早期防御信号,调控植物激素通路及其他通路,或靶向小分子RNA通路。本文还综述了昆虫激发子的最新进展,揭示激发子可以通过诱导释放植物次生代谢物以及调控激素水平、Ca²⁺内流和活性氧爆发增强植物抗性。最后对昆虫效应子的分泌特性、寄主特异性和多功能性作了分析,并对无毒效应子及其对应的植物R基因,以及激发子的模式识别受体的研究进行了展望。     

松果梢斑螟对虫害诱导寄主防御的抑制作用

以松果梢斑螟（Dioryctria pryeri）-油松（Pinus tabuleaformis）（2年生球果和新梢）为研究对象,探讨梢斑螟幼虫对油松球果小卷蛾（Gravitarmata margarotana）先期虫害诱导寄主防御的抑制作用,以及虫害诱导的负防御机制。结果表明,双萜松脂酸作为油松球果和新梢的主要组成和诱导性防御物质,梢斑螟虫害后球果双萜松脂酸极显著增加,10 d后降低到正常水平;而新梢虫害后,松脂酸显著增加,后随新梢基础含量而增加,10 d后虫害新梢松脂酸显著高于球果。梢斑螟幼虫以小卷蛾虫害球果、健康球果和新梢等部位为食料,均为梢斑螟5龄幼虫下唇腺葡萄糖氧化酶（Glucose oxidase,GOX）活性最高,极显著高于4龄和3龄幼虫;且同一龄期,小卷蛾虫害球果中的梢斑螟幼虫GOX活性最高,显著高于新梢和健康球果中幼虫酶活性。研究发现,虫害后萜类防御物质随幼虫GOX活性升高呈下降趋势。梢斑螟幼虫RNA和P含量比较发现,取食小卷蛾虫害球果、健康球果和新梢3种食料,均为梢斑螟3龄幼虫最高,5龄幼虫最小,差异极显著;但同一龄期,3种食料发育的幼虫,其RNA和P含量间无显著差异。这些结果说明,小卷蛾幼虫的先期危害,诱导了寄主防御,但后来的梢斑螟幼虫通过下唇腺GOX抑制了寄主的诱导防御,使其生长率与健康球果和新梢中的幼虫基本一致。     

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。     

Saliva,Salivary Gland,and Hemolymph Collection from Ixodes scapularis Ticks

Ticks are found worldwide and afflict humans with many tick-borne illnesses. Ticks are vectors for pathogens that cause Lyme disease and tick-borne relapsing fever (Borrelia spp.), Rocky Mountain Spotted fever (Rickettsia rickettsii), ehrlichiosis (Ehrlichia chaffeensis and E. equi), anaplasmosis (Anaplasma phagocytophilum), encephalitis (tick-borne encephalitis virus), babesiosis (Babesia spp.), Colorado tick fever (Coltivirus), and tularemia (Francisella tularensis) ^1-8. To be properly transmitted into the host these infectious agents differentially regulate gene expression, interact with tick proteins, and migrate through the tick ^3,9-13. For example, the Lyme disease agent, Borrelia burgdorferi, adapts through differential gene expression to the feast and famine stages of the tick''s enzootic cycle ^14,15. Furthermore, as an Ixodes tick consumes a bloodmeal Borrelia replicate and migrate from the midgut into the hemocoel, where they travel to the salivary glands and are transmitted into the host with the expelled saliva ^9,16-19.As a tick feeds the host typically responds with a strong hemostatic and innate immune response ^11,13,20-22. Despite these host responses, I. scapularis can feed for several days because tick saliva contains proteins that are immunomodulatory, lytic agents, anticoagulants, and fibrinolysins to aid the tick feeding ^{3,11,20,21,23}. The immunomodulatory activities possessed by tick saliva or salivary gland extract (SGE) facilitate transmission, proliferation, and dissemination of numerous tick-borne pathogens ^3,20,24-27. To further understand how tick-borne infectious agents cause disease it is essential to dissect actively feeding ticks and collect tick saliva. This video protocol demonstrates dissection techniques for the collection of hemolymph and the removal of salivary glands from actively feeding I. scapularis nymphs after 48 and 72 hours post mouse placement. We also demonstrate saliva collection from an adult female I. scapularis tick.     

In situ tests on inducible defenses in Dictyota kunthii and Macrocystis integrifolia (Phaeophyceae) from the Chilean coast

Numerous experimental studies have reported inducible defenses in macroalgae, but most of them have been conducted in laboratory environments where algae were maintained detached from the substratum and in artificial flow regimes. The results of those experiments might not reflect the natural situation, which can only be studied in situ. We examined whether the brown macroalgae Dictyota kunthii (C. Agardh) Greville and Macrocystis integrifolia (Bory) show inducible defenses following exposure to different grazing levels (direct, water-borne cues from nearby grazed conspecifics, presence of a non-grazing herbivore and natural grazing) in field experiments, striving to maintain natural conditions as much as possible. We measured palatability of algae after exposure to different grazing levels by using live algae and agar-based food containing non-polar extracts. M. integrifolia showed no induction of defenses (at least not of non-polar compounds), suggesting constitutive defenses, absence of defenses (tolerance) or use of another strategy to avoid herbivory. These results are similar to those from previous laboratory experiments. In D. kunthii, defense was induced after two weeks of direct grazing by amphipods under field conditions. Water-borne cues from nearby grazed conspecifics, presence of a non-grazing herbivore and natural grazing did not induce defenses. Induction of defense in response to direct grazing agrees with results from a previous laboratory study, but while indirect cues induced defenses in the laboratory, there was no measurable induced defense in the field. Probably chemical cues from grazers are diluted quickly in the field, not reaching concentrations that cause induction of defenses. This might be the reason why in some algae induction by direct grazing is a more important defensive strategy than induction by water-borne cues. The results from our study also suggest that laboratory experiments showing induced defenses in response to grazed neighbours or mere grazer presence need to be interpreted with caution.     

Synergistic effects of direct and indirect defences on herbivore egg survival in a wild crucifer

Evolutionary theory of plant defences against herbivores predicts a trade-off between direct (anti-herbivore traits) and indirect defences (attraction of carnivores) when carnivore fitness is reduced. Such a trade-off is expected in plant species that kill herbivore eggs by exhibiting a hypersensitive response (HR)-like necrosis, which should then negatively affect carnivores. We used the black mustard (Brassica nigra) to investigate how this potentially lethal direct trait affects preferences and/or performances of specialist cabbage white butterflies (Pieris spp.), and their natural enemies, tiny egg parasitoid wasps (Trichogramma spp.). Both within and between black mustard populations, we observed variation in the expression of Pieris egg-induced HR. Butterfly eggs on plants with HR-like necrosis suffered lower hatching rates and higher parasitism than eggs that did not induce the trait. In addition, Trichogramma wasps were attracted to volatiles of egg-induced plants that also expressed HR, and this attraction depended on the Trichogramma strain used. Consequently, HR did not have a negative effect on egg parasitoid survival. We conclude that even within a system where plants deploy lethal direct defences, such defences may still act with indirect defences in a synergistic manner to reduce herbivore pressure.     

Trichomes as dangerous lollipops: Do lizards also use caterpillar body and frass odor to optimize their foraging?

When attacked by herbivores, plants produce toxic secondary metabolites that function as direct defenses, as well as indirect defenses that attract and reward predators of the offending herbivores. These indirect defenses include both nutritive rewards such as extra floral nectar, as well as informational rewards, such as the production and release of volatile compounds that betray the location of feeding herbivores to predators. Herbivory of Nicotiana attenuata by the tobacco hornworm (Manduca larvae) alters the volatile profiles of both the plant and larval headspace. Herbivory-elicited specific changes in the volatile profiles are detected by arthropod predators of Manduca larvae. The known predators that perceive volatile cues induced by Manduca herbivory of N. attenuata are insects that target Manduca at early developmental stages, when the larvae are still small; large, late-instar larvae may have outgrown these predation risks. However, here we offer evidence that branched chain aliphatic acids derived from the digestion of plant O-acyl sugars from trichomes may betray Manduca larvae to lizard predators during late developmental stages as well.     

The effect of host plants on Tetranychus evansi, Tetranychus urticae (Acari: Tetranychidae) and on their fungal pathogen Neozygites floridana (Entomophthorales: Neozygitaceae)

In a series of tritrophic-level interaction experiments, the effect of selected host plants of the spider mites, Tetranychus evansi and Tetranychus urticae, on Neozygites floridana was studied by evaluating the attachment of capilliconidia, presence of hyphal bodies in the infected mites, mortality from fungal infection, mummification and sporulation from fungus-killed mite cadavers. Host plants tested for T. evansi were tomato, cherry tomato, eggplant, nightshade, and pepper while host plants tested for T. urticae were strawberry, jack bean, cotton and Gerbera. Oviposition rate of the mites on each plant was determined to infer host plant suitability while host-switching determined antibiosis effect on fungal activity. T. evansi had a high oviposition on eggplant, tomato and nightshade but not on cherry tomato and pepper. T. urticae on jack bean resulted in a higher oviposition than on strawberry, cotton and Gerbera. Attachment of capilliconidia to the T. evansi body, presence of hyphal bodies in infected T. evansi and mortality from fungal infection were significantly higher on pepper, nightshade and tomato. The highest level of T. evansi mummification was observed on tomato. T. evansi cadavers from tomato and eggplant produced more primary conidia than those from cherry tomato, nightshade and pepper. Switching N. floridana infected T. evansi from one of five Solanaceous host plants to tomato had no prominent effect on N. floridana performance. For T. urticae, strawberry and jack bean provided the best N. floridana performance when considering all measured parameters. Strawberry also had the highest primary conidia production. This study shows that performance of N. floridana can vary with host plants and may be an important factor for the development of N. floridana epizootics.     

Molecular Transfer of Nematode Resistance Genes

Recombinant DNA techniques have been used to introduce agronomically valuable traits, including resistance to viruses, herbicides, and insects, into crop plants. Introduction of these genes into plants frequently involves Agrobacterium-mediated gene transfer. The potential exists for applying this technology to nematode control by introducing genes conferring resistance to nematodes. Transferred genes could include those encoding products detrimental to nematode development or reproduction as well as cloned host resistance genes. Host genes that confer resistance to cyst or root-knot nematode species have been identified in many plants. The best characterized is Mi, a gene that confers resistance to root-knot nematodes in tomato. A map-based cloning approach is being used to isolate the gene. For development of a detailed map of the region of the genome surrounding Mi, DNA markers genetically linked to Mi have been identified and analyzed in tomato lines that have undergone a recombination event near Mi. The molecular map will be used to identify DNA corresponding to Mi. We estimate that a clone of Mi will be obtained in 2-5 years. An exciting prospect is that introduction of this gene will confer resistance in plant species without currently available sources of resistance.     

唾液成分在刺吸式昆虫与植物关系中的作用

近年来,人们对刺吸式昆虫唾液成分的研究,揭示出其在刺吸式昆虫与植物关系中的重要作用。对多数刺吸式昆虫而言,他们取食时会分泌胶状和水状两种唾液,其中胶状唾液会在取食早期分泌形成唾液鞘来围绕并保护口针,通过直接和间接的作用来帮助取食;而水状唾液中则包含了果胶酶、纤维素酶、多酚氧化酶、过氧化物酶、碱性磷酸酯酶、蔗糖酶等组分,来帮助刺吸式昆虫对植物穿刺、消化食物、解毒次生物质并破坏植物的防御反应。有趣的是,唾液成分同时还可以诱导植物的防御反应,包括诱导植物的伤信号引起直接防御反应和诱导植物产生挥发物吸引植食者的天敌引起间接防御反应。并且,许多刺吸式昆虫取 食能够特异性地引发植物的病理反应,有研究推测刺吸式昆虫唾液中多聚半乳糖醛酸酶、碱性磷酸酯酶、蔗糖酶、多酚氧化酶等成分可能是某些植物特定病理反应的激发子,但是目前还没有定论,同时许多刺吸式昆虫唾液中的氨基酸和蛋白酶还是引起植物虫瘿的原因之一。 迄今的研究表明,刺吸式昆虫会根据不同的寄主植物和不同的生理需要,通过唾液组分的改变,来达到取食和发育的目的。对刺吸式昆虫唾液成分和作用机理的研究,可以为揭示刺吸式昆虫致害机理特别是传毒机理、指导害虫有效治理、阐明其与植物的协同进化等提供一定的思路。     

Alleviation of Salt Stress by Enterobacter sp. EJ01 in Tomato and Arabidopsis Is Accompanied by Up-Regulation of Conserved Salinity Responsive Factors in Plants

Microbiota in the niches of the rhizosphere zones can affect plant growth and responses to environmental stress conditions via mutualistic interactions with host plants. Specifically, some beneficial bacteria, collectively referred to as Plant Growth Promoting Rhizobacteria (PGPRs), increase plant biomass and innate immunity potential. Here, we report that Enterobacter sp. EJ01, a bacterium isolated from sea china pink (Dianthus japonicus thunb) in reclaimed land of Gyehwa-do in Korea, improved the vegetative growth and alleviated salt stress in tomato and Arabidopsis. EJ01 was capable of producing 1-aminocy-clopropane-1-carboxylate (ACC) deaminase and also exhibited indole-3-acetic acid (IAA) production. The isolate EJ01 conferred increases in fresh weight, dry weight, and plant height of tomato and Arabidopsis under both normal and high salinity conditions. At the molecular level, short-term treatment with EJ01 increased the expression of salt stress responsive genes such as DREB2b, RD29A, RD29B, and RAB18 in Arabidopsis. The expression of proline biosynthetic genes (i.e. P5CS1 and P5CS2) and of genes related to priming processes (i.e. MPK3 and MPK6) were also up-regulated. In addition, reactive oxygen species scavenging activities were enhanced in tomatoes treated with EJ01 in stressed conditions. GFP-tagged EJ01 displayed colonization in the rhizosphere and endosphere in the roots of Arabidopsis. In conclusion, the newly isolated Enterobacter sp. EJ01 is a likely PGPR and alleviates salt stress in host plants through multiple mechanisms, including the rapid up-regulation of conserved plant salt stress responsive signaling pathways.     

ATP hydrolyzing salivary enzymes of caterpillars suppress plant defenses

The oral secretions of herbivores are important recognition cues that can be used by plants to mediate induced defenses. In this study, a degradation of adenosine-5'-triphosphate (ATP) in tomato leaves was detected after treatment with Helicoverpa zea saliva. Correspondingly, a high level of ATPase activity in saliva was detected and three ATP hydrolyzing enzymes: apyrase, ATP synthase and ATPase 13A1 were identified in salivary glands. To determine the functions of these proteins in mediating defenses, they were cloned from H. zea and expressed in Escherichia coli. By applying the purified expressed apyrase, ATP synthase or ATPase 13A1 to wounded tomato leaves, it was determined that these ATP hydrolyzing enzymes suppressed the defensive genes regulated by the jasmonic acid and ethylene pathways in tomato plant. Suppression of glandular trichome production was also observed after treatment. Blood-feeding arthropods employ 5'-nucleotidase family of apyrases to circumvent host responses and the H. zea apyrase, is also a member of this family. The comparatively high degree of sequence similarity of the H. zea salivary apyrase with mosquito apyrases suggests a broader evolutionary role for salivary apyrases than previously envisioned.     

Hatch and Reproduction of Globodera tabacum tabacum in Response to Tobacco,Tomato, or Black Nightshade

The effects of broadleaf tobacco, tomato, and black nightshade on juvenile hatch and reproduction of Globodera tabacum tabacum were determined in laboratory and greenhouse experiments. Root exudates from nightshade stimulated greater egg hatch than those from either ''Rutgers'' tomato or ''86-4'' tobacco. Hatch was greater at higher proportions of root exudates for all three plant species. Root exudates from plants greater than 3 weeks old stimulated more hatch than younger plants. No regression relationships existed between plant age and nematode batch. In other experiments, hatch from eggs in cysts was higher for tomato and nightshade after 10 weeks in greenhouse pots compared to tobacco and bare soil. Numbers of second-stage juveniles in eggs in cysts produced from a previous generation on the same host were highest on nightshade and less on tomato and tobacco. Cysts of variable age recovered from field soil had increased hatch in both root exudates or water compared to recently produced cysts from plants in growth chambers. Globodera t. tabacum may be subject to both host and environmentally mediated diapause.     

Evaluation of 31 Potential Biofumigant Brassicaceous Plants as Hosts for Three Meloiodogyne Species

Brassicaceous cover crops can be used for biofumigation after soil incorporation of the mowed crop. This strategy can be used to manage root-knot nematodes (Meloidogyne spp.), but the fact that many of these crops are host to root-knot nematodes can result in an undesired nematode population increase during the cultivation of the cover crop. To avoid this, cover crop cultivars that are poor or nonhosts should be selected. In this study, the host status of 31 plants in the family Brassicaceae for the three root-knot nematode species M. incognita, M. javanica, and M. hapla were evaluated, and compared with a susceptible tomato host in repeated greenhouse pot trials. The results showed that M. incognita and M. javanica responded in a similar fashion to the different cover cultivars. Indian mustard (Brassica juncea) and turnip (B. rapa) were generally good hosts, whereas most oil radish cultivars (Raphanus. sativus ssp. oleiferus) were poor hosts. However, some oil radish cultivars were among the best hosts for M. hapla. The arugula (Eruca sativa) cultivar Nemat was a poor host for all three nematode species tested. This study provides important information for chosing a cover crop with the purpose of managing root-knot nematodes.     

Exogenous application of liquid diet,previously fed upon by pea aphids Acyrthosiphon pisum (Harris), to broad bean leaves induces volatiles attractive to the specialist parasitic wasp Aphidius ervi (Haliday)

Proof of the existence of aphid-derived molecules that induce emission of volatile organic compounds as indirect defensive responses in plants (hereafter called elicitors) has not yet been obtained. We showed here the presence and some aspects of the chemical nature of these elicitors. Exogenous application of the fed diet (liquid diet previously fed on by the Pea aphid, Acyrthosiphon pisum) on the damaged part of leaves of broad bean plants, made the plants more attractive to a parasitic wasp, Aphidius ervi, than application of the unfed diet. This result suggested that elicitors existed in the fed diet. Chemical characterization using ultrafiltration and subsequent bioassay revealed that the responsible factor was larger than 3 kDa. Heating of the fed diet did not inactivate its ability to induce attractive volatiles, which suggested thermotolerance of the elicitor. These results contribute to the mechanistic understanding of plant defenses against aphids.     

Penetration of Crotalaria juncea,Dolichos lablab,and Sesamum indicum Roots by Meloidogyne javanica

Penetration of Crotalaria juncea (PI 207657 and cv. Tropic Sun) Dolichos lablab cv. Highworth, and Sesamum indicum by juveniles (J2) of Meloidogyne javanica was assessed to investigate the mechanism by which these plants may reduce nematode numbers in the field. Growth chamber experiments were conducted at 25 C, with vials containing 90 g sand infested with 450 J2; tomato (UC 204 C) was included as a susceptible host. Fifteen days after inoculation, roots were stained and the nematodes within stained roots were counted. Both C. juncea lines were highly resistant to penetration, as they contained significantly fewer nematodes per cm of root and per root system than the other plants. Although containing more nematodes per cm of root than C. juncea, S. indicum and D. lablab had significantly fewer nematodes per root system and per cm of root than tomato. Roots were significantly longer in the plants with the lowest nematode penetration. Although C. juncea, D. lablab, and S. indicum may have potential utility as cover or rotation crops in soil infested with M. javanica, further quantitative information on the reproduction of M. javanica and other nematodes in these plants is needed.     

Direct and indirect influences of arbuscular mycorrhizal fungi on phosphorus uptake by two root hemiparasitic Pedicularis species: do the fungal partners matter at low colonization levels?

Background and Aims

Because most parasitic plants do not form mycorrhizal associations, the nutritional roles of arbuscular mycorrhizal (AM) fungi in them have hardly been tested. Some facultative root hemiparasitic Pedicularis species form AM associations and hence are ideal for testing both direct and indirect effects of AM fungi on their nutrient acquisition. The aim of this study was to test the influence of AM inoculation on phosphorus (P) uptake by Pedicularis rex and P. tricolor.

Methods

³²P labelling was used in compartmented pots to assess the contribution of the AM pathway and the influence of AM inoculation on P uptake from a host plant into the root hemiparasites. Laboratory isolates of fungal species (Glomus mosseae and G. intraradices) and the host species (Hordeum vulgare ‘Fleet’) to which the two Pedicularis species showed obvious responses in haustorium formation and growth in previous studies were used.

Key Results

The AM colonization of both Pedicularis spp. was low (<15 % root length) and only a very small proportion of total plant P (<1 %) was delivered from the soil via the AM fungus. In a separate experiment, inoculation with AM fungi strongly interfered with P acquisition by both Pedicularis species from their host barley, almost certainly because the numbers of haustoria formed by the parasite were significantly reduced in AM plants.

Conclusions

Roles of AM fungi in nutrient acquisition by root parasitic plants were quantitatively demonstrated for the first time. Evidence was obtained for a novel mechanism of preventing root parasitic plants from overexploiting host resources through AM fungal-induced suppression of the absorptive structures in the parasites.     

The complex interactions between host immunity and non-biotrophic fungal pathogens of wheat leaves

Significant progress has been made in elucidating the mechanisms used by plants to recognize pathogens and activate “immune” responses. A “first line” of defense can be triggered through recognition of conserved Pathogen or Microbe Associated Molecular Patterns (PAMPs or MAMPs), resulting in activation of basal (or non-host) plant defenses, referred to as PAMP-triggered immunity (PTI). Disease resistance responses can also subsequently be triggered via gene-for-gene type interactions between pathogen avirulence effector genes and plant disease resistance genes (Avr-R), giving rise to effector triggered immunity (ETI). The majority of the conceptual advances in understanding these systems have been made using model systems, such as Arabidopsis, tobacco, or tomato in combination with biotrophic pathogens that colonize living plant tissues. In contrast, how these disease resistance mechanisms interact with non-biotrophic (hemibiotrophic or necrotrophic) fungal pathogens that thrive on dying host tissue during successful infection, is less clear. Several lines of recent evidence have begun to suggest that these organisms may actually exploit components of plant immunity in order to infect, successfully colonize and reproduce within host tissues. One underlying mechanism for this strategy has been proposed, which has been referred to as effector triggered susceptibility (ETS). This review aims to highlight the complexity of interactions between plant recognition and defense activation towards non-biotrophic pathogens, with particular emphasis on three important fungal diseases of wheat (Triticum aestivum) leaves.