Participation of the enzymes involved in the biosynthesis of biogenic amines in biochemical interactions between wheat (Triticum aestivum; Poaceae) and bird cherry-oat aphid (Rhopalosiphum padi; Aphididae)

The studies concerned changes in the activities of ornithine decarboxylase (ODC), lysine decarboxylase (LDC) and tyrosine decarboxylase (TyDC) in tissues of wheat (Triticum aestivum L.) infested with bird cherry-oat aphid (Rhopalosiphum padi L.).Obtained results showed that the activities of the enzymes were stimulated in the less susceptible wheat Kontesa cv. infested by the aphids. In the case of the more susceptible Tonacja cv., on most occasions a decrease in the enzyme activities occurred. Such responses were especially clear for TyDC in both analysed cvs., and for LDC and ODC in the case of Kontesa cv. Thus it may be concluded that amino acid decarboxylation plays an important part in the biochemical defence developed in wheat tissues in response to R. padi infestation. The changes in the activities of the decarboxylases were dependent on the wheat genotype as well as the duration of the infestation.     

Genetic control of different types of the aphid resistance in cereal crops

Inheritance of the two main types of the plant resistance to insects was investigated in the sorghum-greenbug (Schizaphis graminum Rond.) and wheat-bird cherry-oat aphid (Rhopalosiphon padi L.) interaction systems. The data obtained support the hypothesis that antixenosis (avoiding of the plant by the insect, given a choice) and antibiosis (adverse effect of the plant on the insect feeding on it) are pleiotropic manifestations of the same genes. This is confirmed by the following facts. (1) Identical patterns of segregation for antixenosis and antibiosis in different cases of sorghum resistance to the greenbug: monogenic control (gene Sgr4), digenic control (Sgr1, Sgr2 and Sgr7, Sgr8), and complementary action of the genes (Sgr9 and Sgr10). (2) Correlated changes in the levels of antibiosis and antixenosis during long-term reproduction of a greenbug clone on the resistant sorghum variety k-1206 (resistance controlled by one gene). (3) Simultaneous expression of antixenosis and antibiosis in F₃ wheat hybrid families to the bird cherry-oat aphid.     

Changes in amino acid decarboxylation in maize (Zea mays; Poaceae) tissues in response to bird cherry-oat aphid (Rhopalosiphum padi; Aphididae) infestation

The study was focused on changes in the activities of ornithine decarboxylase (ODC), lysine decarboxylase (LDC) and tyrosine decarboxylase (TyDC) in maize seedlings infested by bird cherry-oat aphid (Rhopalosiphum padi L.).Obtained results showed that the aphid infestation induced LDC activity strongly within tissues of less aphid-settled maize (Waza cv.) during the first week of the infestation in comparison to the control plants and the activity was suppressed after two weeks. However, TyDC activity fluctuated under the aphid infestation. In relation to the control, the enzyme activity was inhibited on the first day, activated after the first week and reduced again two weeks into the experiment. A significant reduction in ODC activity was also observed in seedlings of aphid-infested maize Waza cv. during the first week. In a more susceptible maize cv. (Złota Karłowa), an increase in LDC and TyDC activities in relation to the control and a simultaneous decrease in ODC activity were noted after the first day of the infestation. After one week of aphid attack, TyDC activity was induced and ODC was inhibited, whereas after two weeks ODC activity was decreased with a simultaneous increase in LDC activity in the Złota Karłowa seedlings.     

Enzymatic chlorophyll degradation in wheat near-isogenic lines elicited by cereal aphid (Homoptera: Aphididae) feeding

Chlorophyll degradation enzyme (i.e., chlorophyllase, Mg-dechelatase, and chlorophyll oxidase) activities of aphid-infested and uninfested 'Tugela' and Tugela near-isogenic wheat lines (i.e., Tugela-Dn1, Tugela-Dn2, and Tugela-Dn5) were assayed. Chlorophyllase activity was higher in bird cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae),-infested wheat lines compared with Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)]-infested and uninfested plants. Mg-dechelatase activity was higher in D. noxia-infested wheat lines than in R. padi-infested and uninfested plants. Also, Mg-dechelatase activity was lower in Tugela wheat infested with D. noxia than in Tugela near-isogenic lines with Dn genes. Based on the in vitro assays of chlorophyll degradation enzyme (i.e., chlorophyllase and Mg-dechelatase) activities, we proposed that the chlorotic symptoms observed on D. noxia-infested Tugela wheat were most likely to be elicited by unbalanced chlorophyll biosynthesis and degradation.     

A novel theta-class glutathione S-transferase gene in Rhopalosiphum padi (L.) (Hemiptera: Aphididae): Identification,recombinant protein expression and function analyses of RpGSTT1

Glutathione S-transferases (GSTs) play a major role in the detoxification of insecticides and the protection against oxidative damage caused by ROS (reactive oxygen species). The bird cherry-oat aphid, Rhopalosiphum padi (L.), is a major crop pest worldwide. Chemical insecticides are currently used to control aphids, but insecticide resistance is an evolutionary issue for aphid control. In this research, we identified and cloned the full-length cDNA of a theta-class GST gene (RpGSTT1) from R. padi, which contains 702 bp open reading frame encoding 233 amino acids. RpGSTT1 was clustered together with theta classe of insect GSTs in the phylogenetic tree. Effect of insecticide exposure on the GST enzyme activity was investigated in vivo. After affinity purification, the recombinant RpGSTT1 protein was able to catalyze the conjugation of 1-chloro-2, 4-dinitrobenzene (CDNB). A disc diffusion assay showed that the RpGSTT1 can increase resistance to cumene hydroperoxide-induced oxidative stress. In addition, the purified recombinant RpGSTT1 protected super-coiled DNA from oxidative damage. By quantitative PCR, The relative expression level of RpGSTT1 in the aphid was highly up-regulated after 12 h exposure to β-cypermethrin, isoprocarb, malathion and sulfoxaflor, respectively. To our knowledge, RpGSTT1 is the first theta class of GST gene reported in bird cherry-oat aphid. Our findings indicate that RpGSTT1 may be involved in insecticide detoxification in R. padi.     

Plant water stress intensity mediates aphid host choice and feeding behaviour

1. The effects of drought-induced changes in plant quality on aphid performance and population growth is well-studied. The response of aphid behaviour to plant water limitation has received less attention. Water limitation may affect host-plant colonization by altering the attractiveness of plants. Additionally, plant water limitation may inhibit feeding site establishment and phloem ingestion.
2. Our goal was to examine bird cherry-oat aphid (Rhopalosiphum padi L.) host selection and feeding behaviour under water limitation. We assessed aphid response to well-watered, mildly-stressed, and highly-stressed wheat (Triticum aestivum L.) by evaluating (i) host-plant selection through two-choice assays, (ii) feeding behaviour using the electrical penetration graph technique, and (iii) phloem ingestion by quantifying honeydew production.
3. Aphids were less likely to select highly stressed plants than a mildly stressed or well-watered alternative. Aphids did not distinguish between mildly stressed and well-watered plants. Aphid feeding behaviours, including duration of phloem ingestion, were not affected by water availability. However, honeydew production was reduced under both levels of water limitation. These results suggest that the volume of phloem ingested by aphids per unit time declined on stressed plants. The combination of lower colonization and diminished access to food on stressed plants may lead to a reduction in aphid abundance, independent of the direct effects of nutrition on individual aphid performance.
4. This study highlights the potential contribution of herbivore behaviour to documented changes in aphid abundance on stressed plants and underscores the important role of plant water stress intensity in mediating plant-herbivore interactions.

     

Plant response to touch affects the behaviour of aphids and ladybirds

Touching between leaves of the same plant and/or by neighbouring plants is one of the most common mechanical stimuli to which an individual plant has to respond on a daily basis. The possible ecological implications of a plant’s response to touch on plant–insect interactions have not been explicitly investigated. We examined whether plant response to 1 min daily touching over a period of 6 days affects host plant acceptance by the bird cherry-oat aphid Rhopalosiphum padi L. on maize and by the black bean aphid Aphis fabae Scop. on bean, as well as olfactory preference of an aphid predator, seven-spotted ladybird Coccinella septempunctata L. Maize plants responded to touch with significant reduction in plant height, total plant biomass, leaf weight, leaf surface, shoot/root ratio and specific leaf area (SLA), while bean plants responded with reduced stem height and reduced SLA. Both aphid species showed significantly reduced acceptance of touched plants compared with untouched plants. The two aphid species and male and female ladybirds preferred volatiles from untouched plants over those from touched plants. Volatiles in the headspace of touched and untouched plants were collected and identified. Stepwise discriminant analyses identified (E)-nerolidol and (E)-β-caryophyllene in maize and 6-methyl-5-hepten-2-one and an unidentified sesquiterpene in bean as the best discriminating compounds in the volatile profiles of touched plants. Our study suggests that touch-induced changes in plants can potentially affect host plant selection by aphids and habitat searching by ladybirds. Thus, touch-induced changes in plants may have significant effects at higher trophic levels.     

Aphid (Hemiptera: Aphididae) resistance in wheat near-isogenic lines

Plant and aphid biomass, photosynthetic pigment (chlorophylls a and b and carotenoids) concentrations, and chlorophyll a/b and chlorophyll/carotenoid ratios were quantified in aphid-infested 'Tugela' near-isogenic lines (Tugela, Tugela-Dn1, Tugela-Dn2, and Tugela-Dn5). The objectives were to quantify changes of photosynthetic pigments (chlorophylls a and b, and carotenoids) caused by aphid feeding and assess resistance of wheat isolines through aphid and plant biomass analysis. Biomass of bird cherry-oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae)-infested plants was lower than Russian wheat aphid, Diuraphis noxia (Mordvilko) (Hemiptera: Aphididae),- infested plants. When infested by D. noxia, all lines showed increased biomass over time, except Tugela where biomass decreased on day 12. No difference in plant biomass was detected among R. padi-infested and uninfested wheat lines. Biomass of D. noxia from Tugela (D. noxia-susceptible) was significantly higher than from plants with Diuraphis noxia-resistant Dn genes. Diuraphis noxia biomass from Tugela-Dn1 and Dn2 lines was not different from each other, but they were lower than from Tugela-Dn5. In contrast, there was no difference in R. padi biomass among wheat lines. Concentrations of chlorophylls a and b and carotenoids were significantly lower in D. noxia-infested plants compared with R. padi-infested and uninfested plants. When infested by D. noxia, chlorophyll a and b concentrations were not different among wheat lines on day 3, but they were lower in Tugela and Tugela-Dn1 than in Tugela-Dn2 and -Dn5 plants on days 6 and 12. However, no difference was detected in chlorophyll a/b or chlorophyll/carotenoid ratio among Tugela lines. The study demonstrated that Dn genes in the Tugela isolines conferred resistance to D. noxia but not to R. padi. Tugela-Dn1 was antibiotic, Tugela-Dn2 was tolerant and antibiotic, and Tugela-Dn5 was moderately antibiotic.     

Microarray analysis of the interaction between the aphid <Emphasis Type="Italic">Rhopalosiphum padi</Emphasis> and host plants reveals both differences and similarities between susceptible and partially resistant barley lines

The bird cherry-oat aphid (Rhopalosiphum padi L.) is an important pest on cereals causing plant growth reduction without specific leaf symptoms. Breeding of barley (Hordeum vulgare L.) for R. padi resistance shows that there are several resistance genes, reducing aphid growth. To identify candidate sequences for resistance-related genes, we performed microarray analysis of gene expression after aphid infestation in two susceptible and two partially resistant barley genotypes. One of the four lines is a descendant of two of the other genotypes. There were large differences in gene induction between the four lines, indicating substantial variation in response even between closely related genotypes. Genes induced in aphid-infested tissue were mainly related to defence, primary metabolism and signalling. Only 24 genes were induced in all lines, none of them related to oxidative stress or secondary metabolism. Few genes were down-regulated, with none being common to all four lines. There were differences in aphid-induced gene regulation between resistant and susceptible lines. Results from control plants without aphids also revealed differences in constitutive gene expression between the two types of lines. Candidate sequences for induced and constitutive resistance factors have been identified, among them a proteinase inhibitor, a serine/threonine kinase and several thionins. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Airborne interactions between undamaged plants of different cultivars affect insect herbivores and natural enemies

This study investigated the effects of airborne interaction between different barley cultivars on the behaviour of bird cherry-oat aphid Rhopalosiphum padi, the ladybird Coccinella septempunctata and the parasitoid Aphidius colemani. In certain cultivar combinations, exposure of one cultivar to air passed over a different cultivar caused barley to have reduced aphid acceptance and increased attraction of ladybirds and parasitoids. Parasitoids attacked aphids that had developed on plants under exposure more often than those from unexposed plants, leading to a higher parasitisation rate. Ladybirds, but not parasitoids, were more attracted to combined odours from certain barley cultivars than either cultivar alone. The results show that airborne interactions between undamaged plants can affect higher trophic levels, and that odour differences between different genotypes of the same plant species may be sufficient to affect natural enemy behaviour.     

Direct and Indirect Impacts of Infestation of Tomato Plant by Myzus persicae (Hemiptera: Aphididae) on Bemisia tabaci (Hemiptera: Aleyrodidae)

The impacts of infestation by the green peach aphid (Myzus persicae) on sweetpotato whitefly (Bemisia tabaci) settling on tomato were determined in seven separate experiments with whole plants and with detached leaves through manipulation of four factors: durations of aphid infestation, density of aphids, intervals between aphid removal after different durations of infestation and the time of whitefly release, and leaf positions on the plants. The results demonstrated that B. tabaci preferred to settle on the plant leaves that had not been infested by aphids when they had a choice. The plant leaves on which aphids were still present (direct effect) had fewer whiteflies than those previously infested by aphids (indirect effect). The whiteflies were able to settle on the plant which aphids had previously infested, and also could settle on leaves with aphids if no uninfested plants were available. Tests of direct factors revealed that duration of aphid infestation had a stronger effect on whitefly landing preference than aphid density; whitefly preference was the least when 20 aphids fed on the leaves for 72 h. Tests of indirect effects revealed that the major factor that affected whitefly preference for a host plant was the interval between the time of aphid removal after infestation and the time of whitefly release. The importance of the four factors that affected the induced plant defense against whiteflies can be arranged in the following order: time intervals between aphid removal and whitefly release > durations of aphid infestation > density of aphids > leaf positions on the plants. In conclusion, the density of aphid infestation and time for which they were feeding influenced the production of induced compounds by tomatoes, the whitefly responses to the plants, and reduced interspecific competition.     

Silencing of aphid genes by dsRNA feeding from plants

Background

RNA interference (RNAi) is a valuable reverse genetics tool to study gene function in various organisms, including hemipteran insects such as aphids. Previous work has shown that RNAi-mediated knockdown of pea aphid (Acyrthosiphon pisum) genes can be achieved through direct injection of double-stranded RNA (dsRNA) or small-interfering RNAs (siRNA) into the pea aphid hemolymph or by feeding these insects on artificial diets containing the small RNAs.

Methodology/Principal Findings

In this study, we have developed the plant-mediated RNAi technology for aphids to allow for gene silencing in the aphid natural environment and minimize handling of these insects during experiments. The green peach aphid M. persicae was selected because it has a broad plant host range that includes the model plants Nicotiana benthamiana and Arabidopsis thaliana for which transgenic materials can relatively quickly be generated. We targeted M. persicae Rack1, which is predominantly expressed in the gut, and M. persicae C002 (MpC002), which is predominantly expressed in the salivary glands. The aphids were fed on N. benthamiana leaf disks transiently producing dsRNA corresponding to these genes and on A. thaliana plants stably producing the dsRNAs. MpC002 and Rack-1 expression were knocked down by up to 60% on transgenic N. benthamiana and A. thaliana. Moreover, silenced M. persicae produced less progeny consistent with these genes having essential functions.

Conclusions/Significance

Similar levels of gene silencing were achieved in our plant-mediated RNAi approach and published silencing methods for aphids. Furthermore, the N. benthamiana leaf disk assay can be developed into a screen to assess which genes are essential for aphid survival on plants. Our results also demonstrate the feasibility of the plant-mediated RNAi approach for aphid control.     

Role of terpenes from aphid-infested potato on searching and oviposition behavior of Episyrphus balteatus

To cope with pathogen and insect attacks, plants develop different mechanisms of defence, in both direct （physical and chemical） and indirect ways （attractive volatiles to entomophagous beneficials）. Plants are then able to express traits that facilitate ＂top-down＂ control of pests by attracting herbivore predators. Here we investigate the indirect defence mechanism of potato plants by analyzing the volatile patterns of both healthy and aphid- infested plants. Important changes in the emitted terpene pattern by the Myzus persicae infested host plant were observed. Using Solid Phase MicroExtraction （SPME） and GC-MS, the （E）-fl-farnesene （EBF） appeared to be emitted by aphid-infested potato and not by healthy plants. To assess the infochemical role of these volatile releases after aphid damage on the aphidophagous predators Episyrphus balteams, the hoverfly foraging behavior was assessed using the Observer 5.0 software （Noldus, Wageningen, The Netherlands）. Aphidfree potato plants were also used as a control volatile source in the predator behavioral study. While aphid-infested plants induced efficient searching and acceptation behaviors leading to egg-laying, no kairomonal effect of healthy potato plants was observed, leading to longer immobility durations and shorter searching periods in the net cage. High oviposition rate of E. balteatus was observed when aphid-infested potato was used （mean of 48.9 eggs per laying and per female）. On the other hand, no egg was produced by the hoverfly on healthy aphid-free plants. The E. balteatus foraging and reproductive behaviors according to the volatile emission from aphid-infested plants are discussed in relation to the potential use of active infochemical molecules in integrated aphid pest management.     

Identification of genes differentially expressed in husk tomato (<Emphasis Type="Italic">Physalis philadelphica</Emphasis>) in response to whitefly (<Emphasis Type="Italic">Trialeurodes vaporariorum</Emphasis>) infestation

Plants respond to phloem-feeding whiteflies by extensive changes in gene expression. To identify differentially expressed genes in husk tomato plants (Physalis philadelphica) infested with Trialeurodes vaporariorum, young plants were challenged with adult whiteflies, and forward and reverse subtractive libraries were constructed from infested leaves at 5 and 15 days after infestation. Several genes were identified as up-regulated; these included a diversity of genes involved in plant defense responses, protein synthesis or degradation, and cell wall fortification or modification. Genes required for amino acid biosynthesis, lipid metabolism and synthesis, including cell surface components such as suberin, responses to stress, photosynthesis and other functions, were similarly induced. Down-regulated genes were also identified, most prominently kinases and aquaporin genes. Similarities in defense responses between tomato and P. philadelphica were noted regarding the expression of certain genes in response to nematode, aphid, or whitefly. A role for abscisic acid, brassinosteroids, and cytokinins in the regulated response to whitefly infestation in P. philadelphica was also implied by the expression pattern of phytohormone-associated genes, including genes coding for proteins containing F-box motifs. Differential expression of selected genes was validated by quantitative real-time PCR. The possible role played by some of these genes during whitefly infestation is discussed.