Host-specific co-evolution likely driven by diet in Buchnera aphidicola.

BACKGROUND: Russian wheat aphid (Diuraphis noxia Kurd.) is a severe pest to wheat, and even though resistance varieties are available to curb this pest, they are becoming obsolete with the development of new virulent aphid populations. Unlike many other aphids, D noxia only harbours a single endosymbiont, Buchnera aphidicola. Considering the importance of Buchnera, this study aimed to elucidate commonalities and dissimilarities between various hosts, to better understand its distinctiveness within its symbiotic relationship with D. noxia. To do so, the genome of the D. noxia's Buchnera was assembled and compared to those of other aphid species that feed on diverse host species. RESULTS: The overall importance of several features such as gene length and percentage GC content was found to be critical for the maintenance of Buchnera genes when compared to their closest free-living relative, Escherichia coli. Buchnera protein coding genes were found to have percentage GC contents that tended towards a mean of ~ 26% which had strong correlation to their identity to their E. coli homologs. Several SNPs were identified between different aphid populations and multiple isolates of Buchnera were confirmed in single aphids. CONCLUSIONS: Establishing the strong correlation of percentage GC content of protein coding genes and gene identity will allow for identifying which genes will be lost in the continually shrinking Buchnera genome. This is also the first report of a parthenogenically reproducing aphid that hosts multiple Buchnera strains in a single aphid, raising questions regarding the benefits of maintaining multiple strains. We also found preliminary evidence for post-transcriptional regulation of Buchnera genes in the form of polyadenylation.

Physiological and biochemical traits positively modulate tissue-specific withanolides and untargeted metabolites in Withania somnifera (L.) dunal under salinity stress.

Withania somnifera (L.) Dunal (Ashwagandha) has been used in herbal medicines worldwide and in the Indian traditional medicinal system for 3000 years. It is a member of the Solanaceae family distributed across Asia, Africa, Australia, and Europe. Its bioactive secondary metabolite (withanolide) biosynthesis is sensitive to salinity stress, though the mechanism remains unexplored. Therefore, we investigated the effect of Sodium chloride (NaCl) on growth, photosynthesis, biochemical traits, tissue-specific withanolide, and untargeted metabolites in W. somnifera. Ashwagandha plants were raised in pots containing soil mixture and treated with different NaCl concentrations (0 as control, 10, 30, and 50 mM) for one month inside the greenhouse. NaCl stress significantly enhanced withaferin A (WFA) (3.79 mg/g), withanolide A (WA) (0.51 mg/g), and withanone (WN) (0.022 mg/g) at 50 mM NaCl groups in the shoot. Similarly, in the root, a significant increase in WFA (0.19 mg/g) and WN (0.0016 mg/g) were observed at 10 mM, WA (0.059 mg/g) at 30 mM, and withanolide B (WB) (0.013 mg/g) at 50 mM NaCl groups compared to control. LC-MS-based untargeted metabolite profiling revealed 37 differentially accumulated metabolites in all groups. Maximum abundance of glycyl-hydroxyproline (8X) followed by tyrosyl-valine (2X) and 3-hydroxy-beta-ionone (2X) were recorded at 50 mM NaCl groups compared to the control. This study showed for the first time that low NaCl stress enhances the biosynthesis of tissue-specific withanolides through physio-biochemical and metabolites adjustment. Overall, we demonstrated a multifaceted approach for cultivating medicinal crops in salt-affected areas with enhanced bioactive metabolites for healthcare and pharmaceutical industries.

The Effects of High CO2 and Strigolactones on Shoot Branching and Aphid-Plant Compatibility Control in Pea.

Elevated atmospheric CO2 concentrations (eCO2) regulate plant architecture and susceptibility to insects. We explored the mechanisms underpinning these responses in wild type (WT) peas and mutants defective in either strigolactone (SL) synthesis or signaling. All genotypes had increased shoot height and branching, dry weights and carbohydrate levels under eCO2, demonstrating that SLs are not required for shoot acclimation to eCO2. Since shoot levels of jasmonic acid (JA) and salicylic acid (SA) tended to be lower in SL signaling mutants than the WT under ambient conditions, we compared pea aphid performance on these lines under both CO2 conditions. Aphid fecundity was increased in the SL mutants compared to the WT under both ambient and eCO2 conditions. Aphid infestation significantly decreased levels of JA, isopentenyladenine, trans-zeatin and gibberellin A4 and increased ethylene precursor ACC, gibberellin A1, gibberellic acid (GA3) and SA accumulation in all lines. However, GA3 levels were increased less in the SL signaling mutants than the WT. These studies provide new insights into phytohormone responses in this specific aphid/host interaction and suggest that SLs and gibberellins are part of the network of phytohormones that participate in host susceptibility.

Antinutritional factors, nutritional improvement, and future food use of common beans: A perspective.

Common bean seeds are an excellent source of protein as well as of carbohydrates, minerals, vitamins, and bioactive compounds reducing, when in the diet, the risks of diseases. The presence of bioactive compounds with antinutritional properties (e.g., phytic acid, lectins, raffinosaccharides, protease inhibitors) limits, however, the bean's nutritional value and its wider use in food preparations. In the last decades, concerted efforts have been, therefore, made to develop new common bean genotypes with reduced antinutritional compounds by exploiting the natural genetic variability of common bean and also applying induced mutagenesis. However, possible negative, or positive, pleiotropic effects due to these modifications, in terms of plant performance in response to stresses or in the resulting technological properties of the developed mutant genotypes, have yet not been thoroughly investigated. The purpose of the perspective paper is to first highlight the current advances, which have been already made in mutant bean characterization. A view will be further provided on future research directions to specifically explore further advantages and disadvantages of these bean mutants, their potential use in innovative foods and representing a valuable genetic reservoir of combinations to assess the true functional role of specific seed bioactive components directly in the food matrix.

Differential Gene Expression and Withanolides Biosynthesis During in vitro and ex vitro Growth of Withania somnifera (L.) Dunal.

Ashwagandha (Withania somnifera L. Dunal) is a medicinally important plant with withanolides as its major bioactive compounds, abundant in the roots and leaves. We examined the influence of plant growth regulators (PGRs) on direct organogenesis, adventitious root development, withanolide biosynthetic pathway gene expression, withanolide contents, and metabolites during vegetative and reproductive growth phases under in vitro and ex vitro conditions. The highest shooting responses were observed with 6-benzylaminopurine (BAP) (2.0 mg L-1) + Kinetin (KIN) (1.5 mg L-1) supplementation. Furthermore, BAP (2.0 mg L-1) + KIN (1.5 mg L-1) + gibberellic acid (GA3) (0.5 mg L-1) exhibited better elongation responses with in vitro flowering. Half-strength MS medium with indole-3-butyric acid (IBA) (1.5 mg L-1) exhibited the highest rooting responses and IBA (1.0 mg L-1) with highest fruits, and overall biomass. Higher contents of withaferin A (WFA) [∼8.2 mg g-1 dry weight (DW)] were detected in the reproductive phase, whereas substantially lower WFA contents (∼1.10 mg g-1 DW) were detected in the vegetative phase. Cycloartenol synthase (CAS) (P = 0.0025), sterol methyltransferase (SMT) (P = 0.0059), and 1-deoxy-D-xylulose-5-phosphate reductase (DXR) (P = 0.0375) genes resulted in a significant fold change in expression during the reproductive phase. The liquid chromatography-mass spectrometry (LC-MS) analysis revealed metabolites that were common (177) and distinct in reproductive (218) and vegetative (167) phases. Adventitious roots cultured using varying concentrations of indole-3-acetic acid (IAA) (0.5 mg L-1) + IBA (1.0 mg L-1) + GA3 (0.2 mg L-1) exhibited the highest biomass, and IAA (0.5 mg L-1) + IBA (1.0 mg L-1) exhibited the highest withanolides content. Overall, our findings demonstrate the peculiarity of withanolide biosynthesis during distinct growth phases, which is relevant for the large-scale production of withanolides.

Whole-body transcriptome mining for candidate effectors from Diuraphis noxia.

BACKGROUND: Proteins within aphid saliva play a crucial role as the molecular interface between aphids and their host plants. These salivary effectors modulate plant responses to favour aphid feeding and facilitate infestation. The identification of effectors from economically important pest species is central in understanding the molecular events during the aphid-plant interaction. The Russian wheat aphid (Diuraphis noxia, Kurdjumov) is one such pest that causes devastating losses to wheat and barley yields worldwide. Despite the severe threat to food security posed by D. noxia, the non-model nature of this pest and its host has hindered progress towards understanding this interaction. In this study, in the absence of a salivary gland transcriptome, whole-body transcriptomics data was mined to generate a candidate effector catalogue for D. noxia. RESULTS: Mining the transcriptome identified 725 transcripts encoding putatively secreted proteins amongst which were transcripts specific to D. noxia. Six of the seven examined D. noxia putative effectors, termed DnE's (Diuraphis noxia effectors) exhibited salivary gland-specific expression. A comparative analysis between whole-body D. noxia transcriptome data versus the head and body transcriptomes from three other aphid species allowed us to define a catalogue of transcripts putatively upregulated in D. noxia head tissue. Five of these were selected for RT-qPCR confirmation, and were found to corroborate the differential expression predictions, with a further three confirmed to be highly expressed in D. noxia salivary gland tissue. CONCLUSIONS: Determining a putative effector catalogue for D. noxia from whole-transcriptome data, particularly the identification of salivary-specific sequences potentially unique to D. noxia, provide the basis for future functional characterisation studies to gain further insight into this aphid-plant interaction. Furthermore, due to a lack of publicly available aphid salivary gland transcriptome data, the capacity to use comparative transcriptomics to compile a list of putative effector candidates from whole-body transcriptomics data will further the study of effectors in various aphid species.

EMS Derived Wheat Mutant BIG8-1 (Triticum aestivum L.)-A New Drought Tolerant Mutant Wheat Line.

Drought response in wheat is considered a highly complex process, since it is a multigenic trait; nevertheless, breeding programs are continuously searching for new wheat varieties with characteristics for drought tolerance. In a previous study, we demonstrated the effectiveness of a mutant known as RYNO3936 that could survive 14 days without water. In this study, we reveal another mutant known as BIG8-1 that can endure severe water deficit stress (21 days without water) with superior drought response characteristics. Phenotypically, the mutant plants had broader leaves, including a densely packed fibrous root architecture that was not visible in the WT parent plants. During mild (day 7) drought stress, the mutant could maintain its relative water content, chlorophyll content, maximum quantum yield of PSII (Fv/Fm) and stomatal conductance, with no phenotypic symptoms such as wilting or senescence despite a decrease in soil moisture content. It was only during moderate (day 14) and severe (day 21) water deficit stress that a decline in those variables was evident. Furthermore, the mutant plants also displayed a unique preservation of metabolic activity, which was confirmed by assessing the accumulation of free amino acids and increase of antioxidative enzymes (peroxidases and glutathione S-transferase). Proteome reshuffling was also observed, allowing slow degradation of essential proteins such as RuBisCO during water deficit stress. The LC-MS/MS data revealed a high abundance of proteins involved in energy and photosynthesis under well-watered conditions, particularly Serpin-Z2A and Z2B, SGT1 and Calnexin-like protein. However, after 21 days of water stress, the mutants expressed ABC transporter permeases and xylanase inhibitor protein, which are involved in the transport of amino acids and protecting cells, respectively. This study characterizes a new mutant BIG8-1 with drought-tolerant characteristics suited for breeding programs.

Fast developing Russian wheat aphid biotypes remains an unsolved enigma.

Diuraphis noxia, commonly known as the Russian wheat aphid, is an economically important cereal pest species, highly invasive and reproduces mostly asexually. Remarkably, many new virulent populations continue to develop, despite the lack of genetic diversity in the aphid. Russian wheat aphid is a phloem feeder and is therefore engaged in a continuous arms battle with its cereal host, with the acquisition of virulence central to the breakdown of host resistance. In the review, most attention is given to recent topics about mechanisms and strategies whereby the aphid acquires virulence against its host, with special reference given to the role of noncoding RNA elements, bacteria, and the epigenetic pathway in possibly directing virulence.

Factors facilitating sustainable scientific partnerships between developed and developing countries.

International scientific partnerships are key to the success of strategic investments in plant science research and the farm-level adoption of new varieties and technologies, as well as the coherence of agricultural policies across borders to address global challenges. Such partnerships result not only in a greater impact of published research enhancing the career development of early and later stage researchers, but they also ensure that advances in plant science and crop breeding technologies make a meaningful contribution to society by brokering acceptance of emerging solutions to the world problems. We discuss the evidence showing that despite a lack of funding, scientists in some African countries make a significant contribution to global science output. We consider the criteria for success in establishing long-term scientific partnerships between scientists in developing countries in Southern Africa ("the South") and developed countries such as the UK ("the North"). We provide our own personal perspectives on the key attributes that lead to successful institutional collaborations and the establishment of sustainable networks of successful "North-South" scientific partnerships. In addition, we highlight some of the stumbling blocks which tend to hinder the sustainability of long-term "North-South" scientific networks. We use this personal knowledge and experiences to provide guidelines on how to establish and maintain successful long-term "North-South" scientific partnerships.

Wheat Line "RYNO3936" Is Associated With Delayed Water Stress-Induced Leaf Senescence and Rapid Water-Deficit Stress Recovery.

Random mutagenesis was applied to produce a new wheat mutant (RYNO3926) with superior characteristics regarding tolerance to water deficit stress induced at late booting stage. The mutant also displays rapid recovery from water stress conditions. Under water stress conditions mutant plants reached maturity faster and produced more seeds than its wild type wheat progenitor. Wild-type Tugela DN plants died within 7 days after induction of water stress induced at late booting stage, while mutant plants survived by maintaining a higher relative moisture content (RMC), increased total chlorophyll, and a higher photosynthesis rate and stomatal conductance. Analysis of the proteome of mutant plants revealed that they better regulate post-translational modification (SUMOylation) and have increased expression of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) proteins. Mutant plants also expressed unique proteins associated with dehydration tolerance including abscisic stress-ripening protein, cold induced protein, cold-responsive protein, dehydrin, Group 3 late embryogenesis, and a lipoprotein (LAlv9) belonging to the family of lipocalins. Overall, our results suggest that our new mutant RYNO3936 has a potential for inclusion in future breeding programs to improve drought tolerance under dryland conditions.

DNA Methylation and Demethylation Are Regulated by Functional DNA Methyltransferases and DnTET Enzymes in Diuraphis noxia.

Aphids are economically important insect pests of crops worldwide. Despite resistant varieties being available, resistance is continuously challenged and eventually broken down, posing a threat to food security. In the current study, the epigenome of two related Russian wheat aphid (Diuraphis noxia, Kurdjumov) biotypes (i.e., SA1 and SAM) that differ in virulence was investigated to elucidate its role in virulence in this species. Whole genome bisulfite sequencing covered a total of 6,846,597,083 cytosine bases for SA1 and 7,397,965,699 cytosine bases for SAM, respectively, of which a total of 70,861,462 bases (SA1) and 74, 073,939 bases (SAM) were methylated, representing 1.126 ± 0.321% (SA1) and 1.105 ± 0.295% (SAM) methylation in their genomes. The sequence reads were analyzed for contexts of DNA methylation and the results revealed that RWA has methylation in all contexts (CpG, CHG and CHH), with the majority of methylation within the CpG context (± 5.19%), while the other contexts show much lower levels of methylation (CHG - ± 0.27%; CHH - ± 0.34%). The top strand was slightly (0.02%) more methylated than the bottom strand. Of the 35,493 genes that mapped, we also analyzed the contexts of methylation of each of these and found that the CpG methylation was much higher in genic regions than in intergenic regions. The CHG and CHH levels did not differ between genic and intergenic regions. The exonic regions of genes were more methylated (±0.56%) than the intronic regions. We also measured the 5mC and 5hmC levels between the aphid biotypes, and found little difference in 5mC levels between the biotypes, but much higher levels of 5hmC in the virulent SAM. RWA had two homologs of each of the DNA methyltransferases 1 (DNMT1a and DNMT1b) and DNMT3s (DNMT3a and DNMT3b), but only a single DNMT2, with only the expression of DNMT3 that differed significantly between the two RWA biotypes. RWA has a single ortholog of Ten eleven translocase (DnTET) in the genome. Feeding studies show that the more virulent RWA biotype SAM upregulate DnDNMT3 and DnTET in response to wheat expressing antibiosis and antixenosis.

Expression of a Small Ubiquitin-Like Modifier Protease Increases Drought Tolerance in Wheat (Triticum aestivum L.).

Post-translation modification of proteins plays a critical role in cellular signaling processes. In recent years, the SUMO (Small Ubiquitin-Like Modifier) class of molecules has emerged as an influential mechanism for target protein management. SUMO proteases play a vital role in regulating pathway flux and are therefore ideal targets for manipulating stress-responses. In the present study, the expression of an Arabidopsis thaliana cysteine protease (OVERLY TOLERANT TO SALT-1, OTS1) in wheat (Triticum aestivum L.) has led to improved plant growth under water stress conditions. Transformed wheat (pUBI-OTS1) displayed enhanced growth and delayed senescence under water deficit when compared with untransformed Gamtoos-R genotype or plants carrying an empty vector. Transformed pUBI-OTS1 plants also maintained a high relative moisture content (RMC), had a higher photosynthesis rate, and also had a higher total chlorophyll content when compared to untransformed plants or plants carrying an empty vector. SUMOylation of total protein also increased in untransformed plants but not in the AtOTS1 transformed plants. Our results suggest that SUMO-proteases may influence an array of mechanisms in wheat to the advantage of the crop to be more tolerant to water stress caused by drought. This is the first report to elucidate SUMOylation effects in the hexaploid crop wheat (T. aestivum L.).

New Insights into the Methylation Status of Virulent Diuraphis noxia (Hemiptera: Aphididae) Biotypes.

Epigenetic modifications provide a means for aphid biotype development that a lack of genetic variation, owing to an anholocyclic reproduction lifecycle, fails to do. Here we present data on the DNA methylation status in four South African Russian wheat aphids (RWA), Diuraphis noxia (Kurdjomov) (Hemiptera: Aphididae) biotypes expressing different levels of virulence against its host, Triticum aestivum L. (Poales: Poaceae, Triticeae). The DNA methylation status of these biotypes was determined through the use of methylation-sensitive amplification polymorphism analysis, restriction site-specific fluorescence labeling-a novel technique, and measuring relative global DNA methylation and hydroxymethylation. The least virulent RWA biotype, SA1, was methylated, while biotypes displaying intermediate virulence, SA2 and SA3, exhibited intermediate levels of hemimethylation. The genome of the most virulent RWA biotype, SAM, seems to be hypomethylated, which is likely attained through the process of demethylation.

Cysteine proteases and wheat (Triticum aestivum L) under drought: A still greatly unexplored association.

Bread wheat (Triticum aestivum L.) provides about 19% of global dietary energy. Environmental stress, such as drought, affects wheat growth causing premature plant senescence and ultimately plant death. A plant response to drought is an increase in protease-mediated proteolysis with rapid degradation of proteins required for metabolic processes. Among the plant proteases that are increased in their activity following stress, cysteine proteases are the best characterized. Very little is known about particular wheat cysteine protease sequences, their expression and also localization. The current knowledge on wheat cysteine proteases belonging to the five clans (CA, CD, CE, CF and CP) is outlined, in particular their expression and possible function under drought. The first successes in establishing an annotated wheat genome database are further highlighted which has allowed more detailed mining of cysteine proteases. We also share our thoughts on future research directions considering the growing availability of genomic resources of this very important food crop. Finally, we also outline future application of developed knowledge in transgenic wheat plants for environmental stress protection and also as senescence markers to monitor wheat growth under environmental stress conditions.

An evaluation of the endocrine disruptive potential of crude oil water accommodated fractions and crude oil contaminated surface water to freshwater organisms using in vitro and in vivo approaches.

Knowledge regarding the potential impacts of crude oil on endocrine signaling in freshwater aquatic vertebrates is limited. The expression of selected genes as biomarkers for altered endocrine signaling was studied in African clawed frog, Xenopus laevis, tadpoles and juvenile Mozambique tilapia, Oreochromis mossambicus, exposed to weathered bunker and unweathered refinery crude oil water accommodated fractions (WAFs). In addition, the expression of the aforementioned genes was quantified in X. laevis tadpoles exposed to surface water collected from the proximity of an underground oil bunker. The (anti)estrogenicity and (anti)androgenicity of crude oil, crude oil WAFs, and surface water were furthermore evaluated using recombinant yeast. Thyroid hormone receptor beta expression was significantly down-regulated in X. laevis in response to both oil WAF types, whereas a further thyroid linked gene, type 2 deiodinase, was up-regulated in O. mossambicus exposed to a high concentration of bunker oil WAF. In addition, both WAFs altered the expression of the adipogenesis-linked peroxisome proliferator-activated receptor gamma in X. laevis. The crude oil and WAFs exhibited antiestrogenic and antiandrogenic activity in vitro. However, O. mossambicus androgen receptor 2 was the only gene, representing the reproductive system, significantly affected by WAF exposure. Estrogenicity, antiestrogenicity, and antiandrogenicity were detected in surface water samples; however, no significant changes were observed in the expression of any of the genes evaluated in X. laevis exposed to surface water. The responses varied among the 2 model organisms used, as well as among the 2 types of crude oil. Nonetheless, the data provide evidence that crude oil pollution may lead to adverse health effects in freshwater fish and amphibians as a result of altered endocrine signaling. Environ Toxicol Chem 2017;36:1330-1342. © 2016 SETAC.

Genome of Russian wheat aphid an economically important cereal aphid.

Although the hemipterans (Aphididae) are comprised of roughly 50,000 extant insect species, only four have sequenced genomes that are publically available, namely Acyrthosiphon pisum (pea aphid), Rhodnius prolixus (Kissing bug), Myzus persicae (Green peach aphid) and Diuraphis noxia (Russian wheat aphid). As a significant proportion of agricultural pests are phloem feeding aphids, it is crucial for sustained global food security that a greater understanding of the genomic and molecular functioning of this family be elucidated. Recently, the genome of US D. noxia biotype US2 was sequenced but its assembly only incorporated ~ 32% of produced reads and contained a surprisingly low gene count when compared to that of the model/first sequenced aphid, A. pisum. To this end, we present here the genomes of two South African Diuraphis noxia (Kurdjumov, Hemiptera: Aphididae) biotypes (SA1 and SAM), obtained after sequencing the genomes of the only two D. noxia biotypes with documented linked genealogy. To better understand overall targets and patterns of heterozygosity, we also sequenced a pooled sample of 9 geographically separated D. noxia populations (MixIX). We assembled a 399 Mb reference genome (PRJNA297165, representing 64% of the projected genome size 623 Mb) using ± 28 Gb of 101 bp paired-end HiSeq2000 reads from the D. noxia biotype SAM, whilst ± 13 Gb 101 bp paired-end HiSeq2000 reads from the D. noxia biotype SA1 were generated to facilitate genomic comparisons between the two biotypes. Sequencing the MixIX sample yielded ±26 Gb 50 bp paired-end SOLiD reads which facilitated SNP detection when compared to the D. noxia biotype SAM assembly. Ab initio gene calling produced a total of 31,885 protein coding genes from the assembled contigs spanning ~ 399 Mb (GCA_001465515.1).

Applying genotoxicology tools to identify environmental stressors in support of river management.

Although bioassay approaches are useful for identifying chemicals of potential concern, they provide little understanding of the mechanisms of chemical toxicity. Without this understanding, it is difficult to address some of the key challenges that currently face aquatic ecotoxicology. To overcome this, the toxicity potential of the water samples was assessed and surviving organisms (Physa acuta) were used for protein activity measurements and gene expression profiling by making use of complementary DNA amplified fragment length polymorphism (cDNA-AFLP) analysis. From the data it was evident that the impacts of specific pollutants (e.g. sewage) on organisms at the cellular level could be identified, and that the expressed stressor genes can be used as bioindicators/markers/genetic signatures or fingerprints during identification of point source pollution. From an ecosystem management point of view these insights could assist with the forecasting and reduction of environmental risks on catchment level by implementing suitable management interventions.

Phi-class glutathione-S-transferase is involved in Dn1-mediated resistance.

Wheat Dn genes afford resistance to the economically important pest, Diuraphis noxia (Kurdjumov, Russian wheat aphid, RWA) and have been the topic of transcriptomic and proteomic studies aimed at unraveling the pathways involved in resistance. The antibiotic resistance conveyed by Dn1 is characterized by a hypersensitive response (HR) followed by systemic acquired resistance (SAR). Although many candidate genes differentially expressed during the Dn1-mediated resistance response have been identified, few have been functionally verified. The aim of this study was to silence three HR-associated candidate genes in Dn1 containing wheat using virus-induced gene silencing (VIGS): thylakoid-associated ascorbate peroxidase (tAPX), phi-class glutathione-S-transferase (TaGSTF6) and superoxide dismutase Cu/Zn (SOD). D. noxia fertility was used as a measure of antibiotic resistance. Silencing of SOD Cu/Zn had little effect on D. noxia fertility, while increased aphid reproduction was recorded on tAPX- and TaGSTF6-silenced plants. However, tAPX-silencing only affected early measurements and did not have a prolonged effect on resistance. TaGSTF6-silenced plants expressed lowered H2 O2 production in resistant wheat under infestation conditions, suggesting that TaGSTF6 and H2 O2 play an integral role in Dn1-mediated D. noxia resistance in wheat plants.

Near-isogenic lines of Triticum aestivum with distinct modes of resistance exhibit dissimilar transcriptional regulation during Diuraphis noxia feeding.

Russian wheat aphid (Diuraphis noxia, Kurdjumov) feeding on susceptible Triticum aestivum L. leads to leaf rolling, chlorosis and plant death - symptoms not present in resistant lines. Although the effects of several D. noxia (Dn) resistance genes are known, none have been isolated or characterized. Wheat varieties expressing different Dn genes exhibit distinct modes of D. noxia resistance, such as antibiosis (Dn1), tolerance (Dn2), and antixenosis (Dn5). However, the mechanism whereby feeding aphids are perceived, and how subsequent transcriptional responses are partitioned into resistance categories, remains unclear. Here we report on downstream events in near-isogenic wheat lines containing different Dn genes after D. noxia biotype SA1 feeding. Transcripts involved in stress, signal transduction, photosynthesis, metabolism and gene regulation were differentially regulated during D. noxia feeding. Expression analyses using RT-qPCR and RNA hybridization, as well as enzyme activity profiling, provide evidence that the timing and intensity of pathways induced are critical in the development of particular modes of resistance. Pathways involved include the generation of kinase signalling cascades that lead to a sustained oxidative burst, and a hypersensitive response that is active during antibiosis. Tolerance is a passive resistance mechanism that acts through repair or de novo synthesis of photosystem proteins. Results further suggest that ethylene-mediated pathways are possibly involved in generating volatile compounds and cell wall fortification during the antixenosic response.