Duplication of the Rdl GABA receptor subunit gene in an insecticide-resistant aphid, Myzus persicae

Resistance to cyclodiene insecticides is associated with replacements of a single amino acid (alanine 302) in a γ-aminobutyric acid (GABA) receptor subunit encoded by the single-copy gene Resistance to dieldrin (Rdl). Alanine 302 is predicted to reside within the second membrane-spanning region of the Rdl receptor, a region that is thought to line the integral chloride ion channel pore. In all cyclodiene-resistant insects studied to date, this same alanine residue is replaced either by a serine, or, in some resistant strains of Drosophila simulans, a glycine residue. Therefore, individuals can carry only two different Rdl alleles. In contrast, here we report the presence of up to four different Rdl-like alleles in individual clones of the green peach aphid, Myzus persicae. In addition to the wild-type copy of Rdl gene (encoding A302 or allele A), M. persicae carries three other alleles with the following amino acid replacements: A302 → Glycine (allele G), A302 → Serine^TCG (allele S) and A302 → Serine^AGT (allele S′). Evidence from direct nucleotide sequencing and Single Stranded Conformational Polymorphism (SSCP) analysis shows that at least three of these different Rdl alleles (i.e. A, G and S) are commonly present in individual aphids or aphid clones. Southern analysis using allele-specific probes and analysis of sequences downstream of the exon containing the resistance-associated mutation confirm the presence of two independent Rdl-like loci in M. persicae. One locus carries the susceptible alanine (A) and/or resistant glycine (G) allele while the other carries the two serine alleles (S or S′). Whereas resistance levels are correlated with the glycine replacement, the S allele was present in all aphid clones, regardless of their resistance status. These results suggest that target site insensitivity is associated with replacements at the first (A/G) but not the second (S/S′) locus. Phylogenetic analysis of nucleotide sequences indicates that both putative aphid Rdl loci are monophyletic with respect to other insect Rdl genes and may have arisen through a recent gene duplication event. The implications of this duplication with respect to insecticide resistance and insect GABA receptor subunit diversity are discussed. Received: 10 March 1998 / Accepted: 21 July 1998     

Molecular cloning,genomic structure,and genetic mapping of two Rdl‐orthologous genes of GABA receptors in the diamondback moth,Plutella xylostella

The Resistance to dieldrin (Rdl) gene encodes a subunit of the insect γ‐aminobutyric acid (GABA) receptor. Cyclodiene resistance in many insects is associated with replacement of a single amino acid (alanine at position 302) with either a serine or a glycine in the Rdl gene. Two Rdl‐orthologous genes of GABA receptors (PxGABARα1 and PxGABARα2) were cloned and sequenced from a susceptible strain (Roth) of Plutella xylostella. PxGABARα1 and PxGABARα2 showed 84% and 77% identity with the Rdl gene of Drosophila melanogaster at an amino acid level, respectively. The coding regions of PxGABARα1 and PxGABARα2 both comprise ten exons, with two alternative RNA‐splicing forms in exon 3 of both genes. At the orthologous position of alanine‐302 in D. melanogaster Rdl, PxGABARα1 has a conserved alanine at position 282. PxGABARα2 has a serine instead of an alanine at the equivalent position. With two informative DNA markers, both PxGABARα1 and PxGABARα2 were mapped onto the Z chromosome of P. xylostella. © 2010 Wiley Periodicals, Inc.     

Suitability of three aphid species for Aphidius gifuensis (Hymenoptera: Braconidae): Parasitoid performance varies with hosts of origin

Oviposition behavior and offspring fitness of the parasitoid Aphidius gifuensis (Ashmead) were compared on three aphid species, Sitobion avenae F., Myzus persicae (Sulzer), and Aphis gossypii Glover using wasps collected from both S. avenae and M. persicae. A. gifuensis produced more mummies and adults on S. avenae and M. persicae than on A. gossypii regardless of the host of origin. Mummy production was influenced by attack rate and percentage of aphids superparasitized. The F₁ generations from S. avenae and M. persicae were more female-biased and wasps were larger than those from A. gossypii. Although there were significant differences in development time of A. gifuensis in the three aphid species, the difference was generally shorter than one day. Fewer mummies were produced when A. gifuensis was transferred between S. avenae and M. persicae, but no significant difference was observed in emergence rate, percentage of female offspring, or body size. The effects of host species on A. gifuensis female performance and offspring fitness are discussed, along with the potential for using A. gifuensis to control M. persicae and A. gossypii.     

Comparison of short- and long-feed transmission of the cauliflower mosaic virus Cabb-S strain and SΔII hybrid by two species of aphid: Myzus persicae (Sulzer) and Brevicoryne brassicae (L.)

The cauliflower mosaic virus (CaMV) hybrid SΔII, partially deleted in ORFII, loses its transmissibility by the aphid Myzus persicae on 5-min acquisition feed. We have also shown that it is not transmitted after 8-h acquisition feed. The same occurs with Brevicoryne brassicae. Therefore, the aphid transmission factor (ATF) is involved in both means of transmission and in both aphid species. M. persicae can acquire CaMV Cabb-S strain in less than 20 s. M. persicae is a more efficient vector during a short feed than during a long feed, contrary to B. brassicae which transmits better during a long feed.     

Multiple Origins of Cyclodiene Insecticide Resistance in Tribolium castaneum (Coleoptera: Tenebrionidae)

The number of origins of pesticide resistance-associated mutations is important not only to our understanding of the evolution of resistance but also in modeling its spread. Previous studies of amplified esterase genes in a highly dispersive Culex mosquito have suggested that insecticide resistance-associated mutations (specifically a single-gene duplication event) can occur a single time and then spread throughout global populations. In order to provide data for resistance-associated point mutations, which are more typical of pesticide mechanisms as a whole, we studied the number of independent origins of cyclodiene insecticide resistance in the red flour beetle Tribolium castaneum. Target-site insensitivity to cyclodienes is conferred by single point mutations in the gene Resistance to dieldrin (Rdl), which codes for a subunit of a γ-aminobutyric acid (GABA) receptor. These point mutations are associated with replacements of alanine 302 which render the receptor insensitive to block by the insecticide. We collected 141 strains of Tribolium worldwide and screened them for resistance. Twenty-four strains contained resistant individuals. After homozygosing 23 of these resistance alleles we derived a nucleotide sequence phylogeny of the resistant strains from a 694-bp section of Rdl, encompassing exon 7 (which contains the resistance-associated mutation) and part of a flanking intron. The phylogeny also included six susceptible alleles chosen at random from a range of geographical locations. Resistance alleles fell into six clades and three clades contained both resistant and susceptible alleles. Although statistical analysis provided support at only the 5–6% level, the pattern of variation in resistance alleles is more readily explained by multiple independent origins of resistance than by spread of a single resistance-associated mutation. For example, two resistance alleles differed from two susceptible alleles only by the resistance-associated mutation itself, suggesting that they form the susceptible ancestors and that resistance arose independently in several susceptible backgrounds. This suggests that in Tribolium Rdl, de novo mutations for resistance have arisen independently in several populations. Identical alleles were found in geographically distant regions as well, also implying that some Rdl alleles have been exported in stored grain. These differences from the Culex study may stem both from differences in the population genetics of Tribolium versus that of mosquitoes and differences in mutation rates associated with point mutations versus gene duplication events. The Tribolium data therefore suggest that multiple origins of insecticide resistance (associated with specific point mutations) may be more common than the spread of single events. These findings have implications for the way in which we model the evolution and spread of insecticide resistance genes and also suggest that parallel adaptive substitutions may not be uncommon in phyletic evolution. Received: 14 October 1998 / Accepted: 4 January 1999     

Clonal composition of the peach-potato aphid Myzus persicae (Homoptera: Aphididae) in France and Scotland: Comparative analysis with IGS fingerprinting and microsatellite markers

Fourteen colonies of the peach‐potato aphid, Myzus persicae, were taken either from French peach trees or weeds in 2001. Thirty five apomictic parthenogenetic lineages (APLs) were established. Ribosomal DNA intergenic spacer (IGS) fingerprinting was used to characterise these and 28 fingerprints were duly obtained. Those lineages with different fingerprints were considered different genotypes and those with the same fingerprint as the same. The genetic identity of APLs was further tested using four microsatellite loci. APLs that differed by IGS fingerprint had distinct microsatellite allele combinations and those that had the same IGS fingerprint had the same microsatellite allele combinations. The results confirmed that IGS types corresponded to different aphid genotypes. Independent APLs with identical IGS and microsatellite genotype were therefore considered different representatives of the same clone. APLs from M. persicae found on Scottish crops in 1995, 1996 and 2001, as well as a long‐term laboratory line were also examined by the same methods. Their IGS fingerprints were similar or identical suggesting that they all belonged to the same clone. Microsatellite markers also suggested that these lineages were derived from a single clone. Some field lineages exhibited slight modifications to their IGS fingerprints confirming that the IGS evolves more rapidly than these microsatellite alleles. Thus, IGS will continue to provide a useful marker for aphid fieldwork.     

Feeding deterrency of flavonoids and related phenolics towards Schizaphis graminum and Myzus persicae: Aphid feeding deterrents in wheat

A number of naturally occurring flavonoids have been tested for their feeding deterrent activity against two aphid species, Schizaphis graminum and Myzus persicae. Most flavonoids, including a number of dihydrochalcones related to phloretin, showed strong deterrency at concentrations well within the range often found in plants. Flavanone and flavone glycosides showed weak feeding deterrency relative to their corresponding aglycones. S. graminum and M. persicae responded similarly towards the compounds tested. The feeding deterrency of wheat extracts towards S. graminum was confined to the phenolic fraction, which included the flavone tricin. The more polar phenolic fraction showed the strongest feeding deterrency towards S. graminum.     

Molecular cloning of the SUF2 frameshift suppressor gene from Saccharomyces cerevisiae

A genetic approach to the molecular cloning of frameshift suppressor genes from yeast is described. These suppressors act by suppressing +1 G:C base-pair insertion mutations in glycine or proline codons. The cloning regimen involves an indirect screen for yeast transformants which harbor a functional suppressor gene inserted into the autonomously replicating “shuttle” vector YEp13, followed by transfer of the hybrid plasmid from yeast into Escherichia coli. Using this procedure a 10.7-kb DNA fragment carrying the SUF2 frameshift suppressor gene has been isolated. This suppressor acts specifically on +1 G:C insertions in proline codons. When inserted into an integrative vehicle and reintroduced into yeast by transformation, this fragment integrates by homologous recombination in the region of the SUF2 locus on chromosome III. A large proportion of the fragment overlaps with another cloned DNA segment which carries the closely linked CDC10 gene. The SUF2 fragment carries at least two tRNA genes. The SUF2 gene and one of the tRNA genes are located on a 0.85-kb restriction fragment within the 10.7-kb segment. A method is also described for the isolation of DNA fragments carrying alternative alleles of the SUF2 locus. Using this procedure, the wild-type suf2⁺ allele has been cloned.     

A theoretical investigation on the proton transfer tautomerization mechanisms of 2-thioxanthine within microsolvent and long range solvent

A relative complete study on the mechanisms of the proton transfer reactions of 2-thioxanthine was carried out with density functional theory. The models were designed with monohydrated and dihydrated microsolvent catalyses either with or without the presence of water solvent considered with the polarized continuum model (PCM). A total number of 114 complexes and 67 transition states were found with the B3LYP/6-311+G** calculations. The energies were refined with both B3LYP/aug-cc-pVTZ and PCM-B3LYP/aug-cc-pVTZ methods. The activation energies were reported with respect to the Gibbs free energies obtained in conjunction with the standard statistical thermodynamics. Possible reaction pathways were confirmed with the intrinsic reaction coordinates. Pathways via C8 atom on the imidazole ring, via the bridged C4 and C5 atoms between pyrimidine and imidazole rings and via N, O and S atom on the pyrimidine ring were examined. The results show that the most feasible pathway is the proton transfers within the long range solvent surrounding via the N, O and S atoms in the pyrimidine ring with di-hydrated catalysis: N(7)H?+?2H₂O?→?IM89?→?IM90?→?P13?+?2H₂O?→?IM91?→?IM92?→?P6?+?2H₂O?→?IM71?→?IM72?→?P7?+?2H₂O?→?IM107?→?IM108?→?P18?+?2H₂O?→?IM111?→?IM112?→?P19?+?2H₂O?→?IM113?→?IM114?→?P17?+?2H₂O?→?IM105?→?IM106?→?N(9)H?+?2H₂O that has the highest energy barrier of 44.0 kJ mol^?1 in the transition of IM89 to IM90 via TS54. The small energy barrier is in good agreement with the experimental observation that 2-TX tautomerizes at room temperature in water. In the aqueous phase, the most stable intermediate is found to be IM21 [N(7)H?+?2H₂O] and the possible co-existing species are the monohydrated IM1, IM9, IM39 and IM46, and the di-hydrated IM5, IM8, IM13, IM16, IM81, IM89, IM90, IM91 and IM106 complexes that have a relative concentration larger than 10^?6 (1 ppm) with respect to IM21.

Four of the Most Common Mutations in Primary Hyperoxaluria Type 1 Unmask the Cryptic Mitochondrial Targeting Sequence of Alanine:glyoxylate Aminotransferase Encoded by the Polymorphic Minor Allele

The gene encoding the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT, EC. 2.6.1.44) exists as two common polymorphic variants termed the “major” and “minor” alleles. The P11L amino acid replacement encoded by the minor allele creates a hidden N-terminal mitochondrial targeting sequence, the unmasking of which occurs in the hereditary calcium oxalate kidney stone disease primary hyperoxaluria type 1 (PH1). This unmasking is due to the additional presence of a common disease-specific G170R mutation, which is encoded by about one third of PH1 alleles. The P11L and G170R replacements interact synergistically to reroute AGT to the mitochondria where it cannot fulfill its metabolic role (i.e. glyoxylate detoxification) effectively. In the present study, we have reinvestigated the consequences of the interaction between P11L and G170R in stably transformed CHO cells and have studied for the first time whether a similar synergism exists between P11L and three other mutations that segregate with the minor allele (i.e. I244T, F152I, and G41R). Our investigations show that the latter three mutants are all able to unmask the cryptic P11L-generated mitochondrial targeting sequence and, as a result, all are mistargeted to the mitochondria. However, whereas the G170R, I244T, and F152I mutants are able to form dimers and are catalytically active, the G41R mutant aggregates and is inactive. These studies open up the possibility that all PH1 mutations, which segregate with the minor allele, might also lead to the peroxisome-to-mitochondrion mistargeting of AGT, a suggestion that has important implications for the development of treatment strategies for PH1.     

Mutations in lipopolysaccharide-binding protein (LBP) gene change the susceptibility to clinical mastitis in Chinese Holstein

Mastitis is an unsolved human challenge all dairy farms facing with, which leads to immeasurable economic loss to the farmers. LBP gene plays a vital role in the innate immune recognition of Gram-negative bacterium that is a major cause of bovine clinical mastitis, but little is known about LBP mutations and their effects on cows' susceptibility to clinical mastitis. In this study, PCR-SSCP method was adopted to analyze SNPs of LBP gene in Chinese Holstein for the first time. 17 SNPs were found in the promoter core region, exon1, exon2, exon3, exon4 and exon8. The mutation g.-81C?→?T in promoter leads to an AP-2 binding site lost. Two mutations, g.11T?→?C (4 Leu?→?Ser) and g.68G?→?C (23Gly?→?Ala) in signal peptide brought about molecular secondary structural change, meanwhile, g.11T?→?C made a Big-1 domain lost, and there was an N-myristoylation site at the g.68G/C locus. The three mutations above were in complete linkage disequilibrium in allele A. In mature LBP protein, five mutations were found: g.3034G?→?A(36Asp?→?Asn), g.3040A?→?G(38Asn?→?Asp), g.3056T?→?C(43Ile?→?Thr) in allele D; g.4619G?→?A(67Ala?→?Thr) in allele F; 19975G?→?A (282Val?→?Met) in allele J. And SNPs in allele D and F were in complete linkage disequilibrium, also in which 38Asn?→?Asp and 67Ala?→?Thr influenced the protein secondary structure. Prediction of the 3-D structure shows mutations 36Asp?→?Asn, 38Asn?→?Asp and 43 Ile?→?Thr were on the concave surface of LBP protein at barrel-N, 67Ala?→?Thr was in the apolar pocket at barrel-N. Motif analysis shows 36Asp?→?Asn causes loss of a CK2 phosphorylation site, 67 Ala?→?Thr forms a new PKC phosphorylation site. And 43Ile?→?Thr, 67Ala?→?Thr made hydrophobic amino acids to be hydrophilic amino acids. Interestingly, the morbidity of AB (mixed type g.-81C/T, g.11T/C, g.68G/C), CD (mixed type g.3034G/A, g.3040A/G, g.3056T/C) and EF (mixed type g.4619G/A) genotype cows are significant higher than others in this study (P?相似文献   

Do microbial protein elicitors PeaT1 obtained from Alternaria tenuissima and PeBL1 from Brevibacillus laterosporus enhance defense response against tomato aphid (Myzus persicae)?

Tomato aphid (Myzus persicae) is a destructive insect pest of tomato responsible for huge losses in the production as well in the vegetable industry. In the present in vitro study two protein elicitors, PeaT1 and PeBL1 were considered to study their efficacies to exhibit defense response against tomato aphid. Three different concentrations of both protein elicitors were applied on the tomato seedlings. After the application of PeaT1 and PeBL1, population growth rates of tomato aphid were decreased as compared to the control treatment. In host preference assay, the tomato aphid showed a preference to build a colony on the control as compared to the treated tomato plant, because tomato leaves provided hazardous surface for aphid after the formation of wax and trichome. The concentrations of protein showed significant (p < 0.05) results in life-history traits of the aphid. Jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) showed significant accumulation in tomato seedlings treated with PeaT1 and PeBL1. Elicitors treated plants produced resistance against M. persicae. Our finding suggests that PeaT1 and PeBL1 have shown high potentials against the damage of M. persicae, and both elicitors could be used as novel biological tools against tomato aphid.     

Effect of sinigrin on the efficiency of acquisition of turnip mosaic virus byMyzus persicae andBrevicoryne brassicae

The efficiency of turnip mosaic virus (TuMV) acqusition fromSinapis alba L. without sinigrin andBrassica nigra (L.) Koch with a high content of sinigrin by non-fastedMyzus persicae (Sulz.) andBrevicoryne brassicae (L.) was investigated in order to determine the effect of the phagostimulatory glucoside sinigrin on virus transmission. There was a significantly higher acquisition of TuMV fromS. alba byM. persicae than fromB. nigra. Conversely,B. brassicae acquired the virus more efficiently fromB. nigra than fromS. alba. The efficiency of transmission was positively correlated with the response of both aphid species to sinigrin. Saturation ofS. alba leaves with a 1 % solution of sinigrin did not significantly affect the acquisition of TuMV, in neitherM. persicae norB. brassicae, whether the aphids were fasted or not.     

Sulphate utilization in an aphid symbiosis

When two clones of Myzus persicae were maintained on a defined diet with inorganic sulphate as sole sulphur source, their growth and survival were inferior to that on diets containing the sulphur amino acid, methionine. This discrepancy is due, at least in part, to the phagostimulatory properties of methionine, which stimulated aphid feeding rate by 50–150%. Myzus persicae incorporated radioactivity from dietary [³⁵S]sulphate into protein and low molecular weight compounds, including cysteine and methionine. Two lines of evidence indicate that the mycetocyte-symbionts are responsible for the reductive assimilation of sulphate. (1) [³⁵S]sulphate incorporation is abolished by treatment of the aphids with the antibiotic chlortetracycline, which disrupts the symbionts; and (2) [³⁵S]sulphate is utilized by isolated embryos (which contain mycetocyte-symbionts but no gut flora) but not by isolated guts. Tracer studies suggest that 20% of dietary radiosulphur is translocated to the aphid tissues, and it is hypothesized that methionine may be the principal product released by the symbionts.     

The role of Rdl in resistance to phenylpyrazoles in Drosophila melanogaster

Extensive use of older generation insecticides may result in pre-existing cross-resistance to new chemical classes acting at the same target site. Phenylpyrazole insecticides block inhibitory neurotransmission in insects via their action on ligand-gated chloride channels (LGCCs). Phenylpyrazoles are broad-spectrum insecticides widely used in agriculture and domestic pest control. So far, all identified cases of target site resistance to phenylpyrazoles are based on mutations in the Rdl (Resistance to dieldrin) LGCC subunit, the major target site for cyclodiene insecticides. We examined the role that mutations in Rdl have on phenylpyrazole resistance in Drosophila melanogaster, exploring naturally occurring variation, and generating predicted resistance mutations by mutagenesis. Natural variation at the Rdl locus in inbred strains of D. melanogaster included gene duplication, and a line containing two Rdl mutations found in a highly resistant line of Drosophila simulans. These mutations had a moderate impact on survival following exposure to two phenylpyrazoles, fipronil and pyriprole. Homology modelling suggested that the Rdl chloride channel pore contains key residues for binding fipronil and pyriprole. Mutagenesis of these sites and assessment of resistance in vivo in transgenic lines showed that amino acid identity at the Ala³⁰¹ site influenced resistance levels, with glycine showing greater survival than serine replacement. We confirm that point mutations at the Rdl 301 site provide moderate resistance to phenylpyrazoles in D. melanogaster. We also emphasize the beneficial aspects of testing predicted mutations in a whole organism to validate a candidate gene approach.     

Relative suitability of the common pistachio psyllid,Agonoscena pistaciae (Hemiptera: Aphalaridae), as prey for the two-spotted ladybird,Adalia bipunctata (Coleoptera: Coccinellidae)

The suitability of Agonoscena pistaciae Burckhardt & Lauterer as a prey for Adalia bipunctata (Linnaeus) was evaluated by studying the predator’s development and reproduction on this species in comparison to reference diets of nymphs of Myzus persicae (Sulzer) and eggs of Ephestia kuehniella Zeller. Both larval and adult A. bipunctata fed voraciously on A. pistaciae. The development time of the ladybird was shorter when fed on M. persicae and A. pistaciae and longer on E. kuehniella. The survival rate was 87% on M. persicae and 85% on A. pistaciae, both significantly greater than on E. kuehniella eggs (63%). The ladybirds were heaviest at eclosion and their fecundity was higher on M. persicae than on A. pistaciae or E. kuehniella. Both the aphid and psyllid diets yielded higher R₀, r_m values and lower T and DT values than E. kuehniella eggs. Based on total development time, immature survival and adult fecundity, the relative suitability for A. bipunctata was M. persicae > A. pistaciae > E. kuehniella. When ladybirds were reared on psyllids, they showed no preference between aphid or psyllid diets, but when raised on M. persicae, they preferred an aphid diet. A field experiment showed that A. bipunctata preferred to oviposit on pistachio trees at a height of 150–200 cm, i.e. towards the top. The results indicate that A. pistaciae constitutes a complete food for A. bipunctata, supporting both completed development and successful reproduction.     

Electrophoretic study of genetic variation in British Myzus persicae (Sulz.) (hemiptera,aphididae)

Thirty-five clones of the green peach aphid, Myzus persicae Sulz., representing a wide range of host plants and geographical origins, were examined electrophoretically. Only 11 of 26 enzymes were active enough for subsequent work. Since genetic crosses are very difficult to make in the parthenogenetic M. persicae, assigning bands to loci and alleles is necessarily arbitrary. Thirty-two isozyme bands were detected. Only two of these (Est-1 and Est-3) migrated to different distances in some clones. This is a very low level of interclone variation, considering the known properties and origins of the clones. The peculiar feeding habits of aphids may perhaps partly explain the inactivity of so many enzymes in M. persicae (which are active in other insects). The scarcity of interclone variation in isozyme migration distance in M. persicae clones may be the result of its fast parthenogenetic reproduction and high migration ability of alates, combined with the effects of natural and artificial selection (e.g., by insecticides). Surviving genotypes may be rather few, each represented by numerous individuals. The only type of widespread electrophoretic variation is in the intensity of two esterase bands (Est-1 and Est-2). Five hypotheses are presented to explain this variation and discussed in view of evidence from other organisms.     

Origin and Evolution of Sulfadoxine Resistant Plasmodium falciparum

The Thailand-Cambodia border is the epicenter for drug-resistant falciparum malaria. Previous studies have shown that chloroquine (CQ) and pyrimethamine resistance originated in this region and eventually spread to other Asian countries and Africa. However, there is a dearth in understanding the origin and evolution of dhps alleles associated with sulfadoxine resistance. The present study was designed to reveal the origin(s) of sulfadoxine resistance in Cambodia and its evolutionary relationship to African and South American dhps alleles. We sequenced 234 Cambodian Plasmodium falciparum isolates for the dhps codons S436A/F, A437G, K540E, A581G and A613S/T implicated in sulfadoxine resistance. We also genotyped 10 microsatellite loci around dhps to determine the genetic backgrounds of various alleles and compared them with the backgrounds of alleles prevalent in Africa and South America. In addition to previously known highly-resistant triple mutant dhps alleles SGEGA and AGEAA (codons 436, 437, 540, 581, 613 are sequentially indicated), a large proportion of the isolates (19.3%) contained a 540N mutation in association with 437G/581G yielding a previously unreported triple mutant allele, SGNGA. Microsatellite data strongly suggest the strength of selection was greater on triple mutant dhps alleles followed by the double and single mutants. We provide evidence for at least three independent origins for the double mutants, one each for the SGKGA, AGKAA and SGEAA alleles. Our data suggest that the triple mutant allele SGEGA and the novel allele SGNGA have common origin on the SGKGA background, whereas the AGEAA triple mutant was derived from AGKAA on multiple, albeit limited, genetic backgrounds. The SGEAA did not share haplotypes with any of the triple mutants. Comparative analysis of the microsatellite haplotypes flanking dhps alleles from Cambodia, Kenya, Cameroon and Venezuela revealed an independent origin of sulfadoxine resistant alleles in each of these regions.     

Infection of Arabidopsis by cucumber mosaic virus triggers jasmonate-dependent resistance to aphids that relies partly on the pattern-triggered immunity factor BAK1

Many aphid-vectored viruses are transmitted nonpersistently via transient attachment of virus particles to aphid mouthparts and are most effectively acquired or transmitted during brief stylet punctures of epidermal cells. In Arabidopsis thaliana, the aphid-transmitted virus cucumber mosaic virus (CMV) induces feeding deterrence against the polyphagous aphid Myzus persicae. This form of resistance inhibits prolonged phloem feeding but promotes virus acquisition by aphids because it encourages probing of plant epidermal cells. When aphids are confined on CMV-infected plants, feeding deterrence reduces their growth and reproduction. We found that CMV-induced inhibition of growth as well as CMV-induced inhibition of reproduction of M. persicae are dependent upon jasmonate-mediated signalling. BRASSINOSTEROID INSENSITIVE1-ASSOCIATED KINASE1 (BAK1) is a co-receptor enabling detection of microbe-associated molecular patterns and induction of pattern-triggered immunity (PTI). In plants carrying the mutant bak1-5 allele, CMV induced inhibition of M. persicae reproduction but not inhibition of aphid growth. We conclude that in wildtype plants CMV induces two mechanisms that diminish performance of M. persicae: a jasmonate-dependent and PTI-dependent mechanism that inhibits aphid growth, and a jasmonate-dependent, PTI-independent mechanism that inhibits reproduction. The growth of two crucifer specialist aphids, Lipaphis erysimi and Brevicoryne brassicae, was not affected when confined on CMV-infected A. thaliana. However, B. brassicae reproduction was inhibited on CMV-infected plants. This suggests that in A. thaliana CMV-induced resistance to aphids, which is thought to incentivize virus vectoring, has greater effects on polyphagous than on crucifer specialist aphids.