Reproductive incompatibility between genetically differentiated populations of Tetranychus urticae from different host plants

Η μελέτη της προσαρμογής των εχθρών των καλλιεργούμενων φυτών στα φυτά ξενιστές τους παρουσιάζει μεγάλο ενδιαφέρον, καθώς σχετίζεται με την απομόνωση και γενετική διαφοροποίηση των πληθυσμών, με αποτελέσματα που ποικίλλουν από τον περιορισμό της γονιδιακής ροής μέχρι και το σχηματισμό νέων ειδών. Με έναυσμα προηγούμενες μελέτες μας με ισοένζυμα, που κατέδειξαν γενετική διαφοροποίηση μεταξύ πληθυσμών Tetranychus urticae (Koch) από εσπεριδοειδή σε σχέση με άλλους ξενιστές, μελετήσαμε την συμβατότητα των διασταυρώσεων μεταξύ Τ. urticae που συλλέχθηκε σε λεμονιές (ELCI) και Τ. urticae που συλλέχτηκε από το φυτό Mercurialis annua (ELMA) στο ίδιο χωράφι. Η συμβατότητα των διασταυρώσεων όταν πρόκειται για απλοδιπλοειδές είδος, όπου τα αρσενικά προέρχονται από αγονιμοποίητα ωά, μελετάται λαμβάνοντας υπόψη τον αριθμό των απογόνων αλλά και την αναλογία φύλου μεταξύ τους. Η γονιμότητα των θηλυκών ELMA δεν επηρεάστηκε όταν διασταυρώθηκαν με αρσενικά ELCI, όμως η αναλογία θηλυκών : αρσενικών ήταν σημαντικά μειωμένη (16,6% θηλυκά, σε σύγκριση με 66% στην διασταύρωση αναφοράς ELMA x ELMA). Όταν τα θηλυκά ELCI διασταυρώθηκαν με αρσενικά ELMA, η γονιμότητα ήταν κατά 30% μειωμένη και το ποσοστό των θηλυκών απογόνων μειώθηκε από 67% σε 52%, σε σχέση με τη διασταύρωσης αναφοράς (ELCI x ELCI). Τα F1 θηλυκά που προέκυψαν από διασταυρώσεις θηλυκών και αρσενικών από διαφορετικούς πληθυσμούς γέννησαν λιγότερα ωά, που είχαν μεγαλύτερη θνησιμότητα, σε σχέση με τα F1 θηλυκά προερχόμενα από ενδοπληθυσμιακές διασταυρώσεις, μειώνοντας επιπλέον το δυναμικό αναπαραγωγής μεταξύ των πληθυσμών.The study of host plant adaptation in arthropods, and especially agricultural pests, presents great interest, as it relates to patterns of population isolation and differentiation, with effects ranging from gene flow restriction to speciation. Prompted by our earlier isoenzyme studies that revealed genetic differentiation of Tetranychus urticae (Koch) collected on citrus, compared to other host plants, we investigated crossing compatibility between T. urticae collected from citrus (lemon) trees (ELCI) and T. urticae collected from the weed Mercurialis annua (ELMA), in the same citrus grove. Crossing compatibility in haplodiploid species where unfertilised eggs develop into males, like T. urticae, is assessed based on both the number and the sex ratio of the offspring. When ELMA females were crossed with ELCI males, fecundity was not affected, however the sex ratio was significantly biased towards males (16.6 % females, compared to 66% in the control cross ELMAxELMA). In the reciprocal crosses (ELCIxELMA), fecundity was lower by 30% and the proportion of female offspring was reduced to 52% from 67 %, compared to the control. The fecundity of the F1 hybrid females was significantly reduced and the eggs they laid were less viable, compared to the non-hybrids, further reducing the reproductive potential of inter-strain crosses. Combined with previous data, these results suggest the existence of a citrus-associated T. urticae host race

Genetic variability in Tetranychus urticae (Acari : Tetranychidae) from Greece : insecticide resistance and isozymes

Etude de la résistance au méthyl-parathion, au méthidathion et au méthomyl chez une population de #Tetranychus urticae$ Koch originaire de Grèce. A la CL 50 le taux de résistance est hautement variable avec le méthidathion (5 à 63 fois) et avec le méthomyl (6 à 34 fois). Les courbes de mortalité avec le méthyl-parathion présentent un plateau net à une mortalité d'environ 20% et le taux de résistance est d'environ 50 fois à CL 50, dans tous les échantillons. Par utilisation de la focalisation isoélectrique sur des membranes d'acétate de cellulose, les études électrophorétiques de 5 loci codant les estérases (Est-1 et Est-2), l'isomérase gluco-phosphate (Gpi), l'enzyme malique (Me) et la phosphoglucomutase (Pgm), indiquent les différences génétiques importantes parmi les échantillons. (Résumé d'auteur

Identification and functional characterization of a novel acetyl-CoA carboxylase mutation associated with ketoenol resistance in Bemisia tabaci

This is the final version. Available from Elsevier / Academic Press via the DOI in this record. Insecticides of the tetronic/tetramic acid family (cyclic ketoenols) are widely used to control sucking pests such as whiteflies, aphids and mites. They act as inhibitors of acetyl-CoA carboxylase (ACC), a key enzyme for lipid biosynthesis across taxa. While it is well documented that plant ACCs targeted by herbicides have developed resistance associated with mutations at the carboxyltransferase (CT) domain, resistance to ketoenols in invertebrate pests has been previously associated either with metabolic resistance or with non-validated candidate mutations in different ACC domains. A recent study revealed high levels of spiromesifen and spirotetramat resistance in Spanish field populations of the whitefly Bemisia tabaci that was not thought to be associated with metabolic resistance. We confirm the presence of high resistance levels (up to >640-fold) against ketoenol insecticides in both Spanish and Australian B. tabaci strains of the MED and MEAM1 species, respectively. RNAseq analysis revealed the presence of an ACC variant bearing a mutation that results in an amino acid substitution, A2083V, in a highly conserved region of the CT domain. F1 progeny resulting from reciprocal crosses between susceptible and resistant lines are almost fully resistant, suggesting an autosomal dominant mode of inheritance. In order to functionally investigate the contribution of this mutation and other candidate mutations previously reported in resistance phenotypes, we used CRISPR/Cas9 to generate genome modified Drosophila lines. Toxicity bioassays using multiple transgenic fly lines confirmed that A2083V causes high levels of resistance to commercial ketoenols. We therefore developed a pyrosequencing-based diagnostic assay to map the spread of the resistance alleles in field-collected samples from Spain. Our screening confirmed the presence of target-site resistance in numerous field-populations collected in Sevilla, Murcia and Almeria. This emphasizes the importance of implementing appropriate resistance management strategies to prevent or slow the spread of resistance through global whitefly populations.European Union Horizon 2020Australian cotton research and development corporatio

The druggability of the ATP binding site of glycogen phosphorylase kinase probed by coumarin analogues

Glycogen phosphorylase kinase (PhK) converts by phosphorylation, the inactive glycogen phosphorylase (GPb) into active GPa in the glycogenolytic pathway. It is a complex enzyme comprising of the catalytic (γ) and three regulatory subunits (α, β, δ) forming a hexadecamer with stoichiometry (αβγδ)4. Several studies have indicated PhK as a promising target for the development of antihyperglycemics as its inhibition blocks glycogenolysis in liver and a potential therapeutic target for cancer against pathological angiogenesis and tumor progression. The identification of compounds that inhibit the kinase through their direct binding to its catalytic site is an effective approach to identify bioactive molecules of therapeutic significance. Towards this, the structure of the N-terminal kinase domain (residues 1–298) of the catalytic γ subunit of PhK (PhKγtrnc) has been determined by X-ray crystallography while staurosporine and indirubin analogues have been characterized as potent inhibitors targeting the ATP binding site. In this study, a series of 38 synthetic analogues of naturally occurring coumarins were screened for inhibition of PhKγtrnc, in vitro, using a photometric assay. The IC50 values of the two most potent compounds were determined for PhKγtrnc and the pharmacologically relevant target, human liver isoform (PHKG2A). Their cellular efficacy and toxicity in HepG2 cells were further assessed ex vivo. Docking experiments and the structural comparison with previously described inhibitors reveal the binding mode of the coumarin scaffold at a no hinge region of the ATP site of PhK and the role of a conserved β3-Lys in binding. The experimental findings provide structural insights with implications to the kinase targeting and drug design