Three toxins, two receptors, one mechanism: Mode of action of Cry1A toxins from Bacillus thuringiensis in Heliothis virescens.
Insecticidal crystal (Cry) proteins from Bacillus thuringiensis (Bt) are highly active against Lepidoptera. However, field-evolved resistance to Bt toxins is on the rise. The 12-cadherin domain protein HevCaLP and the ABC transporter HevABCC2 are both genetically linked to Cry toxin resistance in Heliothis virescens. We investigated their interaction using stably expressing non-lytic clonal Sf9 cell lines expressing either protein or both together. Untransfected Sf9 cells are innately sensitive to Cry1Ca toxin, but not to Cry1A toxins; and quantitative PCR revealed negligible expression of genes involved in Cry1A toxicity such as cadherin, ABCC2, alkaline phosphatase (ALP) and aminopeptidase N (APN). Cry1Aa, Cry1Ab or Cry1Ac caused swelling of Sf9 cells expressing HevABCC2, and caused faster swelling, lysis and up to 86% mortality in cells expressing both proteins. No such effect was observed in control Sf9 cells or in cells expressing only HevCaLP. The results of a mixing experiment demonstrated that both proteins need to be expressed within the same cell for high cytotoxicity, and suggest a novel role for HevCaLP. Binding assays showed that the toxin-receptor interaction is specific. Our findings confirm that HevABCC2 is the central target in Cry1A toxin mode of action, and that HevCaLP plays a supporting role in increasing Cry1A toxicity.
['Bretschneider|Anne|A|', 'Heckel|David G|DG|', 'Pauchet|Yannick|Y|']
D000818:Animals D001413:Bacillus thuringiensis D000083722:Bacillus thuringiensis Toxins D001426:Bacterial Proteins D015820:Cadherins D004731:Endotoxins D006460:Hemolysin Proteins D019476:Insect Proteins D007814:Larva D009036:Moths D000089762:Multidrug Resistance-Associated Protein 2 D027425:Multidrug Resistance-Associated Proteins D061987:Sf9 Cells
Heliothis virescens ABC transporter Cadherin Bt Cry1A toxin Insecticide resistance