Abstract
PA1b (Pea Albumin 1, subunit b) peptide is an entomotoxin, extracted from Legume seeds, with a lethal activity towards several insect pests, such as mosquitoes, some aphids and cereal weevils. This toxin acts by binding to the subunits c and e of the plasma membrane H+-ATPase (V-ATPase) in the insect midgut. In this study, two cereal weevils, the sensitive Sitophilus oryzae strain WAA42, the resistance Sitophilus oryzae strain ISOR3 and the insensitive red flour beetle Tribolium castaneum, were used in biochemical and histological experiments to demonstrate that a PA1b/V-ATPase interaction triggers the apoptosis mechanism, resulting in insect death. Upon intoxication with PA1b, apoptotic bodies are formed in the cells of the insect midgut. In addition, caspase-3 enzyme activity occurs in the midgut of sensitive weevils after intoxication with active PA1b, but not in the midgut of resistant weevils. These biochemical data were confirmed by immuno-histochemical detection of the caspase-3 active form in the midgut of sensitive weevils. Immuno-labelling experiments also revealed that the caspase-3 active form and V-ATPase are close-localized in the insect midgut. The results concerning this unique peptidic V-ATPase inhibitor pave the way for the utilization of PA1b as a promising, more selective and eco-friendly insecticide.
Highlights
Biochemical studies revealed that PA1b targets a protein complex named vacuolar-ATPase (V-ATPase)[12]
Three situations occur in whole insects upon Pa1b intoxication: (i) insects, such as the Sitophilus oryzae strain WAA42, are sensitive to the toxin and PA1b-I125 binds to their V-ATPase receptors; (ii) insects, such as the Sitophilus oryzae strain ISOR3, are totally resistant to the toxin due to the non-interaction with V-ATPase; and (iii) insects, such as the red flour beetle Tribolium castaneum, were found to be insensitive the PA1b-I125 binding site exists on extracts from this insect, with characteristics similar to those of the sensitive insects[5, 6]
These three insect models, the sensitive S. oryzae strain WAA42, the resistant S. oryzae strain ISOR3 and the insensitive T. castaneum, were used in biochemical and histological experiments to demonstrate that a PA1b/V-ATPase interaction triggers the apoptosis mechanism, resulting in insect death
Summary
Vanessa Eyraud[1], Séverine Balmand[1], Lamis Karaki[1], Isabelle Rahioui[1], Catherine Sivignon[1], Agnès F. Three situations occur in whole insects upon Pa1b intoxication: (i) insects, such as the Sitophilus oryzae strain WAA42, are sensitive to the toxin and PA1b-I125 binds to their V-ATPase receptors; (ii) insects, such as the Sitophilus oryzae strain ISOR3, are totally resistant to the toxin due to the non-interaction with V-ATPase; and (iii) insects, such as the red flour beetle Tribolium castaneum, were found to be insensitive the PA1b-I125 binding site exists on extracts from this insect, with characteristics similar to those of the sensitive insects[5, 6] These three insect models, the sensitive S. oryzae strain WAA42, the resistant S. oryzae strain ISOR3 and the insensitive T. castaneum, were used in biochemical and histological experiments to demonstrate that a PA1b/V-ATPase interaction triggers the apoptosis mechanism, resulting in insect death
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