Ribosome-inactivating proteins from apple have strong aphicidal activity in artificial diet and in planta

• Feeding of pea aphids (Acyrthosiphon pisum) on artificial diet containing recombinant apple ribosome-inactivating proteins exerted high nymphal mortality.
• Feeding of green peach aphids (Myzus persicae) on transgenic tobacco plants expressing apple RIPs showed high nymphal mortality.
• Transgenic lines affected the life parameters of green peach aphids, reducing population buildup.

The apple (Malus domestica) genome contains gene sequences encoding type-1 and type-2 ribosome-inactivating proteins (RIPs). Both types of proteins contain a RIP domain with N-glycosidase activity, but the type-2 RIPs possess an additional domain with lectin activity. Here we investigated the activity of RIPs from apple against two sucking-piercing aphids that are important in agriculture, in particular pea aphids (Acyrthosiphon pisum) and green peach aphids (Myzus persicae).When the recombinant RIPs were dosed in an artificial liquid diet against pea aphids a strong aphicidal activity was observed. Based on LC50s, the type-2 RIP (33 mg/L) was about 10 times more active than the type-1 RIP (341 mg/L), and the LC50 of the recombinant protein corresponding to the type-2 RIP lectin domain alone was 106 mg/L. In in planta experiments with transgenic tobacco plants expressing the type-1 RIP or the type-2 RIP and infected with green peach aphids, mortalities of the nymphal stages amounted to approximately 50% for both types of transgenic lines when compared to wild type plants. In addition, significant sublethal effects were observed in the surviving aphids with a reduction in fecundity, intrinsic rate of increase, net reproductive rate and doubling time of the insect population. The insecticidal activity of the type-1 RIP and type-2 RIP from apple is discussed in relation to the domain structure of the RIPs and potential use in plant protection.

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