Abstract
Aphids are phloem feeders that cause large damage globally as pest insects. They induce a variety of responses in the host plant, but not much is known about which responses are promoting or inhibiting aphid performance. Here, we investigated whether one of the responses induced in barley by the cereal aphid, bird cherry-oat aphid (Rhopalosiphum padi L.) affects aphid performance in the model plant Arabidopsis thaliana L. A barley cDNA encoding the protease inhibitor CI2c was expressed in A. thaliana and aphid performance was studied using the generalist green peach aphid (Myzus persicae Sulzer). There were no consistent effects on aphid settling or preference or on parameters of life span and long-term fecundity. However, short-term tests with apterous adult aphids showed lower fecundity on three of the transgenic lines, as compared to on control plants. This effect was transient, observed on days 5 to 7, but not later. The results suggest that the protease inhibitor is taken up from the tissue during probing and weakly inhibits fecundity by an unknown mechanism. The study shows that a protease inhibitor induced in barley by an essentially monocot specialist aphid can inhibit a generalist aphid in transgenic Arabidopsis.
Highlights
Aphids are phloem feeding insects and serious crop pests
The results showed somewhat higher nymph mortality on the rolC-transformants than those transformed with the CaMV35S-promoter [56]
This was suggested based on the finding that in green peach aphid (GPA) reared on oilseed rape expressing a gene for the cysteine protease inhibitor (PI) oryzacystatin (OC-I), the inhibitor was found in the oenocytes and bacteriocytes of the aphid [27]
Summary
Aphids are phloem feeding insects and serious crop pests. They are vectors of plant viruses and by themselves reduce plant growth at heavy infestations. We suggest that the CI2c protein is ingested during probing and that the targets are within the aphids This idea would be in accordance with recent studies where lower serine protease activities in the GPA gut were correlated to lower fecundity [38]. It is possible that the PI does not act on protein digestion in the gut, but, for example, on functions related to aphid reproduction or the interaction with the bacterial endosymbionts This was suggested based on the finding that in GPA reared on oilseed rape expressing a gene for the cysteine PI oryzacystatin (OC-I), the inhibitor was found in the oenocytes and bacteriocytes of the aphid [27]. This may explain the absence of any preference of GPA for Arabidopsis expressing the CI2c gene
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