Probiotic effects of β-glucuronidase on the peach-potato aphid Myzus persicae (Aphididae)

beta-glucuronidase (GUS) is a reporter protein commonly expressed in transgenic plants allowing the visualization of the transformed individuals. In our recent work, we showed that consumption of transformed potato plants expressing this GUS enzyme improves performance of the phloem, feeding aphid Myzus persicae. Those results led us to the conclusion that the expression of GUS in potato plants might be responsible for the probiotic effect measured in feeding aphids. In the present paper, artificial diets were used to provide active GUS (10 and 500 mug ml(-1)), inactivated heated GUS (500 mug ml(-1)), glucuronic acid (10, 100 and 500 mug ml(-1)), and bovine serum albumin (500 mug ml(-1)) to M. persicae. Our results reveal that these chemicals provided as food intake might influence the biological parameters of this aphid. Experiments showed a probiotic effect of 500 mug ml(-1) GUS diet, resulting in reduced larval mortality, and increased adult reproduction period and fecundity, which led to an increased population growth potential (r(m) = 0.17 +/- 0.01 versus r(m) = 0.12 +/- 0.03 for aphids fed on control diet). A lower amount of added GUS led to fewer variations, biological parameters being only slightly altered (r(m) = 0.14 +/- 0.03). Statistically similar alterations of the biological parameters were obtained when comparing aphids fed on the diet added with inactivated GUS or the non-structural bovine serum albumin protein (r(m) = 0.15 +/- 0.02 and 0.14 +/- 0.03, respectively). Feeding assays conducted with glucuronic acid supplemented diets enhanced longevity and nymph production of the adult aphids and reduced larval mortality, resulting in r(m) = 0.15 +/- 0.02 for the highest dose (500 mug ml(-1)). Although 100 mug ml(-1) glucuronate diet did not induce any effect on M. persicae (r(m) = 0.12 +/- 0.03), aphids fed on 10 mug ml(-1) glucuronate dietexhibited unexpected reduced demographic parameters (r(m) = 0.10 +/- 0.03). Immunohistological analysis showed GUS labeling along the whole digestive epithelium of adults and in various tissues including embryos and bacteriocytes. These results suggest that GUS crosses through the digestive tract. Western blots performed with protein extracts of transformed potato plants expressing the gus gene showed a unique band of molecular weight 76 kDa. On the contrary, in extracts from aphids fed on transgenic potato plants or bred on GUS 500 mug ml(-1) artificial diet, several proteins of lower molecular weight were hybridized, revealing proteolysis of ingested GUS. It is concluded that GUS protein, and more precisely GUS activity, is responsible for the probiotic effects on aphid feeding. The possible pathways of induction of such physiological alterations by GUS are discussed. (C) 2003 Elsevier Ltd. All rights reserved.