Antioxidant defense response in a galling insect

Abstract

Herbivorous insect species are constantly challenged with reactive oxygen species (ROS) generated from endogenous and exogenous sources. ROS produced within insects because of stress and prooxidant allelochemicals produced by host plants in response to herbivory require a complex mode of antioxidant defense during insect/plant interactions. Some insect herbivores have a midgut-based defense against the suite of ROS encountered. Because the Hessian fly (Mayetiola destructor) is the major insect pest of wheat worldwide, and an emerging model for all gall midges, we investigated its antioxidant responses during interaction with its host plant. Quantitative data for two phospholipid glutathione peroxidases (MdesPHGPX-1 and MdesPHGPX-2), two catalases (MdesCAT-1 and MdesCAT-2), and two superoxide dismutases (MdesSOD-1 and MdesSOD-2) revealed high levels of all of the mRNAs in the midgut of larvae on susceptible wheat (compatible interaction). During development of the Hessian fly on susceptible wheat, a differential expression pattern was observed for all six genes. Analysis of larvae on resistant wheat (incompatible interaction) compared with larvae on susceptible wheat showed increased levels of mRNAs in larvae on resistant wheat for all of the antioxidant genes except MdesSOD-1 and MdesSOD-2. We postulate that the increased mRNA levels of MdesPHGPX-1, MdesPHGPX-2, MdesCAT-1, and MdesCAT-2 reflect responses to ROS encountered by larvae while feeding on resistant wheat seedlings and/or ROS generated endogenously in larvae because of stress/starvation. These results provide an opportunity to understand the cooperative antioxidant defense responses in the Hessian fly/wheat interaction and may be applicable to other insect/plant interactions.

Fig. 1.

Dendrogram of the GPX families calculated from aligned amino acid sequences. The topology and branch lengths of the radial phylogram were produced by the distance/neighbor-joining criteria. Numbers at the branches correspond to bootstrap support >50%. M. destructor phosopholipid hydroperoxide GPXs (PHGPXs) MdesPHGPX-1 and MdesPHGPX-2 group with PHGPXs from other Diptera. Taxa and GenBank accession numbers included are as follows: Saccharomyces cerevisiae, P40581; Schistosoma mansoni, QO0277; Tribolium castaneum, XP_969802; Boophilus microplus, ABA62394; Homo sapiens, CAA50793; Sus scrofa, CAA53596; Rattus norvegicus, NP058861; Citrus sinensis, Q06652; M. destructor, DQ418778; D. melanogaster, AAR96123; G. morsitans, AAT85827; A. gambiae, EAA44749; M. destructor, DQ418779; Sus scrofa, NP999366; H. sapiens, P07203; Macaca fuscata, BAC67247; Mus musculus, Q9JHC0; H. sapiens, P18283; Pan troglodytes, XP_522880; Gallus gallus, XP_425211; H. sapiens, P22352; Bos taurus, AAA16579; Mus musculus, NP032187; Rattus rattus, CAA44274; P. troglodytes, XP_527299; H. sapiens, O75715; Canis familiaris, O46607.

Fig. 2.

Temporal gene expression of the Hessian fly antioxidant genes in larval tissues. Gene expression was studied in midgut, salivary glands, and fat body. Expression in the salivary glands was taken as the calibrator, and the expression in midgut and fat body samples was calculated relative to the expression in the salivary glands to reveal the fold changes. The standard error is represented by the error bars for three technical replicates.

Fig. 3.

Temporal gene expression of the Hessian fly antioxidant genes during development. Gene expression was studied for all of the developmental stages including first, second, and third larval instars, pupae, and adults. REV for all of the genes was calculated by using an endogenous Hessian fly ubiquitin gene. The standard error is represented by the error bars for three technical replicates. e2, early second instar; m2, mid second instar; l2, late second instar; e3, early third instar; m3, mid third instar; l3, late third instar.

Fig. 4.

Temporal gene expression patterns of the Hessian fly antioxidant genes during interactions with wheat. Gene expression was studied in compatible and incompatible interactions. Relative fold change for all of the genes was determined by dividing the REV calculated for Biotype L larvae on resistant Iris wheat (incompatible interaction) by the REV calculated for Biotype L larvae on susceptible Newton wheat (compatible interaction). The standard error is represented by the error bars for two biological replicates (two technical replicates within each).