Activity of endo-polygalacturonases in mirid bugs (Heteroptera: Miridae) and their inhibition by plant cell wall proteins (PGIPs)

Francesca FRATI,Gianandrea SALERNO,Giulia DE LORENZO,Roberta GALLETTI,Eric CONTI

doi:10.14411/eje.2006.067

Abstract

Endo-polygalacturonases (PGs) are hydrolytic enzymes involved in the degradation of pectin, one of the major components of plant cell wall. While PGs from fungi, bacteria and plants have been extensively studied, PGs from insects are much less known, although they are likely to play an important role in insect-plant interactions. Presence of PGs has been reported for both piercing-sucking and chewing insect species, and possibly more commonly in mirid bugs (Heteroptera: Miridae). A screening of some common mirid species and other insects, belonging to different orders and families, was conducted using agarose diffusion assays run at different pHs. All the mirid species tested [Lygus rugulipennis Popp., L. pratensis (L.), Orthops kalmi (L.), Adelphocoris lineolatus (Goeze) and Closterotomus norwegicus (Gmelin)] showed PG activity, mainly at pH 7-8, whereas no activity was recorded for the other insect species, except Sitophilus sp. (Coleoptera: Curculionidae). PG activity in females of L. pratensis was significantly higher than in males, whereas there were no differences between the sexes in the other species. In all these species, PGs were present both in the salivary glands and the gut, with a higher activity in the salivary glands, confirming the role of these enzymes in the feeding behaviour of mirid bugs. Inhibition of mirid PGs by polygalacturonase-inhibiting proteins (PGIPs) from different plant sources was analysed at pH 7. PGIPs are extracellular plant proteins known for their ability to inhibit fungal PGs and restrict fungal colonization. Two PGIPs from Phaseolus vulgaris (PvPGIP3 and PvPGIP4) inhibited PGs of all the mirid bugs tested. This information may be helpful for the development of innovative insect-resistant plant varieties, for use in low-impact IPM.

Highlights

Polygalacturonases (PGs; EC 3.2.1.15) are hydrolytic enzymes belonging to the large group of pectinases and involved in the degradation of pectin, one of the major components of plant cell wall
All the mirid species tested [Lygus rugulipennis Popp., L. pratensis (L.), Orthops kalmi (L.), Adelphocoris lineolatus (Goeze) and Closterotomus norwegicus (Gmelin)] showed PG activity, mainly at pH 7–8, whereas no activity was recorded for the other insect species, except Sitophilus sp. (Coleoptera: Curculionidae)
Crop pest species were collected in Umbria, Italy, except for Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae), which was collected in Lazio, Italy, and Murgantia histrionica (Hahn) (Heteroptera: Pentatomidae), which was collected in Beltsville, MD, USA

Summary

Introduction

Polygalacturonases (PGs; EC 3.2.1.15) are hydrolytic enzymes belonging to the large group of pectinases and involved in the degradation of pectin, one of the major components of plant cell wall. The presence of PGs in insects has been known since the late 50s These enzymes are associated with feeding in both piercing-sucking (Adams & McAllan, 1956; Laurema & Nuorteva, 1961; Strong & Kruitwagen, 1968; Strong, 1970; Miles, 1972; Laurema et al, 1985; Ma et al, 1990; Agblor et al, 1994; Cohen & Wheeler, 1998; Miles, 1999; Agusti & Cohen, 2000; Cherqui & Tjallingii, 2000; Boyd et al, 2002; Shen et al, 2003; D’Ovidio et al, 2004; Shackel et al, 2005) and chewing species (Shen et al, 1996; Doostdar et al, 1997; Girard & Jouanin, 1999; Shen et al, 2003), and appear to play an important role in insect-plant interactions. Its function is thought to be related to the weakening of cell walls of root tissue during nematode penetration and intercellular migration (Jaubert et al, 2002)

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