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

Abstract

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.

Polygalacturonase causes lygus-like damage on plants: cloning and identification of western tarnished plant bug (Lygus hesperus) polygalacturonases secreted during feeding

“…However, Varis et al (1983) concluded that it is not the quality of food that has a decisive influence on the variation of salivary enzyme activities in L. rugulipennis, but rather the inter-and intraspecific variation of activities at the level of isozymes. This information and questions related to the origin of the PG activity found in guts of mirids (Frati et al 2006), emphasize the importance of identifying the enzymes that are actually secreted into the insect's diet. From all the predicted amino acid sequences for the Lhpg4 and Lhpg2 gDNA and cDNA clones (17 sequences total), LhPG4-1gDNA and LhPG2-2cDNA were detected in the collection diet with a 100% probability under the parameters used for protein identification.…”

Duration of feeding and superficial and in-depth damage to soybean seed by selected species of stink bugs (Heteroptera: Pentatomidae)

“…Note that for P. guildinii (Figs 3e,f ) the protein bodies are completely dissolved, suggesting that the deleterious action of salivary enzymes to seed tissues is greater for this bug compared to that for the other species. Salivary pectinases are possibly responsible for the start of tissue damage (Miles & Taylor 1994, Frati et al 2006. Pectinases are known to disrupt the middle lamella of plant cell walls (Batemann & Miller 1966) and cause softening and death of cells surrounding the injured area (Hori 2000).…”

Identification of endo‐ and exo‐polygalacturonase activity in Lygus hesperus (Knight) salivary glands

“…In addition, PvPGIP3 and PvPGIP4 inhibit PG activity in whole insect protein extracts of the mirid bugs L. rugulipennis and Adelphocoris lineolatus (D'Ovidio et al, 2004). Subsequently, Frati et al (2006) found that PG activity in similar whole insect protein extracts from other mirid species (L. pratensis, Orthops kalmi, and Closterotomus norwegicus) was also inhibited by bean PGIPs 3 and 4; however, these mirid PGs were not inhibited by Arabidopsis thaliana or Glycine max PGIPs. D 'Ovidio et al (2004) suggested that the redundancy and sub-functionalization of PGIP genes might be important for the adaptation of plant defenses to pathogenic fungi and phytophagous insects.…”