Sexual dimorphism in polygalacturonase expression and activity in the salivary gland of Pyrrhocoris apterus L

Phytophagous insects derive nutritional resources by consuming and digesting plant compounds. In order to access the nutritional components the plant cell wall has to be degraded. Pectin is a major component of the plant cell wall. Enzymes that degrade pectin include polygalacturonases (PG). Some insects harbor PGs in their salivary glands (SGs). It is important to understand how PGs are developmentally regulated as well as if there is any sexual dimorphism in their activity. In this study, we examined PG expression and activity in SGs of the firebug Pyrrhocoris apterus as a representative of a monophagous phytophagous insect which feeds by the piercing-sucking mechanism. Our results revealed a sexually dimorphic pattern of expression and activity of PG. In general, a significantly lower expression as well as activity of PG was observed in females compared to males. PG expression and activity peaked in 1-5 day old adults and thereafter declined with age. This coincided with their peak feeding activity. PG expression as well as activity declined significantly upon starvation, but re-feeding for 24h re-established their activity to pre-starvation levels only in females but not in males. Taken together, our study revealed a sexual dimorphism in PG expression and activity in P. apterus. The reason for such dimorphism in an enzyme which is primarily meant to facilitate a feeding strategy is unclear at present. Future work will focus on clarifying the sexually dimorphic role of this enzyme.