RNA interference and functional characterization of a tergal gland alpha amylase in the German cockroach, Blattella germanica L.

German cockroach males possess tergal glands that secrete a combination of oligosaccharides, lipids and proteins. Four major proteins occur in the secretion, with one being the 63 kDa alpha-amylase Blattella germanica Tergal Gland protein-1 (BGTG-1). Denaturing and starch gel electrophoresis coupled with peptide sequencing verified amylase activity for the BGTG-1 protein. BGTG-1 gene expression profiles were determined by using quantitative real-time PCR to compare messenger RNA abundance among isolated tissues of males, females and gravid females. Differences in BGTG-1 gene expression occurred among male tissues, with tergal gland tissue showing the highest expression. Tissues of nongravid and gravid females had significantly lower expression in comparison with male tergal glands (gravid females lowest). RNA interference (RNAi) was used to silence BGTG-1 gene expression by injecting BGTG-1 homologous double-stranded RNA (dsRNA) into male cockroaches. Groups injected with BGTG-1 dsRNA showed ∼90% lower BGTG-1 gene and protein expression compared to controls, which correlated with lower amylase activity in colorimetric assays. However, behavioural assays comparing precopulatory behaviour and mating success between RNAi and control males did not reveal differences. These results connect amylase gene expression and activity in tergal gland tissue but suggest other factors, such as other tergal gland components, may contribute more strongly to mating success.