Molecular antifungal defenses in subterranean termites: RNA interference reveals in vivo roles of termicins and GNBPs against a naturally encountered pathogen

Subterranean termites face strong pathogenic pressures from the ubiquitous soil fungus Metarhizium anisopliae, and rely on innate humoral and cellular, as well as behavioral immune defenses for protection. Reticulitermes termites secrete antifungal enzymes that exhibit strong β-1,3-glucanase activity associated with Gram-negative bacteria binding proteins (GNBPs), which prevent M. anisopliae from invading the hemocoel where it can evade immune responses. Molecular evolutionary studies of Reticulitermes termicin genes, which code for defensin-like antifungal peptides, suggest that these proteins may be important effector molecules in antifungal defenses. In this study we show that the RNAi knockdown of termicin and GNBP2 expression via the ingestion of dsRNA significantly increases mortality in termites exposed to a naturally encountered strain of M. anisopliae. Termicin and GNBP2 knockdown also decrease external cuticular antifungal activity, indicating a direct role for these proteins in an external antifungal defense strategy that depends on the active dissemination of antifungal secretions among nestmates.

► GNBPs and termicins are antifungal proteins in termites.
► These proteins are expressed in the salivary gland and may be externalized on the cuticle.
► RNAi knockdown of termicin and GNBP2 decreased survival after exposure to a naturally encountered fungus.
► RNAi knockdown of termicin and GNBP2 decreased external cuticular antifungal activity.
► Termicins and GNBP2s are important antifungal molecules in subterranean termites.