Figure 5.

Insect immune defense modulation by lncRNAs upon microbial attacks. The fungal invasion of insects induced alteration of a myriad of insect lncRNAs, which regulate neighboring genes in cis and trans or act by interacting with miRNAs (sponges) or being miRNA precursors. Those trans-and cis-acting predominantly activate material and energy metabolism processes and cellular and humoral immunity, hence helping in control of the infection (red). lncRNAs inhibit bacterial replication via positive regulation of the Toll pathway, the phagosome pathway, or the metabolism process. However, the latter signaling pathway required more investigation to understand how its deactivation contributes to decreased pathogen replication. Additionally, to avoid immune overactivation after bacterial invasion, insect lncRNAs decoy the critical components of the Toll pathway, lowering the expression of AMPs, thus promoting host immune response homeostasis (yellow). During the viral invasion of insects, insect lncRNAs positively trans-regulate insect genes (PI, ATG3, IBP2, PDC6, etc.) involved in cellular and humoral immune-related pathways (HPV, autophagy, apoptosis, etc.). Viral suppression is also achieved through activation of a noncanonical pathway, as an alternative to compensate the RNAi pathway failure; deployed lncRNAs inhibit both the virulence suppressor of RNAi (VSR) and the ubiquitination of cactin in the nucleus or indirectly target the transcription factor Deaf1 and the RNA polymerase II (RNAPII) for transcription of AMPs to control the viral replication (blue).