A Family of CSαβ Defensins and Defensin-Like Peptides from the Migratory Locust, <i>Locusta migratoria</i>, and Their Expression Dynamics during Mycosis and Nosemosis
<div><p>Insect defensins are effector components of the innate defense system. During infection, these peptides may play a role in the control of pathogens by providing protective antimicrobial barriers between epithelial cells and the hemocoel. The cDNAs encoding four defensins of the migratory locust, <i>Locusta migratoria</i>, designated LmDEF 1, 3–5, were identified for the first time by transcriptome-targeted analysis. Three of the members of this CSαβ defensin family, LmDEF 1, 3, and 5, were detected in locust tissues. The pro regions of their sequences have little-shared identities with other insect defensins, though the predicted mature peptides align well with other insect defensins. Phylogenetic analysis indicates a completely novel position of both LmDEF 1 and 3, compared to defensins from hymenopterans. The expression patterns of the genes encoding LmDEFs in the fat body and salivary glands were studied in response to immune-challenge by the microsporidian pathogen <i>Nosema locustae</i> and the fungus <i>Metarhizium anisopliae</i> after feeding or topical application, respectively. Focusing on <i>Nosema</i>-induced immunity, qRT-PCR was employed to quantify the transcript levels of <i>LmDEFs</i>. A higher transcript abundance of <i>LmDEF5</i> was distributed more or less uniformly throughout the fat body along time. A very low baseline transcription of both <i>LmDEFs</i> 1 and 3 in naïve insects was indicated, and that transcription increases with time or is latent in the fat body or salivary glands of infected nymphs. In the salivary glands, expression of <i>LmDEF3</i> was 20-40-times higher than in the fat body post-microbial infection. A very low expression of <i>LmDEF3</i> could be detected in the fat body, but eventually increased with time up to a maximum at day 15. Delayed induction of transcription of these peptides in the fat body and salivary glands 5–15 days post-activation and the differential expression patterns suggest that the fat body/salivary glands of this species are active in the immune response against pathogens. The ability of <i>N</i>. <i>locustae</i> to induce salivary glands as well as fat body expression of defensins raises the possibility that these AMPs might play a key role in the development and/or tolerance of parasitic infections.</p></div
