Résumé
A defence mechanism based on small RNAs called piRNAs (PIWI-interacting RNAs) has evolved to protect the germline from the deleterious effects of transposon (Tn) mobility in genomes such as mutations, deletions or chromosomal rearrangements. Like other small non-coding RNAs (miRNAs and siRNAs), piRNAs have a specific size range (24-36nt) and interact with proteins of the Argonaute family which they guide to their regulatory targets by homology, typically leading to decrease in their expression. The Argonaute protein family consists of two clades AGO and PIWI, the latter showing genes copy number variations depending on the species. PIWI-interacting RNAs not only regulate Tns but also some genes in the germline, and a somatic piRNA pathway has been discovered and shown to be conserved in 20 species of Arthropods. This somatic regulatory pathway targets transposons but also viruses in some insect species.Biogenesis of piRNAs has been well described in Drosophila. Primary piRNAs are produced by slicing of large RNA precursors transcribed from genomic regions containing remnants of Tn, the piRNA clusters. These primary piRNAs guide a protein of the PIWI family (AUB) to transcripts of TE leading by cleavage to new so called secondary piRNAs. These latter guide another protein of the PIWI clade, AGO3 to cleave piRNA cluster transcripts through an amplification loop called the Ping-Pong loop.Spodoptera frugiperda also called Fall armyworm (FAW) is a Lepidopteran pest of crops, described as two strains with different host-plant range (Fiteni et al., 2022; Pashley and Martin, 1987), the corn strain mostly found on corn, the rice strain associated to grasses. Since publication of their genomes (Gouin et al., 2017), miRNAs genes have been annotated (Gimenez et al., 2021; Mone et al., 2018) but almost nothing is known about the piRNA pathway except that PIWI protein homologs play a role in antiviral response (Xia et al., 2023). We will present a phylogeny of the AGO proteins annotated in Spodoptera frugiperda, their expression pattern in gonadal and non-gonadal tissues, CRISPR-Cas9 edition of one of the genes encoding proteins of the PIWI clade and its cellular localization. We have performed piRNA clusters annotation in the two strains genomes, and identified Long Non-Coding RNAs (LNCR) homologous to TE - putative sources of piRNAs. Regarding the piRNA targets, we have compared transposable elements contents in equivalent genome assemblies of the two strains as well as their regulatory patterns by piRNAs. We will also comment on a choice of cellular genes regulated by piRNAs in Spodoptera frugiperda.Fiteni, E., Durand, K., Gimenez, S., Meagher Jr., R., L., Legeai, F., Kergoat, G., J., Nègre, N., d'Alençon, E., and Nam, K.W. (2022). Host-plant adaptation as a driver of incipient speciation in the fall armyworm ( Spodoptera frugiperda ). Bmc Ecol Evol 22, 133.Gimenez, S., Seninet, I., Orsucci, M., Audiot, P., Nègre, N., Nam, K., Streiff, R., and d'Alençon, E. (2021). Integrated miRNA and transcriptome profiling to explore the molecular determinism of convergent adaptation to corn in two lepidopteran pests of agriculture. BMC Genomics 22, 606.Gouin, A., Bretaudeau, A., Nam, K., Gimenez, S., Aury, J.-M., Duvic, B., Hilliou, F., Durand, N., Montagné, N., Darboux, I., et al. (2017). Two genomes of highly polyphagous lepidopteran pests (Spodoptera frugiperda, Noctuidae) with different host-plant ranges. Scientific Reports 7, 1-12.Mone, Y., Nhim, S., Gimenez, S., Legeai, F., Seninet, I., Parrinello, H., Negre, N., and d'Alencon, E. (2018). Characterization and expression profiling of microRNAs in response to plant feeding in two host-plant strains of the lepidopteran pest Spodoptera frugiperda. BMC Genomics 19, 804.Pashley, D.P., and Martin, J.A. (1987). Reproductive incompatibility between host strains of the fall armyworm (Lepidoptera: Noctuidae). Annals of the Entomological Society of America 80, 731–733.Xia, J.M., Fei, S.G., Wu, H.Y., Yang, Y.F., Yu, W.S., Zhang, M.M., Guo, Y.Y., Swevers, L., Sun, J.C., and Feng, M. (2023). The piRNA pathway is required for nucleopolyhedrovirus replication in Lepidoptera. Insect Science 30, 1378-1392.