Functional analysis of microRNAs in maize responding to feeding stress of the fall armyworm (Spodoptera frugiperda)

The fall armyworm, Spodoptera frugiperda, is a major migratory pest of maize, severely endangering maize yield and food security. To elucidate the molecular mechanism of defense responses of maize to S. frugiperda feeding stress, microRNA (miRNA) transcriptome sequencing was performed using high-throughput sequencing technology on maize leaves consumed by the 3^rd-instar larvae of S. frugiperda, combined with bioinformatics analysis methods for prediction and analysis of miRNAs target genes. The results showed that a total of 500 miRNAs were detected in maize leaves after one day (d) and 3 d of S. frugiperda feeding. After 1 d of feeding induction, 317 miRNAs were differentially expressed, of which 93 miRNAs were specifically detected in maize leaves post 1 d of S. frugiperda feeding. After 3 d of feeding induction, 309 miRNAs were differentially expressed, with 90 miRNAs specifically detected in maize leaves post 3 d of S. frugiperda feeding. A total of 170, 003 target genes were predicted for these differentially expressed miRNAs. These target genes were primarily enriched in categories such as protein binding, DNA binding, and cell nucleus. Furthermore, these genes were mainly enriched in signaling pathways related to inositol phosphate metabolism and gene splicing. The upregulated expression of selected miRNAs in maize leaves at 1 d and 3 d post-S. frugiperda feeding was validated by RT-qPCR, which was consistent with the bioinformatics predictions. This study enhances our understanding of the differential expression of miRNAs and their regulated signaling pathways in maize induced by S. frugiperda feeding, and further reveals the complex regulatory mechanisms mediating insects and host plants interaction. The findings will provide a theoretical basis for the function of miRNAs in regulating insects and host plants interaction and offer new regulatory targets for crop insect resistance.