Characterization of the Yellow Gene Family in Nilaparvata lugens and Functional Analysis of NlYellow-b.

Members of the yellow gene family encode conserved Yellow proteins with diverse roles in insect pigmentation, cuticle formation, and reproduction, making them promising targets for RNA interference (RNAi)-mediated pest control strategies. However, little is known about their phylogeny and functions in the brown planthopper (Nilaparvata lugens), a devastating rice pest that serves as a vector for viral rice diseases. Here, we identified and characterized 11 yellow genes in N. lugens, which showed distinct structures and expression profiles. Phylogenetic analysis revealed that N. lugens has retained orthologs of yellow-y, -b, -d, -e, -g, -g2, -h, and -x but lacks those of yellow-c and -f, suggesting lineage-specific gene loss. Nine of the eleven NlYellow genes were localized to chromosome 8, with several positioned in close genomic proximity. The clustering of these loci suggests that tandem duplication events contributed to the expansion of the NlYellow gene family. NlYellow-b exhibited the highest transcript levels among all identified NlYellow genes, particularly in the female ovipositor, and functional characterization via RNAi revealed that it is essential for molting, wing development, and female fertility. Knockdown of NlYellow-b in fourth-instar nymphs caused lethal molting defects and wing malformation and significantly reduced offspring production. These findings highlight the dual roles of NlYellow-b in development and reproduction, advance our understanding of yellow gene function in insects and highlight NlYellow-b as a candidate for RNAi-based management of N. lugens.