The evolution and functional divergence of 10 Apolipoprotein D‐like genes in Nilaparvata lugens

Abstract Apolipoprotein D (ApoD), a member of the lipocalin superfamily of proteins, is involved in lipid transport and stress resistance. Whereas only a single copy of the ApoD gene is found in humans and some other vertebrates, there are typically several ApoD‐like genes in insects. To date, there have been relatively few studies that have examined the evolution and functional differentiation of ApoD‐like genes in insects, particularly hemi‐metabolous insects. In this study, we identified 10 ApoD‐like genes ( NlApoD1−10 ) with distinct spatiotemporal expression patterns in Nilaparvata lugens (BPH), which is an important pest of rice. NlApoD1−10 were found to be distributed on 3 chromosomes in a tandem array of NlApoD1 / 2 , NlApoD3−5 , and NlApoD7 / 8 , and show sequence and gene structural divergence in the coding regions, indicating that multiple gene duplication events occurred during evolution. Phylogenetic analysis revealed that NlApoD1−10 can be clustered into 5 clades, with NlApoD3−5 and NlApoD7/8 potentially evolving exclusively in the Delphacidae family. Functional screening using an RNA interference approach revealed that only NlApoD2 was essential for BPH development and survival, whereas NlApoD4 / 5 are highly expressed in testes, and might play roles in reproduction. Moreover, stress response analysis revealed that NlApoD3−5/9 , NlApoD3−5 , and NlApoD9 were up‐regulated after treatment with lipopolysaccharide, H 2 O 2 , and ultraviolet‐C, respectively, indicating their potential roles in stress resistance.