The Genetic Network of Forkhead Gene Family in Development of Brown Planthoppers

SIMPLE SUMMARY: Forkhead (Fox) genes encode a family of transcription factors defined by a ‘winged helix’ DNA-binding domain and play important roles in regulating the expression of genes involved in cell growth, proliferation, differentiation and longevity. However, we still lack a comprehensive understanding of the Fox gene family in animals. Here, we take an integrated study, which combines genomics, transcriptomics and phenomics, to construct the Fox gene genetic network in the brown planthopper, Nilaparvata lugens, a major rice pest. We show that FoxG, FoxQ, FoxA, FoxN1, FoxN2 and their potential target genes are indispensable for embryogenesis; FoxC, FoxJ1 and FoxP have complementary effects on late embryogenesis; FoxA, FoxNl and FoxQ are pleiotropism and also essential for nymph molting; FoxT belongs to a novel insect-specific Fox subfamily; and FoxL2 and FoxO are involved in the development of eggshells and wings, respectively. These findings may deepen our overall understanding of the regulatory function of the Fox gene family in insect growth and development, and thus ultimately stimulate the design and development of novel insecticides. ABSTRACT: We identified 18 distinct Fox genes in the genome of the brown planthopper, Nilaparvata lugens, and further found a novel insect-specific subfamily that we temporarily named FoxT. A total of 16 genes were highly expressed in the eggs, while NlFoxL2 and NlFoxT are female- and male-specific genes, respectively. Large scale RNAi and RNA-seq analyses were used to reveal the functions and potential targets of NlFoxs. In the eggs, NlFoxA, NlFoxN1 and NlFoxN2 are indispensable to early embryogenesis by regulating different target genes; NlFoxG and NlFoxQ co-regulate NlSix3 for brain development; and NlFoxC, NlFoxJ1 and NlFoxP have complementary effects on late embryogenesis. Moreover, NlFoxA, NlFoxNl and NlFoxQ have pleiotropism. NlFoxA and NlFoxQ regulate the expression of NlCHS1 and cuticular proteins, respectively, thereby participating in the formation of cuticles. NlFoxN1, which regulates the expression of NlKrt9 is involved in the formation of intermediate filament frameworks. Our previous studies have revealed that NlFoxL2 and NlFoxO play important roles in chorion formation and wing polyphenism. Altogether, N. lugens Fox genes exhibit functional diversity in embryonic development and organogenesis. This comprehensive study combines genomics, transcriptomics and phenomics, thereby constructing a complex genetic network that spans the entire life cycle of the brown planthopper.