Fork head transcription factor is required for ovarian mature in the brown planthopper, Nilaparvata lugens (Stal)

Background: The brown planthopper (BPH), Nilaparvata lugens, is the most devastating rice pest in many areas throughout Asia. The reproductive system of female N. lugens consists of a pair of ovaries with 24-33 ovarioles per ovary in most individuals which determine its fecundity. The fork head (Fox) is a transcriptional regulatory molecule, which regulates and controls many physiological processes in eukaryotes. The Fox family has several subclasses and members, and several Fox factors have been reported to be involved in regulating fecundity. Results: We have cloned a fork head gene in N. lugens. The full-length cDNA of N/FoxA is 1789 bp and has an open reading frame of 1143 bp, encoding a protein of 380 amino acids. Quantitative real-time PCR (RT-qPCR) and Reverse Transcription- PCR (RT-PCR) analysis revealed that N/FoxA mRNA was mainly expressed in the fat body, midgut, cuticle and Malpighian tube, and was expressed continuously with little change during all the developmental stages. N/FoxA belongs to the FoxA subfamily of the Fox transcription factors. Knockdown of N/FoxA expression by RNAi using artificial diet containing double-stranded RNA (dsRNA) significantly decreased the number of offspring and impacted the development of ovaries. ELISA and Western blot analyses showed that feeding-based RNAi of N/FoxA gene also resulted in decreased expression of vitellogenin (Vg) protein. Conclusion: N/FoxA plays an important role in regulation of fecundity and development of ovaries in the BPH via regulating vitellogenin expression.