Pleiotropic Functions of FoxN1: Regulating Different Target Genes during Embryogenesis and Nymph Molting in the Brown Planthopper

FoxN1 gene belongs to the forkhead box gene family that comprises a diverse group of “winged helix” transcription factors that have been implicated in a variety of biochemical and cellular processes. In the brown planthopper (BPH), FoxN1 is highly expressed in the ovaries and newly laid eggs, where it acted as an indispensable gene through its molecular targets to regulate early embryonic development. Moreover, the results of the RNAi experiments indicated that Nilaparvata lugens FoxN1 (NlFoxN1) exhibited pleiotropism: they not only affected the embryogenesis, but also played an important role in molting. RNA-seq and RNAi were further used to reveal potential target genes of NlFoxN1 in different stages. In the eggs, ten downregulated genes were defined as potential target genes of NlFoxN1 because of the similar expression patterns and functions with NlFoxN1. Knockdown of NlFoxN1 or any of these genes prevented the development of the eggs, resulting in a zero hatchability. In the nymphs, NlFoxN1 regulated the expression of a keratin gene, type I cytoskeletal keratin 9 (NlKrt9), to participate in the formation of an intermediate filament framework. Depletion of NlFoxN1 or NlKrt9 in nymphs, BPHs failed to shed their old cuticle during nymph-to-nymph or nymph-to-adult molting and the mortality was almost 100%. Altogether, the pleiotropic roles of NlFoxN1 during embryogenesis and nymph molting were supported by the ability to coordinate the temporal and spatial gene expression of their target genes.

FoxN1基因属于叉头框基因家族，该家族包含一组多样的“翼状螺旋”转录因子，这些转录因子涉及多种生化和细胞过程。在褐飞虱中，FoxN1在卵巢和新产的卵中高度表达，它通过其分子靶点作为一个不可或缺的基因来调控早期胚胎发育。此外，RNA干扰实验结果表明褐飞虱FoxN1（NlFoxN1）表现出多效性：它们不仅影响胚胎发生，而且在蜕皮过程中也起着重要作用。进一步利用RNA测序和RNA干扰来揭示NlFoxN1在不同阶段的潜在靶基因。在卵中，由于与NlFoxN1具有相似的表达模式和功能，10个下调的基因被确定为NlFoxN1的潜在靶基因。抑制NlFoxN1或这些基因中的任何一个都会阻止卵的发育，导致孵化率为零。在若虫中，NlFoxN1调节角蛋白基因I型细胞骨架角蛋白9（NlKrt9）的表达，以参与中间丝框架的形成。若虫中NlFoxN1或NlKrt9缺失时，褐飞虱在若虫与若虫之间或若虫到成虫蜕皮过程中无法蜕去旧表皮，死亡率几乎为100%。总之，NlFoxN1在胚胎发生和若虫蜕皮过程中的多效性作用通过其协调靶基因的时空基因表达的能力得以证实。