Molecular cloning and characterization of a phenylalanine hydroxylase from the common cutworm Spodoptera litura

In the present study, a phenylalanine hydroxylase (PAH) was cloned and characterized from the common cutworm Spodoptera litura (SlPAH). The SlPAH gene is an 1863bp full-length cDNA with a 1371bp open reading frame that encodes a predicted 52.35kDa protein of 457 amino acid residues with an isoelectric point of 5.39. The SlPAH gene contains 6 exons and 5 introns. A multiple sequence analysis of SlPAH showed an 88–68% sequence identity to Papilio xuthus PAH and other insect PAHs. A phylogenetic tree revealed that SlPAH is a novel member of the PAH family. Tissue distribution analyses indicated that SlPAH is constitutively expressed in the epidermis, midgut, and fat body, with the highest expression occurring in the fat body on days 2 and 3 of the sixth-instar larval stage and day 1 of the prepupa stage. However, RNAi-mediated SlPAH gene silencing had no observable phenotype in S. litura larvae. Additionally, SlPAH expression is acutely up-regulated in the fat body after injection with Bacillus thuringiensis, Escherichia coli, or Beauveria bassiana. Therefore, these results provide a molecular basis for the functional roles of SlPAH during development and the innate immune response in S. litura.