Physiological basis of the white gene in the southern green stink bug (Nezara viridula L.)

In Drosophila, the protein subunit encoded by white is needed to form a functional ATP-binding cassette (ABC) transporter that loads up their eye pigment granules with pigment precursors. Null mutations of white orthologs often generate white-eyed insects lacking pigmentation in their eyes, which provides a helpful phenotype to evaluate the efficiency of genetic transformation methods. We previously identified an ortholog of the white gene in the southern green stink bug (SGSB) Nezara viridula L and demonstrated through RNA interference-based experiments that white transcript knockdown in this species was not lethal and changed their eyes and integumental color pattern. Further investigations were performed to determine the physiological basis of white transcript knockdown on the pigmentation of the SGSB. Following injection of white dsRNA, levels of the ommochrome precursors tryptophan, kynurenine and 3-hydroxy-DL-kynurenine were compared between white and wild type phenotypes of adults and first instar nymphs of the SGSB. Additionally, we compared the same treatment groups for the expression of other genes (vermilion and cinnabar) involved in the ommochrome pathway and for the levels of riboflavin. The impact of white transcript knockdown on the pathway for the conversion of tryptophan to ommochromes in the SGSB was confirmed and a potential function of white in the transport of riboflavin in this species will be discussed.