De Novo Assembly of Cydia pomonella Gonad Transcriptomes Provides Insights into Dosage Compensation and Chromosome Evolution in Lepidoptera

In XX/XY system, dosage compensation plays an important role in equalizing sex-linked expression due to dose difference between males (XY) and females (XX). However for ZZ/ZW system where females are the one baring heterogametic sex chromosomes, compensation effect only seems to be partial for the species examined so far. In this study, we examined dosage compensation in a lepidopteran species, the codling moth Cydia pomonella, by performing RNA seq and de novo assembly of gonad tissues (ovary and testis). According to orthology and inferred synteny to Bombyx mori, over 800 transcripts were mapped to Z chromosome, and expression levels were evaluated between two tissues by FPKM. In ovary, Z chromosome reveals polarized expressions in two segments that correspond to Bombyx chromosome Z and chromosome 15 (an autosome), but displays overall same expression level as autosomes. For the first time we demonstrated an example of complete dosage compensation in ZZ/ZW system. Relationship between chromosome evolution and dosage compensation were also discussed.