phytanoyl-CoA dioxygenase domain-containing protein 1 plays an important role in egg shell formation of silkworm (Bombyx mori)

Yun7(Ge) is a giant egg mutant found in the silkworm variety Yun7. In comparison with the giant mutant Ge, the eggs of Yun7(Ge) are larger. The number of laid eggs and hatching rate of Yun7(Ge) are reduced, which is not conducive to reproduction. In this work, the target gene controlling giant egg trait is located on the Z chromosome and was determined through genetic analysis. Transcriptome results showed that phytanoyl-CoA dioxygenase domain-containing protein 1 (PHYHD1) on the Z chromosome was silenced, and the 25 chorion genes on chromosome 2 were remarkably downregulated. Sequence analysis showed that the 73.5 kb sequence including the PHYHD1 was replaced by a ~3.0 kb sequence. After knocking out the PHYHD1 by using CRISPR/Cas9, the chorion genes were significantly downregulated. Hence, the silencing of PHYHD1 leads to the downregulation of many chorion protein genes, thus directly causing giant eggs.