Knockout of <i>DOPA decarboxylase</i> induces complete albinism in <i>Spodoptera frugiperda</i>

Dopa decarboxylase (DDC) is a crucial enzyme that regulates melanin synthesis and plays an essential role in cuticular pigmentation and insect development. However, the function of DDC in the fall armyworm, Spodoptera frugiperda, is not yet well understood. In this study, we knocked out the DDC gene and found that mosaic mutants displayed an albino phenotype across all life stages, including larval, pupal, and adult stages. Notably, homozygous DDC mutants showed complete larval albinism, exhibited developmental delays, and frequently failed to pupate, ultimately leading to death. Histological analyses revealed that tissue remodeling during metamorphosis was disrupted and became disorganized. A few individuals survived to adulthood, but they developed severely curled forewings. To clarify the molecular basis of these phenotypes, we performed a transcriptomic analysis and found that DDC influences pigmentation by regulating melanin-related and pteridine-related metabolic pathways. Additionally, DDC disruption altered the expression of genes involved in chitin metabolism and cuticular proteins, and affected the juvenile hormone and ecdysone signaling pathways. Overall, these results provide the first evidence that DDC is critical for pigmentation and development in S. frugiperda and shed new light on the molecular mechanisms underlying body color formation.