Molecular functional analyses of larval adhesion in a highly fouling invasive model ascidian

Successful papillary adhesion is the first essential step for serious ascidian biofouling in marine ecosystems; however, the mechanisms of papillary adhesion have not been fully elucidated. Here, we employed micro-transcriptome sequencing to assess the differentially expressed genes (DEGs) between papillae and remaining body in the larvae of the highly fouling invasive model ascidian Ciona robusta. Enrichment results for DEGs showed that papillae were adhesive structures with the combined functions of substrate recognition, environmental perception, and adhesive protein synthesis and secretion. Two candidate ascidian papilla adhesive proteins (APAPs), APAP-1 and APAP-2, were identified, expressed, and purified in vitro. Surface coating tests showed that APAP-1 was a cohesive protein while APAP-2 was an interfacial protein involved in the adhesion between papillae and material surface. Collectively, the obtained DEGs and adhesive proteins provide candidates to deeply understand molecular mechanisms of underwater adhesion and further develop anti-fouling strategies in marine ecosystems.