Cloning and functional characterization of PmΔ5FAD in pearl oyster Pinctada fucata martensii

Pinctada fucata martensii produces high-quality pearls. However, excess immune and inflammatory response after grafting operation will lead to nucleus rejection, pearl sac formation failure, and death of the host pearl oyster. Polyunsaturated fatty acids (PUFAs) are critically important for its regulation function in inflammation and their synthesis process was limited by the related enzymes including fatty acid desaturase (FAD). In this study, FAD gene in the pearl oyster was characterized in P. f. martensii (Pm Delta 5FAD). We established that the full-length sequence of Pm Delta 5FAD contained a 1302-bp open reading frame that encoded a sequence of 433 amino acids. Pm Delta 5FAD domain analysis revealed the presence of a distinctive Cyt-b5 domain and a FA-desaturase domain that were highly similar to the Delta 5FAD protein sequences identified in Haliotis discus hannai (69.25%) and Mimachlamys nobilis (62.96%). Pm Delta 5FAD expressed in all detected tissues. Functional analysis of Pm Delta 5FAD in recombinant Saccharomyces cerevisiae yeast showed the existence of Delta 5-desaturation activity, which towards PUFA substrates and it efficiently desaturated exogenous PUFA C20:3n-6 to C20:4n-6 (ARA) with a desaturation conversion rate of 19.49%. Furthermore, Pm Delta 5FAD showed a significantly higher expression level on day 1 after the grafting operation, which may upregulate ARA synthesis in response to inflammatory and immune. These results provide important information concerning the function of FADs during pearl oyster PUFA biosynthesis and grafting operation.

Automated summary

This study characterized the FAD gene in P. f. martensii and found that Pm Delta 5FAD plays an important role in regulating inflammation. Functional analysis showed that Pm Delta 5FAD has Delta 5-desaturation activity towards PUFA substrates and its expression level significantly increases on day 1 after grafting operation.