Plastid engineering of a marine alga, Nannochloropsis gaditana, for co-expression of two recombinant peptides

The purpose of this study was to establish a plastid transformation system for expressing recombinant proteins in Nannochloropsis gaditana. On the basis of the sequenced plastid genome, the homologous flanking region, 16S-trnI/trnA-23S, and the endogenous regulatory fragments containing the psbA promoter, rbcL promoter, rbcL terminator, and psbA terminator were amplified from N. gaditana as elements of a plastid transformation vector. Then, the herbicide resistant gene (bar) was used as a selectable marker, regulated by the psbA promoter and rbcL terminator. Finally, two codon-optimized antimicrobial peptide-coding genes linked by endogenous ribosome binding site (RBS) in a polycistron were inserted into the constructed vector under the regulation of the rbcL promoter and psbA terminator. After microparticle bombardment, the positive clones were detected using polymerase chain reaction (PCR), and Southern and western blotting were used to assess the co-expression of the two antimicrobial peptides from the plastid. Nannochloropsis gaditana showed the potential to express recombinant proteins for biotechnological applications, for example, for the development of oral vaccines in aquaculture.