Use of microalgae Chlamydomonas reinhardtii for production of double-stranded RNA against shrimp virus

• Stable transformation of microalgae nuclear genome with dsRNA-expression vector.
• Transgenic microalgae expressing dsRNA specific to shrimp yellow head virus (YHV).
• Microalgae expressing dsRNA-YHV increased shrimp survival after YHV infection.

RNA interference has been proposed to be a promising tool for combating shrimp viruses. Antiviral double-stranded (ds)RNA has been mostly produced in Escherichia coli-expression system because of its high efficiency and inexpensive operations. However, overusing the bacteria may raise concerns regarding public health and environmental contamination, and seeking for a new dsRNA production platform would be alternative for future molecular farming. In this study, we exploited the green microalgae Chlamydomonas reinhardtii to produce dsRNA targeting the lethal shrimp yellow head virus (YHV). The expression plasmid pSL18 for C. reinhardtii was constructed to contain YHV-specific hairpin RNA expression cassette, and the successful assembly of pSL18-YHV was confirmed by PCR and enzymatic digestions. Glass bead method was employed for transformation of C. reinhardtii nuclear genome with pSL18-YHV. Microalgal expression of dsRNA-YHV, approximately 45 ng from 100-mL culture, was detected by qRT-PCR. Oral feeding experiment on postlarval shrimp revealed that the formulated feed with C. reinhardtii expressing dsRNA-YHV, at the ratio of 1 × 108 transformants per gram feed, improved 22% survival rate after YHV challenge. The present study suggests that C. reinhardtii can be bioengineered to produce viral-specific dsRNA for shrimp viral disease control, and the developed qRT-PCR could detect microalgal dsRNA with detection limit of subpicogram.