The present disclosure generally relates to viral-based expression systems suitable for the production of molecule of interests in recombinant host cells. The disclosure particularly relates to nucleic acid constructs, such as expression vectors, containing a modified arterivirus genome or replicon RNA in which at least some of its original viral sequence has been deleted. Also included in the disclosure are viral-based expression vectors including one or more expression cassettes encoding heterologous polypeptides. In some embodiments, the expression cassettes are configured and positioned at defined locations on the viral genome so as to enable expression of the heterologous polypeptides in a tunable manner.

Disclosed are an rBJ-VVL plasmid, a mutant strain of NADC34-like PRRSV-2 and a preparation method therefor and application thereof. Further disclosed is an NADC34-like PRRSV-2-specific vaccine. In the present disclosure, a modified strain rBJ-VVL with tropism for Marc-145 cells is obtained by precisely mutating an amino acid at positions 91/97/98 of GP2a; the modified virus constructed in the present disclosure can be propagated in Marc-145 cells, cause cytopathic effects and form plaques when inoculated into Marc-145 cells for serial passage; the resulting Marc-145 cell-passaged viruses have an extremely viral load, and a large number of new progeny viruses can be obtained in a short time; and the Marc-145-adapative modified strain cultured in the present disclosure is used to create a first NADC34-like PRRSV-2-specific vaccine.