Genetic Approach of Molecular Farming | Biotechnology

In this article we will discuss about the genetic approach of molecular farming.

One of the key objectives in molecular farming is the production of recombinant proteins at high yields. To accomplish high yield, expression construct must optimise every stages of gene expression, i.e., from transcription to protein stability.

For high-level transcription, pro­moter and poly adenylation site, which are often derived from 19S and 35S of cauliflower mo­saic virus is required in Franssinic strategy. Due to its lower activities in monocots, plants ubiquitin-1 promoters are preferred.

In addition, presence of intron in the 5′ untranslated re­gion of the expression vector has shown to increase transcription rate in monocots. This phe­nomenon is known as intron mediated enhancement. For specific tissue expression pattern, particularly to seeds, potato tubers etc., tissue specific promoter like Zein gene promoter, wheat glutenin and pea legumin promoters are commonly employed.

There have been reports on the discrimination of transgene expression due to different codon bias exhibited by plant, which can be corrected by increasing GC content in the transgene as preferred by plant codon usage and also introducing silent mutation in the coding region by site directed mutagenesis.

Another factor governing the yield of recombinant protein is organellar targetting, which facilitates folding, assembly and post translational modification. Endoplasmic reticulum is one such site in the cell for the production of functional protein due to the lack of protease, and the abundance of molecular chaperons which are important for correct protein folding and assem­bly.

Besides, protein glycosylation occurs only in the endoplasmic membrane system. Antibodies targeted to the secretary pathway using either plant or animal N-terminal signal peptides usually accumulate at high level than those of antibodies expressed in cyto­plasm.

The stability of antibodies in the apoplast is lower than in lumen of the ER. Therefore, antibody expression level can be increased even further of the protein is passed to the ER lumen using H/KDELC terminal tetrapeptide tag.

There are several other factors that influence transgene expression that includes posi­tion of transgene integration, to structure of the transgene locus, gene-copy number and to presence of truncated or rearranged transgene copies.