5-5.7.3. Regulatory sequences

• The level of gene expression in plastids is predominately determined by regulatory sequences such as promoter as well as 5′UTR elements.
  
  
• Strong promoter is required to ensure high mRNA level for high-level of protein accumulation e.g. rRNA operon (rrn) promoter (Prrn). Most commonly used promoter is CaMV 35S promoter of cauliflower mosaic virus which drives high level of transgene expression in dicots.
  
  
• In plastid expression vectors, a suitable 5′ untranslated region (5′-UTRs) containing a ribosomal binding site (RBS) is an important element.
  
  
• Stability of the transgenic mRNA is ensured by the 5′ UTR and 3′ UTR sequences flanking the transgene. Protein accumulation from the transgene depends on the 5′-UTR inserted upstream of the open reading frame encoding the genes of interest.
  

5-5.8. Applications of chloroplast engineering

Chloroplast transformation can be used in the production of transgenic plants with herbicide resistance, insect resistance, viral resistance, fungal resistance, abiotic and biotic stress tolerance, production of biopharmaceuticals etc. (described in detail in Lecture 1 of Module 6)