The invention provides a novel method of controlling gene expression in plastids, using a peptide extension that can be fused to a desired protein, expression cassettes that include the genetic constructs, and plants comprising the novel expression systems. A nucleic acid sequence encoding a peptide extension fused in frame to a protein coding sequence. This genetic construct is subsequently inserted into the chloroplast genome, where the peptide extension increases expression of the fused protein. The present invention further describes the use of this method for increased production of cellulose-degrading enzymes in chloroplasts.