Mitochondria and chloroplasts are essential organelles that carry out the fundamental cellular process of respiration and photosynthesis, respectively. Organelles possess their own genomes that are physically separated from the nuclear genes, and mutations in their genome lead to serious consequences on organismal homeostasis and viability e.g. flower sterility in plants and mitochondrial myopathies in humans. However, contrary to the nucleus, methods for the genetic engineering of organellar genomes in multicellular organisms are either lacking or too laborious to be widely applied. Thus, there is a need for the development of such tools. The overall objectif of the project is to establish a new tool for the manipulation of organellar genomes in plants by exploiting the largest family of organelle RNA binding proteins in eukaryotes, the PPR family. We propose to engineer the RNA binding specificity of synthetic PPR tracts to bind specified mRNA genes in Arabidopsis organelles in order to control the expression of their cognate gene targets in vivo. We reported the in vivo functions of a synthetic PPR protein, made of consensus PPR motifs that were designed to bind a sequence near the 5’ end of a transcript in Arabidopsis chloroplasts. We used a functional complementation assay to demonstrate that this protein bound its intended RNA target with specificity in vivo and that it substituted for a natural PPR protein by stabilizing its cognate processed mRNA. Our results showed that synthetic PPRs can be engineered to functionally mimic the class of native PPR proteins that serve as physical barriers against exoribonucleases. Our work provided example for the use of synthetic PPR proteins for the control of organellar gene expression in plants.