Novel pathways for glycoprotein import into chloroplasts

Although the chloroplast contains its own genome, majority of its protein components are encoded by nuclear genes and must be imported post-translationally. In general, proteins synthesized by cytosolic ribosomes are post-translationally targeted to the chloroplast through interactions between their N-terminal transit sequence and protein translocon Toc/Tic complexes in the chloroplast membranes. An alternative pathway that mediates post-translational delivery of proteins to the chloroplast via the secretory pathway was recently described. This pathway provides new opportunities for complementation of the chloroplast protein maturation machinery with chaperones needing endoplasmic reticulum and/or Golgi typical maturations such as N-glycosylation for their biological activity or using chloroplasts as a storage compartment for glycoproteins.