The major chloroplast envelope membrane protein E29 is central for the communication between chloroplasts and cytosol. It has been identified as the triose phosphate translocator (TPT) exporting the primary products of the Calvin cycle (i.e., triose phosphates and 3-phosphoglycerate) out of the chloroplast in a strict counter exchange for Pi. To study the in vivo role of the TPT, transgenic potato plants were constructed that have a reduced expression of the TPT at both the RNA and protein level due to antisense inhibition. Chloroplasts isolated from these plants show a 20-30% reduction with respect to their ability to import Pi. The reduced TPT activity leads to a reduction of maximal photosynthesis by 40-60%, to a change in carbon partitioning into starch at the expense of sucrose and amino acids, and to an increase of the leaf starch content by a factor of approximately 3. At early developmental stages the inhibited plants are retarded in growth compared to the wild type.

Riesmeier, J. W., Flügge, U. I., Schulz, B., Heineke, D., Heldt, H. W., Willmitzer, L., & Frommer, W. B. (1993). Antisense repression of the chloroplast triose phosphate translocator affects carbon partitioning in transgenic potato plants. Proceedings of the National Academy of Sciences, 90(13), 6160–6164.