Post‐harvest light treatment increases expression levels of recombinant proteins in transformed plastids of potato tubers

Plastid genetic engineering represents an attractive system for the production of foreign proteins in plants. Although high expression levels can be achieved in leaf chloroplasts, the results for non‐photosynthetic plastids are generally discouraging. Here, we report the expression of two thioredoxin genes (trx f and trx m) from the potato plastid genome to study transgene expression in amyloplasts. As expected, the highest transgene expression was detected in the leaf (up to 4.2% of TSP). The Trx protein content in the tuber was approximately two to three orders of magnitude lower than in the leaf. However, we demonstrate that a simple post‐harvest light treatment of microtubers developed in vitro or soil‐grown tubers induces up to 55 times higher accumulation of the recombinant protein in just seven to ten days. After the applied treatment, the Trx f levels in microtubers and soil‐grown tubers increased to 0.14% and 0.11% of TSP, respectively. Moreover, tubers stored for eight months maintained the capacity of increasing the foreign protein levels after the light treatment. Post‐harvest cold induction (up to five times) at 4°C was also detected in microtubers. We conclude that plastid transformation and post‐harvest light treatment could be an interesting approach for the production of foreign proteins in potato.