Experimental evolution in photoautotrophic microorganisms as a means of enhancing chloroplast functions.

The term 'experimental evolution' refers to short-term evolutionary experiments with microorganisms under controlled conditions in which selection is expected to occur. In combination with whole-genome sequencing and genetic engineering, the method has become a powerful tool to study evolutionary mechanisms and engineer new microbial variants. It has been most extensively used in the model species Escherichia coli and Saccharomyces cerevisiae, but more recently photosynthetic microorganisms have been subjected to experimental evolution. In such assays, strains were generated that had become more tolerant to certain abiotic environmental factors or evolved new traits during co-propagation with other organisms. These strains were viable under conditions that were lethal to the non-adapted progenitor and in a few cases, the causative mutations were identified. Because cyanobacteria like Synechocystis or green algae like Chlamydomonas reinhardtii share many features with crop plants - which are not amenable to such experiments - experimental evolution with photosynthetic microorganisms has the potential to identify novel targets for improving the capacity of plants to acclimate to environmental change. Here, I provide a survey of the experiments performed so far in cyanobacteria and green algae, focusing on Synechocystis and C. reinhardtii, and discuss the promise and the challenges of such approaches.