Isolation and molecular characterisation of Dunaliella tertiolecta with truncated light-harvesting antenna for enhanced photosynthetic efficiency

Here we report the development of a high-throughput selection protocol using random mutagenesis and live single-cell sorting to isolate cell lines from the algae Dunaliella tertiolecta with reduced chlorophyll content, with the aim to optimise the antenna size for increased photosynthetic efficiency. Two promising cell lines (Ica1 and Ica2) have been isolated that display a truncated light-harvesting antenna, and hence improved photosynthetic energy conversion efficiency by increasing the light intensity at which photosynthesis becomes saturated (I-s). Ica1 and Ica2 differ significantly: the Ica2 phenotype retains an ability to alter its antenna size in response to varying light intensity, whereas Ica1 appears to have lost this ability and is 'locked' to a truncated antenna and high-light phenotype. Despite these clear differences, transcriptomic analysis shows that the expression profiles for differentially expressed nuclear-encoded photosynthetic genes is similar in both Ica1 and Ica2, possibly suggesting underlying mutations in the regulation of photosynthesis are causing the observed changes in phenotype rather than mutations impacting specific components of the photosynthetic apparatus. The combination of approaches presented here offer the capacity to substantially improve photosynthetic efficiency from any microalgal species irrespective of the extent to which it has been characterised genetically or the availability of molecular tools for rational engineering. It thus offers the potential to begin to exploit the huge natural diversity of microalgae for enhanced biomass production.