Enhancing photosynthesis under salt stress via directed evolution in cyanobacteria

Area of Science:

• Photosynthesis research
• Plant stress physiology
• Synthetic biology

Background:

• Improving photosynthesis is crucial for crop yield, especially under environmental stress like salt.
• Salt stress combined with high light severely impacts cyanobacteria and crop plants.
• Genetic modifications are needed for salt tolerance without compromising photosynthetic efficiency.

Purpose of the Study:

• To identify genetic traits for enhanced photosynthesis under salt stress using accelerated evolution in cyanobacteria.
• To investigate mutations conferring salt tolerance and improved photosynthetic performance.
• To explore the evolutionary relevance of these traits in photosynthetic organisms.

Main Methods:

• Applied accelerated evolution in Synechococcus elongatus PCC 7942 by suppressing the methyl-directed mismatch repair system.
• Screened over 10,000 mutants to isolate strains with improved biomass or sucrose productivity under salt stress.
• Utilized genome sequencing to identify genetic variations, including single nucleotide polymorphisms and indels, in selected mutants.

Main Results:

• Isolated 8 mutant strains exhibiting increased biomass or sucrose productivity under salt stress.
• Identified specific mutations in the photosystem II (PSII) D1-encoding gene (L353F, I358N, H359N) at the precursor-D1 (pD1) protein carboxyl terminus.
• Observed improved photosynthetic performance under combined salt and light stress, potentially due to accelerated D1 maturation during PSII repair.

Conclusions:

• Accelerated evolution is effective in generating beneficial genetic traits for photosynthesis under stress.
• Mutations in the pD1 protein enhance photosynthesis and productivity in cyanobacteria under salt stress.
• These findings highlight the potential of evolutionary insights for improving crop photosynthesis in fluctuating environments.