A Genome-Wide, Mapped Algal Mutant Library Enables High-Throughput Genetic Studies in a Photosynthetic Eukaryote

Photosynthetic organisms provide food and energy for nearly all life on Earth, yet half of their genes remain uncharacterized. Characterization of gene functions could be greatly accelerated by new genetic resources in unicellular model organisms. We have generated a genome-wide, indexed library of mapped insertion mutants for the unicellular alga Chlamydomonas reinhardtii, which includes disruptions in 83% of nuclear genes. The abundance of individual mutants can be tracked with unique DNA barcodes, allowing the library to be screened as a pool. We demonstrated the power of this platform by performing a genome-wide screen that identified 3,109 mutants with defects in photosynthetic growth. Multiple alleles allowed identification of 44 genes required for photosynthesis, 21 of which are novel. Characterization of one of these genes, CPL3, showed it is important for photosystem I activity. The availability of the 62,389 mutants in our library will accelerate characterization of gene functions in photosynthetic eukaryotes.