the generation of stable nuclear transformants in microalgae has relied primarily on random genomic integration,intensive screening,and the subsequent isolation of knockout mutants. The identification of disruptions in target loci typically requires the screening of tens of thousands of transformants using suitable activity assays and/or extensive DNA analysis. The ability to generate targeted gene knockouts through homologous recombination (as in yeast and cyanobacteria)has been difficult to achieve in algae.