An improved ARG7-based selection cassette with highly efficient transformation rates and a small size suitable for complex expression constructs

In Chlamydomonas reinhardtii, the ARG7 locus constitutes one of the first and most widely used selection markers. Until now it has been available only as a large, intractable genomic fragment unsuitable for incorporation in complex expression constructs and exhibiting poor transformation efficiency. Here we succeed in significantly improving the ARG7 nuclear marker by placing the short arginosuccinate lyase (ASL) cDNA under its own promoter and 5′ UTR and by including the first ASL intron. We test the new ARG7 marker in three different arginine auxotrophic strains and show highly superior transformation efficiencies compared to the conventional genomic ARG7 marker. The plasmid carrying the shorter ARG7 selection cassette has been deposited at the Chlamydomonas Resource Center under the name pHR11.