5' UTR introns reduce nuclear transgene silencing and enable robust protein expression in Chlamydomonas reinhardtii.

While Chlamydomonas is a widely used model organism, nuclear transgene expression in this system is well documented to face notorious difficulties. Here, we show that 5' untranslated region (UTR) introns can play a positive role in reducing gene silencing. By screening promoter-5' UTR complexes containing introns (PUTRis) from highly expressed genes, we identify many candidates that outperform the two most widely used promoters, HR and PSAD. Truncation analyses reveal that intron removal increases gene silencing to a similar extent as promoter deletion. These 5' UTR introns promote open chromatin configurations that support gene expression. Leveraging two identified PUTRis, we achieve robust expression of previously recalcitrant Chlamydomonas proteins and visualize the subcellular localization of over 100 such proteins. Taken together, our findings demonstrate the role of 5' UTR introns in reducing gene silencing while providing the research community with molecular tools for algal genetic engineering.