Body of Abstract: Peroxisomes are dynamic organelles that perform diverse functions. In plants, peroxisomes are the site of fatty acid β-oxidation and are involved in development, photorespiration, biosynthesis of several phytohormones, and defense against pathogens and herbivores. To perform these metabolic functions, peroxisomes must continuously import newly synthesized proteins from the cytosol. Like the nucleus, peroxisomes can import fully-folded and even oligomeric proteins. The proteins mediating peroxisomal protein import are called peroxins (PEX proteins), and most are conserved among fungi, plants, and mammals. An exception is yeast Pex8, the only peroxin found fully in the lumen of the peroxisome, which is essential for peroxisomal protein import but has not been found outside of fungi. Traditional sequence homology searches failed to identify a Pex8 ortholog in plants or mammals, so we used HHPred software to identify an uncharacterized Arabidopsis thaliana protein with predicted structural similarity to Saccharomyces cerevisiae Pex8. Like yeast Pex8, this protein has a predicted HEAT (Huntingtin, EF3, a-PP2A, TOR1) repeat structure and two peroxisomal targeting signals: PTS1 and PTS2. We found that insertional mutations or CRISPR-derived frameshifts in our candidate gene are lethal when homozygous, as are most null pex mutations in Arabidopsis. Intriguingly, our preliminary evidence suggests CRISPR-induced mutations disrupting the PTS1 enhance the peroxisome-defective phenotypes seen in other pex mutants. Using microscopy of fluorescent reporter fusions, we found this protein localized to puncta associated with peroxisome membranes when both or one PTS is intact, which is consistent with yeast Pex8 peripheral membrane localization. These observations, once paired with localization and interaction analysis in known pex mutants and peroxisome-associated phenotypes of knocked-down PEX8 expression via RNA interference, will determine if the putative Arabidopsis PEX8 is a yeast Pex8 ortholog.