Postdoctoral Associate Texas A&M University College Station, Texas
Body of Abstract: Telomeres solve the end-replication problem and protect the ends of eukaryotic chromosomes. Recent studies suggest that telomere-associated factors play essential roles in response to extrinsic and intrinsic stress, especially oxidative stress, but such mechanisms are poorly understood. The most conserved telomere protein is Protection of Telomeres 1 (POT1). POT1 functions in telomere replication and chromosome end protection, and it is encoded by a single-copy gene in most organisms, including humans. However, in the Brassicaceae family, which includes Arabidopsis thaliana, POT1 gene duplication gave rise to two functional POT1 paralogs, AtPOT1a, and AtPOT1b. We previously reported that AtPOT1a associates with the telomerase RNP and positively regulates enzyme activity. Here we show that AtPOT1b is not required for canonical telomere-related functions and instead modulates the response to oxidative stress. AtPOT1b is enriched at telomeres when plants are grown without the natural anti-oxidant sucrose. Loss of AtPOT1b results in higher 8-oxoG content at telomeres and stochastic telomere shortening, implying that AtPOT1b association with telomeres mitigates DNA oxidation. In addition, pot1b mutants exhibit a decrease in antioxidant enzyme activities, elevated Reactive Oxygen Species (ROS) accumulation in seeds, roots, leaves, and flowers, as well as DNA hypomethylation and chromatin relaxation. Strikingly, the ancestral single-copy POT1 gene from Physcomitrella patens cannot rescue the telomeric phenotype of an AtPOT1a deficiency, but it can complement the ROS phenotypes of null atpot1b mutants. These findings suggest that POT1 proteins directly regulate redox homeostasis, and this function predates the POT1 duplication in Brassicaceae. Finally, yeast two-hybrid assays and TurboID-based proximity labeling indicate that AtPOT1b interacts with Catalase 2 and peroxidases, suggesting that AtPOT1b interaction with antioxidants may protect the genome from oxidative damage. Altogether, these results imply that redox homeostasis is an evolutionarily conserved function for POT1 proteins that offers a novel mode of genome protection in response to stress.