Sebastian Hoernstein, Buğra Özdemir, Nico Gessel, Alessandra A. Miniera, Bruno Rogalla von Bieberstein, Lars Nilges, Joana Schweikert Farinha, Ramona Komoll, Stella Glauz, Tim Weckerle, Friedrich Scherzinger, Marta Rodríguez-Franco, Stefanie J. Müller-Schüssele, Ralf Reski
- Protein oxidation results from the reaction of amino-acid side chains with reactive oxygen species (ROS) and is partly irreversible. In non-photosynthetic tissues, mitochondria are a main source of ROS, whereas plastids are the major source in photosynthetic tissues. Oxidized proteins suffer from decreased structural integrity and even loss of function, and their accumulation leads to cytotoxic aggregates. In mammals, aggregate formation correlates with aging and is linked to several age-related pathologies. Mammalian proteolytic pathways for clearance of oxidized proteins are under intensive research, while mechanistic insights into this process in plants is scarce. Acylamino acid-releasing (AARE) enzymes are ATP-independent serine proteases, presumably acting on oxidized proteins and operating in a dual exo-/endopeptidase mode. They are found in all domains of life. Here, we investigated AARE enzymes in the moss Physcomitrella and the angiosperm Arabidopsis and identified three homologous nuclear genes in Physcomitrella (PpAARE1-3) and a single nuclear gene in Arabidopsis (AtAARE). Surprisingly, we observed triple localization of the proteins AtAARE and PpAARE1 to plastids, mitochondria and the cytosol in vivo, likely conserved across the plant lineage. This represents an ATP-independent possibility for degradation of oxidized proteins in the major source organelles of ROS in plants, which is distinct to mammals. Combinatorial knockout plants and protein interaction analysis revealed specific interactions of the moss AARE isoforms and functions in progressive aging. Analysis of an AtAARE T-DNA mutant further suggests the evolutionary conservation of AARE function in age-related development.
