PROTEIN PHOSPHATSE 2A IN LIGHT-RELATED REGULATION OF METABOLISM AND DEVELOPMENT

In mammals protein phosphatase 2A (PP2A) is of special interest as a tumor suppressor and importance in cell division. In plants, PP2A is known as a regulator of enzymes in primary metabolism and known for taking part in hormone signal transduction. PP2A consists of a catalytic, scaffolding, and regulatory (B) subunit. In the model plant Arabidopsis there are 17 different genes encoding B subunits. The regulatory B subunits are believed to be important for cellular localization of the PP2A complex, and for determining the role of the different PP2A complexes regarding substrates and physiological functions. We have shown that all three types of PP2A subunits (C2/C5, A2, Btheta) can target peroxisomes in addition to nucleus, cytosol and mitochondria. Using reverse genetics (T-DNA knockout mutants) we showed that PP2A regulates hormone (brassinosteroid) signaling and fatty acid metabolism in Arabidopsis. We also showed that Btheta was important for the response of the plant to bacteria (innate immunity), and for time of flowering. We have cloned several PP2A subunits into vectors for heterologous expression in E. coli, and shown they that they interact with key proteins in cell division (meiosis). Mutants with impaired meiosis due to mutations in PP2A developed polyploidy which resulted in severe various phenotypes.

Protein phosphatase 2A (PP2A) is an important group of protein phosphatases in eukaryotes that accounts for approximately 25% of the total protein phosphatase activity in crude homogenates from several plants. Canonical PP2As are heterotrimeric complexes consisting of a catalytic subunit (C), a scaffolding subunit (A), and a regulatory subunit (B). The regulatory B subunits play an important role in conferring substrate specificity to the full complex and determining subcellular localization of PP2As in m ammals. In Arabidopsis at least 17 different genes encoding B subunits are present, but their physiological role and targets are hardly known. This project will contribute to the molecular understanding of networks involving protein phosphatase 2A in regu lation of a) nitrogen assimilation and b) flowering time; both these subjects are of profound academic, environmental and economic interest.