Diversification of Protein Phosphatase 2A Regulatory Subunits in Plants: Functional and Phylogenetic AnalysisBooker, Matthew AcreatorDeLong, AlisonAdvisorJohnson, MarkReaderHart, AnneReaderWelch, David MarkReaderShiu, Shin-HanReaderBrown University. Department of Molecular Biology, Cell Biology and Biochemistrysponsor2017xviii, 400 p.born digitalThesis (Ph. D.)--Brown University, 2017thesesProtein Phosphatase 2A (PP2A) is heterotrimeric enzyme that regulates key signaling pathways in eukaryotes by dephosphorylating target proteins. PP2A enzymes are composed of a structural (A) subunit, catalytic (C) subunit, and regulatory (B) subunit with the latter subunit encoded by three gene families conserved in plants and animals: the B55, B56, and B72 gene families. The gene families that encode these subunits have diversified, largely independently, into multiple isoforms in both plants and animals. Data from mammalian systems indicates that the B subunits – even within the same family – enable PP2A to recognize and target different sets of substrates. However, data from plant systems suggest that B subunits exhibit a mix of functional overlap and specificity. Phylogenetic analysis indicates that expansion of PP2A subunits in both plants and animals was driven by ancient whole genome du/triplication events. Plant B subunit lineages are typically much younger than animal lineages because of the frequency of genome duplication events during plant evolution relative to animals. The ethylene biosynthesis enzyme ACS6 is dephosphorylated by PP2A and in vitro dephosphorylation assays suggest that the B56 B subunit family is responsible, but no single isoform was identified, possibly because plant B56 isoforms are functionally overlapping for this activity. However, functional overlap fails to explain why the B56 gene family in plants is maintained over evolution as a multi-gene family. Computational analyses suggest that plant B56 isoforms do vary, at least subtly, in their affinities for substrates and/or interacting partners. This may enable the B56 family, and possibly the B55 and/or B72 families, to provide finely tuned modulation of PP2A-regulated developmental and environmental response pathways.ethyleneProtein Phosphatase 2Agene expansionACS6EnglishRPB2017061610.7301/Z0SQ8XVVIn CopyrightCollection is open for research.dissertations