Atypical Protein Phosphatase 2A Gene Families Do Not Expand via Paleopolyploidization

Abstract

Protein phosphatase 2A (PP2A) presents unique opportunities for analyzing molecular mechanisms of functional divergence between gene family members. The canonical PP2A holoenzyme regulates multiple eukaryotic signaling pathways by dephosphorylating target proteins and contains a catalytic (C) subunit, a structural/scaffolding (A) subunit, and a regulatory (B) subunit. Genes encoding PP2A subunits have expanded into multigene families in both flowering plants and mammals, and the extent to which different isoform functions may overlap is not clearly understood. To gain insight into the diversification of PP2A subunits, we used phylogenetic analyses to reconstruct the evolutionary histories of PP2A gene families in Arabidopsis (Arabidopsis thaliana). Genes encoding PP2A subunits in mammals represent ancient lineages that expanded early in vertebrate evolution, while flowering plant PP2A subunit lineages evolved much more recently. Despite this temporal difference, our data indicate that the expansion of PP2A subunit gene families in both flowering plants and animals was driven by whole-genome duplications followed by nonrandom gene loss. Selection analysis suggests that the expansion of one B subunit gene family (B56/PPP2R5) was driven by functional diversification rather than by the maintenance of gene dosage. We also observed reduced expansion rates in three distinct B subunit subclades. One of these subclades plays a highly conserved role in cell division, while the distribution of a second subclade suggests a specialized function in supporting beneficial microbial associations. Thus, while whole-genome duplications have driven the expansion and diversification of most PP2A gene families, members of functionally specialized subclades quickly revert to singleton status after duplication events.

Methylation of protein phosphatase 2A—Influence of regulators and environmental stress factors

“…The protein phosphatase 2A (PP2A) complex is made up of three types of subunits, a catalytic (C), scaffolding (A), and regulatory (B) subunit. These three classes of building blocks are conserved among eukaryotes, but isoforms within each group have arisen, almost exclusively, after the evolutionary splitting of plants and animals (Booker & DeLong, ; Moorhead, De Wever, Templeton, & Kerk, ). In Arabidopsis, there are 5 C, 3 A, and 17 B subunits, theoretically enabling up to 255 combinations in the PP2A complex.…”

PROTEIN PHOSPHATASE 2A-B′γ Controls Botrytis cinerea Resistance and Developmental Leaf Senescence

“…PP2A forms a heterotrimeric holoenzyme that consists of a catalytic C subunit, a scaffold A subunit, and a variable regulatory B subunit. The Arabidopsis genome encodes five PP2A-C subunits, three A subunits, and 17 B subunits, which are divided into evolutionarily conserved B, B9, and B99 families (Booker and DeLong, 2017). The specificity of PP2As is conferred by the variable PP2A-B subunits, which direct the holoenzymes toward specific target phosphoproteins (Farkas et al, 2007;Moorhead et al, 2009;Sents et al, 2013;Lillo et al, 2014).…”

Has the Polyploid Wave Ebbed?

“…Consider first additional rounds of polyploidy. Hybridization between a tetraploid species and a diploid can yield sterile triploid hybrids, whose unreduced triploid gametes may fuse to produce fertile hexaploids (Ramsey and Schemske, 1998). Or sterile tetraploids from hybridization between chromosomally differentiated tetraploid species can produce unreduced tetraploid gametes which may fuse to produce fertile octaploid individuals.…”

“…Polyploidy can produce the antecedents of new species in one generation (autopolyploidy) or two generations (allopolyploidy) through the production of unreduced gametes or doubled somatic cells (Ramsey and Schemske, 1998;Mason and Pires, 2015). Autopolyploids can arise anywhere in a species' range from single individuals via the formation of unreduced gametes.…”