Multifaceted roles ofArabidopsisPP6 phosphatase in regulating cellular signaling and plant development

Abstract

Protein phosphorylation and dephosphorylation mediated by kinases and phosphatases are major reversible post-translational modifications used to regulate many cellular processes. In eukaryotes, up to a third of proteins are regulated by protein phosphorylation. The genomes of eukaryotes encode a large number of kinases and phosphatases. For example, the human genome encodes at least 518 putative protein kinases that can be generally classified into two families: 90 protein tyrosine (Tyr) kinases (PTKs) and 428 protein serine/ threonine (Ser/Thr) kinases (PSKs). [1][2][3] As the exquisite specificity of signaling and the reversible nature of phosphorylation, it would be expected that there are similar numbers of protein phosphatases in the human genome. Surprisingly, however, there are only 107 putative protein Tyr phosphatases (PTPs) 4 and fewer protein Ser/Thr phosphatases (PSPs) (~30) encoded by the human genome.5 In Arabidopsis, there are more than 1000 kinases, 6 of which the PTK-like kinases are around 20 and the PSKs are most abundant.7 However, the Arabidopsis genome only encodes 150 phosphatases, which can be classified into PSPs (125) and PTPs (25). 8Whereas the numbers of PTKs and PTPs roughly match each other in both the human and plant genome, the number of catalytic subunits of PSPs is greatly lower than that of PSKs. This raises a question of how limited phoshatases, especially PSPs, can Reversible protein phosphorylation catalyzed by kinases and phosphatases is a major form of posttranslational regulation that plays a central role in regulating many signaling pathways. While large families of both protein kinases and protein phosphatases have been identified in plants, kinases outnumber phosphatases. This raises the question of how a relatively limited number of protein phosphatases can maintain protein phosphorylation homeostasis in a cell. Recent studies have shown that Arabidopsis FyPP1 (Phytochrome-associated serine/threonine protein phosphatase 1) and FyPP3 encode the catalytic subunits of protein phosphatase 6 (PP6), and that they directly binds to the A subunits of protein phosphatase 2A (PP2AA proteins), and SAL (SAPS domain-like) proteins to form the heterotrimeric PP6 holoenzyme complex. Emerging evidence is suggesting that PP6, acts in opposition with multiple classes of kinases, to regulate the phosphorylation status of diverse substrates and subsequently numerous developmental processes and responses to environmental stimuli.

TYPE-ONE PROTEIN PHOSPHATASE4 Regulates Pavement Cell Interdigitation by Modulating PIN-FORMED1 Polarity and Trafficking in Arabidopsis

“…As a catalytic subunit of protein phosphatase, TOPP4 must bind to different regulatory subunits to form a functional enzyme to participate in multiple signaling pathways (Tian and Wang, 2002). Because the regulatory subunits of phosphatases are dynamic at different developmental stages or in response to various environmental signals (Dai et al, 2013), PP1 and PP6 may respond to different developmental signals in different organs or tissues at various developmental stages. The topp4-1 mutant showed PC defects only in and after the third true leaves, whereas the fypp1 mutant has PC defects in cotyledons and true leaves (Li et al, 2011).…”

Interactome Analysis of the Influenza A Virus Transcription/Replication Machinery Identifies Protein Phosphatase 6 as a Cellular Factor Required for Efficient Virus Replication

“…PP6 regulates the activities of many host proteins (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), and it is therefore possible that PP6 silencing perturbs the virus life cycle by affecting other cellular processes. However, the fact that PP6 interacts directly with the viral RdRP suggests that it plays a direct role in the viral life cycle by regulating the posttranslational modifications of viral proteins.…”

“…PP6 is a member of the PP2A subfamily of protein phosphatases, cellular enzymes that catalyze the liberation of inorganic phosphate from proteins and peptides at serine or threonine residues (22). PP6 is a significant regulator of a number of cellular processes, including chromosome stability and the DNA damage response (23)(24)(25)(26)(27), mitosis and the regulation of cell cycle progression (22,(28)(29)(30)(31), signaling (32,33), pre-mRNA splicing (34), and vesicular trafficking (35). The catalytic subunit PPP6C and the regulatory subunits PPP6R1 and PPP6R3 were found to copurify with the viral RdRP.…”

The PP6 Phosphatase Regulates ABI5 Phosphorylation and Abscisic Acid Signaling inArabidopsis

“…In a recent study, we showed that Arabidopsis FyPP1 (for Phytochrome-associated serine/threonine protein phosphatase1) and FyPP3, two homologous catalytic subunits of PP6, physically interact with SAL (for SAPS-domain like protein) and PP2AA proteins (RCN1/PP2AA1, PP2AA2, and PP2AA3) to form a PP6-type heterotrimeric holoenzyme that directly regulates the phosphorylation status of PIN-FORMED (PIN) proteins (auxin efflux carriers) and subsequently affects auxin efflux and plant development (Dai et al, 2012a(Dai et al, , 2012b. In this study, we extend these findings by showing that FyPP also plays a critical role in regulating ABA signaling in Arabidopsis.…”