title: Molecular functions of the PP2A regulatory subunit Tap46 in plants.
abstract: Tap42/α4 is a regulatory subunit of the protein phosphatase 2A (PP2A) family of phosphatases and plays a role in the target of rapamycin (TOR) pathway that regulates cell growth, ribosome biogenesis, translation and cell cycle progression in both yeast and mammals. We determined the cellular functions of Tap46, the plant homolog of Tap42/α4, in both Arabidopsis thaliana and Nicotiana benthamiana. Tap46 associated with the catalytic subunits of PP2A and the PP2A-like phosphatases PP4 and PP6 in vivo. Tap46 was phosphorylated by TOR in vitro, indicating that Tap46 is a direct substrate of TOR kinase. Tap46 deficiency caused cellular phenotypes that are similar to TOR-depletion phenotypes, including repression of global translation and activation of both autophagy and nitrogen recycling. Furthermore, Tap46 depletion regulated total PP2A activity in a time-dependent manner similar to TOR deficiency. These results suggest that Tap46 acts as a positive effector of the TOR signaling pathway in controlling diverse metabolic processes in plants. However, Tap46 silencing caused acute cell death, while TOR silencing only hastened senescence. Furthermore, mitotic cells with reduced Tap46 levels exhibited chromatin bridges at anaphase, while TOR depletion did not cause a similar defect. These findings suggest that Tap46 may have TOR-independent functions as well as functions related to TOR signaling in plants.
authors: Department of Biology, Yonsei University, Seoul, Korea.
authors: Chang Sook
authors: CS
authors: Ahn
authors: Ho-Seok
authors: HS
authors: Lee
authors: Hyun-Sook
authors: HS
authors: Pai
references: EMBO J. 1999 May 17;18(10):2782-92
references: 10329624
references: EMBO Rep. 2007 Sep;8(9):864-70
references: 17721444
references: Science. 2004 Oct 22;306(5696):695-8
references: 15499020
references: Curr Top Microbiol Immunol. 2004;279:19-38
references: 14560949
references: Trends Cell Biol. 2009 Oct;19(10):531-41
references: 19734049
references: Biochem Biophys Res Commun. 1998 Jun 29;247(3):827-32
references: 9647778
references: Nat Rev Mol Cell Biol. 2003 Feb;4(2):117-26
references: 12563289
references: Curr Biol. 2007 Feb 20;17(4):293-303
references: 17306545
references: Nature. 2006 May 4;441(7089):46-52
references: 16541025
references: Curr Biol. 2002 Sep 3;12(17):1448-61
references: 12225660
references: EMBO J. 2006 Aug 9;25(15):3546-55
references: 16874307
references: Trends Cell Biol. 2005 Jun;15(6):285-7
references: 15953545
references: Cell. 2007 Jan 12;128(1):115-27
references: 17218259
references: Curr Genet. 2010 Feb;56(1):1-32
references: 20054690
references: Genetics. 2005 Jun;170(2):733-40
references: 15802506
references: Cell. 2006 Feb 10;124(3):471-84
references: 16469695
references: Cell. 1993 Feb 26;72(4):621-33
references: 8382567
references: J Cell Biochem. 2008 Sep 1;105(1):290-300
references: 18543252