title: Silencing of subfamily I of protein phosphatase 2A catalytic subunits results in activation of plant defense responses and localized cell death.
abstract: The central importance of protein phosphorylation in plant defense responses has been demonstrated by the isolation of several disease-resistance genes that encode protein kinases. In addition, there are many reports of changes in protein phosphorylation accompanying plant responses to pathogens. In contrast, little is known about the role of protein dephosphorylation in regulating plant defenses. We report that expression of the LePP2Ac1 gene, which encodes a catalytic subunit of the heterotrimeric protein phosphatase 2A (PP2Ac), is rapidly induced in resistant tomato leaves upon inoculation with an avirulent strain of Pseudomonas syringae pv. tomato. By analysis of PP2Ac gene sequences from several plant species, we found that PP2Ac genes cluster into two subfamilies, with LePP2Ac1 belonging to subfamily I. Virus-induced gene silencing (VIGS) in Nicotiana benthamiana was used to suppress expression of genes from subfamily I and not from subfamily II. The PP2Ac-silenced plants had greatly decreased PP2A activity, constitutively expressed pathogenesis-related (PR) genes, and developed localized cell death in stems and leaves. In addition, the plants were more resistant to a virulent strain of P. syringae pv. tabaci and showed an accelerated hypersensitive response (HR) to effector proteins from both P. syringae and the fungal pathogen, Cladosporium fulvum. Thus, catalytic subunits of PP2Ac subfamily I act as negative regulators of plant defense responses likely by de-sensitizing protein phosphorylation cascades.
authors.affiliation: Boyce Thompson Institute for Plant Research, Tower Rd., Ithaca, NY 14853-1801, USA.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: He
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Anderson
authors.forename: Olga
authors.initials: O
authors.lastname: del Pozo
authors.forename: Yong-Qiang
authors.initials: YQ
authors.lastname: Gu
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Tang
authors.forename: Gregory B
authors.initials: GB
authors.lastname: Martin
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D001483:Base Sequence; D017931:DNA Primers; D020868:Gene Silencing; D018551:Solanum lycopersicum / Q000201:enzymology / Q000235:genetics; D008969:Molecular Sequence Data; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D010935:Plant Diseases / Q000235:genetics; D018515:Plant Leaves / Q000201:enzymology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D054648:Protein Phosphatase 2; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D017931:DNA Primers; D010940:Plant Proteins; D021122:Protein Subunits; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2