Poster: Late and Moved Abstracts

Abs # 1438: Protein Ser/Thr phosphatase PP7: A new player in plant signaling

Presenter:	Andreeva, Alexandra V, andreeva@mail.wsu.edu
Authors	Andreeva, Alexandra V (A) (B)  Evans, David E (B)   Hawes, Chris R (B)   Solovieva, Olga V (C) (D)  Kakuev, Dmitry L (D)   Bennett, Nelly  (C)   Kutuzov, Mikhail A (B) (C)
Affiliations:	(A): School of Molecular Biosciences, Washington State University, Pullman, US (B): Res. School of Biological & Molecular Sciences, Oxford Brookes University, UK (C): Departement de Biologie Moleculaire et Structurale, C.E.A.-Grenoble, France (D): Shemyakin Institute of Bioorganic Chemistry, Moscow, Russia

We have recently identified a novel group of plant protein Ser/Thr phosphatases, termed PP7 (see also poster 1469). PP7 appear to be plant-specific and are likely to be conserved throughout the land plants. Catalytic domains of PP7 are distantly related to the protein phosphatases PPEF/rdgC found in subsets of sensory neurons in animals. Since PP7 is highly expressed in specialized sensory cells (stomata), we hypothesized that it may function in sensory signaling. Indeed, PP7 was recently found to be a blue light-specific signaling component downstream of chryptochrome (Moller et al., Plant Cell, 2003, 15: 1111-1119). PP7 is likely to be multifunctional. The activity of recombinant PP7 is inhibited by submillimolar concentrations of orthophosphate in a mainly non-competitive manner. Preliminary observations suggest a possibility of redox regulation of PP7. A unique feature of PP7 is the presence of 3 conserved inserts in the catalytic domain, the first one may play an autoinhibitory role, likely by a pseudosubstrate mechanism. On the basis of sequence similarity of the first insert of PP7 to the CaM-binding site of a G protein-coupled receptor kinase, we suggested that PP7 may interact with CaM and confirmed by SPR experiments. Possible identity of PP7 with elusive plant "calcineurin-like" phosphatase will be duscussed. Overexpression of PP7-GFP in tobacco correlates with disturbed leaf development. Transient or stable expression of PP7-GFP fusion protein demonstrates its predominantly nuclear localization, which requires a short region in the C-terminus. Structural and functional conservation of a similar sequence in ubiquitous PP5 phosphatases suggests the existence of a receptor required for nuclear import of these phosphatases, shared by plants and other eukaryotes.