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Plant Physiology Preview Published on June 30, 2006; 10.1104/pp.106.084681
Received June 8, 2006 Overexpression of a protein phosphatase 2C from Fagus sylvatica L. (FsPP2C2) in Arabidopsis shows phenotypes related with ABA responses and GA biosynthesis
Departamento de Fisiología Vegetal, Centro Hispano-Luso de Investigaciones Agrarias, Facultad de Biología, Universidad de Salamanca, Plaza de los Doctores de la Reina s/n, 37007 Salamanca. Spain * Corresponding author; email: cnicolas{at}usal.es.
A functional ABA (abscisic acid)-induced protein phosphatase type-2C (PP2C) (FsPP2C2) was previously isolated from Fagus sylvatica seeds. Since transgenic work is not possible in beech, in the present study we overexpressed this gene in Arabidopsis thaliana to provide genetic evidence on FsPP2C2 function in seed dormancy and other plant responses. In contrast with other PP2Cs described so far, constitutive expression of FsPP2C2 in Arabidopsis, under the cauliflower mosaic virus (CaMV) 35S promoter, produced enhanced sensitivity to ABA (abscisic acid) and abiotic stress in seeds and vegetative tissues, dwarf phenotype and delayed flowering, and all these effects were reverted by GA3 (gibberellic acid) application. The levels of active GAs (gibberellins) were reduced in 35S:FsPP2C2 plants, although transcript levels of AtGA20ox1 and AtGA3ox1 increased, probably as a result of negative feed-back regulation, while the expression of GASA1 was induced by GAs. Additionally, FsPP2C2 overexpressing plants showed a strong induction of the Responsive to ABA 18 (RAB18) gene. Interestingly, FsPP2C2 contains two nuclear targeting sequences and transient expression assays revealed that ABA directed this protein to the nucleus. While other plant protein phosphatase 2Cs have been shown to act as negative regulators, our results support the hypothesis that FsPP2C2 is a positive regulator of ABA. Moreover, our results indicate the existence of a potential crosstalk between ABA signaling and GA biosynthesis.
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