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DEVELOPMENT AND HORMONE ACTION

Expression of a Constitutively Activated Plasma Membrane H⁺-ATPase Alters Plant Development and Increases Salt Tolerance^1,[C],[OA]

Unité de Biochimie Physiologique, Institut des Sciences de la Vie, Université catholique de Louvain, B–1348 Louvain-La-Neuve, Belgium

The plasma membrane proton pump ATPase (H⁺-ATPase) plays a major role in the activation of ion and nutrient transport and has been suggested to be involved in several physiological processes, such as cell expansion and salt tolerance. Its activity is regulated by a C-terminal autoinhibitory domain that can be displaced by phosphorylation and the binding of regulatory 14-3-3 proteins, resulting in an activated enzyme. To better understand the physiological consequence of this activation, we have analyzed transgenic tobacco (Nicotiana tabacum) plants expressing either wild-type plasma membrane H⁺-ATPase4 (wtPMA4) or a PMA4 mutant lacking the autoinhibitory domain (PMA4), generating a constitutively activated enzyme. Plants showing 4-fold higher expression of wtPMA4 than untransformed plants did not display any unusual phenotype and their leaf and root external acidification rates were not modified, while their in vitro H⁺-ATPase activity was markedly increased. This indicates that, in vivo, H⁺-ATPase overexpression is compensated by down-regulation of H⁺-ATPase activity. In contrast, plants that expressed PMA4 were characterized by a lower apoplastic and external root pH, abnormal leaf inclination, and twisted stems, suggesting alterations in cell expansion. This was confirmed by in vitro leaf extension and curling assays. These data therefore strongly support a direct role of H⁺-ATPase in plant development. The PMA4 plants also displayed increased salt tolerance during germination and seedling growth, supporting the hypothesis that H⁺-ATPase is involved in salt tolerance.

² These authors contributed equally to this article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Marc Boutry (boutry{at}fysa.ucl.ac.be).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

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www.plantphysiol.org/cgi/doi/10.1104/pp.107.103762

^* Corresponding author; e-mail boutry{at}fysa.ucl.ac.be; fax 32–10–473872.

Received June 12, 2007; accepted June 22, 2007; published June 28, 2007.

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