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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Complex Signaling Network in Regulation of Adenosine 5'-Phosphosulfate Reductase by Salt Stress in Arabidopsis Roots^1,[W]

Department of Metabolic Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom

Sulfur-containing compounds play an important role in plant stress defense; however, only a little is known about the molecular mechanisms of regulation of sulfate assimilation by stress. Using known Arabidopsis (Arabidopsis thaliana) mutants in signaling pathways, we analyzed regulation of the key enzyme of sulfate assimilation, adenosine 5'-phosphosulfate reductase (APR), by salt stress. APR activity and mRNA levels of all three APR isoforms increased 3-fold in roots after 5 h of treatment with 150 mM NaCl. The regulation of APR was not affected in mutants deficient in abscisic acid (ABA) synthesis and treatment of the plants with ABA did not affect the mRNA levels of APR isoforms, showing that APR is regulated by salt stress in an ABA-independent manner. In mutants deficient in jasmonate, salicylate, or ethylene signaling, APR mRNA levels were increased upon salt exposure similar to wild-type plants. Surprisingly, however, APR enzyme activity was not affected by salt in these plants. The same result was obtained in mutants affected in cytokinin and auxin signaling. Signaling via gibberellic acid, on the other hand, turned out to be essential for the increase in APR mRNA by salt treatment. These results demonstrate an extensive posttranscriptional regulation of plant APR and reveal that the sulfate assimilation pathway is controlled by a complex network of multiple signals on different regulatory levels.

² Present address: Professional Development, Loughborough University, Loughborough LE11 3TU, UK.

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: Stanislav Kopriva (stanislav.kopriva{at}bbsrc.ac.uk).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.113175

^* Corresponding author; e-mail stanislav.kopriva{at}bbsrc.ac.uk.

Received November 14, 2007; accepted January 16, 2008; published January 24, 2008.