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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The Role of Annexin 1 in Drought Stress in Arabidopsis^1,[W]

Institute of Biochemistry and Biophysics, Polish Academy of Sciences, 02–106 Warsaw, Poland (D.K.-P., G.G., J.D., K.F., B.F., J.H.); and Molecular, Cell, and Developmental Biology, University of Texas, Austin, Texas 78712 (G.C., A.C., S.R.)

Annexins act as targets of calcium signals in eukaryotic cells, and recent results suggest that they play an important role in plant stress responses. We found that in Arabidopsis (Arabidopsis thaliana), AnnAt1 (for annexin 1) mRNA levels were up-regulated in leaves by most of the stress treatments applied. Plants overexpressing AnnAt1 protein were more drought tolerant and knockout plants were more drought sensitive than ecotype Columbia plants. We also observed that hydrogen peroxide accumulation in guard cells was reduced in overexpressing plants and increased in knockout plants both before and after treatment with abscisic acid. Oxidative protection resulting from AnnAt1 overexpression could be due to the low level of intrinsic peroxidase activity exhibited by this protein in vitro, previously linked to a conserved histidine residue found in a peroxidase-like motif. However, analyses of a mutant H40A AnnAt1 protein in a bacterial complementation test and in peroxidase activity assays indicate that this residue is not critical to the ability of AnnAt1 to confer oxidative protection. To further examine the mechanism(s) linking AnnAt1 expression to stress resistance, we analyzed the reactive S3 cluster to determine if it plays a role in AnnAt1 oligomerization and/or is the site for posttranslational modification. We found that the two cysteine residues in this cluster do not form intramolecular or intermolecular bonds but are highly susceptible to oxidation-driven S-glutathionylation, which decreases the Ca²⁺ affinity of AnnAt1 in vitro. Moreover, S-glutathionylation of AnnAt1 occurs in planta after abscisic acid treatment, which suggests that this modification could be important in regulating the cellular function of AnnAt1 during stress responses.

The authors 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) are: Dorota Konopka-Postupolska (konopka{at}ibb.waw.pl) and Greg Clark (gbclark{at}uts.cc.utexas.edu).

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

www.plantphysiol.org/cgi/doi/10.1104/pp.109.135228

^* Corresponding author; e-mail konopka{at}ibb.waw.pl.

Received January 13, 2009; accepted May 18, 2009; published May 29, 2009.

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