75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

401 Auxin stimulates serine phosphorylation of enolase in Arabidopsis roots
Tingfang Yi, Gaofeng Dong, Zenglan Wang, Jiaxu Li
Department of Biochemistry and Molecular Biology, Mississippi State University, Mississippi State, MS 39762
Protein phosphorylation plays an important role in auxin signaling. In order to identify phosphoproteins regulated
by IAA (indole-3-acetic acid), proteins from Arabidopsis roots were separated by two-dimensional gel electrophoresis,
probed with phosphoserine specific antibodies, and identified by tandem mass spectrometry. Enolase was identified as
one of the phosphoproteins stimulated by IAA. Knockout mutant of enlase exhibited defective root development. The
phenotype of enolase mutant could be partially restored to the wild-type phenotype by application of exogenous IAA.
Together, these results suggest that enolase may be critical in regulating auxin homeostasis.
402 SPY Intracellular Site of Action in the Regulation of GA and Cytokinin Responses
Inbar Maymon, David Weiss
The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food and
Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot, Israel
The Arabidopsis SPINDLY (SPY) protein is a negative regulator of gibberellin (GA) responses. We have shown
previously that spy inhibits cytokinin responses and suggested that the protein acts as a positive regulator of cytokinin
signaling. The SPY protein exhibits significant similarity to animal TPR-containing serine and threonine-O-linked N-
acetylglucosamine (O-GlcNAc) transferase (OGT) enzymes. Similar to animal OGTs, SPY is present in both the nucleus
and cytosol. We found that SPY intracellular localization is not affected by GA or cytokinin. To assess whether SPY's
cytosolic/nuclear localization is required for the regulation of GA or cytokinin responses, we generated transgenic
Arabidopsis spy-3 plants expressing a SPY-glucocorticoid receptor (GR) fusion or SPY with a nuclear export signal
(NES) under the regulation of the CaMV-35S or SPY promoters. Transgenic spy-3 plants expressing SPY-GR and SPY-
NES (homozygous lines) were tested for complementation. All transgenic spy-3 lines expressing SPY-NES exhibited
wild type phenotypes (e.g., sensitivity to the GA-biosynthesis inhibitor paclobutrazol, leaf serration and dark leaves).
Similarly, transgenic lines expressing SPY-GR exhibited a wild type phenotype without the addition of dexamethasone
(DEX). Furthermore, both SPY-NES and SPY-GR (without DEX) lines, exhibited wild type sensitivity to cytokinin. Our
preliminary results show that DEX treatment of the GR lines display partial spy-3 phenotypes. These results suggest that
SPY acts in the cytosol to regulate both GA and cytokinin responses.