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Published on October 17, 2008; 10.1104/pp.108.130575

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Received September 30, 2008
Accepted October 14, 2008

Interaction of the WD40 Domain of a Myo-Inositol Polyphosphate 5-Phosphatase with SnRK1 links Inositol, Sugar and Stress Signaling

Elitsa A. Ananieva , Glenda E. Gillaspy *, Amanda Ely , Ryan N. Burnette , and F. Les Erickson

Department of Biochemistry, Virginia Tech, Blacksburg, VA 24061; Department of Biology, Salisbury University, Salisbury, MD 21801

* Corresponding author; email: gillaspy{at}vt.edu.

In plants, myo-inositol signaling pathways have been associated with several stress, developmental and physiological processes, but the regulation of these pathways is largely unknown. In our efforts to better understand myo-inositol signaling pathways in plants, we have found that the WD40 repeat region of a myo-inositol polyphosphate 5-phosphatase, (5PTase13, At1g05630), interacts with the sucrose nonfermenting-1-related kinase (SnRK1.1) in the yeast two-hybrid system and in vitro. Plant SnRK1 proteins (also known as AKIN10 /11) have been described as central integrators of sugar, metabolic, stress and developmental signals. By using mutants defective in 5PTase13, we show that 5PTase13 can act as a regulator of SnRK1 activity, and that regulation differs with different nutrient availability. Specifically, we show that under low nutrient or sugar conditions 5PTase13 acts as a positive regulator of SnRK1 activity. In contrast, under severe starvation conditions, 5PTase13 acts as a negative regulator of SnRK1 activity. To delineate the regulatory interaction that occurs between 5PTase13 and SnRK1.1, we used a cell free degradation assay and found that 5PTase13 is required to reduce the amount of SnRK1.1 targeted for proteasomal destruction under low nutrient conditions. This regulation most likely involves a 5PTase13:SnRK1.1 interaction within the nucleus, as a 5PTase13:green fluorescent protein was localized to the nucleus. We also show that a loss-of-function in 5PTase13 leads to nutrient level-dependent reduction of root growth, along with ABA- and sugar-insensitivity. 5ptase13 mutants accumulate less inositol (1,4,5) trisphosphate in response to sugar stress and have alterations in ABA-regulated gene expression, both of which are consistent with the known role of inositol (1,4,5) trisphosphate in ABA-mediated signaling. We propose that by forming a protein complex with SnRK1.1 protein, 5PTase13 plays a regulatory role linking inositol, sugar and stress signaling.






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