Plant Physiology Preview
Published on January 19, 2007; 10.1104/pp.106.089474
OPEN ACCESS ARTICLE
Received September 4, 2006
Accepted January 10, 2007
Inositol Polyphosphate 5-Phosphatases 1 and 2 Are Required for Regulating Seedling Growth
Bhadra Gunesekera , Javad Torabinejad , Jamille Robinson , and Glenda E. Gillaspy *
Department of Biochemistry and Fralin Biotechnology Center, Virginia Tech, Blacksburg, VA 24061
* Corresponding author; email: gillaspy{at}vt.edu.
Signals can be perceived and amplified at the cell membrane by receptors coupled to the production of a variety of second messengers, including myo-inositol 1,4,5-trisphosphate Ins(1,4,5)P3. The myo-inositol polyphosphate 5-phosphatases (5PTases) (E.C. 3.1.3.56) comprise a large protein family that hydrolyze 5-phosphates from a variety of myo-inositol phosphate (InsP) and phosphoinositide phosphate (PtdInsP) substrates. Arabidopsis thaliana has15 genes encoding 5PTases. Biochemical analyses of a subgroup of 5PTase enzymes suggest that these enzymes have both overlapping and unique substrate preferences. Ectopic expression of these genes in transgenic plants can reduce Ins(1,4,5)P3 levels and alter abscisic acid signaling. To further explore the function of 5PTases in signaling, we have identified and characterized T-DNA insertional mutants for 5PTase1 and 5PTase2, and produced a double mutant. When grown in the dark, the seeds from these mutants germinate faster than wildtype seeds and the mutant seedlings have longer hypocotyls than wildtype seedlings. Seeds from these mutant lines also demonstrate an increase in sensitivity to ABA. These changes in early seedling growth are accompanied by mass increases in Ins(1,4,5)P3, but not by changes in endogenous ABA content. By labeling the endogenous myo-inositol pool in 5ptase1 and 5ptase2 mutants, we detected increases in Ins(1,4,5)P3, and a decrease in PtdIns, PtdIns(4)P and PtdIns(4,5)P2. Taken together, these data indicate that the At5PTase1 and At5PTase2 genes have non-redundant roles in hydrolyzing inositol second messenger substrates, and that regulation of Ins(1,4,5)P3 levels is important during germination and early seedling development.
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