Received April 28, 2004
Returned for revision September 17, 2004
Accepted September 20, 2004
A Role of Arabidopsis Inositol Polyphosphate Kinase, AtIPK2
, in Pollen Germination and Root Growth
Jun Xu , Charles A. Brearley , Wen-Hui Lin , Yuan Wang , Rui Ye , Bernd Mueller-Roeber , Zhi-Hong Xu , and Hong-Wei Xue *
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, 200032 Shanghai, China; Partner Group of the Max-Planck-Institute of Molecular Plant Physiology on Plant Molecular Physiology and Signal Transduction, 200032 Shanghai, China
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
University of Potsdam, Institute for Biochemistry and Biology, Department of Molecular Biology, D-14476 Golm, Germany
National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, 200032 Shanghai, China
* Corresponding author; email: hwxue{at}sibs.ac.cn.
Inositol polyphosphates, such as inositol trisphosphate, are pivotal intracellular signaling molecules in eukaryotic cells. In higher plants the mechanism for the regulation of the type and the level of these signaling molecules is poorly understood. In this study we investigate the physiological function of an Arabidopsis (Arabidopsis thaliana) gene encoding inositol polyphosphate kinase (AtIPK2
), which phosphorylates inositol 1,4,5-trisphosphate successively at the D-6 and D-3 positions, and inositol 1,3,4,5-tetrakisphosphate at D-6, resulting in the generation of inositol 1,3,4,5,6-pentakisphosphate. Semiquantitative reverse transcription-PCR and promoter-
-glucuronidase reporter gene analyses showed that AtIPK2 is expressed in various tissues, including roots and root hairs, stem, leaf, pollen grains, pollen tubes, the flower stigma, and siliques. Transgenic Arabidopsis plants expressing the AtIPK2 antisense gene under its own promoter were generated. Analysis of several independent transformants exhibiting strong reduction in AtIPK2 transcript levels showed that both pollen germination and pollen tube growth were enhanced in the antisense lines compared to wild-type plants, especially in the presence of nonoptimal low Ca2+ concentrations in the culture medium. Furthermore, root growth and root hair development were also stimulated in the antisense lines, in the presence of elevated external Ca2+ concentration or upon the addition of EGTA. In addition, seed germination and early seedling growth was stimulated in the antisense lines. These observations suggest a general and important role of AtIPK2, and hence inositol polyphosphate metabolism, in the regulation of plant growth most likely through the regulation of calcium signaling, consistent with the well-known function of inositol trisphosphate in the mobilization of intracellular calcium stores.
