Roles of OsCKI1, a rice casein kinase I, in root development and plant hormone sensitivity

Authors

  • Wei Liu,

    1. National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (SiBS), Chinese Academy of Sciences, China,
    2. Partner Group of Max-Planck-Institute of Molecular Plant Physiology (MPI-MP) on Plant Molecular Physiology and Signal Transduction, 300 Fenglin Road, 200032 Shanghai, China, and
    3. Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun Road, 100093 Beijing, China
    Search for more papers by this author
  • Zhi-Hong Xu,

    1. National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (SiBS), Chinese Academy of Sciences, China,
    2. Partner Group of Max-Planck-Institute of Molecular Plant Physiology (MPI-MP) on Plant Molecular Physiology and Signal Transduction, 300 Fenglin Road, 200032 Shanghai, China, and
    Search for more papers by this author
  • Da Luo,

    1. National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (SiBS), Chinese Academy of Sciences, China,
    Search for more papers by this author
  • Hong-Wei Xue

    Corresponding author
    1. National Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (SiBS), Chinese Academy of Sciences, China,
    2. Partner Group of Max-Planck-Institute of Molecular Plant Physiology (MPI-MP) on Plant Molecular Physiology and Signal Transduction, 300 Fenglin Road, 200032 Shanghai, China, and
      For correspondence (fax +86 21 64042385; e-mail hwxue@sibs.ac.cn).
    Search for more papers by this author

For correspondence (fax +86 21 64042385; e-mail hwxue@sibs.ac.cn).

Summary

Casein kinases are critical in cell division and differentiation across species. A rice cDNA fragment encoding a putative casein kinase I (CKI) was identified via cDNA macroarray under brassinosteroid (BR) treatment, and a 1939-bp full-length cDNA, OsCKI1, was isolated and found to encode a putative 463-aa protein. RT-PCR and Northern blot analysis indicated that OsCKI1 was constitutively expressed in various rice tissues and upregulated by treatments with BR and abscisic acid (ABA). Enzymatic assay of recombinant OsCKI1 proteins expressed in Escherichia coli showed that the protein was capable of phosphorylating casein. The physiological roles of OsCKI1 were studied through antisense transgenic approaches, and homozygous transgenic plants showed abnormal root development, including fewer lateral and adventitious roots, and shortened primary roots as a result of reduced cell elongation. Treatment of wild-type plants with CKI-7, a specific inhibitor of CKI, also confirmed these functions of OsCKI1. Interestingly, in transgenic and CKI-7-treated plants, exogenously supplied IAA could restore normal root development, and measurement of free IAA content in CKI-deficient primary and adventitious roots revealed altered auxin content, indicating that OsCKI1 is involved in auxin metabolism or that it may affect auxin levels. Transgenic plants were less sensitive than control plants to ABA or BR treatment during germination, suggesting that OsCKI1 may be involved in various hormone-signaling pathways. OsCKI1-GFP fusion studies revealed the localization of OsCKI1 to the nucleus, suggesting a possible involvement in regulation of gene expression. In OsCKI1-deficient plants, differential gene expression was investigated using cDNA chip technology, and results indicated that genes related to signal transduction and hormone metabolism were indeed with altered expression.

Ancillary