Plant Physiology Preview
Published on October 13, 2006; 10.1104/pp.106.088476
Received August 21, 2006
Accepted October 3, 2006
Geminivirus Infection Up-regulates the Expression of Two Arabidopsis Protein Kinases Related to Yeast SNF1 and Mammalian AMPK Activating Kinases
Wei Shen and Linda Hanley-Bowdoin *
Department of Molecular and Structural Biochemistry, North Carolina State University, Raleigh, North Carolina 27695-7622
* Corresponding author; email: linda_hanley-bowdoin{at}ncsu.edu.
GRIK1 and GRIK2 constitute a small protein kinase family in Arabidopsis (Arabidopsis thaliana). An earlier study showed that a truncated version of GRIK1 binds to the geminivirus replication protein AL1. We show here both full-length GRIK1 and GRIK2 interact with AL1 in yeast two-hybrid studies. Using specific antibodies, we showed that both Arabidopsis kinases are elevated in infected leaves. Immunoblot analysis of healthy plants revealed that GRIK1 and GRIK2 are highest in young leaf and floral tissues and low or undetectable in mature tissues. Immunohistochemical staining showed that the kinases accumulate in the shoot apical meristem, leaf primordium, and emerging petiole. Unlike the protein patterns, GRIK1 and GRIK2 transcript levels only show a small increase during infection and do not change significantly during development. Treating healthy seedlings and infected leaves with the proteasome inhibitor MG132 resulted in higher GRIK1 and GRIK2 protein levels, whereas treatment with the translation inhibitor cycloheximide reduced both kinases, demonstrating that their accumulation is modulated by post-transcriptional processes. Phylogenetic comparisons indicated that GRIK1, GRIK2 and related kinases from Medicago truncatula and rice (Oryza sativa) are most similar to the yeast kinases PAK1, TOS3 and ELM1 and the mammalian kinase CaMKK, which activate the yeast kinase SNF1 and its mammalian homolog AMPK, respectively. Complementation studies using a PAK1/TOS3/ELM1 triple mutant showed that GRIK1 and GRIK2 can functionally replace the yeast kinases, suggesting that the Arabidopsis kinases mediate one or more processes during early plant development and geminivirus infection by activating SNF1-related kinases.
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