Abstract
SAPKs, rice SnRK2 protein kinases, are rapidly activated by hyperosmotic stress and ABA. A rice cDNA library was screened by the yeast two-hybrid method for SAPK-interacting proteins. One of the positive clones encoded a phosphatidylinositol 4-kinase-ß (PI4K-ß). Because phosphoinositides are implicated in the signal transduction of hyperosmotic stress and ABA, we chose this clone for further analysis. A GST-fusion protein with a fragment of PI4K-ß was found to be phosphorylated by SAPK2 in vitro. We constructed an Arabidospsis double knockout line with T-DNA insertions into the two genes highly homologous to the rice PI4K-ß clone to investigate the in vivo functions of PI4K-ßs. The double knockout line exhibited a dwarf phenotype and osmotic strength-dependent abnormalities in cell elongation/expansion of the root cortex and epidermal cells including root hairs. These results suggested possible involvement of PI4K-ß in the signal transduction of hyperosmotic stress. Further characterization of this mutant is being performed.
