Abscisic acid-induced gene-expression requires the activity of protein(s) sensitive to the protein-tyrosine phosphatase inhibitor phenylarsine oxide

Abscisic acid-induced gene-expression requires the activity of protein(s) sensitive to the protein-tyrosine phosphatase inhibitor phenylarsine oxide. It is generally accepted that phosphorylation/dephosphorylation of proteins plays an important role in signal transduction cascades. evidence is now accumulating that for plants the same holds true. To study the role of phosphorylation in ABA signal transduction, we used six different compounds which were reported to inhibit phosphatase action. Three of these inhibitors: phenylarsine oxide (PAO), Calyculin A (CA) and Okadaic Acid (OA) appeared capable of inhibiting ABA-induced gene-expression. The same three inhibitors are shown to bring about hyperphosphorylation of two approximately 40 kDa proteins, present in the membrane-bound fraction of barley aleurone cells. The other three inhibitors had no visible effect on the phosphorylation status of the barley proteins. The hyperphosphorylation of the two 40 kDa proteins coincided with an increase of tyrosine-phosphorylation of two 40 kDa proteins with different pI, as determined with anti-phosphotyrosine antibodies.