Low temperature-stimulated phosphorylation regulates the binding of nuclear factors to the promoter of Wcs120, a cold-specific gene in wheat

The Wcs120 gene encodes a highly abundant protein which appears to play an important role during cold acclimation of wheat. To understand the regulatory mechanism controlling its expression at low temperature, the promoter region has been characterized. Electrophoretic mobility shift assays using short promoter fragments revealed the presence in nuclear extracts from non-acclimated (NA) plants of multiple DNA-binding proteins which interact with several elements. In contrast, no DNA-binding activity was observed in the nuclear extracts from cold-acclimated (CA) plants. In vitro dephosphorylation of these CA nuclear extracts with alkaline phosphatase restored the binding activity. Moreover, okadaic acid (a potent phosphatase inhibitor) markedly stimulated the in vivo accumulation of the WCS120 family of proteins. This suggests that protein phosphatases PP1 and/or PP2A negatively regulate the expression of the Wcs120 gene. In addition, both Ca2+-dependent and Ca2+-independent kinase activities were found to be significantly higher in the CA nuclear extracts. Western analysis using antibodies directed against protein kinase C (PKC) isoforms showed that a PKCγ homolog (84 kDa) is selectively translocated into the nucleus in response to low temperature. Taken together, our results suggest that, in vivo, the expression of the Wcs120 gene may be regulated by nuclear factors whose binding activity is modulated by a phosphorylation/dephosphorylation mechanism.