Barley nitrate transporter protein is phosphorylated by Ca²⁺-dependent and nitrate-inducible protein kinase from roots.

Abstract

It is known that plant has two types of nitrate uptake system, a high-affinity nitrate uptake system (HATS) and a low-affinity nitrate uptake system. In barely four nitrate transporter (HvNRT2) genes which is considered to encode low-affinity nitrate uptake system have been identified. We previously reported that HvNRT2 protein was localized in the plasma membrane of barley root cells and the HATS activity was regulated at post-translational levels. It has been considered that the post-translational regulation of HATS activities are mediated by phosphorylation of NRT2 protein at C-terminal region. In this study, we examined the possibility of in vitro phosphorylation of HvNRT2 protein. As a result, C-terminal region of HvNRT2 protein was phosphorylated in vitro by protein kinase in the soluble fraction of barley roots, and its activity was Ca²⁺-dependent and nitrate-inducible.