Characterization of SnRK3 type protein kinase from stomatal guard cells of Vicia faba L.

Abstract

Protein phosphorylations are involved in signal transduction pathway in blue light (BL)-induced stomatal opening and ABA-induced stomatal closure. However, the protein kinase involved in guard-cell signal transduction pathway is largely unknown. We isolated the protein kinase (vfPK1) from stomatal guard cells of Vicia faba L. The vfPK1 encoded a new type protein kinase that belongs to SnRK3 subgroup. To identify the protein that interact with vfPK1, we used vfPK1 as a bait in a yeast two-hybrid screening and identified a positive cDNA (vfCBL1) encoding a calcineurin B-like Ca²⁺ binding protein. The vfCBL1 interacted with vfPK1 in vitro, and activated the vfPK1 kinase activity. This interaction was decreased by Ca²⁺. The vfPK1 was localized in mitochondria by Western blot analysis and transient expression assay of vfPK1 fused to GFP. These results suggest that vfPK1 may mediate Ca²⁺ signaling and is related to mitochondrial function in guard cells.