Characterization of SnRK3 Type Protein Kinase From Stomatal Guard Cells of Vicia faba L.

Abstract

Protein phosphorylation is 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. In this study, we tried to isolate and analyze protein kinase (vfPK1) from stomatal guard cells of Vicia faba L. The vfPK1 encoded a new type protein kinase that belongs to SnRK3 subgroup. Northern blotting analysis showed that the transcripts were predominantly expressed in guard cells and roots. Recombinant vfPK1 purified from E.coli showed autophosphorylation activity. 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 is 88.3% identical to AtCBL2. These results suggest that vfPK1 may mediate Ca²⁺ signaling pathway in guard cells.