Functional analysis of the Raf-like kinase VIK involved in light-induced stomatal opening

Taku Sakakibara, Miya Mizutani, Maki Hayashi, Yoshikatsu Matsubayashi, Toshinori Kinoshita
Department of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya-shi, Aichi, 464-8602, JAPAN

Stomata open in response to red light and blue light. In the blue light-induced stomatal opening, blue light perceived by blue light receptor phototropin leads to the phosphorylation a penultimate residue, Thr (Thr948, numbering according to AHA1) of plasma membrane (PM) H+-ATPase, and activation of PM H+-ATPase. Activated PM H+-ATPase induces PM hyperpolarization and uptakes K+ into guard cells through the inward-rectifying K+ channels. Accumulated K+ and increase the osmotic pressure within guard cells, which induces water uptake and stomatal opening. However, the detail of signaling mechanisms leading to H+-ATPase activation and the regulation mechanisms of K+ channel activity remain unknown. Previously, VH1-interacting kinase（VIK） has been identified as a positive regulator of stomatal opening in response to light. Knockout mutants of VIK, vik, exhibit impaired light-induced stomatal opening. However, blue light-induced phosphorylation of Thr948 of PM H+-ATPase was normally observed, suggesting that VIK positively regulates light-induced stomatal opening not through PM H+-ATPase activation, but rather through downstream or alternative signaling pathways. We will report the results of investigations of VIK function and phosphoproteomics analysis using guard cell protoplasts.