A Raf-like protein kinase BHP mediates blue light-dependent stomatal opening

Shin-Ichiro Inoue,Yoshihisa Ueno,Toshinori Kinoshita,Maki Hayashi

doi:10.1038/srep45586

Abstract

Stomata in the plant epidermis open in response to blue light and affect photosynthesis and plant growth by regulating CO2 uptake and transpiration. In stomatal guard cells under blue light, plasma membrane H+-ATPase is phosphorylated and activated via blue light-receptor phototropins and a signaling mediator BLUS1, and H+-ATPase activation drives stomatal opening. However, details of the signaling between phototropins and H+-ATPase remain largely unknown. In this study, through a screening of specific inhibitors for the blue light-dependent H+-ATPase phosphorylation in guard cells, we identified a Raf-like protein kinase, BLUE LIGHT-DEPENDENT H+-ATPASE PHOSPHORYLATION (BHP). Guard cells in the bhp mutant showed impairments of stomatal opening and H+-ATPase phosphorylation in response to blue light. BHP is abundantly expressed in the cytosol of guard cells and interacts with BLUS1 both in vitro and in vivo. Based on these results, BHP is a novel signaling mediator in blue light-dependent stomatal opening, likely downstream of BLUS1.

Highlights

Stomata in the plant epidermis play critical roles in the regulation of photosynthesis and transpiration by promoting CO2 uptake and O2 and H2O release
Epidermal fragments from wild-type (WT) leaves were illuminated by red light (50 μmol m−2 s−1) with or without blue light (10 μmol m−2 s−1), after which phosphorylation of the guard cell H+-ATPase was detected by an immunohistochemical method using specific antibodies against phosphorylated Thr of the H+-ATPase[23]
We investigated the effects of the inhibitors on blue light-dependent stomatal opening in leaf epidermis (Fig. 1c)

Summary

Introduction

Stomata in the plant epidermis play critical roles in the regulation of photosynthesis and transpiration by promoting CO2 uptake and O2 and H2O release. C-terminal phosphorylation and subsequent activation of the guard cell H+-ATPase by blue light creates the driving force for K+ uptake and are crucial steps in stomatal opening[2,3]. Two signaling components, BLUE LIGHT SIGNALING1 (BLUS1) and type 1 protein phosphatase (PP1), act as positive regulators between the phots and the H+-ATPase[17,18]. It has been shown that several kinase inhibitors suppress the blue light-dependent H+-ATPase activation and stomatal opening in Vicia and Arabidopsis guard cells[19,20,21,22,23]. We identified a Raf-like protein kinase, BHP, as a novel signaling-mediator for blue light-dependent phosphorylation of the H+-ATPase and stomatal opening. We found that BHP interacts with BLUS1, which is an early blue light-signaling component

Methods

Results

Conclusion