CIPK23 regulates blue light-dependent stomatal opening in Arabidopsis thaliana.

Shin‐Ichiro Inoue,Hirotaka Takahashi,Xiang Zhao,Thomas Waksman,Ken‐Ichiro Shimazaki,Atsushi Takemiya,Kazuo Shinozaki,John M Christie,Eirini Kaiserli,Masaki Okumura,Tatsuya Sawasaki,Yaeta Endo,Xiao Zhang,Toshinori Kinoshita,Motoaki Seki

doi:10.1111/tpj.14955

Abstract

Phototropins (phot1 and phot2) are plant blue light receptor kinases that function to mediate phototropism, chloroplast movement, leaf flattening, and stomatal opening in Arabidopsis. Considerable progress has been made in understanding the mechanisms associated with phototropin receptor activation by light. However, the identities of phototropin signaling components are less well understood by comparison. In this study, we specifically searched for protein kinases that interact with phototropins by using an in vitro screening method (AlphaScreen) to profile interactions against an Arabidopsis protein kinase library. We found that CBL-interacting protein kinase 23 (CIPK23) interacts with both phot1 and phot2. Although these interactions were verified by in vitro pull-down and in vivo bimolecular fluorescence complementation assays, CIPK23 was not phosphorylated by phot1, as least in vitro. Mutants lacking CIPK23 were found to exhibit impaired stomatal opening in response to blue light but no deficits in other phototropin-mediated responses. We further found that blue light activation of inward-rectifying K+ (K+ in ) channels was impaired in the guard cells of cipk23 mutants, whereas activation of the plasma membrane H+ -ATPase was not. The blue light activation of K+ in channels was also impaired in the mutant of BLUS1, which is one of the phototropin substrates in guard cells. We therefore conclude that CIPK23 promotes stomatal opening through activation of K+ in channels most likely in concert with BLUS1, but through a mechanism other than activation of the H+ -ATPase. The role of CIPK23 as a newly identified component of phototropin signaling in stomatal guard cells is discussed.

Highlights

Phototropins are plasma membrane-associated, autophosphorylating blue light receptor kinases that induce a range of physiological responses in Arabidopsis thaliana, which help optimize photosynthetic efficiency under weak light conditions by increasing light capture and CO2 absorption in leaves (Christie et al, 1998; Takemiya et al, 2005; Inoue et al, 2010; Gotoh et al, 2018)
The abundance of H+-ATPase was unaltered in guard cell protoplasts (GCPs) from the cipk23-5 mutant. These results indicate that the H+-ATPase is normally activated by blue light in the absence of calcineurin Blike (CBL)-interacting protein kinase 23 (CIPK23) and further suggest that signaling components downstream of the H+-ATPase were impaired in cipk23 mutants
We found that blue light activation of the K+in channel current was impaired in the guard cells of the cipk23-5 mutant compared to wild-type guard cells (Figure 6; Figure S6)

Summary

Introduction

Phototropins (phot and phot2) are plasma membrane-associated, autophosphorylating blue light receptor kinases that induce a range of physiological responses in Arabidopsis thaliana, which help optimize photosynthetic efficiency under weak light conditions by increasing light capture and CO2 absorption in leaves (Christie et al, 1998; Takemiya et al, 2005; Inoue et al, 2010; Gotoh et al, 2018). These findings indicate that the primary signaling events associated with different phototropin-mediated responses are likely to be distinct, with signal propagation diverging from the phosphorylation of specific substrates

Results

Discussion

Conclusion