Reconstitution of CO2 Regulation of SLAC1 Anion Channel and Function of CO2-Permeable PIP2;1 Aquaporin as CARBONIC ANHYDRASE4 Interactor
by Wang C., Hu H., Qin X., Zeise B., Xu D., Rappel W.-J., Walter F. Boron W. F., Julian I. Schroeder J. I. (2016)
- Cun Wanga,1,
- Honghong Hua,b,1,2,
- Xue Qinc,
- Brian Zeisec,
- Danyun Xub,
- Wouter-Jan Rappeld,
- Walter F. Boronc and
- Julian I. Schroedera,2
aDivision of Biological Sciences, Section of Cell and Developmental Biology, University of California San Diego, La Jolla, California 92093-0116
bCollege of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
cDepartment of Physiology and Biophysics, Case Western Reserve University, Ohio 44106
dPhysics Department, University of California San Diego, La Jolla, California 92093
in The Plant Cell February 2016 vol. 28 no. 2 568-582 – doi: http://dx.doi.org/10.1105/tpc.15.00637 –
Dark respiration causes an increase in leaf CO2 concentration (Ci), and the continuing increases in atmospheric [CO2] further increases Ci. Elevated leaf CO2 concentration causes stomatal pores to close.
Here, we demonstrate that high intracellular CO2/HCO3−enhances currents mediated by the Arabidopsis thaliana guard cell S-type anion channel SLAC1 upon coexpression of any one of the Arabidopsis protein kinases OST1, CPK6, or CPK23 in Xenopus laevis oocytes.
Split-ubiquitin screening identified the PIP2;1 aquaporin as an interactor of the βCA4 carbonic anhydrase, which was confirmed in split luciferase, bimolecular fluorescence complementation, and coimmunoprecipitation experiments. PIP2;1 exhibited CO2 permeability. Mutation of PIP2;1 in planta alone was insufficient to impair CO2– and abscisic acid-induced stomatal closing, likely due to redundancy.
Interestingly, coexpression of βCA4 and PIP2;1 with OST1-SLAC1 or CPK6/23-SLAC1 in oocytes enabled extracellular CO2 enhancement of SLAC1 anion channel activity. An inactive PIP2;1 point mutation was identified that abrogated water and CO2 permeability and extracellular CO2 regulation of SLAC1 activity.
These findings identify the CO2-permeable PIP2;1 as key interactor of βCA4 and demonstrate functional reconstitution of extracellular CO2 signaling to ion channel regulation upon coexpression of PIP2;1, βCA4, SLAC1, and protein kinases.
These data further implicate SLAC1 as a bicarbonate-responsive protein contributing to CO2 regulation of S-type anion channels.