Abstract
Stomata of plant leaves open to enable CO2 entry for photosynthesis and close when CO2 in the leaf is elevated. CO2 is thought to promote stomatal closure in part by activating the SLAC1 anion channel at the guard cell plasma membrane. Carbonic anhydrases (CAs) contribute to this activation, but their contribution as distinct from CO2-H2CO3 catalysis remains controversial. Here we show that the β-carbonic anhydrase CA4 binds selectively with the guard-cell anion channel SLAC1 to enhance channel current. The interaction is CO2-dependent, but binding is mediated by amino acids distal from the CO2-binding site of CA4 and is separable from carbonic-anhydrase activity. CA4 mutants impaired in channel binding eliminate the CO2-sensitivity of SLAC1 in vivo and slow stomatal kinetics with a commensurate loss in water use efficiency. The findings demonstrate that CA4 contributes directly to the CO2-response mechanics regulating SLAC1 at near-ambient CO2 in guard cells and to stomatal kinetics in the plant.
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Data generated and analysed during this study are included in the article and its supplementary files. Unique biological materials are available on reasonable request to the corresponding author. Source data are provided with this paper.
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The OnGuard3 platform and the model parameter sets are freely available to academic users and may be downloaded from www.plantscienceglasgow.org.
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Acknowledgements
This work was supported by BBSRC grants BB/T013508/1 and BB/T006153/1 to MRB, BB/W001217/1 and BB/X013383/1 to MRB and RK, by Royal Society University Fellowship grant URF1500364 and URF\R\211002 and BBSRC grants BB/Z516788/01 and BB/Y010272/1 to RK. We thank Naomi Donald for support in mbSUS assays and Amparo Ruiz-Pardo for help in plant maintenance.
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M.R.B. and R.K. conceived the work and developed the strategies for analysis with J.C.A., L.X. and C.L.; L.X. and J.C.A. carried out and analyzed the mbSUS assays; C.L. carried out oocyte electrophysiology and, with THN and FALS-A, guard cell electrophysiology; J.C.A., Z.Y. and L.X. carried out confocal, gas exchange and growth studies; M.R.B. and R.K. helped analyse the electrophysiology, gas exchange and growth data; S.W. expressed and purified channel peptides for antibodies and, with S.F., carried out and analysed co-IP experiments; M.R.B. and M.K. carried out the modelling with T.H.N.; M.R.B. wrote the manuscript with L.X., J.C.A. and R.K.; all authors edited and approved the manuscript.
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Xia, L., Alvim, J.C., Nguyen, TH. et al. A guard cell carbonic anhydrase binds and regulates SLAC1 separate from its catalytic activity. Nat Commun (2026). https://doi.org/10.1038/s41467-026-70596-9
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DOI: https://doi.org/10.1038/s41467-026-70596-9
