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Summary Plants integrate environmental stimuli to optimize photosynthesis vs water loss by controlling stomatal apertures. However, stomatal responses to temperature elevation and the underlying molecular genetic mechanisms remain less studied.We developed an approach for clamping leaf‐to‐air vapor pressure difference (VPDleaf) to fixed values, and recorded robust reversible warming‐induced stomatal opening in intact plants. We analyzed stomatal temperature responses of mutants impaired in guard cell signaling pathways for blue light, abscisic acid (ABA), CO2, and the temperature‐sensitive proteins, Phytochrome B (phyB) and EARLY‐FLOWERING‐3 (ELF3).We confirmed thatphot1‐5/phot2‐1leaves lacking blue‐light photoreceptors showed partially reduced warming‐induced stomatal opening. Furthermore, ABA‐biosynthesis, phyB, and ELF3 were not essential for the stomatal warming response. Strikingly,Arabidopsis(dicot) andBrachypodium distachyon(monocot) mutants lacking guard cell CO2sensors and signaling mechanisms, includinght1,mpk12/mpk4‐gc, andcbc1/cbc2abolished the stomatal warming response, suggesting a conserved mechanism across diverse plant lineages. Moreover, warming rapidly stimulated photosynthesis, resulting in a reduction in intercellular (CO2). Interestingly, further enhancing heat stress caused stomatal opening uncoupled from photosynthesis.We provide genetic and physiological evidence that the stomatal warming response is triggered by increased CO2assimilation and stomatal CO2sensing. Additionally, increasing heat stress functions via a distinct photosynthesis‐uncoupled stomatal opening pathway.
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MPK12 in stomatal CO2 signaling: function beyond its kinase activity
Summary Protein phosphorylation is a major molecular switch involved in the regulation of stomatal opening and closure. Previous research defined interaction between MAP kinase 12 and Raf‐like kinase HT1 as a required step for stomatal movements caused by changes in CO2concentration. However, whether MPK12 kinase activity is required for regulation of CO2‐induced stomatal responses warrants in‐depth investigation.We apply genetic, biochemical, and structural modeling approaches to examining the noncatalytic role of MPK12 in guard cell CO2signaling that relies on allosteric inhibition of HT1.We show that CO2/HCO3−‐enhanced MPK12 interaction with HT1 is independent of its kinase activity. By analyzing gas exchange of plant lines expressing various kinase‐dead and constitutively active versions of MPK12 in a plant line whereMPK12is deleted, we confirmed that CO2‐dependent stomatal responses rely on MPK12's ability to bind to HT1, but not its kinase activity. We also demonstrate that purified MPK12 and HT1 proteins form a heterodimer in the presence of CO2/HCO3−and present structural modeling that explains the MPK12:HT1 interaction interface.These data add to the model that MPK12 kinase‐activity‐independent interaction with HT1 functions as a molecular switch by which guard cells sense changes in atmospheric CO2concentration.
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- Award ID(s):
- 1900567
- PAR ID:
- 10418496
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 239
- Issue:
- 1
- ISSN:
- 0028-646X
- Page Range / eLocation ID:
- p. 146-158
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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