GABA does not regulate stomatal CO2 signalling in Arabidopsis.

Area of Science:

• Plant Physiology
• Molecular Biology
• Biochemistry

Background:

• Optimal stomatal regulation is crucial for plant adaptation and crop yield.
• Guard cells utilize signaling molecules like γ-aminobutyric acid (GABA) and respond to environmental cues such as carbon dioxide (CO2).
• GABA is synthesized by glutamate decarboxylase (GAD), producing CO2 as a byproduct, suggesting a potential link with CO2 signaling.

Purpose of the Study:

• To investigate the connection between GABA signaling and CO2 signaling pathways in plant guard cells.
• To determine the role of GABA in stomatal sensitivity to varying CO2 concentrations.
• To identify genetic factors influencing stomatal responses to CO2.

Main Methods:

• Analysis of GABA-deficient Arabidopsis mutant lines (gad2-1, gad2-2, gad1/2/4/5) for stomatal sensitivity to CO2.
• Transcriptomic and genomic investigations to identify genetic underpinnings of observed phenotypes.
• Guard cell-specific complementation experiments to validate gene function.

Main Results:

• A phenotypic discrepancy was observed between allelic mutant lines gad2-1 and gad2-2 regarding CO2 response.
• The gad2-1 mutant exhibited a weakened CO2 response attributed to a deletion in Mitogen-activated protein kinase 12 (MPK12).
• Complementation of MPK12 in the gad2-1 mutant restored wild-type CO2 sensitivity, confirming MPK12's role.
• Stomatal opening under low CO2 was independent of the ALUMINIUM-ACTIVATED MALATE TRANSPORTER 9 (ALMT9) channel.

Conclusions:

• GABA plays a role in modulating the rate of stomatal opening and closing.
• GABA signaling is not directly involved in the guard cell response to CO2 concentrations.
• Mitogen-activated protein kinase 12 (MPK12) is essential for guard cell CO2 sensitivity.