Heterotrimeric G protein alpha and beta subunits antagonistically modulate stomatal density in Arabidopsis thaliana.

Stomata are essential for efficient gas and water-vapor exchange between the atmosphere and plants. Stomatal density and movement are controlled by a series of signal molecules including phytohormones and peptides as well as by environmental stimuli. It is known that heterotrimeric G-proteins play an important role in the ABA-inhibited stomatal opening. In this study, the G-protein signaling pathway was also found to regulate stomatal density on the lower epidermis of Arabidopsis cotyledons. The loss-of-function mutation of the G-protein alpha-subunit (GPA1) showed a reduction in stomatal density, while overexpression of the constitutively active form of GPA1(QL) increased stomatal density, indicating a positive role of the active form of GPA1 in stomatal development. In contrast, stomatal density increased in the null mutant of the G-protein beta-subunit (AGB1) but decreased in transgenic lines that overexpressed AGB1. Stomatal analysis of the gpa1 agb1 double mutants displayed an average value of stomatal density compared to the single mutants. Taken together, these results suggest that the stomatal density in Arabidopsis is modulated by GPA1 and AGB1 in an antagonistic manner.