ZmGDI1 Modulates Stomatal Development and Drought Response via the Rho GTPase Pathway Regulation in Maize

Guanine nucleotide dissociation inhibitors (GDIs) regulate cell signaling in mammals, but their role in stomatal development in plants remains unknown. This study investigates the role of the maize GDI1 (ZmGDI1) in stomatal formation and drought stress responses. Heterologous expression of ZmGDI1 in Arabidopsis reduced the transcription of key stomatal development genes including SPEECHLESS (SPCH), FAMA, and MUTE, resulting in reduced stomatal density by 13% compared to wild-type plants. Conversely, atgdi1 loss-of-function mutants exhibited increased stomatal density and upregulation of these master regulators, resulting in enhanced drought sensitivity. The phenotypes observed in the atgdi1 mutant were rescued by the expression of ZmGDI1, suggesting that the function of GDIs in stomatal development is conserved across different plant species. ZmGDI1-silenced maize plants generated via virus-induced gene silencing (VIGS) showed a marked increase in stomatal density, confirming the functional conservation of the ZmGDI1 gene. ZmGDI1 was demonstrated to interact with and inhibit the activity of the Rho GTPase ZmROP4, which subsequently associates with ZmPAN1/2 to promote stomatal development. These findings uncover a conserved GDI-ROP signaling module that governs stomatal patterning and provides molecular targets for engineering improved drought tolerance in crops.