Guard Cell Actin Cytoskeleton

Abstract

Stomata are adjustable pores found predominantly in the leaf epidermis that control CO 2 influx into the apoplast and transpirational water loss. Guard cells enclosing the stomatal pore can perceive and respond to diverse stimuli via a complex signalling network: central to this signalling network is the actin cytoskeleton, which has been proposed as a critical component of stomatal guard cell function. Indeed, guard cell actin cytoskeletal filaments undergo dramatic conformational changes during biotic and abiotic stimulus‐induced stomatal movement. As a function of the genetic requirement for these highly regulated conformational changes, disruption of actin filament dynamics using pharmacological or genetic‐based approaches leads to stomatal insensitivity to the opening and closing signals. Recent advances in high‐resolution live‐cell microscopy have enabled the visualisation of the dynamic features of individual actin filaments, and in total, provided new knowledge about the quantitative properties of filament distribution and turnover. Additional studies have also revealed a spectrum of actin regulatory components and stomatal signalling events that are associated with cytoskeletal actin function in guard cells. Future research on stomatal actin signalling mutants will shed light on the mechanisms underlying the regulation of cell physiological processes and activation of responses to external stresses via actin re‐modelling. Key Concepts The guard cell actin cytoskeleton serves as a hub of the stomatal signalling network. The cortical actin arrays in guard cells rearrange rapidly to facilitate stomatal movement induced by biotic and abiotic stimuli. Reorganisation of actin filaments in guard cells is orchestrated by a diverse of actin‐binding proteins. The activation and repression of actin‐binding proteins are coordinated by a multitude of early signalling components of the stomatal signalling network. The reorganisation of cytoskeletal actin is mechanistically coupled to key guard cell signalling events such as transmembrane ion flux, membrane recycling and morphological changes of vacuoles.