Intracellular ion flux coordination, a novel perspective on the mechanisms regulating ion transport in A. thaliana guard cells

Ion fluxes across cellular membranes are at the basis of fundamental biological functions. In plants, fluxes of ions across cellular membranes need to be coordinated to mediate biological responses to environmental stimuli. The function of a specialized plant cell type, the guard cell, rely on ion flux coordination. A pair of guard cells delimits the pore of a specific structure, the stomata, at the leaf surface. Stomata control water evaporation and CO₂ uptake for photosynthesis. The control of the stomata aperture depends on the capacity of guard cells to absorb/release massive amounts of ions (K⁺, H⁺, Cl^–, NO₃^–, malate^2-) in a short time scale inducing a change in osmotic pressure and trigger opening/closure of the stomata. Signaling pathways responding to drought, light or CO₂ control the absorption/release of ions in guard cells. Guard cells present the typical cell architecture of mature plant cells: a central vacuole occupying up to 90% of the cell volume squeezing the cytosol against the plasma membrane and the cell wall. The large majority of ions reside in the vacuole and consequently during stomata opening/closure cross the cytosol which is a crossroad at the interface of the extracellular space and intracellular compartments. Notably, the cytosol is a minor fraction of the cell volume, thus the massive ion fluxes through the plasma and the vacuolar membranes are tightly controlled to avoid cytosolic “traffic jams”. Despite the importance of ion flux coordination, we still have an extremely limited knowledge on the mechanisms involved in this process.

I will present the research project that I will develop in the next years at B&PMP aiming at understanding how ion fluxes at the plasma and vacuolar membranes are coordinated. We plan to analyze the mechanisms operating for the coordination at different levels: i) the properties of ion transport systems mediating ion fluxes across the plasma and vacuolar membrane; ii) the in vivo dynamics of the ion concentrations in the cytosol of guard cells; iii)  in silico modelling of ion fluxes.