Sensing and regulation of plant extracellular pH

In plants, pH determines nutrient acquisition and sensing, and triggers responses to osmotic stress, whereas pH homeostasis protects the cellular machinery. Extracellular pH (pH_e) controls the chemistry and rheology of the cell wall to adjust its elasticity and regulate cell expansion in space and time. Plasma membrane (PM)-localized proton pumps, cell-wall components, and cell wall-remodeling enzymes jointly maintain pH_e homeostasis. To adapt to their environment and modulate growth and development, plant cells must sense subtle changes in pH_e caused by the environment or neighboring cells. Accumulating evidence indicates that PM-localized cell-surface peptide-receptor pairs sense pH_e. We highlight recent advances in understanding how plants perceive and maintain pH_e, and discuss future perspectives.