The ongoing search for the molecular basis of plant osmosensing

Introduction: Cell viability and metabolism depend on cytoplasmic water and solute content, and organisms have evolved mechanisms to sense changes in cell water content, solute concentrations, cell volume, and/or turgor. This Perspective addresses the response to osmotic challenge in land plants and describes their special dependence on cellular water status for growth and development. Understanding how plants cope with water limitation may allow us to mitigate the agricultural effects of drought, a critical limitation on global crop productivity that is likely to increase in severity as the climate changes (Long and Ort, 2010). The signaling pathways by which plants respond to osmotic challenge are intriguing from an evolutionary standpoint: some aspects of these pathways resemble those of fungal or mammalian cells, some are similar to prokaryotic mechanisms, and yet others are unique to plants (as described below and in Hamann, 2012). In addition to the importance of osmotic homeostasis in land plants, we will discuss some of the specific context and language of plant stress biology, and describe what is known (and not known) about the molecular pathways by which plants sense and respond to osmotic challenges.