Modulation of Guard Cell Turgor and Drought Tolerance by a Peroxisomal Acetate–Malate Shunt

In plants, stomatal movements are tightly controlled by changes in cellular turgor pressure. Carbohydrates produced by glycolysis and the tricarboxylic acid cycle play an important role in regulating turgor pressure. Here, we describe an Arabidopsis mutant, bzu1, isolated in a screen for elevated leaf temperature in response to drought stress, which displays smaller stomatal pores and higher drought resistance than wild-type plants. BZU1 encodes a known acetyl-coenzyme A synthetase, ACN1, which acts in the first step of a metabolic pathway converting acetate to malate in peroxisomes. We showed that BZU1/ACN1-mediated acetate-to-malate conversion provides a shunt that plays an important role in osmoregulation of stomatal turgor. We found that the smaller stomatal pores in the bzu1 mutant are a consequence of reduced accumulation of malate, which acts as an osmoticum and/or a signaling molecule in the control of turgor pressure within guard cells, and these results provided new genetic evidence for malate-regulated stomatal movement. Collectively, our results indicate that a peroxisomal BZU1/ACN1-mediated acetate-malate shunt regulates drought resistance by controlling the turgor pressure of guard cells in Arabidopsis.