Expression and manipulation of PHOSPHOENOLPYRUVATE CARBOXYKINASE 1 identifies a role for malate metabolism in stomatal closure

Abstract

SUMMARYMalate, along with potassium and chloride ions, is an important solute for maintaining turgor pressure during stomatal opening. Although malate is exported from guard cells during stomatal closure, there is controversy as to whether malate is also metabolised. We provide evidence that phosphoenolpyruvate carboxykinase (PEPCK), an enzyme involved in malate metabolism and gluconeogenesis, is necessary for full stomatal closure in the dark. Analysis of the Arabidopsis PCK1 gene promoter indicated that this PEPCK isoform is specifically expressed in guard cells and trichomes of the leaf. Spatially distinct promoter elements were found to be required for post-germinative, vascular expression and guard cell/trichome expression of PCK1. We show that pck1 mutant plants have reduced drought tolerance, and show increased stomatal conductance and wider stomatal apertures compared with the wild type. During light-dark transients the PEPCK mutant plants show both increased overall stomatal conductance and less responsiveness of the stomata to darkness than the wild type, indicating that stomata get 'jammed' in the open position. These results show that malate metabolism is important during dark-induced stomatal closure and that PEPCK is involved in this process.

Rethinking Guard Cell Metabolism

“…NADP-ME also is expressed in Arabidopsis guard cells (Wheeler et al, 2005) and was implicated in the mechanism of stomatal closure when NADP-ME was overexpressed in tobacco (Nicotiana tabacum) plants (Laporte et al, 2002). Thus, a role for PEPCK was nearly forgotten until Penfield et al (2012) revisited the importance of this metabolic step by taking advantage of an Arabidopsis mutant lacking PEPCK1, a highly expressed guard cell isoform in this plant. The pck1 mutants have increased stomatal conductance and wider stomatal aperture than wild-type plants, pointing toward a function for PCK1 in full stomatal closure in the dark (Penfield et al, 2012).…”

“…Thus, a role for PEPCK was nearly forgotten until Penfield et al (2012) revisited the importance of this metabolic step by taking advantage of an Arabidopsis mutant lacking PEPCK1, a highly expressed guard cell isoform in this plant. The pck1 mutants have increased stomatal conductance and wider stomatal aperture than wild-type plants, pointing toward a function for PCK1 in full stomatal closure in the dark (Penfield et al, 2012). Furthermore, pck1 mutants close their stomata normally in response to ABA or high [CO 2 ], supporting previous observations that malate export may be more important than malate metabolism when stomata lose turgor within minutes.…”

Relationships of Leaf Net Photosynthesis, Stomatal Conductance, and Mesophyll Conductance to Primary Metabolism: A Multispecies Meta-Analysis Approach

“…Indeed, it has been shown that this metabolite can act as a counter-ion of K + in the vacuole of guard cells or as a signaling molecule to activate guard cell vacuolar chloride channels during stomatal opening (Hedrich and Marten, 1993;De Angeli et al, 2013). Further evidence for the importance of malate and their products and precursors for guard cell metabolism and stomatal movements is demonstrated by the higher g s found in transgenic plants for enzymes related to organic acid metabolism (Laporte et al, 2002;Nunes-Nesi et al, 2007;Araújo et al, 2011b;Penfield et al, 2012) or guard cell malate transporters (Meyer et al, 2010;Medeiros et al, 2015). The findings of these works are reflected across our entire data compilation, which revealed a strong and positive correlation between the levels of malate and g s ( Fig.…”

Alteration of the Interconversion of Pyruvate and Malate in the Plastid or Cytosol of Ripening Tomato Fruit Invokes Diverse Consequences on Sugar But Similar Effects on Cellular Organic Acid, Metabolism, and Transitory Starch Accumulation

“…This finding led to follow-up work demonstrating that the level of malate played an important role in tomato fruit ripening influencing starch accumulation, total soluble solid levels at ripening, and postharvest properties (Centeno et al, 2011), when taken alongside the results of many recent studies on the control of stomatal aperture by malate (NunesNesi et al, 2007;Lee et al, 2008;Araújo et al, 2011;Penfield et al, 2012), thus expanding the documented biological roles for this acid beyond those previously documented (Fernie and Martinoia, 2009;Meyer et al, 2010). This finding thus suggests that malate metabolism may exert a key influence on the normal ripening and metabolism of tomato fruit.…”