NRGA1, a Putative Mitochondrial Pyruvate Carrier, Mediates ABA Regulation of Guard Cell Ion Channels and Drought Stress Responses in Arabidopsis

Abstract

Abscisic acid (ABA) regulates ion channel activity and stomatal movements in response to drought and other stresses. Here, we show that the Arabidopsis thaliana gene NRGA1 is a putative mitochondrial pyruvate carrier which negatively regulates ABA-induced guard cell signaling. NRGA1 transcript was abundant in the A. thaliana leaf and particularly in the guard cells, and its product was directed to the mitochondria. The heterologous co-expression of NRGA1 and AtMPC1 in yeast complemented a loss-of-function mitochondrial pyruvate carrier (MPC) mutant. The nrga1 loss-of-function mutant was very sensitive to the presence of ABA in the context of stomatal movements, and exhibited a heightened tolerance to drought stress. Disruption of NRGA1 gene resulted in increased ABA inhibition of inward K(+) currents and ABA activation of slow anion currents in guard cells. The nrga1/NRGA1 functional complementation lines restored the mutant's phenotypes. Furthermore, transgenic lines of constitutively overexpressing NRGA1 showed opposite stomatal responses, reduced drought tolerance, and ABA sensitivity of guard cell inward K(+) channel inhibition and anion channel activation. Our findings highlight a putative role for the mitochondrial pyruvate carrier in guard cell ABA signaling in response to drought.

The Mitochondrial Pyruvate Carrier and Metabolic Regulation

“…We now await the structural analysis of these proteins in anticipation of the functional insights that shall be obtained. Interestingly, another recent report implicated an Arabidopsis thaliana gene, NRGA1, which is homologous to MPC2 and when coexpressed with AtMPC1, complemented the yeast mpc2Δ/mpc3Δ mutation [23]. NRGA1 negatively regulates abscisic acid-induced signaling in Arabdopsis guard cells in response to drought, but how this is connected to pyruvate transport is unclear at the moment.…”

The ongoing story: the mitochondria pyruvate carrier 1 in plant stress response in Arabidopsis

“…We recently identified a putative MPC gene, Negative Regulator of Guard Cell ABA Signaling 1 (NRGA1), which mediates ABA regulation of guard cell ion channels and drought stress responses in Arabidopsis. 8 The Arabidopsis MPC family comprises 5 members (At4G05590, At4G14695, At5G20090, At4G22310 and At4G26780), and the phylogenetic analysis showed that these proteins are classified into 3 categories: MPC1 (At5G20090), MPC2-like proteins (At4G14695, At4G22310 and At4G05590) and At4G26780 (Fig. 1A).…”

“…A complementation analysis in yeast showed that AtMPC1 and NRGA1 together functionally complement the absence of a native pyruvate transport protein. 8 To assess whether MPC1 has direct interaction with NRGA1 or other putative MPC proteins, we performed yeast 2-hybrid assay.…”

“…Since the yeast mpc2Dmpc3D cells were rescued by coexpressing MPC1 and NRGA1, 8 the products of these genes presumably had a similar subcellular localization pattern. The subcellular localization of MPC1 was determined by transiently expressing in Arabidopsis mesophyll protoplasts a fusion of GFP to the MPC1 terminus driven by the CaMV 35S promoter.…”

“…Previously 35S::NRGA1-GFP was shown to be targeted to mitochondria. 8 To confirm the location of MPC1, the 35S::…”