Chloroplast envelope K/H antiporters are involved in cytosol pH regulation.

Variations in light intensity induce cytosol pH changes in photosynthetic tissues, providing a possible signal to adjust a variety of biochemical, physiological and developmental processes to the energy status of the cells. It was shown that these pH changes are partially due to the transport of protons in or out of the thylakoid lumen. However, the ion transporters in the chloroplast that transmit these pH changes to the cytosol are not known.

Loss of function of the chloroplast membrane K/H antiporters AtKEA1 and AtKEA2 alters the ROS and NO metabolism but promotes drought stress resilience.

Potassium (K) exerts key physiological functions such as osmoregulation, stomatal movement, membrane transport, protein synthesis and photosynthesis among others. Previously, it was demonstrated in Arabidopsis thaliana that the loss of function of the chloroplast KEfflux Antiporters KEA1 and KEA2, located in the inner envelope membrane, provokes inefficient photosynthesis. Therefore, the main goal of this study was to evaluate the potential impact of the loss of function of those cation transport systems in the metabolism of reactive oxygen and nitrogen species (ROS and RNS).

Plastidial transporters KEA1 and KEA2 at the inner envelope membrane adjust stromal pH in the dark.

Photosynthesis and carbon fixation depend critically on the regulation of pH in chloroplast compartments in the daylight and at night. While it is established that an alkaline stroma is required for carbon fixation, it is not known how alkaline stromal pH is formed, maintained or regulated. We tested whether two envelope transporters, AtKEA1 and AtKEA2, directly affected stromal pH in isolated Arabidopsis chloroplasts using the fluorescent probe 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF).

Deletion of the N-terminal domain of the yeast vacuolar (Na ,K )/H antiporter Vnx1p improves salt tolerance in yeast and transgenic Arabidopsis.

Cation/proton antiporters play a major role in the control of cytosolic ion concentrations in prokaryotes and eukaryotes organisms. In yeast, we previously demonstrated that Vnx1p is a vacuolar monovalent cation/H exchanger showing Na /H and K /H antiporter activity. We have also shown that disruption of VNX1 results in an almost complete abolishment of vacuolar Na /H exchange, but yeast cells overexpressing the complete protein do not show improved salinity tolerance.

Envelope K+/H+ Antiporters AtKEA1 and AtKEA2 Function in Plastid Development.

It is well established that thylakoid membranes of chloroplasts convert light energy into chemical energy, yet the development of chloroplast and thylakoid membranes is poorly understood. Loss of function of the two envelope K(+)/H(+) antiporters AtKEA1 and AtKEA2 was shown previously to have negative effects on the efficiency of photosynthesis and plant growth; however, the molecular basis remained unclear. Here, we tested whether the previously described phenotypes of double mutant kea1kea2 plants are due in part to defects during early chloroplast development in Arabidopsis (Arabidopsis thaliana).

Heterotrimeric G proteins interact with defense-related receptor-like kinases in Arabidopsis.

Heterotrimeric G proteins (G-proteins) are versatile signaling elements conserved in Eukaryotes. In animals G-proteins relay signals from 7-transmembrane spanning G protein-coupled receptors (GPCRs) to intracellular downstream effectors; however, the existence of GPCRs in plants is controversial. Contrastingly, a surplus of receptor-like kinases (RLKs) provides signal recognition at the plant cell surface.

Arabidopsis KEA2, a homolog of bacterial KefC, encodes a K(+)/H(+) antiporter with a chloroplast transit peptide.

KEA genes encode putative K(+) efflux antiporters that are predominantly found in algae and plants but are rare in metazoa; however, nothing is known about their functions in eukaryotic cells. Plant KEA proteins show homology to bacterial K(+) efflux (Kef) transporters, though two members in the Arabidopsis thaliana family, AtKEA1 and AtKEA2, have acquired an extra hydrophilic domain of over 500 residues at the amino terminus. We show that AtKEA2 is highly expressed in leaves, stems and flowers, but not in roots, and that an N-terminal peptide of the protein is targeted to chloroplasts in Arabidopsis cotyledons.

Vacuolar cation/H+ antiporters of Saccharomyces cerevisiae.

We previously demonstrated that Saccharomyces cerevisiae vnx1Δ mutant strains displayed an almost total loss of Na(+) and K(+)/H(+) antiporter activity in a vacuole-enriched fraction. However, using different in vitro transport conditions, we were able to reveal additional K(+)/H(+) antiporter activity. By disrupting genes encoding transporters potentially involved in the vnx1 mutant strain, we determined that Vcx1p is responsible for this activity.