Identification of a Novel Adenine Nucleotide Transporter in the Endoplasmic Reticulum of Arabidopsis

Abstract

Many metabolic reactions in the endoplasmic reticulum (ER) require high levels of energy in the form of ATP, which is important for cell viability. Here, we report on an adenine nucleotide transporter residing in the ER membranes of Arabidopsis thaliana (ER-ANT1). Functional integration of ER-ANT1 in the cytoplasmic membrane of intact Escherichia coli cells reveals a high specificity for an ATP/ADP antiport. Immunodetection in transgenic ER-ANT1-C-MYC-tag Arabidopsis plants and immunogold labeling of wild-type pollen grain tissue using a peptide-specific antiserum reveal the localization of this carrier in ER membranes. Transgenic ER-ANT1-promoter-b-glucuronidase Arabidopsis lines show high expression in ER-active tissues (i.e., pollen, seeds, root tips, apical meristems, or vascular bundles). Two independent ER-ANT1 Arabidopsis knockout lines indicate a high physiological relevance of ER-ANT1 for ATP transport into the plant ER (e.g., disruption of ER-ANT1 results in a drastic retardation of plant growth and impaired root and seed development). In these ER-ANT1 knockout lines, the expression levels of several genes encoding ER proteins that are dependent on a sufficient ATP supply (i.e., BiP [for luminal binding protein] chaperones, calreticulin chaperones, Ca 2þ -dependent protein kinase, and SEC61) are substantially decreased.

From Endoplasmic Reticulum to Mitochondria: Absence of the Arabidopsis ATP Antiporter Endoplasmic Reticulum Adenylate Transporter1 Perturbs Photorespiration

“…ER-ANT1 was shown to act as an ATP/ADP antiporter when heterologously expressed in Escherichia coli and to exhibit a submillimolar affinity for both substrates. Arabidopsis ER-ANT1 loss-of-function mutants contain substantially decreased protein and lipid levels in seeds and exhibit a dwarf phenotype (Leroch et al, 2008). The metabolic changes are in line with the essential role of the ER in protein and storage lipid accumulation.…”

“…ER-ANT1 Loss-of-Function Plants Accumulate Gly in a Light-Dependent Manner ER-ANT1 was shown to be capable of ATP/ADP exchange and to reside in the membrane of the ER (Leroch et al, 2008). The fact that direct homologs are missing in yeasts and animals suggests that ER-ANT1 fulfills a plant-specific function and that basic energy provision to the ER is generally catalyzed by a different carrier type or system.…”

“…PM-ANT1 catalyzes ATP export out of the plant cell and is involved in signaling processes required for controlled anther development (Rieder and Neuhaus, 2011), whereas ER-ANT1 is proposed to mediate energy provision to the ER of Arabidopsis (Leroch et al, 2008). ER-ANT1 was shown to act as an ATP/ADP antiporter when heterologously expressed in Escherichia coli and to exhibit a submillimolar affinity for both substrates.…”

The Arabidopsis Thylakoid ADP/ATP Carrier TAAC Has an Additional Role in Supplying Plastidic Phosphoadenosine 5′-Phosphosulfate to the Cytosol

“…It may be noted that Arabidopsis also contains orthologs of animal PAPS transporters; however, these proteins do not share sequence similarities with MCF family members (see Supplemental Figure 5 online), are not localized to the plastid envelope (see Supplemental Figure 4 online), and corresponding mutant plants are not affected in GS contents (see Supplemental Figure 3 online). MCF members are not confined to mitochondria but are also found in other cell compartments, namely, chloroplasts, peroxisomes, the endoplasmic reticulum, or the plasma membrane (Bedhomme et al, 2005;Bouvier et al, 2006;Thuswaldner et al, 2007;Kirchberger et al, 2008;Leroch et al, 2008;Linka et al, 2008;Palmieri et al, 2008Palmieri et al, , 2009Rieder and Neuhaus, 2011;Bernhardt et al, 2012). They mediate the transport of various substrates, including nucleotides, mainly in an antiport manner (Palmieri et al, 2011).…”

Molecular Identification and Functional Characterization of Arabidopsis thaliana Mitochondrial and Chloroplastic NAD+ Carrier Proteins

“…The most prominent member is the mitochondrial ADP/ATP carrier AAC (4), but MCF-type nucleotide transporters have also been identified in peroxisomes (7,18), in plastids (19,20), and in the endoplasmic reticulum of higher plants (21). The transport modes catalyzed by MCF-type adenylate nucleotide transporters range from typical ADP/ATP counterexchange in mitochondria (4) to ATP/AMP exchange in peroxisomes (7,18) and in Arabidopsis mitochondria (22) range from ADP-glucose/ADP exchange in maize endosperm amyloplasts (23) to unidirectional adenylate export from plastids (20,23).…”