The Arabidopsis TSPO‐related protein is a stress and abscisic acid‐regulated, endoplasmic reticulum–Golgi‐localized membrane protein

Abstract

SUMMARYThe Arabidopsis gene At2g47770 encodes a membrane-bound protein designated AtTSPO (Arabidopsis thaliana TSPO-related). AtTSPO is related to the bacterial outer membrane tryptophan-rich sensory protein (TspO) and the mammalian mitochondrial 18-kDa translocator protein (18 kDa TSPO), members of the group of TspO/MBR domain-containing membrane proteins. In this study we show that AtTSPO is mainly detected in dry seeds, but can be induced in vegetative tissues by osmotic or salt stress or abscisic acid (ABA) treatment, corroborating available transcriptome data. Using subcellular fractionation, immunocytochemistry and fluorescent protein tagging approaches we present evidence that AtTSPO is targeted to the secretory pathway in plants. Induced or constitutively expressed AtTSPO can be detected in the endoplasmic reticulum and the Golgi stacks of plant cells. AtTSPO tagged with fluorescent protein in transgenic plants (Arabidopsis and tobacco) was mainly detected in the Golgi stacks of leaf epidermal cells. Constitutive expression of AtTSPO resulted in increased sensitivity to NaCl, but not to osmotic stress, and in reduced greening of cultured Arabidopsis cells under light growing conditions. Transgenic Arabidopsis plants overexpressing AtTSPO were more sensitive to ABA-induced growth inhibition, indicating that constitutive expression of AtTSPO may enhance ABA sensitivity. AtTSPO is rapidly downregulated during seed imbibition, and the ABA-dependent induction in plant is transient. Downregulation of AtTSPO seems to be boosted by treatment with aminolevulinic acid. Taken together, these results suggest that AtTSPO is a highly regulated protein, induced by abiotic stress to modulate, at least in part, transient intracellular ABA-dependent stress perception and/or signalling.

POLYPRENOL REDUCTASE2 Deficiency Is Lethal in Arabidopsis Due to Male Sterility

“…Proteins were isolated according to Guillaumot et al (2009). Protein extracts (30 µg/line) were separated by SDS-PAGE (10%), and two methods, using either Concanavalin A or Emerald 300, were subsequently employed to detect glycosylated proteins.…”

Analysis of the role of RNS2 and autophagy in the turnover of ribosomal RNA in Arabidopsis thaliana

“…Tryptophan-rich sensory protein/peripheral-type benzodiazepine receptor domainanchored proteins (TSPOs) are membrane-anchored proteins likely involved in transmembrane signaling (Guillaumot et al 2009). One characterized member of this large group of proteins is the mammalian 18-kDa translocator protein which is located in the outer mitochondrial membrane, binds cholesterol and porphyrins, and is central to the import of cholesterol into the mitochondrion (Lacapere et al 2001;Papadopoulos et al 2006).…”

“…One characterized member of this large group of proteins is the mammalian 18-kDa translocator protein which is located in the outer mitochondrial membrane, binds cholesterol and porphyrins, and is central to the import of cholesterol into the mitochondrion (Lacapere et al 2001;Papadopoulos et al 2006). A TSPO protein has also been identified in Arabidopsis (AtTSPO; At2g47770) and is found mostly in desiccated plant structures (Corsi et al 2004;Guillaumot et al 2009). AtTSPO is upregulated in vegetative tissues by exposure to abiotic stress or abscisic acid (ABA) treatment, and the protein is targeted to the secretory pathway.…”

“…It too is a membrane protein and is localized to the ER and Golgi membrane. (Guillaumot et al 2009). Currently it is thought to be a regulator of multiple abiotic stress responses (Kant et al 2008;Vanhee et al 2011).…”

“…In plants, porphyrins (tetrapyrroles), namely chlorophyll and hemes, are synthesized within plastids but are also required elsewhere in the cell. During Moreover, since the experimental overexpression of AtTSPO causes cells to be more sensitive to salt stress and ABA, AtTSPO may only be needed by the cells temporarily, requiring downregulation shortly after induction to avoid cellular imbalances (Guillaumot et al 2009). …”