The multi-stress regulator TSPO is transiently induced by abiotic stresses. at

The multi-stress regulator TSPO is transiently induced by abiotic stresses. at the endoplasmic reticulum and Golgi membranes in planta. Intriguingly constitutive expression of fluorescently tagged PIP2;7 in TSPO-overexpressing transgenic lines resulted in patchy distribution of the fluorescence reminiscent of the pattern of constitutively expressed yellow fluorescent protein-TSPO in transcriptome is responsive to ABA signaling (Wang et al. 2011 Extensive studies of stress and ABA-induced gene expression during vegetative growth revealed MGCD0103 two waves of response: an early transient response peaking at ~3 h and a late sustained response from 10 h onward (reviewed in Finkelstein 2013 Characteristically the so-called “early” genes encode regulatory proteins such as transcription factors protein kinases and phosphatases and a set of proteins of unknown function (Yamaguchi-Shinozaki and Shinozaki 2006 Fujita et al. 2006 The “late” genes are presumed to contribute to plant adaptation to the stress and encode proteins such as the late MGCD0103 embryonic abundant proteins chaperonins enzymes ion and water-channel proteins and reactive oxygen species scavengers (Fujita et al. 2006 MGCD0103 Yamaguchi-Shinozaki and Shinozaki 2006 The tryptophan-rich sensory protein/translocator (TSPO) is a multi-stress regulator that is transiently induced in the plant cell (Kreps et al. 2002 Seki et al. 2002 Zimmermann et al. 2004 Winter et al. 2007 Guillaumot et al. 2009 Hermans et al. 2010 Vanhee et al. 2011 Transcriptionally ABA-induced TSPO expression peaks at ~3 MGCD0103 h postinduction; also SAT1 it is one of the most strongly induced “early” genes and is of unknown function. This polytopic membrane protein is encoded by a single locus (At2g47770) in and belongs to the so-called tryptophan-rich sensory protein/peripheral-type benzodiazepine receptor (TspO/MBR) group of proteins (Papadopoulos et al. 2006 Members of this group of membrane proteins are found with few exceptions in organisms ranging from Archaea to metazoans (reviewed in Gavish et al. 1999 Lacapère and Papadopoulos 2003 Papadopoulos et al. 2006 Since their identification in the late 1970s (Braestrup et al. 1977 TSPOs have been the subject of intensive research almost exclusively in animal cells to pinpoint their function. The mammalian 18-kD translocator protein TSPO1 was thought to be encoded by an essential gene and involved in a range of physiological functions and pathologies (Papadopoulos et al. 2006 Rupprecht et al. 2009 A second isoform TSPO2 is cell specific and functions in erythroid development (Fan et al. 2009 One of the main functions attributed to mammalian TSPOs is their possible involvement in steroid metabolism and mitochondrial physiology (reviewed in Rupprecht et al. 2010 although recent evidence has challenged these acceptations showing for example that mice TSPO1 is not essential and plays no role in steroidogenesis (Morohaku et al. 2014 Sileikyte et al. 2014 Stocco 2014 It is well documented that TSPOs can form functional homo-oligomers and hetero-oligomers with soluble and membrane-bound partners (reviewed in Papadopoulos et al. 2006 In addition mammalian TSPOs can regulate the expression or stability of their MGCD0103 interacting partner. For instance overexpression of TSPO1 inhibits the expression of the mitochondrial voltage-dependent anion channel 1 (VDAC1) and the silencing of TSPO1 increases VDAC1 expression in endothelial MGCD0103 cells (Joo et al. 2012 Mammalian TSPO can also regulate the expression of a noninteracting protein. For example TSPO1 is upregulated in CD4+ T cells infected by the human immunodeficient virus 1 (HIV1) and inhibits virus envelope protein expression by promoting its degradation through the endoplasmic reticulum-associated degradation pathway (Zhou et al. 2014 TSPOs were only recently described in plants (Corsi et al. 2004 Lindemann et al. 2004 Frank et al. 2007 Guillaumot et al. 2009 and in contrast to the situation in mammals plant TSPOs appear to be nonessential suggesting a potential functional divergence through the evolution of these proteins. TSPO is.