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OsGAP1 Functions as a Positive Regulator of OsRab11-mediated TGN to PM or Vacuole Trafficking
Heo, Jae Bok,Rho, Hee Sun,Kim, Se Won,Hwang, Sung Min,Kwon, Hyun Jin,Nahm, Min Yeop,Bang, Woo Young,Bahk, Jeong Dong Oxford University Press 2005 Plant & cell physiology Vol.46 No.12
<P>The Ypt/Rab family of small G-proteins is important in regulating vesicular transport. Rabs hydrolyze GTP very slowly on their own and require GTPase-activating proteins (GAPs). Here we report the identification and characterization of OsGAP1, a Rab-specific rice GAP. OsGAP1 strongly stimulated OsRab8a and OsRab11, which are homologs of the mammalian Rab8 and Rab11 proteins that are essential for Golgi to plasma membrane (PM) and <I>trans</I>-Golgi network (TGN) to PM trafficking, respectively. Substitution of two invariant arginines within the catalytic domain of <I>Oryza sativa</I> GTPase-activating protein 1 (OsGAP1) with alanines significantly inhibited its GAP activity. In vivo targeting experiments revealed that OsGAP1 localizes to the TGN or pre-vacuolar compartment (PVC). A yeast expression system demonstrated that wild-type OsGAP1 facilitates <I>O. sativa</I> dissociation inhibitor 3 (OsGDI3)-catalyzed OsRab11 recycling at an early stage, but the OsGAP1(R385A) and (R450A) mutants do not. Thus, GTP hydrolysis is essential for Rab recycling. Moreover, expression of the OsGAP1 mutants in <I>Arabidopsis</I> protoplasts inhibited the trafficking of some cargo proteins, including the PM-localizing H<SUP>+</SUP>-ATPase–green fluorescent protein (GFP) and Ca<SUP>2+</SUP>-ATPase8–GFP and the central vacuole-localizing <I>Arabidopsis</I> aleurain-like protein (AALP)–GFP. The OsGAP1 mutants caused these proteins to accumulate at the Golgi apparatus. Surprisingly, OsRab11 overproduction relieved the inhibitory effect of the OsGAP1 mutants on vesicular trafficking. OsRab8a had no such effect. Thus, the OsGAP1 mutants may inhibit TGN to PM or central vacuole trafficking because they induce the sequestration of endogenous Rab11. We propose that OsGAP1 facilitates vesicular trafficking from the TGN to the PM or central vacuole by both stimulating the GTPase activity of OsRab11 and increasing the recycling of inactive OsRab11.</P>
Rice Small GTPase Rab11 is involved in Pathogen Defense Signaling
Jae Bok Heo 한국육종학회 2014 한국육종학회 심포지엄 Vol.2014 No.07
Small GTP binding protein, Rab GTPases are a large family of proteins with a variety of regulatory functions in membrane traffic and development. Previously, we characterized OsRab11, which in concert with OsGAP1 and OsGDI3 regulates vesicular trafficking from the trans-Golgi network (TGN) to the plasma membrane or vacuole. To further elucidate the physiological function of OsRab11 in plants, we performed yeast two-hybrid screens using OsRab11 as bait. OsOPR8 was isolated and shown to interact with OsRab11. A co-immunoprecipitation assay confirmed this interaction. The green fluorescent protein-OsOPR8 fusion product was targeted to the cytoplasm and peroxisomes of protoplasts from Arabidopsis thaliana. OsOPR8 exhibited NADPH-dependent reduction activity when 2-cyclohexen-1-one (CyHE) and 12-oxophytodienoic acid (OPDA) were supplied as possible substrates. Interestingly, NADPH oxidation by OsOPR8 was increased when wild-type OsRab11 or the constitutively active form of OsRab11 (Q78L) were included in the reaction mix, but not when the dominant negative form of OsRab11 (S28N) was included. OsRab11 was expressed broadly in plants and both OsRab11 and OsOPR8 were induced by jasmonic acid (JA) and elicitor treatments. Overexpressed OsRab11 transgenic plants showed resistance to pathogens through induced expression of JA-responsive genes. In conclusion, OsRab11 may be required for JA-mediated defense signaling by activating the reducing activity of OsOPR8.
Epigenetic repression of flowering pathway genes by long non-coding RNA in Arabidopsis
Jae Bok Heo 한국육종학회 2013 한국육종학회 심포지엄 Vol.2013 No.07
In some plant species, prolonged exposure to low temperature during the winter season is necessary to acquire the competence to flower in the following spring. This process, known as vernalization, is an epigenetic change in which a mitotically stable change of the developmental potential of the meristem (competence to flower) is maintained even in the absence of the inducing signal (prolonged cold exposure). In Arabidopsis, vernalization results in stable epigenetic repression of a potent floral repressor, FLOWERING LOCUS C (FLC). Increased enrichment of Polycomb Repressive Complex 2 (PRC2) and trimethylated Histone H3 Lys 27 (H3K27me3) at FLC chromatin is necessary for the stable maintenance of FLC repression by vernalization. A long intronic noncoding RNA (termed as COLDAIR) is required for the vernalization-mediated epigenetic repression of FLC. COLDAIR physically associates with a component of PRC2 and targets PRC2 to FLC. COLDAIR is required for establishing stable repressive chromatin at FLC through its interaction with PRC2. In addition, floral integrator genes are targets of PRC2 complex, resulting in delayed flowering time through repression mechanism of PRC2 complex. Recently another long non-coding RNA was isolated from floral integrator gene and characterized the function of this long non coding RNA.
Overexpression of Constitutively Active OsRab11 in Plants Enhances Tolerance to High Salinity Levels
Jae Bok Heo,Chong Chen 한국식물학회 2018 Journal of Plant Biology Vol.61 No.3
Rab proteins are key regulators of intracellulartrafficking between specific compartments in a cell. Amongthem, Rab11, a widely conserved sub-group, mainly regulatesplasma membrane (PM) trafficking. Previously, we reportedthat Oryza sativa Rab11 (OsRab11) plays an importantrole in the intracellular trafficking from the trans-Golginetwork(TGN) to the plasma membrane (PM) andprevacuolar compartments (PVCs), and in the plant’sresponse to high salt stress. In this study, when theconstitutively active mutant of OsRab11, (CA OsRab11(Q73L))was co-transformed with Arabidopsis Ca2+-ATPase8-GFP(ACA8-GFP) or sporamin-GFP (Spo-GFP) into Arabidopsisprotoplasts, the PM or vacuolar trafficking proportion ofthe reporter proteins was highly increased. TransgenicArabidopsis plants overexpressing (OE) CA OsRab11(Q73L)exhibited enhanced tolerance to high salt stress andexogenous abscisic acid (ABA) compared to Col plants. Moreover, certain stress-responsive genes were expressedunder high salt stress and ABA treatment in OEOsRab11(Q73L) plants. Thus, these results suggest thatthe active conformation of OsRab11 may be required tomodulate plant responses to salt and ABA via theregulation of the expression of stress-responsive genes.
XLG2 and RTV1 overexpression promote flowering
Minji Hong,Jae Bok Heo 한국육종학회 2012 한국육종학회 심포지엄 Vol.2012 No.07
Heterotrimeric G proteins, consisting of Gα, Gβ and Gγ subunits, play important roles in plant development and cell signaling. In Arabidopsis, in addition to one prototypical G protein a subunit gene, GPA1, there are three extra-large G proteins, XLG1, XLG2, and XLG3 of largely unknown function. Yeast two-hybrid library screening and in vitro protein pull-down assays revealed that XLG2 interacts with the nuclear protein RELATED TO VERNALIZATION1 (RTV1). A mutant XLG2 that lacks GTP binding does not interact with RTV1, suggesting the dependence of this protein interaction on the G-protein cycle. Electrophoretic mobility shift assays show that RTV1 binds to DNA in vitro in a non-sequence specific manner and that GTP-bound XLG2 promotes the DNA binding activity of RTV1. Overexpression of RTV1 results in early flowering. Combined overexpression of XLG2 and RTV1 enhances this early flowering phenotype, and elevates expression of the floral pathway integrator genes, FT and SOC1, but does not repress expression of the floral repressor, FLC. Chromatin immunoprecipitation assays show that XLG2 increases RTV1 binding to FT and SOC1 promoters. Thus, a Ca2+-dependent Gprotein, XLG2, promotes RTV1 DNA binding activity for a subset of floral integrator genes, and contributes to floral transition.