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- 저자 : rtensteiner, S. (검색결과 4 건)
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The Arabidopsis vacuolar malate channel is a member of the ALMT family
Kovermann, Peter,Meyer, Stefan,Hö,rtensteiner, Stefan,Picco, Cristiana,Scholz-Starke, Joachim,Ravera, Silvia,Lee, Youngsook,Martinoia, Enrico Blackwell Publishing Ltd 2007 The Plant journal Vol.52 No.6
<P>Summary</P><P>In plants, malate is a central metabolite and fulfills a large number of functions. Vacuolar malate may reach very high concentrations and fluctuate rapidly, whereas cytosolic malate is kept at a constant level allowing optimal metabolism. Recently, a vacuolar malate transporter (<I>Arabidopsis thaliana</I> tonoplast dicarboxylate transporter, <I>At</I>tDT) was identified that did not correspond to the well-characterized vacuolar malate channel. We therefore hypothesized that a member of the aluminum-activated malate transporter (ALMT) gene family could code for a vacuolar malate channel. Using GFP fusion constructs, we could show that <I>At</I>ALMT9 (<I>A. thaliana</I> ALMT9) is targeted to the vacuole. Promoter-GUS fusion constructs demonstrated that this gene is expressed in all organs, but is cell-type specific as GUS activity in leaves was detected nearly exclusively in mesophyll cells. Patch-clamp analysis of an <I>Atalmt9</I> T-DNA insertion mutant exhibited strongly reduced vacuolar malate channel activity. In order to functionally characterize <I>At</I>ALMT9 as a malate channel, we heterologously expressed this gene in tobacco and in oocytes. Overexpression of <I>At</I>ALMT9-GFP in <I>Nicotiana benthamiana</I> leaves strongly enhanced the malate current densities across the mesophyll tonoplasts. Functional expression of <I>At</I>ALMT9 in <I>Xenopus</I> oocytes induced anion currents, which were clearly distinguishable from endogenous oocyte currents. Our results demonstrate that <I>At</I>ALMT9 is a vacuolar malate channel. Deletion mutants for <I>At</I>ALMT9 exhibit only slightly reduced malate content in mesophyll protoplasts and no visible phenotype, indicating that <I>At</I>tDT and the residual malate channel activity are sufficient to sustain the transport activity necessary to regulate the cytosolic malate homeostasis.</P>
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Arabidopsis NAC016 promotes chlorophyll breakdown by directly upregulating STAYGREEN1 transcription
Sakuraba, Y.,Han, S. H.,Lee, S. H.,Hö,rtensteiner, S.,Paek, N. C. Springer International 2016 Plant cell reports Vol. No.
<P>During leaf senescence or abiotic stress in Arabidopsis thaliana, STAYGREEN1 (SGR1) promotes chlorophyll (Chl) degradation, acting with Chl catabolic enzymes, but the mechanism regulating SGR1 transcription remains largely unknown. Here, we show that the Arabidopsis senescence-associated NAC transcription factor NAC016 directly activates SGR1 transcription. Under senescence-promoting conditions, the expression of SGR1 was downregulated in nac016-1 mutants and upregulated in NAC016-overexpressing (NAC016-OX) plants. By yeast one-hybrid and chromatin immunoprecipitation assays, we found that NAC016 directly binds to the SGR1 promoter, which contains the NAC016-specific binding motif (termed the NAC016BM). Furthermore, nac016-1 SGR1-OX plants showed an early leaf yellowing phenotype, similar to SGR1-OX plants, confirming that NAC016 directly activates SGR1 expression in the leaf senescence regulatory cascade. Although we found that NAC016 activates SGR1 expression in senescing leaves, this transcriptional regulation is considerably weaker in maturing seeds; the seeds of sgr1-1 mutants (also known as nonyellowing1-1, nye1-1) stayed green, while the seeds of nac016-1 mutants turned from green to yellow normally. We also found that the abscisic acid (ABA) signaling-related transcription factor genes ABI5 and EEL and the ABA biosynthesis gene AAO3, which activate SGR1 expression directly or indirectly, were significantly downregulated in nac016-1 mutants and upregulated in NAC016-OX plants. However, the NAC016BM does not exist in their promoter regions, indicating that NAC016 may indirectly activate these ABA signaling and biosynthesis genes, probably by directly activating transcriptional cascades regulated by the NAC transcription factor NAP. The NAC016-mediated regulatory cascades of SGR1 and other Chl degradation-related genes are discussed.</P>
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Sakuraba, Yasuhito,Lee, Sang-Hwa,Kim, Ye-Sol,Park, Ohkmae K.,Hö,rtensteiner, Stefan,Paek, Nam-Chon Oxford University Press 2014 Journal of experimental botany Vol.65 No.14
<P>Plant autophagy, one of the essential proteolysis systems, balances proteome and nutrient levels in cells of the whole plant. Autophagy has been studied by analysing <I>Arabidopsis thaliana</I> autophagy-defective <I>atg</I> mutants, but the relationship between autophagy and chlorophyll (Chl) breakdown during stress-induced leaf yellowing remains unclear. During natural senescence or under abiotic-stress conditions, extensive cell death and early yellowing occurs in the leaves of <I>atg</I> mutants. A new finding is revealed that <I>atg5</I> and <I>atg7</I> mutants exhibit a functional stay-green phenotype under mild abiotic-stress conditions, but leaf yellowing proceeds normally in wild-type leaves under these conditions. Under mild salt stress, <I>atg5</I> leaves retained high levels of Chls and all photosystem proteins and maintained a normal chloroplast structure. Furthermore, a double mutant of <I>atg5</I> and non-functional stay-green <I>nonyellowing1-1</I> (<I>atg5 nye1-1</I>) showed a much stronger stay-green phenotype than either single mutant. Taking these results together, it is proposed that autophagy functions in the non-selective catabolism of Chls and photosynthetic proteins during stress-induced leaf yellowing, in addition to the selective degradation of Chl–apoprotein complexes in the chloroplasts through the senescence-induced STAY-GREEN1/NYE1 and Chl catabolic enzymes.</P>
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송원용,Stefan Hörtensteiner,Rie Tomioka,이영숙,Enrico Martinoia 한국분자세포생물학회 2011 Molecules and cells Vol.31 No.1
PLAC8 motif-containing proteins form a large family and members can be found in fungi, algae, higher plants and animals. They include the PCR proteins of plants. The name giving PLAC8 domain was originally found in a protein residing in the spongiotrophoblast layer of the placenta of mammals. A further motif found in a large number of these proteins including several PCR proteins is the CCXXXXCPC or CLXXXXCPC motif. Despite their wide distribution our knowledge about the function of these proteins is very limited. For most of them two membrane-spanning -helices are predicted, indicating that they are membrane associated or membrane intrinsic proteins. In plants PLAC8 motif-containing proteins have been described to be implicated in two very different functions. On one hand, it has been shown that they are involved in the determination of fruit size and cell number. On the other hand, two members of this family, AtPCR1 and AtPCR2 play an important role in transport of heavy metals such as cadmium or zinc. Transport experiments and approaches to model the 3_D structure of these proteins indicate that they could act as transporters for these divalent cations by forming homomultimers. In this minireview we discuss the present knowledge about this protein family and try to give an outlook on how to integrate the different proposed functions into a common picture about the role of PLAC8 motif-containing proteins.
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