Plant Cell Polarity: The Ins-and-Outs of Sterol Transport

Betts, Hazel; Moore, Ian

doi:10.1016/j.cub.2003.09.023

Cited by 15 publications

(7 citation statements)

References 18 publications

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“…Sterol trafficking in plants was shown to be actin dependent and BFA sensitive, and the PIN2 putative auxin transporter was colocalized with sterols after BFA treatments . Consistently, PIN1 localization was altered in sterol methyltransferase1 mutants (Willemsen et al, 2003), and several sterol biosynthetic Arabidopsis mutants were shown to be disturbed in cell and tissue polarity (Betts and Moore, 2003). The ectopic expression of mutant forms of AtRAC10 in Arabidopsis affected plant morphology, leaf mesophyll cell shape (Figures 1 and 2), vascular differentiation, and auxin response (our unpublished data).…”

Section: Membrane Localization Of Atrac10mentioning

confidence: 60%

Ectopic Expression of an Activated RAC inArabidopsisDisrupts Membrane Cycling

Bloch

Lavy

Efrat

et al. 2005

MBoC

133

117

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Rho GTPases regulate the actin cytoskeleton, exocytosis, endocytosis, and other signaling cascades. Rhos are subdivided into four subfamilies designated Rho, Racs, Cdc42, and a plant-specific group designated RACs/Rops. This research demonstrates that ectopic expression of a constitutive active Arabidopsis RAC, AtRAC10, disrupts actin cytoskeleton organization and membrane cycling. We created transgenic plants expressing either wild-type or constitutive active INTRODUCTIONRho GTPases are molecular switches best known for regulating actin organization (Hall, 1998). Rhos are subdivided into four subfamilies designated Rho, Racs, Cdc42, and a plant-specific group designated RACs or Rops (Hall, 1998;Winge et al., 2000;Yang, 2002). In animal cells, Rhos, Racs, and Cdc42 differentially regulate the actin cytoskeleton (Hall, 1998). Similarly, plant RACs are shown to regulate actin organization (Fu et al., 2001Molendijk et al., 2001;Jones et al., 2002;Yang, 2002;Chen et al., 2003;Cheung et al., 2003).Rhos seem to regulate exocytosis and endocytosis events such as pinocytosis, endocytosis of clathrin-coated pits, and localization of the multiprotein vesicle-tethering complex, the exocyst (Ridley et al., 1992;Lamaze et al., 1996;Di Cesare et al., 2000;Donaldson and Jackson, 2000;Malecz et al., 2000;Guo et al., 2001;Etienne-Manneville and Hall, 2002). Vesicle transport can be divided into five major steps: budding from a source membrane, targeting of the vesicle to specific regions, priming, docking at the target membrane, and fusion of the vesicles with the target membrane (Pfeffer, 1994(Pfeffer, , 2001Jurgens and Geldner, 2002). In yeast, Cdc42 and Rho1 have been shown to regulate homotypic vesicle docking during vacuole formation in an actin-dependent manner (Eitzen et al., 2001(Eitzen et al., . 2002Muller et al., 2001;Eitzen, 2003), whereas Rho3 and Cdc42 regulate vesicle docking late in exocytosis during polar growth in budding yeast independent of their role in actin polarization (Adamo et al., 1999(Adamo et al., , 2001. In addition, it is well established that actin cytoskeleton function is crucial for endocytosis (Engqvist-Goldstein and Drubin, 2003).Like other members of the Ras superfamily of small GTPases, Rhos exist in either GTP-bound active state or GDP-bound inactive state. Rhos have an intrinsic GTPase activity that is enhanced via interaction with GTPase-activating proteins. Activation of the Rhos occurs via interaction with GDP/GTP exchange factors (GEFs). Conserved dominant mutations abolishing the GTPase activity render Rhos constitutive active. Other conserved mutations preventing the GDP/GTP exchange are thought to cause irreversible interactions between the mutant Rhos and GEFs, converting the former dominant negative mutants (Hall, 1998;Winge et al., 2000;Yang, 2002).The plant-specific Rho subfamily, designated either RACs or Rops, is subdivided into two major subgroups called type-I and type-II (Winge et al., 2000;Yang, 2002;Christensen et al., 2003). All type-I RACs are putatively prenylated, whe...

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Section: Membrane Localization Of Atrac10mentioning

confidence: 60%

Ectopic Expression of an Activated RAC inArabidopsisDisrupts Membrane Cycling

Bloch

Lavy

Efrat

et al. 2005

MBoC

133

117

View full text Add to dashboard Cite

show abstract

“…In these studies, annexin XIIIb specifically associates with cholesterolenriched lipid microdomains, and these domains are proposed to determine which apical transport vesicles are targeted for apical transport. There is evidence that plant cells may also have these sterol-enriched membrane microdomains (Peskan et al 2000), and it has been suggested that sterols play an important role in polarity development in plants based on observations of mutants in sterol biosynthesis (Betts and Moore 2003). Specifically, the SMT1-deficient orc mutant (smt1 orc ) exhibits pleiotropic developmental defects and this phenotype is attributed to reduced membrane sterol content and suggested to occur due to a loss of cell and tissue polarity (Willemsen et al 2003).…”

Section: Discussionmentioning

confidence: 97%

Immunolocalization and histochemical evidence for the association of two different Arabidopsis annexins with secretion during early seedling growth and development

Clark

Lee

Dauwalder

et al. 2004

Planta

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Annexins are a multigene, multifunctional family of calcium-dependent, membrane-binding proteins found in animal and plant cells. In plants, annexins have been localized in the cytoplasm and at the cell periphery of highly secretory cell types, and in the tip region of polarly growing cells. Consequently, one proposed function for annexins in plant cells is participation in the Golgi-mediated secretion of new wall materials. In Arabidopsis, there are eight different annexin cDNAs, which share between 30% and 81% deduced amino acid sequence identity. We have used two monospecific Arabidopsis anti-annexin antibodies, raised against divergent 31-mer peptides from AnnAt1 and AnnAt2 and a previously characterized pea anti-annexin p35 antibody, for Western blot and immunolocalization studies in Arabidopsis. Western blot analyses of various Arabidopsis protein fractions showed that the two Arabidopsis antibodies are able to specifically recognize annexins in both soluble and membrane fractions. Immunofluorescence results with the three annexin antibodies show staining of secretory cells, especially at the cell periphery in developing sieve tubes, outer root cap cells, and in root hairs, consistent with previous results. In developmentally different stages some staining was also seen near the apical meristem, in some leaf cells, and in phloem-associated cells. Autoradiography following 3H-galactose incorporation was used to more clearly correlate active secretion of wall materials with the localization patterns of a specific individual annexin protein in the same cells at the same developmental stage. The results obtained in this study provide further support for the hypothesis that these two Arabidopsis annexins function in Golgi-mediated secretion during early seedling growth and development.

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“…ER flippase activity (NBD-PC) was affected by ~60% after DEPC and DTNB treatment, ~50% after PG and ~10% after AEBSF [12]. Cholesterol accounts for only 3-10% of total sterols in plant membranes [27]. Also, they do not accumulate at the ER in steady state.…”

Section: Discussionmentioning

confidence: 99%

Inhibition of biogenic membrane flippase activity in reconstituted ER proteoliposomes in the presence of low cholesterol levels

Rajasekharan

Gummadi

2012

Cellular and Molecular Biology Letters

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Abstract:Biogenic membranes or self-synthesizing membranes are the site of synthesis of new lipids such as the endoplasmic reticulum (ER) in eukaryotes. Newly synthesized phospholipids (PLs) at the cytosolic leaflet of ER need to be translocated to the lumen side for membrane biogenesis and this is facilitated by a special class of lipid translocators called biogenic membrane flippase. Even though ER is the major site of cholesterol synthesis, it contains very low amounts of cholesterol, since newly synthesized cholesterol in ER is rapidly transported to other organelles and is highly enriched in plasma membrane. Thus, only low levels of cholesterol are present at the biosynthetic compartment (ER), which results in loose packing of ER lipids. We hypothesize that the prevalence of cholesterol in biogenic membranes might affect the rapid flip-flop. To validate our hypothesis, detergent solubilized ER membranes from both bovine liver and spinach leaves were reconstituted into proteoliposomes with varying mol% of cholesterol. Our results show that (i) with increase in the cholesterol/PL ratio, the half-life time of PL translocation increased, suggesting that cholesterol affects the kinetics of flipping, (ii) flipping activity was completely inhibited in proteoliposomes reconstituted with 1 mol% cholesterol, and (iii) FRAP and DSC experiments revealed that 1 mol% cholesterol did not

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Plant Cell Polarity: The Ins-and-Outs of Sterol Transport

Cited by 15 publications

References 18 publications

Ectopic Expression of an Activated RAC inArabidopsisDisrupts Membrane Cycling

Ectopic Expression of an Activated RAC inArabidopsisDisrupts Membrane Cycling

Immunolocalization and histochemical evidence for the association of two different Arabidopsis annexins with secretion during early seedling growth and development

Inhibition of biogenic membrane flippase activity in reconstituted ER proteoliposomes in the presence of low cholesterol levels

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