Download Endomembrane proton pumps: connecting membrane and vesicle

Endomembrane proton pumps: connecting membrane
and vesicle transport
Karin Schumacher
pH-homeostasis in the endomembrane system requires the
activity of proton-pumps. In animals, the progressive
acidification of compartments along the endocytic and
secretory pathways is critical for protein sorting and vesicle
trafficking, and is achieved by the activity of the vacuolar
H+-ATPase (V-ATPase). Plants have an additional
endomembrane pump, the vacuolar H+-pyrophosphatase
(V-PPase), and previous research was largely focused on the
respective functions of the two pumps in secondary active
transport across the tonoplast. Recent approaches, including
reverse genetics, have not only provided evidence that both
enzymes play unique and essential roles but have also
highlighted the important functions of the two proton pumps in
endocytic and secretory trafficking.
Addresses
ZMBP-Plant Physiology, Universität Tübingen, Auf der Morgenstelle 1,
72076 Tübingen, Germany
Corresponding author: Schumacher, Karin
([email protected])
Current Opinion in Plant Biology 2006, 9:595–600
This review comes from a themed issue on
Cell biology
Edited by Laurie G Smith and Ulrike Mayer
Available online 27th September 2006
1369-5266/$ – see front matter
# 2006 Elsevier Ltd. All rights reserved.
DOI 10.1016/j.pbi.2006.09.001
Introduction
Compartmentation allows the simultaneous occurrence of
biochemical processes in different reaction spaces and
necessitates the exchange of material via membrane
transport or vesicular intermediates. The compartments
of the highly dynamic eukaryotic endomembrane system
are acidified to varying degrees by the activity of the
vacuolar H+-ATPase (V-ATPase). The pH-differential
between the cytosol and the lumina is a crucial parameter
as it not only affects most biochemical reactions but also
enables secondary active transport. In addition to the
V-ATPase, plants possess a second endomembrane proton pump, the vacuolar H+-pyrophosphatase (V-PPase).
V-ATPase and V-PPase represent up to 30% of total
tonoplast protein, and it is therefore not surprising that
to date their best-studied function is to maintain ion and
metabolite homeostasis by energizing secondary active
www.sciencedirect.com
transport across the tonoplast [1,2]. The purpose of this
review is to highlight recent results demonstrating that
both ‘vacuolar’ proton-pumps have important and nonredundant functions in secretory and endocytic
trafficking.
V-ATPase deficient-mutants
V-ATPases constitute a family of highly conserved, multisubunit proton-pumps that are found throughout the
endomembrane systems of all eukaryotes [3]. They share
a common ancestor with F-ATPases and, like their distant
relatives, are composed of two subcomplexes. The peripheral V1 complex, which consists of eight different
subunits (subunits A–H), is responsible for ATP hydrolysis; whereas the membrane-integral V0 complex comprises six different subunits (subunits a, c, c0 , c00 , d and e)
and is responsible for proton translocation [4].
Yeast vacuolar membrane ATPase (Vma) mutants display a conditional-lethal phenotype, which has greatly
facilitated the analysis of V-ATPase subunit composition
[5]. Vma-mutants fail to grow at neutral pH, but surprisingly the identity of the cellular organelle whose acidification is essential is still not known. The fact that other
yeast mutants that have defects in vacuolar acidification
are viable at neutral pH argues, however, that it is not the
vacuole [6]. In contrast to the conditional lethality of yeast
mutants, mutants identified in several multicellular
organisms have shown that V-ATPase activity is essential
for embryonic or larval development [7–9]. The underlying cellular defects have only been analyzed in mouse
embryos where the lack of the proteolipid subunit leads to
the swelling and vacuolation of the Golgi apparatus [10].
The analysis of null-alleles for Arabidopsis genes that
encode V-ATPase subunits (VHA) has provided evidence
that the V-ATPase is essential, despite the presence of
the V-PPase. A T-DNA insertion allele of VHA-A, the
single-copy gene that encodes the catalytic subunit of the
Arabidopsis V-ATPase, causes complete male and partial
female gametophytic lethality [11]. At the cellular level,
severe changes in the morphology of Golgi stacks and
Golgi-derived vesicles but not of vacuoles were observed
in vha-A mutant pollen [11].
Embryos that lack VHA-E1, one of the three isoforms of
the VHA-E subunit of V-ATPase, are not viable and
display a range of defects including multinucleate cells,
cell wall stubs and abnormal division planes that are
characteristic of cytokinesis-defective mutants [12].
Like vha-A, vha-E1(tuff)-mutants display an abnormal
Current Opinion in Plant Biology 2006, 9:595–600
596 Cell biology
organization of Golgi-stacks, indicating that the V-ATPase
is required to maintain a functional secretory system during
pollen and embryo development [12].
subunit VHA-A of carrot [20], but a recent study of the
two highly homologous isoforms of tomato demonstrates
that they are expressed in a tissue-specific manner [21].
Plants that have reduced V-ATPase activity, caused
either by a weak allele [13] or by RNA interference
(RNAi) [14] are viable, but show reduced growth and
disturbed ion homeostasis [14,15]. Given the effects on
the Golgi apparatus observed in the null mutants, it seems
possible that the growth reduction is caused by problems
in secretory trafficking rather than by reduced turgor
pressure resulting from a lack of osmolyte transport into
the vacuole. Further support for this notion comes from
the analysis of plants lacking activity of the vacuolar H+/
Ca2+-antiporters of the cation exchanger family (CAX). In
cax1 mutants [16] and cax1 cax3 double mutants [17],
V-ATPase activity at the tonoplast is, for reasons that
remain to be determined, reduced to levels comparable
those found in the det3 mutant, which carries a weak allele
of VHA-C [13]. The phenotype of det3 is, however, much
more severe, indicating that V-ATPase activity in a nonvacuolar compartment is largely responsible for the
defects in growth.
In yeast, the two isoforms of subunit a, VPH1 (Vacuolar
acidification-defective 1) and STV1 (Similar To VPH)
[22,23] are differentially localized. Vph1p resides at the
tonoplast, whereas Stv1p cycles continuously between a
late Golgi compartment and prevacuolar endosomes
[23,24]. Two recent publications have addressed the subcellular localization of VHA-a isoforms. Using antibodies
raised against one of the VHA-a isoforms of Mesembryanthemum, Kluge et al. [25] demonstrate convincingly that VHAa is an integral part of V-ATPase complexes found in
tonoplast-enriched vesicles. Nevertheless, the same antibody labels the endoplasmic reticulum (ER) but fails to
detect tonoplast V-ATPase complexes in maize root cells.
On this basis, it is argued that an ER-specific VHA-a
isoform exists in maize [25]. A systematic analysis of the
subcellular localization of the three Arabidopsis VHA-a
isoforms, using green fluorescent protein (GFP)-fusion
proteins expressed under the endogenous promoters, did
not detect an ER-specific isoform. Instead, the distribution
of VHA-a isoforms in Arabidopsis is very similar to that in
yeast: VHA-a2 and VHA-a3 are found at the tonoplast,
whereas VHA-a1 is localized in the trans-Golgi network
(TGN) ([26]; see Figure 1). As in yeast Stv1p, the
targeting information for TGN localization resides in the
amino-terminal cytosolic domain [26]. Moreover, the two
yeast isoforms confer different stability and kinetic properties to the holocomplex [24]. The function and regulation
of the V-ATPase in the TGN are of particular interest as
the use of VHA-a1 as a marker for this compartment has
revealed that it is not only the central sorting station of the
secretory pathway but also that it functions as an early
endosome [26].
V-ATPase isoforms
As null alleles are lethal and weak alleles cause pleiotropic
phenotypes, more specific approaches are needed to
study the biological function of the V-ATPase in different
compartments, tissues, developmental stages or stress
situations. In Arabidopsis, as in other higher eukaryotes,
most V-ATPase subunits are encoded by small gene
families [18]. How this vast potential to form V-ATPase
complexes with different kinetic and regulatory properties is exploited is only beginning to become apparent.
In contrast to the null-allele of the single-copy gene VHAA, which causes male gametophytic lethality, a loss of
VHA-E1 is only manifested during embryo development.
As both VHA-E2 and VHA-E3 are expressed in developing pollen [12], it seems likely that they act redundantly during this stage of development. During
embryogenesis, however, VHA-E1 is the predominant
isoform, whereas VHA-E3 is expressed mainly in the
endosperm and surrounding maternal tissues, and
VHA-E2 is pollen-specific. Interestingly, V-ATPases that
differ only in the presence of two isoforms of VHA-E have
been isolated from pea epicotyls and showed differences
in the kinetics of ATP hydrolysis [19]. Unlike the VHA-E
isoforms, which show considerable divergence in protein
sequence, isoforms of VHA-c are so similar that differences in targeting or activity changes seem impossible.
However, promoter::b-glucuronidase (GUS) analysis
revealed that VHA-c1 is highly expressed in expanding
tissues whereas VHA-c3 is restricted to tissues that have
high demand for V-ATPase, possibly because of particularly active exocytosis [14]. The presence of organellespecific isoforms was first suggested for the catalytic
Current Opinion in Plant Biology 2006, 9:595–600
V-ATPase inhibitors
The identification of organelle-specific V-ATPase isoforms now allows us to address their functions in the
different compartments more specifically but, to date,
most of our knowledge of V-ATPase functions in trafficking is based on pharmacology. Concanamycin A (ConcA)
and Bafilomycin A (BafA) are membrane-permeable
macrolide antibiotics that bind to subunits c [27,28]
and a [29], thus inhibiting proton transport by V-ATPases.
Numerous pharmacological studies using these potent
and specific inhibitors in mammalian cells have established that V-ATPase activity is crucial for many aspects
of the mammalian secretory and endocytic pathways,
including the dissociation of receptor–ligand complexes
[30], the recruitment of proteins that are involved in
vesicle formation [31,32], and transport between different
endosomal compartments [33–35].
Only a few studies have described the effects of ConcA or
BafA on trafficking in plants. In tobacco cells, inhibition
www.sciencedirect.com
Endomembrane proton pumps Schumacher 597
Figure 1
Proton pumps in the plant endomembrane system. A schematic depiction of the distribution of proton pumps in the plant endomembrane system.
Recent findings by Dettmer et al. [26] suggest that endocytic and secretory trafficking merge in the TGN/early endosome, highlighting the
importance of this compartment as the central hub of protein trafficking. Question marks indicate that localization of the V-PPase isoforms needs
to be identified. PVC: prevacuolar compartment; MVB: multivesicular body.
of the V-ATPase interferes with secretion and leads to the
mis-sorting of vacuolar proteins, suggesting that the functionality of a non-vacuolar compartment depends on
V-ATPase function [36]. It has never been shown that
ConcA induces an alkalinization of plant vacuoles. Nevertheless, several recent studies have ascribed the ConcAinduced stabilization of GFP [37] or autophagic bodies in
the vacuolar lumen to an increase in vacuolar pH [38,39]
rather than to a defect in the sorting of vacuolar hydrolases. Electron microscopy of chemically fixed BY2 cells
showed that both ConcA and BafA cause massive vacuolation of the Golgi apparatus [40]. High-pressure-frozen
Arabidopsis root cells that were treated with ConcA
showed changes in Golgi morphology and aggregations
of vesicles [26], similar to those observed in vha-mutant
cells. In support of the proposed dual function of the
TGN, ConcA blocks both the trafficking of newly synthesized proteins to the PM and transport of endocytic
tracers from the PM to the vacuole.
How does a lack of V-ATPase activity lead to a
block in vesicle trafficking?
It is possible that the structural integrity of the Golgi
apparatus requires acidification [41], but a direct connection between acidification and vesicle trafficking is now
becoming apparent. Recruitment of components of the
vesicle budding machinery to membranes can depend on
www.sciencedirect.com
luminal acidification [31,32,42], but we did not know
how the pH information is transmitted across the membrane. Recently, Hurtado-Lorenzo et al. [43] have
provided very convincing evidence that subunits of the
mammalian V-ATPase interact directly, and in a luminalpH-dependent manner, with proteins that regulate endocytic trafficking. The V-ATPase can thus be regarded as a
pH-sensor that is able to communicate luminal pH to
cytosolic proteins. Moreover, a function for Vo subunits in
membrane fusion, which was first demonstrated for
homotypic vacuole fusion in yeast [44], has recently
also been identified during synaptic vesicle fusion in
Drosophila [45], indicating that this could be a common
feature of vesicle-fusion events.
The V-PPase
In comparison to the V-ATPase, the V-PPase is a much
simpler enzyme. It is a homodimer of a single polypeptide
and it uses the energy of the phosphoanhydride bond of
pyrophosphate (PPi) to drive proton transport across
membranes [46]. PPi is a by-product of several biosynthetic processes, and it has therefore been argued that the
V-PPase is the predominant proton pump in the vacuoles
of young, growing cells [47]. Like the V-ATPase, it has
long been known that the V-PPase is not restricted to the
tonoplast but is also present and active at the PM,
the TGN and in multivesicular bodies [48]. In fact,
Current Opinion in Plant Biology 2006, 9:595–600
598 Cell biology
Arabidopsis VACUOLAR H+-PYROPHOSPHATASE2
(AVP2)/AVPL1, a representative of the K+-independent
type II H+-PPases, is found exclusively in Golgi stacks
[49].
beyond proton-pumping is accumulating in other
systems, and it will be of great interest to see if plant
V-ATPases are also more than just ‘simple’ proton pumps.
Acknowledgements
A null-allele of AVP1 causes a severe phenotype that is
reminiscent of seedlings treated with inhibitors of polar
auxin transport [50]. Indeed, levels of the auxin-efflux
carrier PIN-FORMED1 (PIN1) and consequently polar
auxin transport are reduced in avp1 mutant roots.
Furthermore, Li et al. [50] showed that the levels and
activity of the plasma membrane P-type H+-ATPase are
reduced in these mutants, resulting in an increase in
apoplastic pH. Overexpression of AVP1 causes opposite,
yet more pronounced, effects on apoplastic pH but,
unexpectedly, does not increase levels of PIN1. According to the acid-growth theory, a change in apoplastic pH
would directly affect cell expansion and could impinge on
the uptake component of polar auxin transport. However,
the causal relation between V-PPase levels, the abundance and activity of the plasma membrane H+-ATPase,
and the abundance and activity of PIN1 still remains to be
elucidated. Manipulation of AVP1 expression not only
reveals a close connection between endomembrane proton pumps and auxin-mediated development but might
also represent an efficient approach for the engineering of
drought-tolerant crops. Overexpression of AVP1 confers
tolerance towards water stress in both Arabidopsis [51] and
tomato [52]. Initially this effect was ascribed to the
‘classic’ function of the V-PPase in vacuolar uptake of
ions, causing increased water uptake. In the light of the
recent results, however, it seems likely to be caused by
auxin-enhanced root growth.
I would like to thank members of my laboratory for many discussions and
Felicity de Courcy for critical reading of the manuscript. Work in my
laboratory is funded by the German Research Council through grants within
SPP1108 and SFB446.
The avp1 phenotype clearly indicates that the V-PPase
cannot be considered as a mere back-up for the V-ATPase
that is only important under conditions in which ATP
becomes limiting. Yet the functional relation between the
two pumps needs further investigation because several
results indicate that they are co-regulated and might
interact physically [53]. Most recently, it was shown that
Arabidopsis plants that overexpress a V-PPase from the
halophyte Suaeda salsa show increased V-ATPase activity
under salt and drought stress [54].
Conclusions
Although it has been known for a long time that the
V-ATPase and the V-PPase are found throughout the
endomembrane system, our view of their biological function was dominated by their role in energizing transport
across the tonoplast. In recent years, our view has
been substantially widened and it is now clear that they
are also important players in trafficking vesicles along
the endocytic and secretory pathways. The next challenge is to understand how the two proton-pumps
contribute to the dynamics of the endomembrane system.
Moreover, evidence for functions of the V-ATPase
Current Opinion in Plant Biology 2006, 9:595–600
References and recommended reading
Papers of particular interest, published within the annual period of
review, have been highlighted as:
of special interest
of outstanding interest
1.
Sze H, Li X, Palmgren MG: Energization of plant cell membranes
by H+-pumping ATPases. Regulation and biosynthesis.
Plant Cell 1999, 11:677-690.
2.
Kluge C, Lahr J, Hanitzsch M, Bolte S, Golldack D, Dietz KJ: New
insight into the structure and regulation of the plant vacuolar
H+-ATPase. J Bioenerg Biomembr 2003, 35:377-388.
3.
Nishi T, Forgac M: The vacuolar (H+)-ATPases — nature’s most
versatile proton pumps. Nat Rev Mol Cell Biol 2002, 3:94-103.
4.
Beyenbach KW, Wieczorek H: The V-type H+ ATPase: molecular
structure and function, physiological roles and regulation.
J Exp Biol 2006, 209:577-589.
5.
Kane PM: The where, when, and how of organelle acidification
by the yeast vacuolar H+-ATPase. Microbiol Mol Biol Rev 2006,
70:177-191.
6.
Nelson N, Perzov N, Cohen A, Hagai K, Padler V, Nelson H:
The cellular biology of proton-motive force generation
by V-ATPases. J Exp Biol 2000, 203:89-95.
7.
Davies SA, Goodwin SF, Kelly DC, Wang Z, Sozen MA, Kaiser K,
Dow JA: Analysis and inactivation of vha55, the gene encoding
the vacuolar ATPase B-subunit in Drosophila melanogaster
reveals a larval lethal phenotype. J Biol Chem 1996,
271:30677-30684.
8.
Inoue H, Noumi T, Nagata M, Murakami H, Kanazawa H: Targeted
disruption of the gene encoding the proteolipid subunit of
mouse vacuolar H+-ATPase leads to early embryonic lethality.
Biochim Biophys Acta 1999, 1413:130-138.
9.
Oka T, Futai M: Requirement of V-ATPase for ovulation and
embryogenesis in Caenorhabditis elegans. J Biol Chem 2000,
275:29556-29561.
10. Sun-Wada G, Murata Y, Yamamoto A, Kanazawa H, Wada Y,
Futai M: Acidic endomembrane organelles are required for
mouse postimplantation development. Dev Biol 2000,
228:315-325.
11. Dettmer J, Schubert D, Calvo-Weimar O, Stierhof YD, Schmidt R,
Schumacher K: Essential role of the V-ATPase in male
gametophyte development. Plant J 2005, 41:117-124.
See annotation for [12].
12. Strompen G, Dettmer J, Stierhof YD, Schumacher K, Jürgens G,
Mayer U: Arabidopsis vacuolar H-ATPase subunit E isoform 1
is required for Golgi organization and vacuole function in
embryogenesis. Plant J 2005, 41:125-132.
The analysis of vha-null alleles provides evidence for something that was
long assumed: that the V-ATPase is essential. The underlying cellular
defects show that the V-ATPase is required to maintain Golgi structure
and function.
13. Schumacher K, Vafeados D, McCarthy M, Sze H, Wilkins T,
Chory J: The Arabidopsis det3 mutant reveals a central role for
the vacuolar H+-ATPase in plant growth and development.
Genes Dev 1999, 13:3259-3270.
14. Padmanaban S, Lin X, Perera I, Kawamura Y, Sze H: Differential
expression of vacuolar H+-ATPase subunit c genes in tissues
www.sciencedirect.com
Endomembrane proton pumps Schumacher 599
active in membrane trafficking and their roles in plant growth
as revealed by RNAi. Plant Physiol 2004, 134:1514-1526.
15. Allen GJ, Chu SP, Schumacher K, Shimazaki CT, Vafeados D,
Kemper A, Hawke SD, Tallman G, Tsien RY, Harper JF et al.:
Alteration of stimulus-specific guard cell calcium oscillations
and stomatal closing in Arabidopsis det3 mutant.
Science 2000, 289:2338-2342.
16. Cheng NH, Pittman JK, Barkla BJ, Shigaki T, Hirschi KD: The
Arabidopsis cax1 mutant exhibits impaired ion homeostasis,
development, and hormonal responses and reveals interplay
among vacuolar transporters. Plant Cell 2003, 15:347-364.
17. Cheng NH, Pittman JK, Shigaki T, Lachmansingh J, LeClere S,
Lahner B, Salt DE, Hirschi KD: Functional association of
Arabidopsis CAX1 and CAX3 is required for normal growth and
ion homeostasis. Plant Physiol 2005, 138:2048-2060.
18. Sze H, Schumacher K, Muller ML, Padmanaban S, Taiz L: A simple
nomenclature for a complex proton pump: VHA genes encode
the vacuolar H+-ATPase. Trends Plant Sci 2002, 7:157-161.
19. Kawamura Y, Arakawa K, Maeshima M, Yoshida S: Tissue
specificity of E subunit isoforms of plant vacuolar H+-ATPase
and existence of isotype enzymes. J Biol Chem 2000,
275:6515-6522.
20. Gogarten JP, Fichmann J, Braun Y, Morgan L, Styles P, Taiz SL,
DeLapp K, Taiz L: The use of antisense mRNA to inhibit the
tonoplast H+ ATPase in carrot. Plant Cell 1992, 4:851-864.
21. Bageshwar UK, Taneja-Bageshwar S, Moharram HM, Binzel ML:
Two isoforms of the A subunit of the vacuolar H+-ATPase in
Lycopersicon esculentum: highly similar proteins but
divergent patterns of tissue localization. Planta 2005,
220:632-643.
22. Manolson MF, Proteau D, Preston RA, Stenbit A, Roberts BT,
Hoyt MA, Preuss D, Mulholland J, Botstein D, Jones EW: The
VPH1 gene encodes a 95-kDa integral membrane polypeptide
required for in vivo assembly and activity of the yeast vacuolar
H+-ATPase. J Biol Chem 1992, 267:14294-14303.
30. Forgac M: Structure and properties of the clathrin-coated
vesicle and yeast vacuolar V-ATPases. J Bioenerg Biomembr
1999, 31:57-65.
31. Aniento F, Gu F, Parton RG, Gruenberg J: An endosomal beta
COP is involved in the pH-dependent formation of transport
vesicles destined for late endosomes. J Cell Biol 1996,
133:29-41.
32. Maranda B, Brown D, Bourgoin S, Casanova JE, Vinay P,
Ausiello DA, Marshansky V: Intra-endosomal pH-sensitive
recruitment of the Arf-nucleotide exchange factor ARNO and
Arf6 from cytoplasm to proximal tubule endosomes.
J Biol Chem 2001, 276:18540-18550.
33. Clague MJ, Urbe S, Aniento F, Gruenberg J: Vacuolar ATPase
activity is required for endosomal carrier vesicle formation.
J Biol Chem 1994, 269:21-24.
34. van Weert AW, Dunn KW, Gueze HJ, Maxfield FR, Stoorvogel W:
Transport from late endosomes to lysosomes, but not sorting
of integral membrane proteins in endosomes, depends on the
vacuolar proton pump. J Cell Biol 1995, 130:821-834.
35. Tawfeek HA, Abou-Samra AB: Important role for the V-type
H+-ATPase and the Golgi apparatus in the recycling of
PTH/PTHrP receptor. Am J Physiol Endocrinol Metab 2004,
286:E704-E710.
36. Matsuoka K, Higuchi T, Maeshima M, Nakamura K: A vacuolartype H+-ATPase in a nonvacuolar organelle is required for the
sorting of soluble vacuolar protein precursors in tobacco
cells. Plant Cell 1997, 9:533-546.
37. Tamura K, Shimada T, Ono E, Tanaka Y, Nagatani A, Higashi SI,
Watanabe M, Nishimura M, Hara-Nishimura I: Why green
fluorescent fusion proteins have not been observed in the
vacuoles of higher plants. Plant J 2003, 35:545-555.
38. Yoshimoto K, Hanaoka H, Sato S, Kato T, Tabata S, Noda T,
Ohsumi Y: Processing of ATG8s, ubiquitin-like proteins,
and their deconjugation by ATG4s are essential for plant
autophagy. Plant Cell 2004, 16:2967-2983.
23. Manolson MF, Wu B, Proteau D, Taillon BE, Roberts BT, Hoyt MA,
Jones EW: STV1 gene encodes functional homologue of
95-kDa yeast vacuolar H+–ATPase subunit Vph1p.
J Biol Chem 1994, 269:14064-14074.
39. Thompson AR, Doelling JH, Suttangkakul A, Vierstra RD:
Autophagic nutrient recycling in Arabidopsis directed by the
ATG8 and ATG12 conjugation pathways. Plant Physiol 2005,
138:2097-2110.
24. Kawasaki-Nishi S, Bowers K, Nishi T, Forgac M, Stevens TH: The
amino-terminal domain of the vacuolar proton-translocating
ATPase a subunit controls targeting and in vivo dissociation,
and the carboxyl-terminal domain affects coupling of
proton transport and ATP hydrolysis. J Biol Chem 2001,
276:47411-47420.
40. Robinson DG, Albrecht S, Moriyasu Y: The V-ATPase inhibitors
concanamycin A and bafilomycin A lead to Golgi swelling in
tobacco BY-2 cells. Protoplasma 2004, 224:255-260.
25. Kluge C, Seidel T, Bolte S, Sharma SS, Hanitzsch M, SatiatJeunemaitre B, Ross J, Sauer M, Golldack D, Dietz KJ:
Subcellular distribution of the V-ATPase complex in plant
cells, and in vivo localisation of the 100 kDa subunit VHA-a
within the complex. BMC Cell Biol 2004, 5:29.
26. Dettmer J, Hong-Hermesdorf A, Stierhof YD, Schumacher K:
Vacuolar H+-ATPase activity is required for endocytic and
secretory trafficking in Arabidopsis. Plant Cell 2006,
18:715-730.
The authors use GFP-fusion proteins and immunogold labeling to show
that the Arabidopsis isoforms of VHA-a are localized at the tonoplast and
the TGN, respectively. They provide evidence that the TGN can be
regarded as an early endosome, a compartment that was previously
ill-defined. Moreover, they show that V-ATPase activity is required for
endocytic and secretory trafficking.
27. Huss M, Ingenhorst G, Konig S, Gassel M, Drose S, Zeeck A,
Altendorf K, Wieczorek H: Concanamycin A, the specific
inhibitor of V-ATPases, binds to the V(o) subunit c.
J Biol Chem 2002, 277:40544-40548.
28. Bowman EJ, Graham LA, Stevens TH, Bowman BJ: The
bafilomycin/concanamycin binding site in subunit c of
the V-ATPases from Neurospora crassa and Saccharomyces
cerevisiae. J Biol Chem 2004, 279:33131-33138.
29. Wang Y, Inoue T, Forgac M: Subunit a of the yeast V-ATPase
participates in binding of bafilomycin. J Biol Chem 2005,
280:40481-40488.
www.sciencedirect.com
41. Staehelin LA, Giddings TH Jr, Kiss JZ, Sack FD: Macromolecular
differentiation of Golgi stacks in root tips of Arabidopsis and
Nicotiana seedlings as visualized in high pressure frozen and
freeze-substituted samples. Protoplasma 1990, 157:75-91.
42. Zeuzem S, Feick P, Zimmermann P, Haase W, Kahn RA, Schulz I:
Intravesicular acidification correlates with binding of
ADP-ribosylation factor to microsomal membranes.
Proc Natl Acad Sci USA 1992, 89:6619-6623.
43. Hurtado-Lorenzo A, Skinner M, El Annan J, Futai M, Sun Wada GH, Bourgoin S, Casanova J, Wildeman A, Bechoua S,
Ausiello DA et al.: V-ATPase interacts with ARNO and Arf6 in
early endosomes and regulates the protein degradative
pathway. Nat Cell Biol 2006, 8:124-136.
This impressive paper establishes a molecular link between endosomal
acidification and trafficking in mammalian cells. Membrane recruitment of
the small GTPase ARF6 and its exchange factor ARNO is shown to require
a direct and luminal pH-dependent interaction with two subunits of the
V-ATPase.
44. Peters C, Bayer MJ, Buhler S, Andersen JS, Mann M, Mayer A:
Trans-complex formation by proteolipid channels in the
terminal phase of membrane fusion. Nature 2001, 409:581-588.
45. Hiesinger PR, Fayyazuddin A, Mehta SQ, Rosenmund T,
Schulze KL, Zhai RG, Verstreken P, Cao Y, Zhou Y, Kunz J et al.:
The V-ATPase V0 subunit a1 is required for a late step in
synaptic vesicle exocytosis in Drosophila. Cell 2005,
121:607-620.
A forward genetic screen in Drosophila identifies the VO-subunit a as part
of the fusion pore during synaptic vesicle fusion. Biochemical studies that
analyzed the fusion of yeast vacuoles had previously allowed a similar
Current Opinion in Plant Biology 2006, 9:595–600
600 Cell biology
conclusion, and thus it seems possible that VO has an important function
in membrane fusion that is independent of acidification.
46. Maeshima M: Tonoplast transporters: organization and
function. Annu Rev Plant Physiol Plant Mol Biol 2001, 52:469-497.
47. Maeshima M: Vacuolar H+-pyrophosphatase. Biochim Biophys
Acta 2000, 1465:37-51.
48. Ratajczak R, Hinz G, Robinson DG: Localization of
pyrophosphatase in membranes of cauliflower inflorescence
cells. Planta 1999, 208:205-211.
49. Mitsuda N, Enami K, Nakata M, Takeyasu K, Sato MH: Novel type
Arabidopsis thaliana H+-PPase is localized to the Golgi
apparatus. FEBS Lett 2001, 488:29-33.
50. Li J, Yang H, Peer WA, Richter G, Blakeslee J, Bandyopadhyay A,
Titapiwantakun B, Undurraga S, Khodakovskaya M, Richards EL
et al.: Arabidopsis H+-PPase AVP1 regulates auxin-mediated
organ development. Science 2005, 310:121-125.
This article establishes a connection between the levels of the V-PPase
AVP1, the PM H+-ATPase and the auxin efflux carrier PIN1. Although the
causality of the observed effects remains to be elucidated, it provides
striking evidence of the importance of endomembrane proton-pumps in
trafficking of PM proteins.
Current Opinion in Plant Biology 2006, 9:595–600
51. Gaxiola RA, Li J, Undurraga S, Dang LM, Allen GJ, Alper SL,
Fink GR: Drought- and salt-tolerant plants result from
overexpression of the AVP1 H+-pump. Proc Natl Acad Sci USA
2001, 98:11444-11449.
52. Park S, Li J, Pittman JK, Berkowitz GA, Yang H, Undurraga S,
Morris J, Hirschi KD, Gaxiola RA: Up-regulation of a
H+-pyrophosphatase (H+-PPase) as a strategy to engineer
drought-resistant crop plants. Proc Natl Acad Sci USA 2005,
102:18830-18835.
The authors show that overexpression of the V-PPase might provide a
general strategy to create drought-tolerant crop plants.
53. Fischer-Schliebs E, Mariaux JB, Luettge U: Stimulation of
H+-transport activity of vacuolar H+-ATPase by activation
of H+-PPase in Kalanchoe blossfeldiana. Biol Plant 1997,
39:169-177.
54. Guo S, Yin H, Zhang X, Zhao F, Li P, Chen S, Zhao Y,
Zhang H: Molecular cloning and characterization of a
vacuolar H+-pyrophosphatase gene, SsVP, from the halophyte
Suaeda salsa and its overexpression increases salt and
drought tolerance of Arabidopsis. Plant Mol Biol 2006, 60:41-50.
Interestingly, this paper shows that overexpression of the V-PPase might
also lead to enhanced activity of the V-ATPase.
www.sciencedirect.com