Technical Focus:a guide to Agrobacterium binary Ti vectors

Monitoring autophagy in Magnaporthe oryzae

Autophagy is a ubiquitous degradative pathway for the bulk degradation of eukaryotic macromolecules and organelles in eukaryotic cells (Klionsky, 2005; Levine and Klionsky, 2004). Previously, the role of autophagy in turgor generation in plant pathogenic fungi was unknown. Currently, autophagy is confirmed as an important pathway for turgor accumulation in the appressorium (the tips of the invasive hyphae; Liu et al., 2007b) using a technique of targeted gene replacement, deleting the genes that code for Magnaporthe oryzae homologs of yeast autophagy-related (ATG) genes ATG2, ATG4, ATG5, ATG8, ATG9, and ATG18 (Liu et al., 2007a). All of these null mutants fail to breach the cuticle of the host. This chapter will first look at some methodologies to analyze the functions of autophagy-related gene products at the biological, cellular, and molecular level in this model plant pathogenic fungi, and then provide some research evidence of the role of autophagy in the promotion of the formation of the infection structure and pathogenicity to point out some significant areas for further research in this field.

The pCLEAN dual binary vector system for Agrobacterium-mediated plant transformation

The development of novel transformation vectors is essential to the improvement of plant transformation technologies. Here, we report the construction and testing of a new multifunctional dual binary vector system, pCLEAN, for Agrobacterium-mediated plant transformation. The pCLEAN vectors are based on the widely used pGreen/pSoup system and the pCLEAN-G/pCLEAN-S plasmids are fully compatible with the existing pGreen/pSoup vectors. A single Agrobacterium can harbor (1) pCLEAN-G and pSoup, (2) pGreen and pCLEAN-S, or (3) pCLEAN-G and pCLEAN-S vector combination. pCLEAN vectors have been designed to enable the delivery of multiple transgenes from distinct T-DNAs and/or vector backbone sequences while minimizing the insertion of superfluous DNA sequences into the plant nuclear genome as well as facilitating the production of marker-free plants. pCLEAN vectors contain a minimal T-DNA (102 nucleotides) consisting of direct border repeats surrounding a 52-nucleotide-long multiple cloning site, an optimized left-border sequence, a double left-border sequence, restriction sites outside the borders, and two independent T-DNAs. In addition, selectable and/or reporter genes have been inserted into the vector backbone sequence to allow either the counter-screening of backbone transfer or its exploitation for the production of marker-free plants. The efficiency of the different pCLEAN vectors has been assessed using transient and stable transformation assays in Nicotiana benthamiana and/or Oryza sativa.

Distribution and replication of the pathogenicity plasmid pPATH in diverse populations of the gall-forming bacterium Pantoea agglomerans

Pantoea agglomerans has been transformed from a commensal bacterium into two related gall-forming pathovars by acquisition of pPATH plasmids containing a pathogenicity island (PAI). This PAI harbors an hrp/hrc gene cluster, type III effectors, and phytohormone biosynthetic genes. DNA typing by pulsed-field gel electrophoresis revealed two major groups of P. agglomerans pv. gypsophilae and one group of P. agglomerans pv. betae. The pPATH plasmids of the different groups had nearly identical replicons (98% identity), and the RepA protein showed the highest level of similarity with IncN plasmid proteins. A series of plasmids, designated pRAs, in which the whole replicon region (2,170 bp) or deleted derivatives of it were ligated with nptI were generated for replicon analysis. A basic 929-bp replicon (pRA6) was sufficient for replication in Escherichia coli and in nonpathogenic P. agglomerans. However, the whole replicon region (pRA1) was necessary for expulsion of the pPATH plasmid, which resulted in the loss of pathogenicity. The presence of direct repeats in the replicon region suggests that the pPATH plasmid is an iteron plasmid and that the repeats may regulate its replication. The pPATH plasmids are nonconjugative but exhibit a broad host range, as shown by replication of pRA1 in Erwinia, Pseudomonas, and Xanthomonas. Restriction fragment length polymorphism analyses indicated that the PAIs in the two groups of P. agglomerans pv. gypsophilae are similar but different from those in P. agglomerans pv. betae. The results could indicate that the pPATH plasmids evolved from a common ancestral mobilizable plasmid that was transferred into different strains of P. agglomerans.

Transformation of Acinetobacter baylyi in non-sterile soil using recombinant plant nuclear DNA

To provide estimates of horizontal gene transfer from transgenic crops to indigenous soil bacteria, transformation frequencies were obtained for naturally transformable Acinetobacter baylyi BD413 using a chromosomally integrated plant transgene. The transgene comprised sequences for two phenotypic markers: kanamycin resistance (npt II) and green fluorescent protein (gfp), expressed from their own bacterial promoters. Recipient bacteria carried a copy of these two genes, with deletions in their 3'-termini abolishing the marker activity, these genes were integrated into a 16S rRNA gene in the bacterial chromosomal genome or carried on a broad host range plasmid. Successful recombination between the plant transgene and the bacterial genome resulted in restoration of the markers, allowing detection through antibiotic selection and fluorescence. Transformation parameters of increasing complexity, without any enrichment steps, were used to approach the field conditions, while still obtaining measurable transformation frequencies. In pure culture filter experiments, transformation was detected using ground, chopped and whole leaves, as well as whole sterile seedlings, and ground roots. In sterile soil microcosms, transformation was detected using pure plant DNA (3.6 x 10(-8) transformants per recipient) and ground leaves (2.5 x 10(-11)). Transformation was also detected for the first time in non-sterile soil using pure plant DNA (5.5 x 10(-11)). Since the same constructs were used throughout, these data allow predictions of even more complex environmental systems where measurable frequencies are not easily obtainable.

N-myristoylation regulates the SnRK1 pathway in Arabidopsis

Cotranslational and posttranslational modifications are increasingly recognized as important in the regulation of numerous essential cellular functions. N-myristoylation is a lipid modification ensuring the proper function and intracellular trafficking of proteins involved in many signaling pathways. Arabidopsis thaliana, like human, has two tightly regulated N-myristoyltransferase (NMT) genes, NMT1 and NMT2. Characterization of knockout mutants showed that NMT1 was strictly required for plant viability, whereas NMT2 accelerated flowering. NMT1 impairment induced extremely severe defects in the shoot apical meristem during embryonic development, causing growth arrest after germination. A transgenic plant line with an inducible NMT1 gene demonstrated that NMT1 expression had further effects at later stages. NMT2 did not compensate for NMT1 in the nmt1-1 mutant, but NMT2 overexpression resulted in shoot and root meristem abnormalities. Various data from complementation experiments in the nmt1-1 background, using either yeast or human NMTs, demonstrated a functional link between the developmental arrest of nmt1-1 mutants and the myristoylation state of an extremely small set of protein targets. We show here that protein N-myristoylation is systematically associated with shoot meristem development and that SnRK1 (for SNF1-related kinase) is one of its essential primary targets.

Adaptive evolution has targeted the C-terminal domain of the RXLR effectors of plant pathogenic oomycetes

Oomycete plant pathogens deliver effector proteins inside host cells to modulate plant defense circuitry and to enable parasitic colonization. These effectors are defined by a conserved motif, termed RXLR (for Arg, any amino acid, Leu, Arg), that is located downstream of the signal peptide and that has been implicated in host translocation. Because the phenotypes of RXLR effectors extend to plant cells, their genes are expected to be the direct target of the evolutionary forces that drive the antagonistic interplay between pathogen and host. We used the draft genome sequences of three oomycete plant pathogens, Phytophthora sojae, Phytophthora ramorum, and Hyaloperonospora parasitica, to generate genome-wide catalogs of RXLR effector genes and determine the extent to which these genes are under positive selection. These analyses revealed that the RXLR sequence is overrepresented and positionally constrained in the secretome of Phytophthora relative to other eukaryotes. The three examined plant pathogenic oomycetes carry complex and diverse sets of RXLR effector genes that have undergone relatively rapid birth and death evolution. We obtained robust evidence of positive selection in more than two-thirds of the examined paralog families of RXLR effectors. Positive selection has acted for the most part on the C-terminal region, consistent with the view that RXLR effectors are modular, with the N terminus involved in secretion and host translocation and the C-terminal domain dedicated to modulating host defenses inside plant cells.

A class I KNOX gene from the palm species Elaeis guineensis (Arecaceae) is associated with meristem function and a distinct mode of leaf dissection

Class I Knotted-like homeobox (KNOX) transcription factors are important regulators of shoot apical meristem function and leaf morphology by their contribution to dissected leaf development. Palms are of particular interest as they produce dissected leaves generated by a distinct mechanism compared with eudicots. The question addressed here was whether class I KNOX genes might be involved in meristem function and leaf dissection in palms. Here, we characterized the EgKNOX1 gene from oil palm (Elaeis guineensis, Arecaceae) and compared it with available sequences from other plant species using phylogenetic analysis. Gene expression pattern was investigated using reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization. Functional analysis was carried out by ectopic expression in Arabidopsis and rice. EgKNOX1 was orthologous to STM from Arabidopsis and to OSH1 from rice. It was expressed in the central zone of both vegetative and reproductive meristems. During leaf development, its expression was associated with plications from which the leaflets originate. Different modes of leaf dissection are seen to involve a similar class of genes to control meristematic activities, which govern the production of dissected morphologies.

Visualization of the interaction between the precursors of VPg, the viral protein linked to the genome of turnip mosaic virus, and the translation eukaryotic initiation factor iso 4E in Planta

The RNA genome of Turnip mosaic virus is covalently linked at its 5' end to a viral protein known as VPg. This protein binds to the translation eukaryotic initiation factor iso 4E [eIF(iso)4E]. This interaction has been shown to be important for virus infection, although its exact biological function(s) has not been elucidated. In this study, we investigated the subcellular site of the VPg-eIF(iso)4E interaction using bimolecular fluorescence complementation (BiFC). As a first step, eIF(iso)4E, 6K-VPg-Pro, and VPg-Pro were expressed as full-length green fluorescent protein (GFP) fusions in Nicotiana benthamiana, and their subcellular localizations were visualized by confocal microscopy. eIF(iso)4E was predominantly associated with the endoplasmic reticulum (ER), and VPg-Pro was observed in the nucleus and possibly the nucleolus, while 6K-VPg-Pro-GFP induced the formation of cytoplasmic vesicles budding from the ER. In BiFC experiments, reconstituted green fluorescence was observed throughout the nucleus, with a preferential accumulation in subnuclear structures when the GFP split fragments were fused to VPg-Pro and eIF(iso)4E. On the other hand, the interaction of 6K-VPg-Pro with eIF(iso)4E was observed in cytoplasmic vesicles embedded in the ER. These data suggest that the association of VPg with the translation factor might be needed for two different functions, depending of the VPg precursor involved in the interaction. VPg-Pro interaction with eIF(iso)4E may be involved in perturbing normal cellular functions, while 6K-VPg-Pro interaction with the translation factor may be needed for viral RNA translation and/or replication.

Vectors and agrobacterium hosts for Arabidopsis transformation

INTRODUCTIONArabidopsis can be stably transformed using Agrobacterium tumefaciens-mediated transfer of T-DNA. A. tumefaciens is a soil-dwelling bacterium that transforms normal plant cells into tumor-forming cells by inserting a piece of bacterial DNA (the transfer, or "T," DNA) into the plant cell genome. The T-DNA, which is flanked by left- and right-border (LB and RB) sequences, resides on a tumor-inducing (Ti) plasmid. The Ti plasmid also carries many of the transfer functions for mobilizing the T-DNA. This article provides a brief discussion of the principles of T-DNA transformation, including consideration of T-DNA vectors and their hosts.

Down-regulation of the maize and Arabidopsis thaliana caffeic acid O-methyl-transferase genes by two new maize R2R3-MYB transcription factors

The maize (Zea mays L.) caffeic acid O-methyl-transferase (COMT) is a key enzyme in the biosynthesis of lignin. In this work we have characterized the involvement of COMT in the lignification process through the study of the molecular mechanisms involved in its regulation. The examination of the maize COMT gene promoter revealed a putative ACIII box, typically recognized by R2R3-MYB transcription factors. We used the sequence of known R2R3-MYB factors to isolate five maize R2R3-MYB factors (ZmMYB2, ZmMYB8, ZmMYB31, ZmMYB39, and ZmMYB42) and study their possible roles as regulators of the maize COMT gene. The factors ZmMYB8, ZmMY31, and ZmMYB42 belong to the subgroup 4 of the R2R3-MYB family along with other factors associated with lignin biosynthesis repression. In addition, the induction pattern of ZmMYB31 and ZmMYB42 gene expression on wounding is that expected for repressors of the maize COMT gene. Arabidopsis thaliana plants over-expressing ZmMYB31 and ZmMYB42 down-regulate both the A. thaliana and the maize COMT genes. Furthermore, the over-expression of ZmMYB31 and ZmMYB42 also affect the expression of other genes of the lignin pathway and produces a decrease in lignin content of the transgenic plants.

Transport of antimony salts byArabidopsis thalianaprotoplasts over-expressing the human multidrug resistance-associated protein 1 (MRP1/ABCC1)

ABC transporters from the multidrug resistance-associated protein (MRP) subfamily are glutathione S-conjugate pumps exhibiting a broad substrate specificity illustrated by numerous xenobiotics, such as anticancer drugs, herbicides, pesticides and heavy metals. The engineering of MRP transporters into plants might be interesting either to reduce the quantity of xenobiotics taken up by the plant in the context of "safe-food" strategies or, conversely, in the development of phytoremediation strategies in which xenobiotics are sequestered in the vacuolar compartment. In this report, we obtained Arabidopsis transgenic plants overexpressing human MRP1. In these plants, expression of MRP1 did not increase plant resistance to antimony salts (Sb(III)), a classical glutathione-conjugate substrate of MRP1. However, the transporter was fully translated in roots and shoots, and targeted to the plasma membrane. In order to investigate the functionality of MRP1 in Arabidopsis, mesophyll cell protoplasts (MCPs) were isolated from transgenic plants and transport activities were measured by using calcein or Sb(III) as substrates. Expression of MRP1 at the plasma membrane was correlated with an increase in the MCPs resistance to Sb(III) and a limitation of the metalloid content in the protoplasts due to an improvement in Sb(III) efflux. Moreover, Sb(III) transport was sensitive to classical inhibitors of the human MRP1, such as MK571 or glibenclamide. These results demonstrate that a human ABC transporter can be functionally introduced in Arabidopsis, which might be useful, with the help of stronger promoters, to reduce the accumulation of xenobiotics in plants, such as heavy metals from multi-contaminated soils.

The C-terminal half of Phytophthora infestans RXLR effector AVR3a is sufficient to trigger R3a-mediated hypersensitivity and suppress INF1-induced cell death in Nicotiana benthamiana

The RXLR cytoplasmic effector AVR3a of Phytophthora infestans confers avirulence on potato plants carrying the R3a gene. Two alleles of Avr3a encode secreted proteins that differ in only three amino acid residues, two of which are in the mature protein. Avirulent isolates carry the Avr3a allele, which encodes AVR3aKI (containing amino acids C19, K80 and I103), whereas virulent isolates express only the virulence allele avr3a, encoding AVR3aEM (S19, E80 and M103). Only the AVR3aKI protein is recognized inside the plant cytoplasm where it triggers R3a-mediated hypersensitivity. Similar to other oomycete avirulence proteins, AVR3aKI carries a signal peptide followed by a conserved motif centered on the consensus RXLR sequence that is functionally similar to a host cell-targeting signal of malaria parasites. The interaction between Avr3a and R3a can be reconstructed by their transient co-expression in Nicotiana benthamiana. We exploited the N. benthamiana experimental system to further characterize the Avr3a-R3a interaction. R3a activation by AVR3aKI is dependent on the ubiquitin ligase-associated protein SGT1 and heat-shock protein HSP90. The AVR3aKI and AVR3aEM proteins are equally stable in planta, suggesting that the difference in R3a-mediated death cannot be attributed to AVR3aEM protein instability. AVR3aKI is able to suppress cell death induced by the elicitin INF1 of P. infestans, suggesting a possible virulence function for this protein. Structure-function experiments indicated that the 75-amino acid C-terminal half of AVR3aKI, which excludes the RXLR region, is sufficient for avirulence and suppression functions, consistent with the view that the N-terminal region of AVR3aKI and other RXLR effectors is involved in secretion and targeting but is not required for effector activity. We also found that both polymorphic amino acids, K80 and I103, of mature AVR3a contribute to the effector functions.

Two cell-cycle regulated SET-domain proteins interact with proliferating cell nuclear antigen (PCNA) in Arabidopsis

The proliferating cell nuclear antigen (PCNA) functions as a sliding clamp for DNA polymerase, and is thus a key actor in DNA replication. It is also involved in DNA repair, maintenance of heterochromatic regions throughout replication, cell cycle regulation and programmed cell death. Identification of PCNA partners is therefore necessary for understanding these processes. Here we identify two Arabidopsis SET-domain proteins that interact with PCNA: ATXR5 and ATXR6. A truncated ATXR5Deltaex2, incapable of interacting with PCNA, also occurs in planta. ATXR6, upregulated during the S phase, is upregulated by AtE2F transcription factors, suggesting that it is required for S-phase progression. The two proteins differ in their subcellular localization: ATXR5 has a dual localization in plastids and in the nucleus, whereas ATXR6 is solely nuclear. This indicates that the two proteins may play different roles in plant cells. However, overexpression of either ATXR5 or ATXR6 causes male sterility because of the degeneration of defined cell types. Taken together, our results suggest that both proteins may play a role in the cell cycle or DNA replication, and that the activity of ATXR5 may be regulated via its subcellular localization.

A comprehensive structure-function analysis of Arabidopsis SNI1 defines essential regions and transcriptional repressor activity

The expression of systemic acquired resistance (SAR) in plants involves the upregulation of many Pathogenesis-Related (PR) genes, which work in concert to confer resistance to a broad spectrum of pathogens. Because SAR is a costly process, SAR-associated transcription must be tightly regulated. Arabidopsis thaliana SNI1 (for Suppressor of NPR1, Inducible) is a negative regulator of SAR required to dampen the basal expression of PR genes. Whole genome transcriptional profiling showed that in the sni1 mutant, Nonexpresser of PR genes (NPR1)-dependent benzothiadiazole S-methylester-responsive genes were specifically derepressed. Interestingly, SNI1 also repressed transcription when expressed in yeast, suggesting that it functions as an active transcriptional repressor through a highly conserved mechanism. Chromatin immunoprecipitation indicated that histone modification may be involved in SNI1-mediated repression. Sequence comparison with orthologs in other plant species and a saturating NAAIRS-scanning mutagenesis of SNI1 identified regions in SNI1 that are required for its activity. The structural similarity of SNI1 to Armadillo repeat proteins implies that SNI1 may form a scaffold for interaction with proteins that modulate transcription.

The gene controlling the quantitative trait locus EPITHIOSPECIFIER MODIFIER1 alters glucosinolate hydrolysis and insect resistance in Arabidopsis

Glucosinolates are sulfur-rich plant secondary metabolites whose breakdown products have a wide range of biological activities in plant-herbivore and plant-pathogen interactions and anticarcinogenic properties. In Arabidopsis thaliana, hydrolysis by the enzyme, myrosinase, produces bioactive nitriles, epithionitriles, or isothiocyanates depending upon the plant's genotype and the glucosinolate's structure. A major determinant of this structural specificity is the epithiospecifier locus (ESP), whose protein causes the formation of epithionitriles and nitriles. A quantitative trait locus (QTL) on chromosome 3 epistatically affects nitrile formation in combination with ESP; this QTL has been termed EPITHIOSPECIFIER MODIFIER1 (ESM1). We identified a myrosinase-associated protein as the ESM1 QTL in Arabidopsis using map-based cloning with recombinant inbred lines, natural variation transcriptomic analysis, and metabolic profiling. In planta and in vitro analyses with natural ESM1 alleles, ESM1 knockouts, and overexpression lines show that ESM1 represses nitrile formation and favors isothiocyanate production. The glucosinolate hydrolysis profile change influenced by ESM1 is associated with the ability to deter herbivory by Trichoplusia ni. This gene could provide unique approaches toward improving human nutrition.

Genetic transformation of barley (Hordeum vulgare L.) via infection of androgenetic pollen cultures with Agrobacterium tumefaciens

A novel genetic transformation method for barley (Hordeum vulgare L.), based on infection of androgenetic pollen cultures with Agrobacterium tumefaciens, is presented. Winter-type barley cv. 'Igri' was amenable to stable integration of transgenes mediated by A. tumefaciens strain LBA4404 harbouring a vector system that confers hypervirulence, or by the non-hypervirulent strain GV3101 with a standard binary vector. The efficacy of gene transfer was substantially influenced by pollen pre-culture time, choice of Agrobacterium strain and vector system, Agrobacterium population density, medium pH and the concentrations of acetosyringone, CaCl(2) and glutamine. After co-culture, rapid removal of viable agrobacteria was crucial for subsequent development of the pollen culture. To this end, the growth of agrobacteria was suppressed by the concerted effects of appropriate antibiotics, low pH, reduced level of glutamine and high concentrations of CaCl(2) and acetosyringone. Following infection with LBA4404 and GV3101, about 31% and 69%, respectively, of the primary transgenic (T(0)) plants carried a single copy of the sequence integrated. The use of hypervirulent A. tumefaciens and hygromycin resistance as a selectable marker resulted in 3.7 T(0) plants per donor spike. About 60% of the primary transgenic plants set seed, indicating spontaneous genome doubling. An analysis of 20 T(1) populations revealed that four progenies did not segregate for reporter gene expression. This indicates that the approach pursued enables the generation of instantly homozygous primary transgenic plants. The method established will be a valuable tool in functional genomics as well as for the biotechnological improvement of barley.

Transformation of a muskmelon 'Galia' hybrid parental line (Cucumis melo L. var. reticulatus Ser.) with an antisense ACC oxidase gene

'Galia' muskmelon (Cucumis melo L. var. reticulatus Ser.) has been recalcitrant to transformation by Agrobacterium tumefaciens. Transformation of the 'Galia' male parental line, 'Krymka', with an ACC oxidase (CMACO-1) gene in antisense orientation is described herein. Explants were transformed using A. tumefaciens strain ABI, which contained a vector pCmACO1-AS plasmid, bearing an antisense gene of CMACO-1 and the CP4 syn gene (glyphosate-tolerance). Both CMACO-1 and CP4 syn genes were assessed by a polymerase chain reaction method. Flow cytometry analysis was performed to determine plant ploidy level of primary transformants. Two completely diploid independent transgenic plants were obtained. Southern blot and segregation analysis in the T1 generation determined that each independent transgenic line had one single insertion of the transgene. These transgenic muskmelon male parental lines have potential for use in the production of 'Galia' F1 hybrids with improved shelf life.

Development of Transformation System of Rice Based on Binary Bacterial Artificial Chromosome (BIBAC) Vector

An Agrobacterium-mediated transformation protocol using binary bacterial artificial chromosome (BIBAC) vector system in rice (Oryza sativa L.) was developed. Calli derived from mature embryos of japonica rice cv. H1493 were used as target tissues. Various aspects in transformation and regeneration processes including callus induction and culture, Agrobacterium concentration and duration of co-cultivation, bacterial elimination and transformant selection were examined in order to improve the transformation efficiency. An optimized transformation conditions was established including: using an Agrobacterium strain, LBA4404(HP4404), which carries a super-virulent helper plasmid pCH32, for the infection; a modified N6 medium system for callus induction and culture; pH 5.6 for media in pre-cultivation and co-cultivation; Agrobacterium concentration at OD600 = 1.0 for 3 days co-cultivation and 7 days for a resting period of the infected calli. Based on PCR and Southern blot analysis, it was demonstrated that insert DNA and marker genes carried by BIBAC2 were integrated into the rice genome.

Agrobacterium T-DNA-mediated integration and gene replacement in the brown rot pathogen Monilinia fructicola

A transformation system utilizing Agrobacterium tumefaciens was developed for targeted gene disruption in Monilinia fructicola, a fungal pathogen that causes brown rot disease of stone fruits. Transformation with a vector containing the neomycin phosphotransferase II (nptII) cassette flanked with 4 kb cutinase gene (Mfcut1) flanking sequences resulted in an average of 13 transformants per 10(5) spores. When assayed by PCR and DNA blot analyses, more than 50% of the transformants recovered had integrated in the targeted Mfcut1 locus. Both target-gene-specific and non-specific integrations carried direct (head-to-tail) repeat T-DNA integrations. Sequence analysis of these T-DNA integrations revealed that 26 bp of the T-DNA right border were missing at the junctions between direct repeats in all cases. The recombination event during non-specific T-DNA integration in this fungus was unlike that reported in Agrobacterium-mediated transformation in plants.

Rapid, transient expression of fluorescent fusion proteins in tobacco plants and generation of stably transformed plants

Expression and tracking of fluorescent fusion proteins has revolutionized our understanding of basic concepts in cell biology. The protocol presented here has underpinned much of the in vivo results highlighting the dynamic nature of the plant secretory pathway. Transient transformation of tobacco leaf epidermal cells is a relatively fast technique to assess expression of genes of interest. These cells can be used to generate stable plant lines using a more time-consuming, cell culture technique. Transient expression takes from 2 to 4 days whereas stable lines are generated after approximately 2 to 4 months.

Transient expression vectors for functional genomics, quantification of promoter activity and RNA silencing in plants

BACKGROUND

We describe novel plasmid vectors for transient gene expression using Agrobacterium, infiltrated into Nicotiana benthamiana leaves. We have generated a series of pGreenII cloning vectors that are ideally suited to transient gene expression, by removing elements of conventional binary vectors necessary for stable transformation such as transformation selection genes.

RESULTS

We give an example of expression of heme-thiolate P450 to demonstrate effectiveness of this system. We have also designed vectors that take advantage of a dual luciferase assay system to analyse promoter sequences or post-transcriptional regulation of gene expression. We have demonstrated their utility by co-expression of putative transcription factors and the promoter sequence of potential target genes and show how orthologous promoter sequences respond to these genes. Finally, we have constructed a vector that has allowed us to investigate design features of hairpin constructs related to their ability to initiate RNA silencing, and have used these tools to study cis-regulatory effect of intron-containing gene constructs.

CONCLUSION

In developing a series of vectors ideally suited to transient expression analysis we have provided a resource that further advances the application of this technology. These minimal vectors are ideally suited to conventional cloning methods and we have used them to demonstrate their flexibility to investigate enzyme activity, transcription regulation and post-transcriptional regulatory processes in transient assays.

PEPPER, a novel K-homology domain gene, regulates vegetative and gynoecium development in Arabidopsis

Pistil final morphology relies on floral meristem homeostasis, proper organ specification and regional differentiation. These are developmental processes in which sophisticated signaling networks are being uncovered. However, further elements for fine-tuning adjustment still remain to be disclosed. At the molecular level, posttranscriptional modulators may fit such a profile. In this work, we describe the characterization of PEPPER (PEP), a novel Arabidopsis gene encoding a polypeptide with K-homology (KH) RNA-binding modules, which acts on vegetative growth and pistil development. PEP was initially identified as one of the gene functions affected in a complex mutant carrying a chromosomal reorganization, which exhibits aberrant phyllotaxy and small fruits with supernumerary carpels. In contrast, plants carrying single-gene pep null mutations exhibit subtle morphological alterations. Individuals bearing a stronger-than-null allele present a phenotype comprising leaf alterations, phyllotactic errors and sporadic presence of fruits with multiple valves. Accordingly, dynamic PEP expression was detected in all major organs examined. Complementation experiments with a PEP genomic clone confirmed a role for PEP as a regulator in vegetative and reproductive development. Moreover, our genetic studies suggest that PEP interacts with element(s) of the CLAVATA signaling pathway.

Agrobacterium-mediated transformation of the ectomycorrhizal symbiont Laccaria bicolor S238N

The development of an efficient transformation system is required to alter the expression of symbiosis-regulated genes and to develop insertional mutagenesis in the ectomycorrhizal basidiomycete Laccaria bicolor S238N. Vegetative mycelium of this fungus was transformed by Agrobacterium tumefaciens-mediated gene transfer. The selection marker was the hygromycin resistance gene of Escherichia coli (hph) under the control of the gpd promoter from Agaricus bisporus and the CaMV 35S terminator as part of the T-DNA. PCR amplification of hph and Southern blot analyses showed that the genome of the hygromycin-resistant transformants contained the cassette. The latter proved mostly single copy and random integration of part of the transgene into the fungal genome. A. tumefaciens-mediated gene transfer should facilitate future development of insertional mutagenesis, targeted gene disruption and RNA interference technology in L. bicolor.

Resveratrol glucoside (Piceid) synthesis in seeds of transgenic oilseed rape (Brassica napus L.)

Resveratrol is a phytoalexin produced in various plants like wine, peanut or pine in response to fungal infection or UV irradiation, but it is absent in members of the Brassicaceae. Moreover, resveratrol and its glucoside (piceid) are considered to have beneficial effects on human health, known to reduce heart disease, arteriosclerosis and cancer mortality. Therefore, the introduction of the gene encoding stilbene synthase for resveratrol production in rapeseed is a tempting approach to improve the quality of rapeseed products. The stilbene synthase gene isolated from grapevine (Vitis vinifera L.) was cloned under control of the seed-specific napin promotor and introduced into rapeseed (Brassica napus L.) by Agrobacterium-mediated co-transformation together with a ds-RNA-interference construct deduced from the sequence of the key enzyme for sinapate ester biosynthesis, UDP-glucose:sinapate glucosyltransferase (BnSGT1), assuming that the suppression of the sinapate ester biosynthesis may increase the resveratrol production in seeds through the increased availability of the precursor 4-coumarate. Resveratrol glucoside (piceid) was produced at levels up to 361 microg/g in the seeds of the primary transformants. This value exceeded by far piceid amounts reported from B. napus expressing VST1 in the wild type sinapine background. There was no significant difference in other important agronomic traits, like oil, protein, fatty acid and glucosinolate content in comparison to the control plants. In the third seed generation, up to 616 microg/g piceid was found in the seeds of a homozygous T3-plant with a single transgene copy integrated. The sinapate ester content in this homozygous T3-plant was reduced from 7.43 to 2.40 mg/g. These results demonstrate how the creation of a novel metabolic sink could divert the synthesis towards the production of piceid rather than sinapate ester, thereby increasing the value of oilseed products.

Molecular characterization of marker-free transgenic lines of indica rice that accumulate carotenoids in seed endosperm

A single Agrobacterium strain harbouring two binary plasmids was successfully used for the first time to develop a marker-free transgenic rice of improved nutritional value. Sixty-eight T0 co-transformants were obtained in three indica rice cultivars--two popular high-yielding Bangladeshi varieties (BR28 and BR29), and one high-iron rice cultivar (IR68144). Marker-free lines were obtained from 14 out of 24 selected co-transformants screened in the T1 generation. The accumulation of total carotenoids in polished T2 rice seeds of the primary transgenic VPBR29-17-37 reached levels of up to 3.0 microg/g, with the level of beta-carotene reaching 1.8 microg/g. In the cultivars BR28 and IR68144, total carotenoid levels in the transformants reached 2.0 microg/g of polished rice seeds. The levels of lutein and other carotenoids in the seeds were also significantly enhanced. T1 plants obtained from primary transgenics with simple gene-integration patterns tended to have a lower carotenoid content than the original parental lines. This study describes the development of marker-free transgenic rice lines containing high levels of carotenoids, and addresses the relationship between the rearrangement of transgenes and the presence of metabolic end products in transgenic rice.

Isolation of a rice regeneration quantitative trait loci gene and its application to transformation systems

Regeneration of plant organs is often the essential step in genetic transformation; however, the regeneration ability of a plant varies depending on the genetic background. By conventional crosses of low-regeneration rice strain Koshihikari with high-regeneration rice strain Kasalath, we identified some quantitative trait loci, which control the regeneration ability in rice. Using a map-based cloning strategy, we isolated a main quantitative trait loci gene encoding ferredoxin-nitrite reductase (NiR) that determines regeneration ability in rice. Molecular analyses revealed that the poor regeneration ability of Koshihikari is caused by lower expression than in Kasalath and the specific activity of NiR. Using the NiR gene as a selection marker, we succeeded in selectively transforming a foreign gene into rice without exogenous marker genes. Our results demonstrate that nitrate assimilation is an important process in rice regeneration and also provide an additional selectable marker for rice transformation.

Metabolic engineering of isoflavonoid biosynthesis in alfalfa

The potential health benefits of dietary isoflavones have generated considerable interest in engineering the synthesis of these phytoestrogens into plants. Genistein glucoside production (up to 50 nmol g(-1) fresh weight) was engineered in alfalfa (Medicago sativa) leaves by constitutive expression of isoflavone synthase from Medicago truncatula (MtIFS1). Glucosides of biochanin A (4'-O-methylgenistein) and pratensein (3'-hydroxybiochanin A) also accumulated. Although MtIFS1 was highly expressed in all organs examined, genistein accumulation was limited to leaves. MtIFS1-expressing lines accumulated several additional isoflavones, including formononetin and daidzein, in response to UV-B or Phoma medicaginis, whereas the chalcone and flavanone precursors of these compounds accumulated in control lines. Enhanced accumulation of the phytoalexin medicarpin was observed in P. medicaginis-infected leaves of MtIFS1-expressing plants. Microarray profiling indicated that MtIFS1 expression does not significantly alter global gene expression in the leaves. Our results highlight some of the challenges associated with metabolic engineering of plant natural products, including tissue-specific accumulation, potential for further modification by endogenous enzyme activities (hydroxylation, methylation, and glycosylation), and the differential response of engineered plants to environmental factors.

Delay in flowering and increase in biomass of transgenic tobacco expressing the Arabidopsis floral repressor gene FLOWERING LOCUS C

FLOWERING LOCUS C (FLC), a gene from Arabidopsis thaliana (L.) Heynh. that acts as a flowering repressor, was expressed in tobacco (Nicotiana tabacum L. 'Samsun'). Five putative transgenic lines were selected and examined for the presence of FLC. Genomic DNA and total RNA were isolated from the Leaves and used for polymerase chain reaction (PCR) and RNA blot analysis, respectively. Both DNA and RNA tests confirmed the integration and transcription of FLC in all five Lines and their T1 progenies. Transgenic plants in one Line showed an average of 36 d delay in flowering time compared to control plants, and the overall mean for all lines was 14 d. Transgenic plants also displayed increased leaf size and biomass yield and reduced height at flowering time. It is important to note that the delay in flowering might have been caused by a slower rate of leaf initiation (i.e. nodes/day) rather than by a change in the flowering mechanism itself.

A dual selection based, targeted gene replacement tool for Magnaporthe grisea and Fusarium oxysporum

Rapid progress in fungal genome sequencing presents many new opportunities for functional genomic analysis of fungal biology through the systematic mutagenesis of the genes identified through sequencing. However, the lack of efficient tools for targeted gene replacement is a limiting factor for fungal functional genomics, as it often necessitates the screening of a large number of transformants to identify the desired mutant. We developed an efficient method of gene replacement and evaluated factors affecting the efficiency of this method using two plant pathogenic fungi, Magnaporthe grisea and Fusarium oxysporum. This method is based on Agrobacterium tumefaciens-mediated transformation with a mutant allele of the target gene flanked by the herpes simplex virus thymidine kinase (HSVtk) gene as a conditional negative selection marker against ectopic transformants. The HSVtk gene product converts 5-fluoro-2'-deoxyuridine to a compound toxic to diverse fungi. Because ectopic transformants express HSVtk, while gene replacement mutants lack HSVtk, growing transformants on a medium amended with 5-fluoro-2'-deoxyuridine facilitates the identification of targeted mutants by counter-selecting against ectopic transformants. In addition to M. grisea and F. oxysporum, the method and associated vectors are likely to be applicable to manipulating genes in a broad spectrum of fungi, thus potentially serving as an efficient, universal functional genomic tool for harnessing the growing body of fungal genome sequence data to study fungal biology.

Optimization of Agrobacterium-mediated transient assays of gene expression in lettuce, tomato and Arabidopsis

Agrobacterium-mediated transient assays for gene function are increasingly being used as alternatives to genetic complementation and stable transformation. However, such assays are variable and not equally successful in different plant species. We analysed a range of genetic and physiological factors affecting transient expression following agroinfiltration, and developed a protocol for efficient and routine transient assays in several plant species. Lettuce exhibited high levels of transient expression and was at least as easy to work with as Nicotiana benthamiana. Transient expression occurred in the majority of cells within the infiltrated tissue and approached 100% in some regions. High levels of transient expression were obtained in some ecotypes of Arabidopsis; however, Arabidopsis remains recalcitrant to routine, genotype-independent transient assays. Transient expression levels often exceeded those observed in stably transformed plants. The laboratory Agrobacterium tumefaciens strain C58C1 was the best strain for use in plant species that did not elicit a necrotic response to A. tumefaciens. A wild A. tumefaciens strain, 1D1246, was identified that provided high levels of transient expression in solanaceous plants without background necrosis, enabling routine transient assays in these species.

Efficient GFP expression in the mushrooms Agaricus bisporus and Coprinus cinereus requires introns

We have developed a "Molecular Toolkit" comprising interchangeable promoters and marker genes to facilitate transformation of homobasidiomycete mushrooms. We describe the evaluation of a range of promoters in the homobasidiomycetes Agaricus bisporus and Coprinus cinereus using green fluorescent protein (GFP) as a reporter gene; the C. cinereus trp1 promoter and A. bisporus trp2 and gpdII promoters proving successful in driving expression in C. cinereus, with the gpdII promoter also functioning in A. bisporus. Our investigations demonstrate that a prerequisite for GFP expression in C. cinereus and A. bisporus is the presence of an intron. This is the first reported expression of GFP in either C. cinereus or A. bisporus.

Genetic transformation of selected mature cork oak (Quercus suber L.) trees

A transformation system for selected mature cork oak (Quercus suber L.) trees using Agrobacterium tumefaciens has been established. Embryos obtained from recurrent proliferating embryogenic masses were inoculated with A. tumefaciens strains EHA105, LBA4404 or AGL1 harbouring the plasmid pBINUbiGUSint [carrying the neomycin phosphotransferase II (nptII) and beta-glucuronidase (uidA) genes]. The highest transformation efficiency (4%) was obtained when freshly isolated explants were inoculated with A. tumefaciens strain AGL1. Evidence of stable transgene integration was obtained by PCR for the nptII and uidA genes, Southern blotting and expression of the uidA gene. The transgenic embryos were germinated and successfully transferred to soil.

Assessment of the safety of foods derived from genetically modified (GM) crops

This paper provides guidance on how to assess the safety of foods derived from genetically modified crops (GM crops); it summarises conclusions and recommendations of Working Group 1 of the ENTRANSFOOD project. The paper provides an approach for adapting the test strategy to the characteristics of the modified crop and the introduced trait, and assessing potential unintended effects from the genetic modification. The proposed approach to safety assessment starts with the comparison of the new GM crop with a traditional counterpart that is generally accepted as safe based on a history of human food use (the concept of substantial equivalence). This case-focused approach ensures that foods derived from GM crops that have passed this extensive test-regime are as safe and nutritious as currently consumed plant-derived foods. The approach is suitable for current and future GM crops with more complex modifications. First, the paper reviews test methods developed for the risk assessment of chemicals, including food additives and pesticides, discussing which of these methods are suitable for the assessment of recombinant proteins and whole foods. Second, the paper presents a systematic approach to combine test methods for the safety assessment of foods derived from a specific GM crop. Third, the paper provides an overview on developments in this area that may prove of use in the safety assessment of GM crops, and recommendations for research priorities. It is concluded that the combination of existing test methods provides a sound test-regime to assess the safety of GM crops. Advances in our understanding of molecular biology, biochemistry, and nutrition may in future allow further improvement of test methods that will over time render the safety assessment of foods even more effective and informative.

An Arabidopsis homolog of the bacterial cell division inhibitor SulA is involved in plastid division

Plastids have evolved from an endosymbiosis between a cyanobacterial symbiont and a eukaryotic host cell. Their division is mediated both by proteins of the host cell and conserved bacterial division proteins. Here, we identified a new component of the plastid division machinery, Arabidopsis thaliana SulA. Disruption of its cyanobacterial homolog (SSulA) in Synechocystis and overexpression of an AtSulA-green fluorescent protein fusion in Arabidopsis demonstrate that these genes are involved in cell and plastid division, respectively. Overexpression of AtSulA inhibits plastid division in planta but rescues plastid division defects caused by overexpression of AtFtsZ1-1 and AtFtsZ2-1, demonstrating that its role in plastid division may involve an interaction with AtFtsZ1-1 and AtFtsZ2-1.

pthG from Pantoea agglomerans pv. gypsophilae encodes an avirulence effector that determines incompatibility in multiple beet species

SUMMARY Pantoea agglomerans pv. gypsophilae (Pag) causes root and crown gall disease on gypsophila, whereas P. agglomerans pv. betae (Pab) induces the disease on beet as well as gypsophila. Both pathovars harbour a pathogenicity plasmid (pPATH(Pag) or pPATH(Pab)) that determines disease development. We have previously isolated and partially characterized a pleiotropic gene from the pPATH(Pag), designated as pthG, that encodes a virulence factor in gypsophila and an elicitor of a hypersensitive-like response in beet roots. The present study was undertaken to characterize pthG further as an avr gene. The infiltration of beet leaves with strains expressing PthG (i.e. Pag or Pab containing pthG in trans) caused an hypersensitive reaction (HR) response within 48 h, whereas strains lacking intact pthG (i.e. Pab or Pag mutated in pthG) resulted in gall formation after 5 days. A hypersensitive reaction was elicited by PthG on multiple beet species, whereas a marker exchange mutant of Pag in pthG extended its host range on these beet species. A marker exchange mutant of Pag in hrpJ, encoding a component of the Type III secretion system, prevented HR elicitation. Mutations in each of the hrp regulatory genes (hrpY, hrpS and hrpL) substantially reduced the transcriptional activity of pthG in gypsophila cuttings. PthG could only be detected inside Pag cells during over-expression of hrpS or hrpL. Particle bombardment of GFP-PthG fusion caused cell death in beet, but not in non-host (melon) leaves. Present and previous results have established pthG as a broad-host-range avr gene that functions in multiple host plant species and the first functional avr gene in Pantoea spp.

Over-expression and production of plant allergens by molecular farming strategies

Recombinant allergens have become a valuable tool for diagnosis and may also be used for therapy in the near future. To supply the required large amounts of functional recombinant proteins on a cost-effective basis, the production of allergens in plants by molecular farming is an alternative to microbial expression systems. Especially as post-translational modifications of the allergens, e.g., phosphorylation and glycosylation, may be important for recognition by the human immune system, the plant-based production of recombinant allergens enables the correct folding, glycosylation, and other modifications of the recombinant allergen. An introduction to the methods for plant transformation via the tumor-inducing bacterium, Agrobacterium tumefaciens, is given in this paper.

A one-step method to convert vectors into binary vectors suited for Agrobacterium-mediated transformation

Bacterial artificial chromosomes (BACs) are widely used for the construction of physical maps, positional-cloning and whole-genome sequencing strategies. Unfortunately, their use for functional genomics is limited, as currently there is no efficient method to use BACs directly for complementation. We describe a novel strategy for one-step conversion of any BAC into a binary BAC (BIBAC). Using Agrobacterium tumefaciens, these BIBACs can be efficiently transformed to virtually all organisms, including plants, fungi, yeasts and human cells. As the strategy is based on in vivo recombineering and does not depend on restriction sites, it is applicable to any vector. To show the feasibility of the method five BACs, containing 0-75 kb of fungal DNA, were converted into BIBACs. These were subsequently transformed to the plant pathogenic fungus Fusarium oxysporum f.sp. lycopersici and to Aspergillus awamori, a filamentous fungus often used for large-scale protein production. Molecular characterisation of the transformants showed that the BIBACs were efficiently transferred to the fungi and stably integrated into their genomes.

Agrobacterium tumefaciens-mediated transformation ofParacoccidioides brasiliensis

Paracoccidioides brasiliensis is the causative agent of paracoccidioidomycosis, an important mycosis endemic to Latin America. As the tools to study gene function in P. brasiliensis are only in the early stage of development, there is presently no system that allows for both the delivery and integration of exogenous nucleic acids into its genome. We report in this paper the transformation of the yeast phase of P. brasiliensis (ATCC-60855) with Agrobacterium tumefaciens (GV3101) carrying the vector pAD1625. The microorganisms were co-cultivated for 2 days and then incubated for 10 days at 35 degrees C on selective media. PCR and dot-blot targeted at a fragment of 222 bp from the hph (hygromycin phosphotransferase) gene which confers Hygr confirmed the transformation of P. brasiliensis.

The Arabidopsis-accelerated cell death gene ACD1 is involved in oxygenation of pheophorbide a: inhibition of the pheophorbide a oxygenase activity does not lead to the "stay-green" phenotype in Arabidopsis

Oxygenation of pheophorbide a is a key step in chlorophyll breakdown. Several biochemical studies have implicated that this step was catalyzed by an iron-containing and ferredoxin-dependent monooxygenase, pheophorbide a oxygenase (PaO). It has been proposed that inhibition of its activity arrests the chlorophyll breakdown and leads to the "stay-green" phenotype. We searched the Arabidopsis genome for a possible PaO-encoding gene and hypothesized that it has homology to known iron-containing Rieske-type monooxygenase sequences. We identified three such open reading frames, Tic55, ACD1 and ACD1-like. We produced transgenic Arabidopsis plants which expressed antisense RNA as a method to inhibit the expression of these genes. The appearance of these antisense plants were indistinguishable from that of the wild type under illumination. However, after they were kept under darkness for 5 d and again illuminated, the leaves of the antisense ACD1 plants (AsACD1) were bleached. Leaves of AsACD1 accumulated 387 nmol (g FW)(-1) pheophorbide a which corresponded to 60% of chlorophyll a degraded. The rate of decrease in chlorophyll a was not influenced in senesced AsACD1 leaves. These results demonstrated that ACD1 is involved in PaO activity, and its inhibition led to photooxidative destruction of the cell instead of the "stay-green" phenotype.

Transgene behaviour in populations of rice plants transformed using a new dual binary vector system: pGreen/pSoup

Transgene integration, expression level and stability have been studied, across two generations, in a population of rice plants transformed using a new dual binary vector system: pGreen/pSoup. pGreen is a small Ti binary vector unable to replicate in Agrobacterium without the presence of another binary plasmid, pSoup, in the same strain. We engineered both pGreen and pSoup to contain each a different T-DNA. Transformation experiments were conducted using a pGreen vector containing the bar and gusA expression units (no transgene in pSoup) or with a pSoup vector containing an aphIV and gfp expression units (no transgene in pGreen). High plant transformation frequencies (up to 40%) were obtained using herbicide resistance ( bar) or antibiotic resistance ( aphIV) genes. Around 80% of the independently transformed plants expressed unselected reporter genes ( gusA or gfp) present in the vectors. Backbone sequences transfer was frequent (45% of lines) and occurred often in multicopy lines. Around 15-20% of the rice plant lines contained a single T-DNA integration without backbone. Integration of additional transgene copies did not improve expression levels in either T(0) plants or T(1) progenies. Nearly all multicopy lines contained transgenes integrated at several loci in the plant genome, showing that T-DNAs from either pGreen or pSoup frequently integrated at unlinked loci. Precise determination of loci number required the analysis of transgene presence in progeny. Segregation of transgene phenotype was generally misleading and tended to underestimate the real number of transgenic loci. The contribution of this new dual-binary vector system to the development of high-throughput rice transformation systems and to the production of marker-free transgenic rice plants is discussed.

Agrobacterium-mediated plant transformation: the biology behind the "gene-jockeying" tool

Agrobacterium tumefaciens and related Agrobacterium species have been known as plant pathogens since the beginning of the 20th century. However, only in the past two decades has the ability of Agrobacterium to transfer DNA to plant cells been harnessed for the purposes of plant genetic engineering. Since the initial reports in the early 1980s using Agrobacterium to generate transgenic plants, scientists have attempted to improve this "natural genetic engineer" for biotechnology purposes. Some of these modifications have resulted in extending the host range of the bacterium to economically important crop species. However, in most instances, major improvements involved alterations in plant tissue culture transformation and regeneration conditions rather than manipulation of bacterial or host genes. Agrobacterium-mediated plant transformation is a highly complex and evolved process involving genetic determinants of both the bacterium and the host plant cell. In this article, I review some of the basic biology concerned with Agrobacterium-mediated genetic transformation. Knowledge of fundamental biological principles embracing both the host and the pathogen have been and will continue to be key to extending the utility of Agrobacterium for genetic engineering purposes.

Novel type Arabidopsis thaliana H(+)-PPase is localized to the Golgi apparatus

Vacuolar H(+)-PPase, a membrane bound proton-translocating pyrophosphatase found in various species including plants, some protozoan and prokaryotes, has been demonstrated to be localized to the vacuolar membrane in plants. Using a GUS reporter system and a green fluorescent protein (GFP) fusion protein, we investigated the tissue distribution and the subcellular localization, respectively, of a novel type H(+)-PPase encoded by AVP2/AVPL1 identified in the Arabidopsis thaliana genome. We showed that AVP2/AVPL1 is highly expressed at the trichome and the filament of stamen. Furthermore, the fluorescence of GFP-tagged AVP2/AVPL1 showed small dot-like structures that were observed throughout the cytoplasm of various Arabidopsis cells under a fluorescent microscope. The distribution of this dot-like fluorescent pattern was apparently affected by a treatment with brefeldin A. Moreover, we demonstrated that most dot-like fluorescent structures colocalized with a Golgi resident protein. These findings suggest that this novel type H(+)-PPase resides on the Golgi apparatus rather than the vacuolar membrane.