The plant PDR family of ABC transporters

The plant pleiotropic drug resistance (PDR) family of ATP-binding cassette (ABC) transporters has been implicated in the transport of antifungal agents. In this paper, we provide an analysis of the entire family of PDR genes present in the Arabidopsis thaliana (L.) Heynh. genome. This analysis both resolves discrepancies in published inventories of plant ABC proteins and provides an expression analysis of all the annotated Arabidopsis PDR genes. The results indicate that the Arabidopsis genome contains 15 genes encoding PDR proteins and that these genes show a spectrum of specific expression patterns, both at the organ level and in response to various hormonal, environmental and chemical factors. These data provide a scaffold for the future molecular genetic analysis of this important family of ABC transporters. In addition, we demonstrate the usefulness of such data by using them to identify an Arabidopsis PDR protein that may play a role in the extrusion of the antifungal diterpene sclareol. Electronic Supplementary Material is available if you access this article at http://dx.doi.org/10.1007/s00425-002-0889-z. On that page (frame on the left side), a link takes you directly to the supplementary material.     

A new member of the NY-ESO-1 gene family is ubiquitously expressed in somatic tissues and evolutionarily conserved

Three single copy ATP-binding cassette (ABC) transporter encoding genes, designated MgAtr3, MgAtr4, and MgAtr5, were cloned and sequenced from the plant pathogenic fungus Mycosphaerella graminicola. The encoded ABC proteins all exhibit the [NBD-TMS(6)](2) configuration and can be classified as novel members of the pleiotropic drug resistance (PDR) class of ABC transporters. The three proteins are highly homologous to other fungal and yeast, ABC proteins involved in multidrug resistance or plant pathogenesis. MgAtr4 and MgAtr5 possess a conserved ABC motif at both the N- and C-terminal domain of the protein. In contrast, the Walker A motif in the N-terminal and the ABC signature in the C-terminal domain of MgAtr3, deviate significantly from the consensus sequence found in other members of the PDR class of ABC transporters. Expression of MgAtr3 could not be detected under any of the conditions tested. However, MgAtr4 and MgAtr5 displayed distinct expression profiles when treated with a range of compounds known to be either substrates or inducers of ABC transporters. These included synthetic fungitoxic compounds, such as imazalil and cyproconazole, natural toxic compounds, such as the plant defence compounds eugenol and psoralen, and the antibiotics cycloheximide and neomycin. The expression pattern of the genes was also dependent on the morphological state of the fungus. The findings suggest a role for MgAtr4 and MgAtr5 during plant pathogenesis and in protection against toxic compounds.     

Cloning and characterization of a novel Nicotiana tabacum ABC transporter involved in shoot branching

The ATP‐binding cassette (ABC) superfamily is a large protein family with diverse physiological functions in all kingdoms of life. One distinguished subfamily, the pleiotropic drug resistance (PDR) transporters, has only been identified in plants and fungi. Here, we identified a Nicotiana tabacum PDR gene, NtPDR6, which is a homolog of Petunia hybrida PDR1. The full‐length cDNA of NtPDR6 had a 4482‐bp open reading frame encoding a full‐size ABC transporter with 1493 amino acids. Sequence comparison showed that NtPDR6 had high homology with plant PDR proteins. NtPDR6 was strongly induced by phosphate starvation as well as by 1‐naphthalene acetic acid. Tissue expression pattern analysis showed that NtPDR6 was detected in all surveyed tissues but preferentially in roots. We cloned the 1.3‐kb NtPDR6 promoter and found that there was one phosphate starvation response‐related element Pho‐like and several root‐specific expression‐related elements rootmotiftapox1 in the NtPDR6 promoter. A tissue‐specific pattern of NtPDR6 promoter‐β‐glucuronidase expression was dominantly observed in subepidermal cells and the elongation zone of lateral roots. RNA interference technology was used to knock down NtPDR6 expression, and there was a significantly increased branching phenotype in the NtPDR6 knockdown plants. These data suggest that NtPDR6 plays a key role in regulation of shoot branching processes.     

CB1 cannabinoid receptor-mediated tyrosine phosphorylation of focal adhesion kinase-related non-kinase

We isolated an INF1 elicitin-inducible cDNA encoding a pleiotropic drug resistance (PDR)-type ATP-binding cassette (ABC) transporter homolog (NtPDR1) in suspension-cultured tobacco Bright Yellow-2 (BY-2) cells by application of differential display PCR. The NtPDR1 (Nicotiana tabacum PDR protein 1) gene also encodes a 162 kDa protein that includes two putative hydrophilic domains containing the ABC signature motif and two putative hydrophobic domains. Expression of the NtPDR1 gene was rapidly and strongly activated by treatment of BY-2 cells with INF1 elicitin. Further, treatment of BY-2 cells with flagellin, a bacterial proteinaceous hypersensitive reaction elicitor, or yeast extract, a general elicitor, also induced NtPDR1 gene expression. These results indicate that NtPDR1 may be involved in the general defense response in tobacco. This is the first report that microbial elicitors induce the expression of a plant ABC transporter gene.     

真菌的多向耐药性ABC转运蛋白

真菌的多向耐药性ABC转运蛋白(ATP-binding cassette transporters)是导致多药耐药性和抗真菌药物治疗效果明显下降的主要原因。文章对酿酒酵母(Saccharomyces cerevisiae)和主要致病真菌白色假丝酵母(Candida albicans)、新型隐球酵母(Cryptococcus neoformans)和烟曲霉(Aspergillus fumigatus)中的多向耐药性ABC转运蛋白的种类、药物外排机制以及基因表达调控网络的研究进展作一综述,为深入了解真菌的多向耐药性机制以及探讨克服多向耐药性的策略和提高药效提供参考。     

Organization and function of the plant pleiotropic drug resistance ABC transporter family

Among the ABC transporters, the pleiotropic drug resistance (PDR) family is particular in that its members are found only in fungi and plants and have a reverse domain organization, i.e., the nucleotide binding domain precedes the transmembrane domain. In Arabidopsis and rice, for which the full genome has been sequenced, the family of plant ABC transporters contains 15 and 23 PDR genes, respectively, which can be tentatively organized using the sequence data into five subfamilies. Most of the plant PDR genes so far characterized belong to subfamily I and have been shown to be involved in responses to abiotic and biotic stress, in the latter case, probably by transporting antimicrobial secondary metabolites to the cell surface. Only a single subfamily II member has been characterized. Induction of its expression by iron deficiency suggests its involvement in iron deficiency stress, thus, enlightening a new physiological role for a PDR gene.     

Plant pleiotropic drug resistance transporters:Transport mechanism,gene expression,and function

Pleiotropic drug resistance(PDR) transporters belonging to the ABCG subfamily of ATP-binding cassette(ABC)transporters are identified only in fungi and plants. Members of this family are expressed in plants in response to various biotic and abiotic stresses and transport a diverse array of molecules across membranes. Although their detailed transport mechanism is largely unknown, they play important roles in detoxification processes, preventing water loss, transport of phytohormones,and secondary metabolites. This review provides insights into transport mechanisms of plant PDR transporters, their expression profiles, and multitude functions in plants.     

Plant ABC transporters

The ATP binding cassette (ABC) superfamily is a large, ubiquitous and diverse group of proteins, most of which mediate transport across biological membranes. ABC transporters have been shown to function not only as ATP-dependent pumps, but also as ion channels and channel regulators. Whilst members of this gene family have been extensively characterised in mammalian and microbial systems, the study of plant ABC transporters is a relatively new field of investigation. Sequences of over 20 plant ABC proteins have been published and include homologues of P-glycoprotein, MRP, PDR5 and organellar transporters. At present, functions have been assigned to a small proportion of these genes and only the MRP subclass has been extensively characterised. This review aims to summarise literature relevant to the study of plant ABC transporters, to review methods of cloning, to discuss the utility of yeast and mammalian systems as models and to speculate on possible roles of uncharacterised ABC transporters in plants.     

Antagonistic Changes in Sensitivity to Antifungal Drugs by Mutations of an Important ABC Transporter Gene in a Fungal Pathogen

Fungal pathogens can be lethal, especially among immunocompromised populations, such as patients with AIDS and recipients of tissue transplantation or chemotherapy. Prolonged usage of antifungal reagents can lead to drug resistance and treatment failure. Understanding mechanisms that underlie drug resistance by pathogenic microorganisms is thus vital for dealing with this emerging issue. In this study, we show that dramatic sequence changes in PDR5, an ABC (ATP-binding cassette) efflux transporter protein gene in an opportunistic fungal pathogen, caused the organism to become hypersensitive to azole, a widely used antifungal drug. Surprisingly, the same mutations conferred growth advantages to the organism on polyenes, which are also commonly used antimycotics. Our results indicate that Pdr5p might be important for ergosterol homeostasis. The observed remarkable sequence divergence in the PDR5 gene in yeast strain YJM789 may represent an interesting case of adaptive loss of gene function with significant clinical implications.     

The multidrug transporter Pdr5: a molecular diode?

A subset of the family of ATP-binding cassette (ABC) transporters has been in focus owing to their involvement in conferring multidrug resistance in cancer cells and among immune compromised individuals. Saccharomyces cerevisiae is protected against xenobiotics by similar machineries that are part of the pleitropic drug resistance (PDR) network. The ABC transporter Pdr5 is an important member of this PDR network in yeast and is involved in cellular detoxification by the efflux of a wide variety of drugs and substrates. In this review, we focus on the aspects of detergent effects and the degeneracy in conserved sequences that is observed in the nucleotide binding domains of Pdr5 and discuss their functional relevance.     

Multifunctionality of plant ABC transporters – more than just detoxifiers

The ABC-transporter superfamily is one of the largest protein families, and members can be found in bacteria, fungi, plants and animals. The first reports on plant ABC transporters showed that they are implicated in detoxification processes. The recent completion of the genomic sequencing of Arabidopsis thaliana (L.) Heynh. [Arabidopsis Genome Initiative (2000) Nature 408:796-815] showed that Arabidopsis contains more than 100 ABC-type proteins; 53 genes code for so-called full-size transporters, which are large proteins of about 150 kDa consisting of two hydrophobic and two hydrophilic domains. The large number of genes in the MDR/MRP and PDR5-like sub-clusters and the strong sequence homology found in many cases suggest functional redundancy. One reason for the high number of genes can be attributed to the duplication of large segments of Arabidopsis chromosomes. Recent results indicate that the function of this protein family is not restricted to detoxification processes. Plant ABC transporters have been demonstrated to participate in chlorophyll biosynthesis, formation of Fe/S clusters, stomatal movement, and probably ion fluxes; hence they may play a central role in plant growth and developmental processes.     

A plant plasma membrane ATP binding cassette-type transporter is involved in antifungal terpenoid secretion

ATP binding cassette (ABC) transporters, which are found in all species, are known mainly for their ability to confer drug resistance. To date, most of the ABC transporters characterized in plants have been localized in the vacuolar membrane and are considered to be involved in the intracellular sequestration of cytotoxins. Working on the assumption that certain ABC transporters might be involved in defense metabolite secretion and their expression might be regulated by the concentration of these metabolites, we treated a Nicotiana plumbaginifolia cell culture with sclareolide, a close analog of sclareol, an antifungal diterpene produced at the leaf surface of Nicotiana spp; this resulted in the appearance of a 160-kD plasma membrane protein, which was partially sequenced. The corresponding cDNA (NpABC1) was cloned and shown to encode an ABC transporter. In vitro and in situ immunodetection showed NpABC1 to be localized in the plasma membrane. Under normal conditions, expression was found in the leaf epidermis. In cell culture and in leaf tissues, NpABC1 expression was strongly enhanced by sclareolide and sclareol. In parallel with NpABC1 induction, cells acquired the ability to excrete a labeled synthetic sclareolide derivative. These data suggest that NpABC1 is involved in the secretion of a secondary metabolite that plays a role in plant defense.     

A mutation in intracellular loop 4 affects the drug-efflux activity of the yeast multidrug resistance ABC transporter Pdr5p

Multidrug resistance protein Pdr5p is a yeast ATP-binding cassette (ABC) transporter in the plasma membrane. It confers multidrug resistance by active efflux of intracellular drugs. However, the highly polymorphic Pdr5p from clinical strain YJM789 loses its ability to expel azole and cyclohexmide. To investigate the role of amino acid changes in this functional change, PDR5 chimeras were constructed by segmental replacement of homologous BY4741 PDR5 fragments. Functions of PDR5 chimeras were evaluated by fluconazole and cycloheximide resistance assays. Their expression, ATPase activity, and efflux efficiency for other substrates were also analyzed. Using multiple lines of evidence, we show that an alanine-to-methionine mutation at position 1352 located in the predicted short intracellular loop 4 significantly contributes to the observed transport deficiency. The degree of impairment is likely correlated to the size of the mutant residue.     

Plant pleiotropic drug resistance transporters： Transport mechanism,gene expression,and function

Pleiotropic drug resistance （PDR） transporters belonging to the ABCG subfamily of ATP-binding cassette （ABC） transporters are identified only in fungi and plants. Members of this family are expressed in plants in response to various biotic and abiotic stresses and transport a diverse array of moleculesacross membranes, Although their detailed transport mechanism is largely unknown, they play important roles in detoxification processes, preventing water loss, transport of phytohormones, and secondary metabolites. This review provides insights into transport mechanisms of plant PDR transporters, their expression profiles, and multitude functions in plants.