Identification of a cluster IV pleiotropic drug resistance transporter gene expressed in the style of Nicotiana plumbaginifolia

Petunia hybrida PDR2 is involved in herbivore defense by controlling steroidal contents in trichomes

As a first line of defense against insect herbivores many plants store high concentrations of toxic and deterrent secondary metabolites in glandular trichomes. Plant Pleiotropic Drug Resistance (PDR)-type ABC transporters are known secondary metabolite transporters, and several have been implicated in pathogen or herbivore defense. Here, we report on Petunia hybrida PhPDR2 as a major contributor to trichome-related chemical defense. PhPDR2 was found to localize to the plasma membrane and be predominantly expressed in multicellular glandular trichomes of leaves and stems. Down-regulation of PhPDR2 via RNA interference (pdr2) resulted in a markedly higher susceptibility of the transgenic plants to the generalist foliage feeder Spodoptera littoralis. Untargeted screening of pdr2 trichome metabolite contents showed a significant decrease in petuniasterone and petuniolide content, compounds, which had previously been shown to act as potent toxins against various insects. Our findings suggest that PhPDR2 plays a leading role in controlling petuniasterone levels in leaves and trichomes of petunia, thus contributing to herbivory resistance.

Genes Encoding Cucumber Full-Size ABCG Proteins Show Different Responses to Plant Growth Regulators and Sclareolide

Full-size members of the ABCG (ATP-binding cassette, subfamily G) subfamily of ABC transporters have been found only in plants and fungi. The plant genes encoding full-size ABCGs identified so far appeared to be differentially regulated under various environmental constraints, plant growth regulators, and microbial elicitors, indicating a broad functional role of these proteins in plant responses to abiotic and biotic stress. Nevertheless, the structure and physiological function of full-size ABCGs in many plant species are still unknown. We have recently identified 16 genes encoding full-size ABCG proteins in cucumber and found that the transcripts of two of them, CsABCG36 (CsPDR8) and CsABCG40 (CsPDR12), are most abundant in roots and are significantly affected by phytohormones and auxin herbicide. In this study, we analyzed the structure and phylogeny of all the full-size cucumber ABCG transporters and studied the organ expression profiles of the remaining 14 CsABCG genes. In addition, we investigated the effect of different plant growth regulators and the diterpene sclareolide on CsABCG expression in cucumber roots. Until now, the full-size plant ABCG transporters have been grouped into five different clusters. The new phylogenetic analysis of full-size ABCGs from model plants and cucumber clustered these proteins into six different subgroups. Interestingly, the expression profiles of cucumber ABCG genes assigned to the same clusters were not correlated, suggesting functional diversification or different regulatory mechanisms of the full-size cucumber ABCG proteins.

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.

Molecular cloning and expression analysis of PDR1-like gene in ginseng subjected to salt and cold stresses or hormonal treatment

The plant pleiotropic drug resistance (PDR) family of ATP-binding cassette (ABC) transporters is potentially involved in diverse biological processes. Currently, little is known about their actual physiological functions. A Panax ginseng PDR transporter gene (PgPDR1) was cloned and the cDNA has an open reading frame of 4344 bp. The deduced amino acid sequence contained the characteristic domains of PDR transporters: Walker A, Walker B, and ABC signature. Genomic DNA hybridization analysis indicated that one copy of PgPDR1 gene was present in P. ginseng. Subcellular localization showed that PgPDR1-GFP fusion protein was specifically localized in the cell membrane. Promoter region analysis revealed the presence of cis-acting elements, some of which are putatively involved in response to hormone, light and stress. To understand the functional roles of PgPDR1, we investigated the expression patterns of PgPDR1 in different tissues and under various conditions. Quantitative real-time PCR (qRT-PCR) and Western blotting analysis showed that PgPDR1 was expressed at a high level in the roots and leaves compared to seeds and stems. The expression of PgPDR1 was up-regulated by salicylic acid (SA) or chilling, down-regulated by ABA, and regulated differently at transcript and protein levels by MeJA. These results suggest that PgPDR1 might be involved in responding to environmental stresses and hormones.

NtPDR1, a plasma membrane ABC transporter from Nicotiana tabacum, is involved in diterpene transport

ATP-binding cassette transporters are involved in the active transport of a wide variety of metabolites in prokaryotes and eukaryotes. One subfamily, the Pleiotropic Drug Resistance (PDR) transporters, or full-size ABCG transporters, are found only in fungi and plants. NtPDR1 was originally identified in Nicotiana tabacum suspension cells (BY2), in which its expression was induced by microbial elicitors. To obtain information on its expression in plants, we generated NtPDR1-specific antibodies and, using Western blotting, found that this transporter is localized in roots, leaves, and flowers and this was confirmed in transgenic plants expressing the ß-glucuronidase reporter gene fused to the NtPDR1 promoter region. Expression was seen in the lateral roots and in the long glandular trichomes of the leaves, stem, and flowers. Western blot analysis and in situ immunolocalization showed NtPDR1 to be localized in the plasma membrane. Induction of NtPDR1 expression by various compounds was tested in N. tabacum BY2 cells. Induction of expression was observed with the hormones methyl jasmonate and naphthalene acetic acid and diterpenes. Constitutive ectopic expression of NtPDR1 in N. tabacum BY2 cells resulted in increased resistance to several diterpenes. Transport tests directly demonstrated the ability of NtPDR1 to transport diterpenes. These data suggest that NtPDR1 is involved in plant defense through diterpene transport.

Loss of AtPDR11, a plasma membrane-localized ABC transporter, confers paraquat tolerance in Arabidopsis thaliana

Paraquat is one of the most widely used herbicides in the world. However, no paraquat transporter has been isolated in plants. Here, we describe paraquat-tolerant mutant pqt24-1, isolated from an activation-tagging library on the basis of its tolerance to 2 μm paraquat in the seedling stage. Molecular analysis revealed that the T-DNA was inserted in the 13th exon of At1g66950, which encodes AtPDR11, a member of the ATP-binding cassette transporter superfamily. As a result, AtPDR11 was knocked out in the mutant. Loss-of-function mutations of AtPDR11 led to reduced paraquat accumulation in plant cells. In addition, the AtPDR11 protein was specifically localized in the plasmalemma, suggesting AtPDR11 as a potential transporter of paraquat. This conclusion was supported by kinetic analysis of paraquat import. Further studies showed that the transcript level of AtPDR11 could be strongly induced by paraquat and other abiotic stresses including H(2) O(2) , indicating possible up-regulation of AtPDR11 expression by oxidative stress signaling. Thus, our data suggest that paraquat is an opportunistic substrate of AtPDR11 and the enhanced paraquat tolerance of pqt24-1 is due to reduced uptake of paraquat into plant cells.

Histological and molecular analysis of pollen-pistil interaction in clementine

In contrast to model species, the self-incompatibility reaction in citrus has been poorly studied. It is assumed to be gametophytically determined and genetically controlled by the S-locus, which in other species encodes for glycoproteins (S-RNases) showing ribonuclease activity. To investigate pollen-pistil interaction, the pollen tube growth of two clementine varieties, 'Comune' (self-incompatible) and 'Monreal' (a 'Comune' self-compatible mutation) was analysed by histological assays in self- and cross-pollination conditions. Cross-pollination assays demonstrated that the mutation leading to self-compatibility in 'Monreal' occurred in the stylar tissues. Similar rates of pollen germination were observed in both genotypes. However, 'Comune' pollen tubes showed altered morphology and arrested growth in the upper style while in 'Monreal' they grew straight toward the ovary. Moreover, to identify genes putatively involved in pollen-pistil interaction and self-incompatibility, research based on the complementary DNA-amplified fragment length polymorphism technique was carried out to compare the transcript profiles of unpollinated and self-pollinated styles and stigmas of the two cultivars. This analysis identified 96 unigenes such as receptor-like kinases, stress-induced genes, transcripts involved in the phenylpropanoid pathway, transcription factors and genes related to calcium and hormone signalling. Surprisingly, a high percentage of active long terminal repeat (LTR) and non-LTR retrotransposons were identified among the unigenes, indicating their activation in response to pollination and their possible role in the regulation of self-incompatibility genes. The quantitative reverse trascription-polymerase chain reaction analysis of selected gene tags showed transcriptional differences between the two genotypes during pollen germination and pollen tube elongation.

Full-size ABC transporters from the ABCG subfamily in medicago truncatula

Full-size ATP-binding cassette (ABC) transporters belonging to the ABCG subfamily are unique for plants and fungi. There is growing evidence that certain of these proteins play a role in plant defense or signaling systems. As yet, a complete set of full-size ABCG protein genes has been inventoried and classified in only two plants: Arabidopsis thaliana and Oryza sativa. Recently, a domain-based clustering analysis has predicted the presence of at least 12 genes encoding such proteins in the Lotus japonicus genome. Here, we identify and classify 19 genes coding full-size ABCG proteins in Medicago truncatula, a model legume plant. We have found that the majority of these genes are expressed in roots and flowers whereas only a few are expressed in leaves. Expression of several has been induced upon pathogenic infection in both roots and leaves. ABCG messenger RNAs have been detected in root nodules forming during symbiosis of legume plants and nitrogen-fixing bacteria. The data presented provide a scaffold for further studies of the physiological function of Medicago ABCG transporters and their possible role in modulating plant-microorganism interactions.

Transcriptional profiling of the PDR gene family in rice roots in response to plant growth regulators, redox perturbations and weak organic acid stresses

The role of plant pleiotropic drug resistance (PDR) type ATP-binding cassette (ABC) transporters remains poorly understood. We characterized the expression of the rice pleiotropic drug resistance (PDR) gene family in roots, where PDR transporters are believed to have major functions. A prototypical oligonucleotide array was developed containing 70-mers chosen in the gene-specific 3' untranslated regions of the rice PDR genes, other full-molecule rice ABC transporter genes and relevant marker genes. Jasmonates, which are involved in plant defense and secondary metabolism, proved major inducers of PDR gene expression. Over half of the PDR genes were JA-induced in roots of rice; OsPDR9 to the highest level. Salicylic acid, involved in plant pathogen defense, markedly induced the expression of OsPDR20. OsPDR20 was cDNA cloned and characterized. Abscisic acid, typically involved in water deficit responses, particularly induced OsPDR3 in roots and shoot and OsPDR6 in rice leaves. OsPDR9 and OsPDR20 were furthermore up-regulated in response to dithiothreitol- or glutathione-induced redox perturbations. Exogenous application of the weak organic acids lactic acid, malic acid, and citric acid differentially induced the expression of OsPDR3, OsPDR8, OsPDR9 and OsPDR20 in rice seedling roots. This transcriptional survey represents a guide for the further functional analysis of individual PDR transporters in roots of rice.