A poplar tree proteinase inhibitor-like gene promoter is responsive to wounding in transgenic tobacco

Pathogen-induced expression of a blight tolerance transgene in American chestnut

American chestnut (Castanea dentata) is a susceptible host of the invasive necrotrophic fungus Cryphonectria parasitica, which causes chestnut blight disease. The fungal pathogen attacks chestnut stems by invading wounded tissue and secreting oxalate. This process leads to the death of infected host cells and the formation of cankers, eventually girdling stems and killing the tree above the infections. To reduce damage caused by fungal oxalate, American chestnut has been genetically engineered to express a wheat oxalate oxidase (OxO). This enzyme degrades the oxalate produced by the pathogen and confers elevated tolerance to Cryphonectria parasitica infection. We report new lines of transgenic American chestnut that have been developed with the win3.12 inducible promoter from poplar (Populus deltoides) driving OxO expression. This promoter is responsive to both wounding and pathogen infection, with a low level of baseline expression. Targeted expression of OxO to wounded and infected tissue is sought as an alternative to constitutive expression for potential metabolic resource conservation and transgene stability over the long lifetime of a tree and over successive generations of breeding. Transgenic Castanea dentata lines harbouring the win3.12-OxO construct were evaluated for transgene expression patterns and tolerance to chestnut blight infection. OxO transcript levels were low in uninfected plants, but robust infection-induced expression levels were observed, with one transgenic line reaching levels comparable to those of previously characterized CaMV35S-OxO lines. In chestnut blight infection bioassays, win3.12-OxO lines showed elevated disease tolerance similar to blight-resistant Chinese chestnut (Castanea mollissima) controls.

Comparative Studying of Leaf Trichomes, Teeth and Glands in Populus nigra L., Populus deltoides W. Bartram ex Marshall and Their Hybrids

Poplars from Aigeiros Duby section are very widespread in the world. A range of morphological characters were studied in such species of this section as Populus deltoides Bartram ex Marshall, P. nigra L. and their hybrid P. × canadensis Moench. However, there is little information about micromorphological characters of their leaves. The aim of this work was to study these characters and understand their species-specific potential. Thus, the morphological features, density and distribution of non-glandular trichoms, marginal glandular trichomes (salicoid teeth or coleters), epiglandular trichomes and basilaminar nectaries-glands were ontogenetically examined by both light and scanning electron microscopy in the certified by molecular markers P. deltoides, P. nigra and P. × canadensis samples. Non-glandular trichomes belong to the uni-, multicellular, uniseriate category. Marginal glandular trichomes can be classified as coleter types. Other morphological and anatomical trichome features are discussed with regard to their possible function. In summary, some variations in leaf morphology may be useful for the P. nigra, P. deltoides and their hybrid P. × canadensis species identification. These species differ in shape and number of basilaminar glands, as well as non-glandular trichome types and their distribution on the leaf.

Enhancing disease resistance in poplar through modification of its natural defense pathway

Modification of the poplar defense pathway through pathogen-induced expression of an amphibian host defense peptide modulates plant innate immunity and confers robust and reliable resistance against a major poplar pathogen, Septoria musiva. Host defense peptides (HDPs), also known as cationic antimicrobial peptides, represent a diverse group of small membrane-active molecules that are part of the innate defense system of their hosts against pathogen invasion. Here we describe a strategy for development of poplar plants with enhanced HDP production and resistance to the commercially significant fungal pathogen Septoria musiva. The naturally occurring linear amphipathic α-helical HDP dermaseptin B1, which has 31 residues and originated from the skin secretion of arboreal frogs, was N-terminally modified (MsrA2) and evaluated in vitro for antifungal activity and phytotoxicity. The MsrA2 peptide inhibited germination of S. musiva conidia at physiologically relevant low micromolar concentrations that were non-toxic to poplar protoplasts. The nucleotide sequence of MsrA2, optimized for expression in plants, was introduced into the commercial hybrid poplar Populus nigra L. × P. maximowiczii A. Henry (NM6) via Agrobacterium-mediated transformation. Transgene expression was regulated by the pathogen-inducible poplar promoter win3.12T, a part of the poplar innate defense system. Most importantly, the induced accumulation of MsrA2 peptide in poplar leaves was sufficient to confer resistance against S. musiva. The antifungal resistance of plants with high MsrA2 expression and MsrA2 accumulation was strong and reproducible, and without deleterious effects on plant growth and development. These results provide an insight into development of new technologies for engineering durable disease resistance against major pathogens of poplar and other plants.

A novel cis-acting element in the GmERF3 promoter contributes to inducible gene expression in soybean and tobacco after wounding

KEY MESSAGE

Using in silico and functional analyses, we cloned and validated the expression profile of an inducible soybean promoter (GmERF3) along with its novel wound-induced and delayed expression (WIDE) element. Promoters and their contributing promoter elements are the main regulators of gene expression at the transcriptional level. Although the Ethylene Response Factor (ERF) gene family is one of the most well-studied stress-responsive gene families in plants, their promoter regions have received little attention. In this study, we investigated the expression patterns driven by the soybean (Glycine max) GmERF3 promoter and its cis-acting elements in soybean and tobacco. Transcriptomic data revealed that the native GmERF3 gene was differentially expressed in organs and tissues of plants. In transgenic soybeans containing a 1.3 kb GmERF3 promoter fused to the green fluorescent protein (gfp) gene, organ- and tissue-specificity was observed in untreated plants while mechanical wounding led to induction of GFP expression. Further in silico and in planta analyses of the GmERF3 promoter sequence in soybean revealed different cis-acting elements, including a novel cis-acting element, which contributed to increased expression, 1-2 days after mechanical wounding. We have named this DNA motif the wound-induced and delayed expression element (GGATTCAAGTTTAACC). A synthetic promoter containing a tetrameric repeat of this element showed high but late wound-induced GFP expression in leaves of transgenic tobacco. Our study expands the toolbox of inducible promoters and promoter elements for potential use in basic and applied research.

Nascent transcription affected by RNA polymerase IV in Zea mays

All eukaryotes use three DNA-dependent RNA polymerases (RNAPs) to create cellular RNAs from DNA templates. Plants have additional RNAPs related to Pol II, but their evolutionary role(s) remain largely unknown. Zea mays (maize) RNA polymerase D1 (RPD1), the largest subunit of RNA polymerase IV (Pol IV), is required for normal plant development, paramutation, transcriptional repression of certain transposable elements (TEs), and transcriptional regulation of specific alleles. Here, we define the nascent transcriptomes of rpd1 mutant and wild-type (WT) seedlings using global run-on sequencing (GRO-seq) to identify the broader targets of RPD1-based regulation. Comparisons of WT and rpd1 mutant GRO-seq profiles indicate that Pol IV globally affects transcription at both transcriptional start sites and immediately downstream of polyadenylation addition sites. We found no evidence of divergent transcription from gene promoters as seen in mammalian GRO-seq profiles. Statistical comparisons identify genes and TEs whose transcription is affected by RPD1. Most examples of significant increases in genic antisense transcription appear to be initiated by 3'-proximal long terminal repeat retrotransposons. These results indicate that maize Pol IV specifies Pol II-based transcriptional regulation for specific regions of the maize genome including genes having developmental significance.

Comparative nucleotide diversity across North American and European populus species

Nucleotide polymorphisms in two North American balsam poplars (Populus trichocarpa Torr. & Gray and P. balsamifera L.; section Tacamahaca), and one Eurasian aspen (P. tremula L.; section Populus) were compared using nine loci involved in defense, stress response, photoperiodism, freezing tolerance, and housekeeping. Nucleotide diversity varied among species and was highest for P. tremula (θ(w) = 0.005, π(T) = 0.007) as compared to P. balsamifera (θ(w) = 0.004, π(T) = 0.005) or P. trichocarpa (θ(w) = 0.002, π(T) = 0.003). Across species, the defense and the stress response loci accounted for the majority of the observed level of nucleotide diversity. In general, the studied loci did not deviate from neutral expectation either at the individual locus (non-significant normalized Fay and Wu's H) or at the multi-locus level (non-significant HKA test). Using molecular clock analysis, section Tacamahaca probably shared a common ancestor with section Populus approximately 4.5 million year ago. Divergence between the two closely related balsam poplars was about 0.8 million years ago, a pattern consistent with an isolation-with-migration (IM) model. As expected, P. tremula showed a five-fold higher substitution rate (2 × 10(-8) substitution/site/year) compared to the North American species (0.4 × 10(-8) substitution/site/year), probably reflecting its complex demographic history. Linkage disequilibrium (LD) varied among species with a more rapid decay in the North American species (<400 bp) in comparison to P. tremula (≫400 bp). The similarities in nucleotide diversity pattern and LD decay of the two balsam poplar species likely reflects the recent time of their divergence.

RNA-dependent RNA polymerase is required for enhancer-mediated transcriptional silencing associated with paramutation at the maize p1 gene

Paramutation is the ability of an endogenous gene or a transgene to heritably silence another closely related allele or gene. At the maize p1 (pericarp color1) gene, paramutation is associated with decreases in transcript levels and reduced pigmentation of the endogenous allele that normally specifies red seed coat (pericarp) and cob pigmentation. Herein we demonstrate that this silencing occurs at the transcriptional level and that a specific enhancer fragment from p1 is sufficient to induce all aspects of paramutation. Further, we demonstrate that a mutation in the mop1 gene (mediator of paramutation1), which encodes a RNA-dependent RNA polymerase, is absolutely required for establishing the silencing associated with p1 paramutation. In contrast to its effects on other paramutation loci, the mop1 mutation does not immediately reactivate a previously silenced allele; several generations in the presence of the mop1 mutation are required. In addition, the mop1 mutation was also able to release tissue-specific silencing of another p1 allele that does not participate in paramutation, but does contain a tandem repeated structure and is likely regulated through epigenetic mechanisms. These results demonstrate that RNA-mediated gene-silencing mechanisms play key roles in p1 paramutation and the spectrum of roles for MOP1 is broadened to include tissue-specific expression patterns.

Functional analysis of the Kunitz trypsin inhibitor family in poplar reveals biochemical diversity and multiplicity in defense against herbivores

We investigated the functional and biochemical variability of Kunitz trypsin inhibitor (KTI) genes of Populus trichocarpa x Populus deltoides. Phylogenetic analysis, expressed sequence tag databases, and western-blot analysis confirmed that these genes belong to a large and diverse gene family with complex expression patterns. Five wound- and herbivore-induced genes representing the diversity of the KTI gene family were selected for functional analysis and shown to produce active KTI proteins in Escherichia coli. These recombinant KTI proteins were all biochemically distinct and showed clear differences in efficacy against trypsin-, chymotrypsin-, and elastase-type proteases, suggesting functional specialization of different members of this gene family. The in vitro stability of the KTIs in the presence of reducing agents and elevated temperature also varied widely, emphasizing the biochemical differences of these proteins. Significantly, the properties of the recombinant KTI proteins were not predictable from primary amino acid sequence data. Proteases in midgut extracts of Malacosoma disstria, a lepidopteran pest of Populus, were strongly inhibited by at least two of the KTI gene products. This study suggests that the large diversity in the poplar (Populus spp.) KTI family is important for biochemical and functional specialization, which may be important in the maintenance of pest resistance in long-lived plants such as poplar.

Comparison of pathogen-induced expression and efficacy of two amphibian antimicrobial peptides, MsrA2 and temporin A, for engineering wide-spectrum disease resistance in tobacco

The rapid accumulation of defensive transgene products in plants only on pathogen invasion has clear advantages over their constitutive synthesis. In this study, two antimicrobial peptides from the skin secretions of frogs, MsrA2 (N-methionine-dermaseptin B1) and temporin A, were evaluated for engineering pathogen-induced disease resistance in plants. Both peptides inhibited plant-specific pathogens in vitro at micromolar concentrations that were not toxic to plant protoplasts. The plant-optimized nucleotide sequences encoding MsrA2 and temporin A were transcriptionally fused to the inducible win3.12T poplar promoter, which had strong systemic activity in response to fungal infection, and introduced into tobacco (Nicotiana tabacum L. cv. Xanthi). Transgene expression was very low in the leaves of unstressed plants; however, it was strongly increased after pathogen challenge or wounding. The pathogen responsiveness of the win3.12T promoter was found to be universal rather than species specific, with high activity in response to all pathogens tested. On induction, the amount of MsrA2 was up to 6-7 microg per gram of fresh leaf tissue. Most importantly, the induced accumulation of MsrA2 and temporin A in transgenic tobacco was sufficient to confer resistance to a variety of phytopathogenic fungi, such as Fusarium solani, F. oxysporum, Alternaria alternata, Botrytis cinerea, Sclerotinia sclerotiorum, the oomycete Pythium aphanidermatum and the bacterium Pectobacterium carotovorum. The accumulation of these peptides in transgenic plants did not alter the normal phenotype of tobacco. Thus, the expression of MsrA2 and temporin A in a pathogen-inducible manner enables the development of tobacco, and possibly other plant species, with wide-spectrum disease resistance, which can reduce the use of pesticides and the associated environmental risks.

Plant signalling peptides: some recent developments

The subject of this review is plant signalling peptides, peptides of a new generation which regulate growth, differentiation, and other plant physiological functions. These peptides include systemin, the phytosulfokines (PSKs), ENOD40, CLAVATA3, Locus-S, POLARIS, IDA, and ROT4. On the basis of literature data and our own results we discuss their structure, biological properties, and structure/biological function relationship, especially for the more studied systemin and PSK-alpha.

Leaf senescence is delayed in tobacco plants expressing the maize knotted1 gene under the control of a wound-inducible promoter

To extend the shelf life of freshly harvested vegetables and cut flowers, a maize homeobox gene Knotted1 (kn1) was placed under the control of a wound-inducible promoter win3.12 from hybrid poplar (Populus trichocarpa x P. deltoides) and introduced into tobacco plants (Nicotiana tabacum cv. Xanthi). Transgenic win3.12::kn1 plants were morphologically normal. A leaf-detachment assay demonstrated that senescence in win3.12::kn1 leaves could be delayed by at least 2 weeks compared with wild type leaves. Furthermore, all leaves of win3.12::kn1 shoots remained green and healthy 3 weeks after excision and incubation in water, while older leaves of control shoots senesced under the same conditions. Additionally, a number of adventitious roots produced at the cut ends of wild type shoots after a 3-week incubation, but much a less number of adventitious roots appeared in win3.12::kn1 shoots. The delay in senescence was also confirmed by a higher total chlorophyll (a + b) content in win3.12::kn1 leaves relative to that of the control plants. RT-PCR analysis showed that the kn1 transcript was detected in win3.12::kn1 leaves with wounding treatment, but otherwise was not observed in leaves of wild type and unwounded transgenic plants. The results presented here indicate that expression of kn1 gene driven by the wound-inducible promoter win3.12 is potentially useful to delay senescence of vegetable crops and commercial horticulture after harvest.

Genomics of hybrid poplar (Populus trichocarpa× deltoides) interacting with forest tent caterpillars (Malacosoma disstria): normalized and full-length cDNA libraries, expressed sequence tags, and a cDNA microarray for the study of insect-induced defences

As part of a genomics strategy to characterize inducible defences against insect herbivory in poplar, we developed a comprehensive suite of functional genomics resources including cDNA libraries, expressed sequence tags (ESTs) and a cDNA microarray platform. These resources are designed to complement the existing poplar genome sequence and poplar (Populus spp.) ESTs by focusing on herbivore- and elicitor-treated tissues and incorporating normalization methods to capture rare transcripts. From a set of 15 standard, normalized or full-length cDNA libraries, we generated 139,007 3'- or 5'-end sequenced ESTs, representing more than one-third of the c. 385,000 publicly available Populus ESTs. Clustering and assembly of 107,519 3'-end ESTs resulted in 14,451 contigs and 20,560 singletons, altogether representing 35,011 putative unique transcripts, or potentially more than three-quarters of the predicted c. 45,000 genes in the poplar genome. Using this EST resource, we developed a cDNA microarray containing 15,496 unique genes, which was utilized to monitor gene expression in poplar leaves in response to herbivory by forest tent caterpillars (Malacosoma disstria). After 24 h of feeding, 1191 genes were classified as up-regulated, compared to only 537 down-regulated. Functional classification of this induced gene set revealed genes with roles in plant defence (e.g. endochitinases, Kunitz protease inhibitors), octadecanoid and ethylene signalling (e.g. lipoxygenase, allene oxide synthase, 1-aminocyclopropane-1-carboxylate oxidase), transport (e.g. ABC proteins, calreticulin), secondary metabolism [e.g. polyphenol oxidase, isoflavone reductase, (-)-germacrene D synthase] and transcriptional regulation [e.g. leucine-rich repeat transmembrane kinase, several transcription factor classes (zinc finger C3H type, AP2/EREBP, WRKY, bHLH)]. This study provides the first genome-scale approach to characterize insect-induced defences in a woody perennial providing a solid platform for functional investigation of plant-insect interactions in poplar.

Pathogen-induced expression of a cecropin A-melittin antimicrobial peptide gene confers antifungal resistance in transgenic tobacco

Expression of defensive genes from a promoter that is specifically activated in response to pathogen invasion is highly desirable for engineering disease-resistant plants. A plant transformation vector was constructed with transcriptional fusion between the pathogen-responsive win3.12T promoter from poplar and the gene encoding the novel cecropin A-melittin hybrid peptide (CEMA) with strong antimicrobial activity. This promoter-transgene combination was evaluated in transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) for enhanced plant resistance against a highly virulent pathogenic fungus Fusarium solani. Transgene expression in leaves was strongly increased after fungal infection or mechanical wounding, and the accumulation of CEMA transcripts was found to be systemic and positively correlated with the number of transgene insertions. A simple and efficient in vitro regeneration bioassay for preliminary screening of transgenic lines against pathogenic fungi was developed. CEMA had strong antifungal activity in vitro, inhibiting conidia germination at concentrations that were non-toxic to tobacco protoplasts. Most importantly, the expression level of the CEMA peptide in vivo, regulated by the win3.12T promoter, was sufficient to confer resistance against F. solani in transgenic tobacco. The antifungal resistance of plants with high CEMA expression was strong and reproducible. In addition, leaf tissue extracts from transgenic plants significantly reduced the number of fungal colonies arising from germinated conidia. Accumulation of CEMA peptide in transgenic tobacco had no deleterious effect on plant growth and development. This is the first report showing the application of a heterologous pathogen-inducible promoter to direct the expression of an antimicrobial peptide in plants, and the feasibility of this approach to provide disease resistance in tobacco and, possibly, other crops.

Transcriptional regulation of Syndecan-1 expression by growth factors

Syndecan-1 is a prototype member of a family of transmembrane heparan sulfate proteoglycans. Syndecan-1 binds extracellular matrix components and fibroblast growth factors (FGFs) and modifies the function of FGFs. Syndecan-1 is constitutively expressed by several epithelial cells, but expression is also induced during many biological phenomena, such as tissue regeneration and the epithelial-mesenchymal interactions during organ development. Growth factors have been the prime candidates to induce syndecan-1 expression in these situations. In fibroblasts syndecan-1 is induced by FGF-2 and in keratinocytes by epidermal growth factor (EGF) and keratinocyte growth factor (KGF). The search for cis-acting elements regulating the growth factor-induced syndecan-1 expression has led to identification of a novel FGF-inducible response element (FiRE). FiRE is activated in fibroblasts and keratinocytes by the same growth factors that induce syndecan-1 expression in these cells. In adult tissues the activation of FiRE is restricted to migrating keratinocytes of healing wounds. The composition of the transcription factor binding to FiRE differs depending on the cell type and the activating growth factor. The FiRE provides a powerful tool for studies on growth factor specificity and regeneration of tissues. Moreover, it implies a novel transcriptional link that creates an FGF action-controlling autoregulatory loop between the heparan sulfate proteoglycans and the heparin-binding FGFs.

DNA methylation inhibits elongation but not initiation of transcription in Neurospora crassa

In plants, animals, and fungi, DNA methylation is frequently associated with gene silencing, yet little is known about the role of the methylation in silencing. In Neurospora crassa, repeated sequences are silenced by repeat-induced point mutation (RIP) and genes that have suffered numerous GC --> AT mutations by RIP are typically methylated at remaining cytosines. We investigated possible effects on transcription from methylation associated with RIP by taking advantage of 5-azacytidine, which prevents most methylation in Neurospora and a dim-2 mutation that abolishes all detectable methylation. Northern analyses revealed that methylation prevents the accumulation of transcripts from genes mutated by RIP. Measurements of transcription rates in vivo showed that methylation inhibits transcription severely but does not influence mRNA stability. Results of nuclear run-on experiments demonstrated that transcription initiation was not significantly inhibited by the dense methylation in the promoter sequences. In contrast, methylation blocked transcription elongation in vivo.

A wound-inducible gene from Salix viminalis coding for a trypsin inhibitor

A gene designated swin1.1 has been isolated by screening a Salix viminalis genomic library with a heterologous probe, win3 from Populus. The region sequenced included the entire coding sequence for a protein with 199 amino acids plus the promoter and terminator. At the 5' end of the coding region is a sequence that encodes a hydrophobic region of 25-30 amino acids, that could form a signal peptide. A putative TATAA box and polyadenylator sequence were identified. Introns were absent. The gene product showed similarities with serine protease inhibitors from the Kunitz family and especially with win3 from wounded leaves of Populus. Southern blot analysis indicated that swin1.1 is a member of a clustered gene family, swin1. An oligonucleotide corresponding to the putative hypervariable region towards the carboxyl end when used as a probe in Southern hybridization showed high specificity for swin1.1. Expression of the swin1.1 gene was enhanced in wounded leaves. The swin1.1 coding region without the signal sequence was highly expressed in Escherichia coli and the protein showed inhibitory activity against trypsin but at most slight activity against the other proteases tested. A systemically induced protein, SVTI, with inhibitor activity against trypsin, was isolated from Salix leaves by affinity chromatography on a column of trypsin-Sepharose 4B and N-terminal sequenced. It corresponded with the translated swin1.1 gene at 16 of the 19 amino acid sites, suggesting that SVTI is encoded by another member of the swin1 gene family.

Tissue- and cell-specific expression of a cinnamyl alcohol dehydrogenase promoter in transgenic poplar plants

Cinnamyl alcohol dehydrogenase (CAD) which catalyses the synthesis of the cinnamyl alcohols, the immediate precursors of lignins, from the corresponding cinnamaldehydes is considered to be a highly specific marker for lignification. We have isolated and characterized a CAD genomic clone from eucalyptus, a woody species of economic importance. The full-length promoter (EuCAD, 2.5 kb) and a series of 5' deletions were fused to the beta-glucuronidase (GUS) reporter gene. These constructs were tested in a homologous transient expression system of eucalyptus protoplasts which enabled the identification of several regions involved in transcriptional control. In order to study the spatial and developmental regulation of the CAD gene, the chimeric gene fusion (EuCAD-GUS) was then transferred via Agrobacterium tumefaciens-mediated transformation into poplar, an easily transformable woody angiosperm. Quantitative fluorometric assays conducted on eight independent in vitro transformants showed that GUS activity was highest in roots followed thereafter by stems and leaves. Histochemical staining for GUS activity on both in vitro primary transformants and more mature greenhouse-grown plants indicated a specific expression in the vascular tissues of stems, roots, petioles and leaves. At the onset of xylem differentiation, GUS activity was detected in parenchyma cells differentiating between the xylem-conducting elements. After secondary growth has occurred, GUS activity was localized in xylem ray cells and parenchyma cells surrounding the lignified phloem and sclerenchyma fibers. This first characterization of a woody angiosperm CAD promoter provides functional evidence for the role of CAD in lignification and suggests that parenchyma cells expressing CAD may provide lignin precursors to the adjacent lignified elements (vessels and fibres).

Molecular genetics of growth and development in Populus. III. A genetic linkage map of a hybrid poplar composed of RFLP, STS, and RAPD markers

We have evaluated three DNA-based marker types for linkage map construction in Populus: RFLPs detected by Southern blot hybridization, STSs detected by a combination of PCR and RFLP analysis, and RAPDs. The mapping pedigree consists of three generations, with the F1 produced by interspecific hybridization between a P. trichocarpa female and a P. deltoides male. The F2 generation was made by inbreeding to the maximum degree permitted by the dioecious mating system of Populus. The applicability of STSs and RAPDs outside the mapping pedigree has been investigated, showing that these PCR-based marker systems are well-suited to breeding designs involving interspecific hybridization. A Populus genome map (343 markers) has been constructed from a combination of all three types. The length of the Populus genome is estimated to be 2400-2800 cM.

Wound-induced and developmental activation of a poplar tree chitinase gene promoter in transgenic tobacco

Wounding hybrid poplar (Populus trichocarpa x P. deltoides) trees results in the expression of novel wound-inducible (win) mRNAs thought to encode proteins involved in defense against pests and pathogens. Members of the win6 gene family encode acidic multi-domain chitinases, with combined structure and charge characteristics that differ from previously described chitinases. Win6 expression has been shown to occur in pooled unwounded leaves of a wounded (on multiple leaves) poplar plant. Here we demonstrate that wounding a single leaf induces win6 expression locally, in the wounded leaf, and remotely, in specific unwounded leaves with strong vascular connections to the wounded leaf. We also demonstrate that a win6 promoter-beta-glucuronidase (GUS) gene fusion (win6-GUS) responds to wounding locally and remotely in transgenic tobacco. These data indicate that the poplar win6 promoter has regulatory elements that are responsive to 'wound signals' in the heterologous host. In addition, win6-GUS is developmentally activated in unwounded young leaves and floral tissues of transgenic tobacco. Similar developmental expression patterns are found to occur for win6 in poplar trees, demonstrating that a herbaceous plant can serve as a host for woody tree transgene analysis and can accurately predict expression patterns in tree tissues (e.g. flowers) that would be difficult to study in free-living trees.

A family of wound-induced genes in Populus shares common features with genes encoding vegetative storage proteins

Two wound-inducible cDNAs from poplar leaves show sequence identity to vegetative storage proteins (VSP) that accumulate seasonally in poplar bark tissues. We have compared the genomic organization, cDNA sequences and expression of the genes encoding the wound-inducible cDNAs (win4) with that of a bark VSP (called bark storage protein, or BSP). There appear to be several win4 genes in the poplar genome which segregate as a single locus and are therefore likely to be clustered. The same is true of the BSP genes. The win4 locus is linked (map distance of 5 cM) to the BSP locus, consistent with a common evolutionary origin of the genes. A near full-length win4 cDNA shows 75% sequence identity to BSP cDNAs. Both win4 and BSP are systemically wound-inducible; win4 transcripts accumulate in leaves and stems, whereas BSP transcripts accumulate almost exclusively in stems. A phloem transport-dependent signaling mechanism appears to be involved in systemic win4 expression after wounding. In contrast to BSP gene expression, win4 genes are not expressed in response to short day conditions. The data indicate win4 and BSP genes are differentially regulated, and their products may play important roles in the storage and reallocation of nitrogen in perennial plants.