Nucleotide sequence of the PR-1 gene of Nicotiana tabacum

Simple and efficient heterologous expression of necrosis-inducing effectors using the model plant Nicotiana benthamiana

Plant fungal pathogens cause devastating diseases on cereal plants and threaten global food security. During infection, these pathogens secrete proteinaceous effectors that promote disease. Some of these effectors from necrotrophic plant pathogens induce a cell death response (necrosis), which facilitates pathogen growth in planta. Characterization of these effectors typically requires heterologous expression, and microbial expression systems such as bacteria and yeast are the predominantly used. However, microbial expression systems often require optimization for any given effector and are, in general, not suitable for effectors involving cysteine bridges and posttranslational modifications for activity. Here, we describe a simple and efficient method for expressing such effectors in the model plant Nicotiana benthamiana. Briefly, an effector protein is transiently expressed and secreted into the apoplast of N. benthamiana by Agrobacterium-mediated infiltration. Two to three days subsequent to agroinfiltration, the apoplast from the infiltrated leaves is extracted and can be directly used for phenotyping on host plants. The efficacy of this approach was demonstrated by expressing the ToxA, Tox3, and Tox1 necrosis-inducing effectors from Parastagonospora nodorum. All three effectors produced in N. benthamiana were capable of inducing necrosis in wheat lines, and two of three showed visible bands on Coomassie-stained gel. These data suggest that N. benthamiana-agroinfiltration system is a feasible tool to obtain fungal effectors, especially those that require disulfide bonds and posttranslational modifications. Furthermore, due to the low number of proteins typically observed in the apoplast (compared with intracellular), this simple and high-throughput approach circumvents the requirement to lyse cells and further purifies the target proteins that are required in other heterologous systems. Because of its simplicity and potential for high-throughput, this method is highly amenable to the phenotyping of candidate protein effectors on host plants.

Exogenous Nitric Oxide Enhances Disease Resistance by Nitrosylation and Inhibition of S-Nitrosoglutathione Reductase in Peach Fruit

Nitric oxide (NO), a signaling molecule, participates in defense responses during plant-pathogen interactions. S-Nitrosoglutathione (GSNO) is found to be an active intracellular NO storage center and regulated by S-nitrosoglutathione reductase (GSNOR) in plants. However, the role of GSNOR in NO-induced disease resistance is not clear. In this research, the effects of NO and GSNOR inhibitor (N6022) on the defense response of harvested peach fruit to Monilinia fructicola infection were investigated. It was found that the disease incidence and lesion diameter of peach fruits were markedly (P < 0.05) reduced by NO and GSNOR inhibitor. However, the expression of GSNOR was significantly inhibited (P < 0.05) by NO only during 2-6 h. Analyses using iodo-TMT tags to detect the nitrosylation sites of GSNOR revealed that the sulfhydryl group of the 85-cysteine site was nitrosylated after NO treatment in peach fruit at 6 and 12 h, suggesting that exogenous NO enhances disease resistance via initial inhibition of gene expression and the S-nitrosylation of GSNOR, thereby inhibiting GSNOR activity. Moreover, NO and GSNOR inhibitor enhanced the expression of systemic acquired resistance (SAR)-related genes, such as pathogenesis-related gene 1 (PR1), nonexpressor of PR1 (NPR1), and TGACG-binding factor 1 (TGA1). These results demonstrated that S-nitrosylation of GSNOR protein and inhibition of GSNOR activity contributed to the enhanced disease resistance in fruit.

Three unrelated protease inhibitors enhance accumulation of pharmaceutical recombinant proteins in Nicotiana benthamiana

Agroinfiltrated Nicotiana benthamiana is a flexible and scalable platform for recombinant protein (RP) production, but its great potential is hampered by plant proteases that degrade RPs. Here, we tested 29 candidate protease inhibitors (PIs) in agroinfiltrated N. benthamiana leaves for enhancing accumulation of three unrelated RPs: glycoenzyme α-Galactosidase; glycohormone erythropoietin (EPO); and IgG antibody VRC01. Of the previously described PIs enhancing RP accumulation, we found only cystatin SlCYS8 to be effective. We identified three additional new, unrelated PIs that enhance RP accumulation: N. benthamiana NbPR4, NbPot1 and human HsTIMP, which have been reported to inhibit cysteine, serine and metalloproteases, respectively. Remarkably, accumulation of all three RPs is enhanced by each PI similarly, suggesting that the mechanism of degradation of unrelated RPs follows a common pathway. Inhibitory functions HsTIMP and SlCYS8 are required to enhance RP accumulation, suggesting that their target proteases may degrade RPs. Different PIs additively enhance RP accumulation, but the effect of each PI is dose-dependent. Activity-based protein profiling (ABPP) revealed that the activities of papain-like Cys proteases (PLCPs), Ser hydrolases (SHs) or vacuolar processing enzymes (VPEs) in leaves are unaffected upon expression of the new PIs, whereas SlCYS8 expression specifically suppresses PLCP activity only. Quantitative proteomics indicates that the three new PIs affect agroinfiltrated tissues similarly and that they all increase immune responses. NbPR4, NbPot1 and HsTIMP can be used to study plant proteases and improve RP accumulation in molecular farming.

Analysis of gene expression in soybean (Glycine max) roots in response to the root knot nematode Meloidogyne incognita using microarrays and KEGG pathways

BACKGROUND

Root-knot nematodes are sedentary endoparasites that can infect more than 3000 plant species. Root-knot nematodes cause an estimated $100 billion annual loss worldwide. For successful establishment of the root-knot nematode in its host plant, it causes dramatic morphological and physiological changes in plant cells. The expression of some plant genes is altered by the nematode as it establishes its feeding site.

RESULTS

We examined the expression of soybean (Glycine max) genes in galls formed in roots by the root-knot nematode, Meloidogyne incognita, 12 days and 10 weeks after infection to understand the effects of infection of roots by M. incognita. Gene expression was monitored using the Affymetrix Soybean GeneChip containing 37,500 G. max probe sets. Gene expression patterns were integrated with biochemical pathways from the Kyoto Encyclopedia of Genes and Genomes using PAICE software. Genes encoding enzymes involved in carbohydrate and cell wall metabolism, cell cycle control and plant defense were altered.

CONCLUSIONS

A number of different soybean genes were identified that were differentially expressed which provided insights into the interaction between M. incognita and soybean and into the formation and maintenance of giant cells. Some of these genes may be candidates for broadening plants resistance to root-knot nematode through over-expression or silencing and require further examination.

PR-1 gene family of grapevine: a uniquely duplicated PR-1 gene from a Vitis interspecific hybrid confers high level resistance to bacterial disease in transgenic tobacco

A functional contribution of pathogenesis-related 1 (PR-1) proteins to host defense has been established. However, systematic investigation of the PR-1 gene family in grapevine (Vitis spp.) has not been conducted previously. Through mining genomic databases, we identified 21 PR-1 genes from the Vitis vinifera genome. Polypeptides encoded by putative PR-1 genes had a signal sequence of about 25 residues and a mature protein of 10.9-29 kDa in size. PR-1 mature proteins contained a highly conserved six-cysteine motif and pI values ranging from 4.6 to 9. A major cluster with 14 PR-1 genes was mapped to a 280-kb region on chromosome 3. One particular PR-1 gene within the cluster encoding a basic-type isoform (pI 7.77), herein named VvPR1b1, was isolated from various genotypes of grapevine (Vitis spp.) for functional studies. Sequence analysis of PCR-amplified DNA revealed that all genotypes contained a single VvPR1b1 gene except for a broad-spectrum bacterial and fungal disease resistant Florida bunch grape hybrid, 'BN5-4', from which seven different homologues were identified. Duplication of VvPR1b1-related genes encoding acidic-type PR-1 isoforms was also observed among several genotypes. However, transgenic expression analysis of grapevine PR-1 genes under strong constitutive promoters in transgenic tobacco revealed that only the basic-type VvPR1b1 gene duplicated in 'BN5-4' was capable of conferring high level resistance to bacterial disease caused by Pseudomonas syringae pv. tabaci.

Characteristic expression of twelve rice PR1 family genes in response to pathogen infection, wounding, and defense-related signal compounds (121/180)

Pathogenesis-related (PR) proteins have been used as markers of plant defense responses, and are classified into 17 families. However, precise information on the majority members in specific PR families is still limited. We were interested in the individual characteristics of rice PR1 family genes, and selected 12 putatively active genes using rice genome databases for expressed genes. All were upregulated upon compatible and/or incompatible rice-blast fungus interactions; three were upregulated in the early infection period and four in the late infection period. Upon compatible rice-bacterial blight interaction, four genes were upregulated, six were not affected, and one was downregulated. These results are in striking contrast to those among 22 Arabidopsis PR1 genes where only one gene was pathogen-inducible. The responses of individual genes to salicylic acid, jasmonic acid, and ethylene induced defense signaling pathways in rice are likely to be different from those in dicot plants. Transcript levels in healthy leaves, roots, and flowers varied according to each gene. Analysis of the partially overlapping expression patterns of rice PR1 genes in healthy tissues and in response to pathogens and other stresses would be useful to understand their possible functions and for use as characteristic markers for defense-related studies in rice.

Synthesis and application of peptide immunogens related to the sperm tail protein tpx-1, a member of the CRISP superfamily of proteins

The synthesis of peptides containing 0, 1 and 2 cysteine residues related to the human sperm tail protein, tpx-1, is described. These synthetic peptides, following conjugation to keyhole limpet hemocyanin modified with maleimidobenzoic acid N-hydroxysuccinimide ester, were used as immunogens to generate polyclonal antibodies in female New Zealand white rabbits. The binding characteristics of the derived antipeptide sera were evaluated using indirect and competitive ELISA procedures. Western immunoblot experiments also confirmed that these synthetic peptide immunogens are able to generate high-titer polyclonal antibodies capable of cross-reacting with the mature tpx-1 protein present in crude rat sperm tail/testis preparations as well as in outer dense fiber preparations. Consequently, these synthetic peptides represent promising candidates for investigations into the role of tpx-1 in the immunoregulation of sperm function in the rat and other mammalian models, with the derived antisera also providing an avenue to explore possible sites of expression of tpx-1 proteins in other tissues.

Induced expression of sarcotoxin IA enhanced host resistance against both bacterial and fungal pathogens in transgenic tobacco

We demonstrate here that induced expression of sarcotoxin IA, a bactericidal peptide from Sarcophaga peregrina, enhanced the resistance of transgenic tobacco plants to both bacterial and fungal pathogens. The peptide was produced with a modified PR1a promoter, which is further activated by salicylic acid treatment and necrotic lesion formation by pathogen infection. Host resistance to infection of bacteria Erwinia carotovora subsp. carotovora and Pseudomonas syringae pv. tabaci was shown to be dependent on the amounts of sarcotoxin IA expressed. Since we found antifungal activity of the peptide in vitro, transgenic seedlings were also inoculated with fungal pathogens Rhizoctonia solani and Pythium aphanidermatum. Transgenic plants expressing higher levels of sarcotoxin were able to withstand fungal infection and remained healthy even after 4 weeks, while control plants were dead by fungal infection after 2 weeks.

The alternative oxidase lowers mitochondrial reactive oxygen production in plant cells

Besides the cytochrome c pathway, plant mitochondria have an alternative respiratory pathway that is comprised of a single homodimeric protein, alternative oxidase (AOX). Transgenic cultured tobacco cells with altered levels of AOX were used to test the hypothesis that the alternative pathway in plant mitochondria functions as a mechanism to decrease the formation of reactive oxygen species (ROS) produced during respiratory electron transport. Using the ROS-sensitive probe 2',7'-dichlorofluorescein diacetate, we found that antisense suppression of AOX resulted in cells with a significantly higher level of ROS compared with wild-type cells, whereas the overexpression of AOX resulted in cells with lower ROS abundance. Laser-scanning confocal microscopy showed that the difference in ROS abundance among wild-type and AOX transgenic cells was caused by changes in mitochondrial-specific ROS formation. Mitochondrial ROS production was exacerbated by the use of antimycin A, which inhibited normal cytochrome electron transport. In addition, cells overexpressing AOX were found to have consistently lower expression of genes encoding ROS-scavenging enzymes, including the superoxide dismutase genes SodA and SodB, as well as glutathione peroxidase. Also, the abundance of mRNAs encoding salicylic acid-binding catalase and a pathogenesis-related protein were significantly higher in cells deficient in AOX. These results are evidence that AOX plays a role in lowering mitochondrial ROS formation in plant cells.

Identification of a rat testis-specific gene encoding a potential rat outer dense fibre protein

Screening of a rat testis expression library with an antiserum specific for an outer dense fibre (ODF) has led to the identification of a gene encoding for a putative protein previously unknown as a component of the sperm tail. This gene has been designated tpx-1 by virtue of its homology with the mouse and human gene of the same name (79 and 73%, respectively). The tpx-1-like gene encoded a 1.6-kb mRNA and a 243-amino-acid protein that had significant homology with members of the cysteine-rich secretory protein (CRISP) family and partial homology with several venom/allergen proteins from both plants and insects. During rat spermatogenesis, the tpx-1-like transcript was first detected by in situ hybridization in low levels in late pachytene spermatocytes. Low but detectable levels of expression continued up to step 5 round spermatids, after which expression levels increased dramatically to a maximum in step 11-12 spermatids. Progressively decreasing levels of expression were detected in up to step 17 elongating spermatids. Testicular somatic cells did not contain detectable tpx-1-like transcript. This pattern of expression is consistent with published data on the development of the ODF in spermatogenesis and, when taken together with a comparison of the predicted amino acid sequence of tpx-1 with the amino acid analysis of a 29-kDa rat ODF protein, suggests that the tpx-1-like gene may encode for this protein.

The upstream region of the gene for the pathogenesis-related protein 1a from tobacco responds to environmental as well as to developmental signals in transgenic plants

Pathogenesis-related proteins (PR proteins) are a heterogeneous group of proteins which are induced in plants by diverse stimuli, e.g. PR proteins are elicited by pathogen attack in the course of the hypersensitive defense reaction of the plant. To examine the regulation of these genes, the 5'-flanking region of the tobacco (Nicotiana tabacum cv. Wisconsin 38) PR-1a gene up to position -1533 was isolated from genomic DNA by the polymerase chain reaction. Two chimeric gene constructs containing 1533 bp and 906 bp, respectively, of the PR-1a upstream region fused to the GUS reporter gene were stably integrated into the tobacco genome. All primary transformants exhibited induced expression of the reporter gene after infection of the plants with tobacco mosaic virus or treatment with acetylsalicylic acid. In addition, similar expression of the reporter gene was observed in leaves of adult transgenic plants without any prior inductive treatments. To study this phenomenon in more detail, the F1 progeny of independent transgenic lines were monitored during the ontogeny of the plants. In normally developing tobacco plants, strong GUS activities were typically detected approximately 12 weeks after germination in the lowest leaves of vegetative plants. When successive leaves of individual plants were tested during the following weeks, a clear gradient of reporter gene activity had developed in the green leaves including the sepals from the bottom to the top of the plants. In all cases analyzed, this gradient of reporter gene expression was strictly parallelled by the expression of the endogenous PR-1 proteins. These results suggest that the acidic PR-1 proteins from tobacco fulfill a role during the later stages of plant development and that the PR-1a upstream region -906 to -335 contains positive regulatory elements for both environmental and developmental signals.

A rice homeotic gene, OSH1, causes unusual phenotypes in transgenic tobacco

A rice gene, OSH1, which shares homology with animal homeobox genes, has been isolated. We have introduced the OSH1 cDNA into tobacco in order to examine its function. Expression of the OSH1 cDNA in tobacco induced morphological abnormalities in the leaves, petals and stems of the transformants suggesting that OSH1 functions as a morphological regulator. OSH1 cDNA expression was analyzed under the control of three different promoters. This work revealed that not only the level of OSH1 expression but also the site and timing of the expression affect the morphology of the plant.

Sequence-specific binding of protein factors to two independent promoter regions of the acidic tobacco pathogenesis-related-1 protein gene (PR-1)

Gel shift mobility analysis, using the proximal 0.3 kb fragment of the tobacco pathogenesis-related protein 1a gene (PR-1a) and nuclear extracts from healthy Samsun NN tobacco leaves, which do not produce PR-1 proteins, showed a broad shifted signal with low mobility. This signal was not detected with nuclear proteins from the interspecific hybrid of Nicotiana glutinosa x Nicotiana debneyi, which constitutively produces the PR-1a protein. Similar shifted signals were detected with both proximal and distal regions of the 0.3 kb fragment using nuclear proteins from healthy Samsun NN tobacco, but not with proteins from the interspecific hybrid. Further experiments, performed using 5' or 3' truncated fragments of the 0.3 kb fragment, identified two independent binding sites: a distal site between -179 and -168 bp from the transcription start site, and a proximal site between -61 and -37 bp. Footprint analysis revealed two protected sequences, a distal region between -184 and -172 bp, and a proximal region between -68 and -51 bp. These results indicate the presence of regulatory factor(s) for expression of the acidic PR-1a gene. The possibility of negative regulation of the gene is discussed.

Biological activities of human interferon and 2'-5' oligoadenylates in plants

Exogenous human interferon 2 (IFN) and 2'-5' oligoadenylates (2-5A) have been shown to cause at least a dual physiological effect in tobacco and wheat: (i) increased cytokinin activity and (ii) induced synthesis of numerous proteins, among which members of two groups of stress proteins have been identified, namely pathogenesis-related (PR) and heat shock (HS) proteins. These effects were observed only by low concentrations of these substances: IFN at 0.1-1 u/ml and 2-5A at 1-10 nM.

Activation of a truncated PR-1 promoter by endogenous enhancers in transgenic plants

PR-1 genes are induced by various environmental stimuli such as pathogen attack or exposure of the plants to certain chemicals. To examine the regulation of these genes, the 5' flanking regions of the PR-la gene and of two PR-1 pseudogenes were joined by a transcriptional fusion to the Escherichia coli beta-glucuronidase (GUS) gene. These constructs were stably integrated into the tobacco genome and independent primary transformants were monitored for the expression of the reporter gene. Unexpectedly, out of 55 transformants analysed, four plants exhibited considerable GUS activities without any inductive treatment of the plants. Expression of the endogenous PR-1 genes, however, could not be detected in these plants. Primer extension analyses revealed correct initiation of the PR1/GUS hybrid transcripts from the PR-1a TATA box. When the plants were analysed at the cellular level, clear differences regarding the tissue specificity of expression of the reporter gene were observed. These results strongly suggest that the PR1/GUS hybrid promoter expression cassettes may be activated when integrated in the vicinity of heterologous enhancer elements dispersed in the tobacco genome. In order to support this hypothesis, domain B of the enhancer of the 35S RNA promoter from cauliflower mosaic virus (CaMV) was fused to various PR1/GUS hybrid genes upstream as well as downstream from the RNA start site. These constructs were stably introduced into the tobacco genome. In any primary transformant analysed, strong GUS activities were observed with the PR1/GUS hybrid RNAs originating from the normal transcription start site of the PR-1a gene. The tissue specificity of gene expression was identical to that described previously for the CaMV 35S domain B enhancer element. Thus, modulations of the transcriptional activity of the PR-1 promoter can be achieved by heterologous enhancers in transgenic plants and may be encountered upon random integration of PR-1 promoter constructs into the tobacco genome.

The mouse male germ cell-specific gene Tpx-1: molecular structure, mode of expression in spermatogenesis, and sequence similarity to two non-mammalian genes

Tpx-1 is a testis-specific gene that maps on mouse Chromosome (Chr) 17. The deduced TPX-1 protein shows 55% amino acid sequence similarity to acidic epididymal glycoprotein (AEG), assumed to be involved in sperm maturation. In the present study, we determined the genomic structure of the mouse Tpx-1 gene and the cellular localization of its transcripts. The gene was found to contain ten exons, with an unusually large intron (approximately 17.0 kilobase pairs) between exons 8 and 9. In situ hybridization of testicular sections showed that Tpx-1 is transcribed abundantly by haploid male germ cells. A computer search of protein databases revealed that deduced TPX-1/AEG proteins have significant sequence similarity (approximately 30%) to two non-mammalian proteins: "pathogenesis-related" proteins 1 of tobaccos, and venom sac proteins of white-face hornets, known as Dol m V. Amino acid residues encoded by exon 10 of the Tpx-1 gene and most of those encoded by exon 9 were absent in the non-mammalian proteins. This result suggests that the ancestor of Tpx-1 acquired exons 9 and 10 after its divergence from the ancestors of the plant and insect proteins.

Functional analysis of the pathogenesis-related 1a protein gene minimal promoter region. Comparison of reporter gene expression in transient and in stable transfections

Pathogenesis-related (PR) proteins are a heterogeneous group of host encoded, low-molecular-mass proteins that are induced in plants by various external stimuli, such as pathogen attack or exposure of the plants to certain chemicals. To examine the regulation of these genes, the 5'-flanking region of the tobacco PR-1a gene [Pfitzner U.M., Pfitzner, A.J.P. & Goodman, H.M. (1988) Mol. Gen. Genet. 211, 290-295] was joined by a transcriptional fusion to the Escherichia coli beta-glucuronidase (GUS) gene. Expression of the reporter gene was monitored in transient expression assays as well as in stable transformants. The PR-1a 5'-flanking sequences from -335, -149 or -71 to +28 are functional promoter elements in tobacco and carrot protoplasts, as determined by transient expression. These constructs direct correct initiation at the normal transcription-start site of the PR-1a gene. The level of gene expression was about twofold less than that obtained with the cauliflower mosaic virus 35S RNA promoter. Regulation of gene expression by acetylsalicylic acid, however, could not be detected in the transient assays. When the same constructs were stably integrated into the tobacco genome, neither constitutive nor induced beta-glucuronidase activity was observed. A comparison of the results from the transient and the stable transfection experiments suggests that expression of the reporter gene may be due to a constitutive transcriptional activity of the PR-1a 5'-flanking regions under the conditions of the transient assays and that the PR-1a promoter may contain at least two functional domains.

Molecular analysis of two PR-1 pseudogenes from tobacco

Two independent PR-1 lambda genomic clones (W38/1 and W38/3) were isolated and characterized from a tobacco (Nicotiana tabacum cv. Wisconsin 38) library. Neither clone is identical to the previously described PR-1 cDNA clones, and both clones carry mutations within the highly conserved PR-1 protein coding region. For example, clone W38/1 has a GAA Glu codon instead of the translation stop codon thus harbouring an open reading frame extended by 16 additional amino acids. Furthermore, both clones display considerable variations in the genomic flanking sequences when compared to the PR-1a gene. In order to test whether the encoded genes are active, their upstream sequences were fused to the E. coli beta-glucuronidase (GUS) reporter gene. While significant GUS activities as compared to the 35S RNA promoter from cauliflower mosaic virus (CaMV) were obtained with the W38/1 and W38/3 sequences in transient gene expression assays, no transcriptional activities could be observed upon stable transformation of the same constructs. In addition, the protein coding region of W38/1 was joined to the CaMV 35S RNA promoter and transgenic tobacco plants were generated. However, neither transcripts nor a protein could be detected deriving from the W38/1 structural gene with this chimaeric construct in the transformants. Taken together, these data indicate that the genes contained in lambda clones W38/1 and W38/3 are not active in planta.

Disease response to tobacco mosaic virus in transgenic tobacco plants that constitutively express the pathogenesis-related PR1b gene

Correlation of the temporal and spacial pattern of induction of the pathogenesis-related (PR) genes PR1a, PR1b, and PR1c with viral infections in certain tobacco cultivars has implicated PR proteins in viral disease resistance. To test whether the PR1 proteins of tobacco are involved in viral resistance, transgenic Nicotiana tabacum plants were constructed which constitutively express the PR1b gene. This protein was secreted from cells of transgenic plants and accumulated in the extracellular space at levels equivalent to those found in nontransgenic plants in association with disease resistance. Transgenic plants derived from the cultivar (cv.) Xanthi (susceptible to tobacco mosaic virus [TMV] infection) exhibited no delayed onset or reduction in the severity of systemic symptoms after TMV infection. In transgenic plants derived from cv. Xanthi-nc (TMV resistant), the time of appearance, the size and general morphology, and the number of viral lesions produced were similar to the parental control plants after TMV infection. These data indicate that the PR1b protein of tobacco is not sufficient for TMV resistance, and imply that the PR1 proteins may not function as unique antiviral factors.