Overexpression of the Brassica rapa transcription factor WRKY12 results in reduced soft rot symptoms caused by Pectobacterium carotovorum in Arabidopsis and Chinese cabbage

Chinese cabbage (Brassica rapa L. ssp. pekinensis), an important vegetable crop, can succumb to diseases such as bacterial soft rot, resulting in significant loss of crop productivity and quality. Pectobacterium carotovorum ssp. carotovorum (Pcc) causes soft rot disease in various plants, including Chinese cabbage. To overcome crop loss caused by bacterial soft rot, a gene from Chinese cabbage was isolated and characterised in this study. We isolated the BrWRKY12 gene from Chinese cabbage, which is a group II member of the WRKY transcription factor superfamily. The 645-bp coding sequence of BrWRKY12 translates to a protein with a molecular mass of approximately 24.4 kDa, and BrWRKY12 was exclusively localised in the nucleus. Transcripts of BrWRKY12 were induced by Pcc infection in Brassica. Heterologous expression of BrWRKY12 resulted in reduced susceptibility to Pcc but not to Pseudomonas syringae pv. tomato in Arabidopsis. Defence-associated genes, such as AtPDF1.2 and AtPGIP2, were constitutively expressed in transgenic lines overexpressing BrWRKY12. The expression of AtWKRY12, which is the closest orthologue of BrWRKY12, was down-regulated by Pcc in Arabidopsis. However, the Atwrky12-2 mutants did not show any difference in response to Pcc, pointing to a difference in function of WRKY12 in Brassica and Arabidopsis. Furthermore, BrWRKY12 in Chinese cabbage also exhibited enhanced resistance to bacterial soft rot and increased the expression of defence-associated genes. In summary, BrWRKY12 confers enhanced resistance to Pcc through transcriptional activation of defence-related genes.

Expression analysis of rice VQ genes in response to biotic and abiotic stresses

WRKY transcription factors are encoded by a large gene superfamily with a broad range of roles in plants. Proteins containing a short VQ (FxxxVQxLTG) motif have been recently shown to interact with WRKY transcription factors, implying that AtVQ proteins are important in the plant defense responses in Arabidopsis, either as positive or negative cofactors of WRKY transcription factors. Thirty-nine Oryza sativa genes containing the VQ motif (OsVQs) were identified and the genome structures of OsVQ proteins were characterized through genome-wide analysis in rice. Also, phylogenetic tree analysis was performed with the VQ domain of Arabidopsis and rice. The expression patterns of these OsVQ genes in plants under several stress treatments were assessed, specifically, following infection with the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo), treatment with abscisic acid (ABA), or exposure to drought. The cellular localization of a few OsVQ proteins was examined using rice protoplast system. Based on our results, we suggest that OsVQ proteins function as important co-regulators during the plant defense response to biotic and abiotic stresses.

Effect and sustainability of part-time occlusion therapy for patients with anisometropic amblyopia aged > or =8 years

AIMS

To study the effect and long-term sustainability of part-time occlusion therapy for anisometropic amblyopia after 8 years of age.

METHODS

A total of 41 anisometropic amblyopes aged > or =8 years were analysed. In six patients, best-corrected visual acuity (BCVA) of amblyopic eye improved more than two lines within 2 weeks of full-time spectacle wear. The remaining patients were assigned to perform part-time patching during out-of-school hours. Long-term results were assessed in patients who were observed over 1 year after the end of the treatment.

RESULTS

Among 35 patients, four dropped out, refusing further treatment, and one changed to atropine penalisation. The part-time patching schedule was completed in 30 patients. 90% of patients (27/30) complied well. Mean BCVA in the amblyopic eye improved significantly (p<0.001), and 96.7% of patients (29/30) achieved the final BCVA of 0.1 logMAR or better. In long-term results, 87% preserved the BCVA of 0.1 logMAR or better. None of four dropouts achieved the BCVA of 0.1 logMAR or better in long-term results even on the continuous spectacle wear.

CONCLUSIONS

The part-time occlusion treatment in school-aged amblyopes, which had been carried out after school hours, was successful and the effect was sustained in most cases.

HIV-1 integrase inhibitory phenylpropanoid glycosides from Clerodendron trichotomum

Seven phenylpropanoid glycosides named acteoside (1), acteoside isomer (2), leucosceptoside A (3), plantainoside C (4), jionoside D (5), martynoside (6), and isomartynoside (7) were isolated from Clerodendron trichotomum. Compounds 1 and 2 showed potent inhibitory activities against HIV-1 integrase with IC50 values of 7.8 +/- 3.6 and 13.7 +/- 6.0 microM, respectively.

Dicaffeoyl- or digalloyl pyrrolidine and furan derivatives as HIV integrase inhibitors

Human immunodeficiency virus (HIV) integrase (IN) catalyzes the integration of HIV DNA copy into the host cell DNA. Such integration is essential for the production of progeny viruses, and therefore therapeutic agents that can inhibit this process should be effective anti-HIV agents. We have previously reported the inhibitory activity of dicaffeoylglucosides against HIV IN. In the present study, we have synthesized and tested dicaffeoyl or digalloyl compounds joined through a five-membered heterocyclic ring as HIV IN inhibitors to explore the SARs of this family of compounds. The starting heterocyclic diols were prepared from L-tartaric acid, diethyl L-tartarate or D-(+)-ribonic gamma-lactone. We found that the HIV IN inhibitory activities of dicaffeoyl derivatives were comparable to that of L-chicoric acid (IC(50)=24.9 microM). On the other hand, digalloyl derivatives were more potent than L-chicoric acid with IC(50) values of 4.7--15.6 microM.

Chaperone protein GrpE and the GroEL/GroES complex promote the correct folding of tobacco mosaic virus coat protein for ribonucleocapsid assembly in vivo

Several prokaryotic chaperone proteins were shown to promote the correct folding and in vivo assembly of tobacco mosaic virus coat protein (TMV CP) using a chimaeric RNA packaging system in control or chaperone-deficient mutant strains of Escherichia coli. Mutations in groEL or dnaK reduced the amount of both total and soluble TMV CP, and the yield of assembled TMV-like particles, several-fold. Thus both GroEL and DnaK have significant direct or indirect effects on the overall expression, stability, folding and assembly of TMV CP in vivo. In contrast, while cells carrying a mutation in grpE expressed TMV CP to a higher overall level than control E. coli, the amounts of both soluble CP and assembled TMV-like particles were below control levels, suggesting a negative effect of GrpE on overall CP accumulation, but positive role(s) in CP folding and assembly. Curiously, cells with mutations in groES and, to a lesser extent, dnaJ expressed total, soluble and assembled forms of TMV CP significantly above control values, suggesting some form of negative control by these chaperone proteins. To avoid pleiotropic effects or artefacts in chaperone-null mutants, selected chaperone proteins were also over-expressed in control E. coli cells. Overproduction of GroEL or GroES alone had little effect. However, co-overexpression of GroEL and GroES resulted in a two-fold increase in soluble TMV CP and a four-fold rise in assembled TMV-like (pseudovirus) particles in vivo. Moreover, TMV CP was shown to interact directly with GroEL in vivo. Together, these results suggest that GrpE and the GroEL/GroES chaperone complex promote the correct folding and assembly of TMV CP into ribonucleocapsids in vivo.

C-terminal deletion mutant of pokeweed antiviral protein inhibits viral infection but does not depurinate host ribosomes

Pokeweed antiviral protein (PAP), a 29-kDa protein isolated from Phytolacca americana, inhibits translation by catalytically removing a specific adenine residue from the large rRNA of the 60S subunit of eukaryotic ribosomes. In addition to its ribosome-inactivating ability, PAP has potent antiviral activity against many plant and animal viruses, including HIV. We recently described the isolation and characterization of nontoxic PAP mutants, NT123-2, which has a point mutation (E176V) in the active site that abolishes enzymatic activity, and NT124-3, which has a nonsense mutation that results in deletion of the C-terminal 25 aa (W237Stop). In vitro translation of rabbit reticulocyte lysate ribosomes was inhibited by the C-terminal deletion mutant, but not by the active site mutant. We expressed both mutants in transgenic tobacco and showed that, unlike PAP or variant PAP, neither mutant is toxic to transgenic plants. In vivo depurination of rRNA was detected in transgenic tobacco expressing variant PAP, but not in transgenic plants expressing either the active site mutant or the C-terminal deletion mutant PAP. When extracts from transgenic plants containing the mutant PAPs were exogenously applied to tobacco leaves in the presence of potato virus X (PVX), the C-terminal deletion mutant had antiviral activity, while the active site mutant had no antiviral activity. Furthermore, transgenic plants expressing low levels of the C-terminal deletion mutant showed resistance to PVX infection, while transgenic plants expressing very high levels of the active site mutant PAP were not resistant to PVX. Our results demonstrate that an intact active site of PAP is necessary for antiviral activity, toxicity, and in vivo depurination of tobacco ribosomes. However, an intact active site is not sufficient for all these activities. An intact C terminus is also required for toxicity and depurination of tobacco ribosomes in vivo, but not for antiviral activity, suggesting that antiviral activity of PAP can be dissociated from its toxicity.

Isolation and characterization of pokeweed antiviral protein mutations in Saccharomyces cerevisiae: identification of residues important for toxicity

Pokeweed antiviral protein (PAP), a 29-kDa protein isolated from Phytolacca americana inhibits translation by catalytically removing a specific adenine residue from the 28S rRNA of eukaryotic ribosomes. PAP has potent antiviral activity against many plant and animal viruses, including human immunodeficiency virus. We describe here development of a positive selection system to isolate PAP mutants with reduced toxicity. In vitro translation in the presence or absence of microsomal membranes shows that PAP is synthesized as a precursor and undergoes at least two different proteolytic processing steps to generate mature PAP. The PAP cDNA was placed under control of the galactose-inducible GAL1 promoter and transformed into Saccharomyces cerevisiae. Induction of PAP expression was lethal to yeast. The PAP expression plasmid was mutagenized and plasmids encoding mutant PAP genes were identified by their failure to kill S. cerevisiae. A number of mutant alleles were sequenced. In one mutant, a point mutation at Glu-177 inactivated enzymatic function in vitro, suggesting that this glutamic acid residue is located at or near the catalytic site. Mutants with either point mutations near the N terminus or a nonsense mutation at residue 237 produced protein that was enzymatically active in vitro, suggesting that the toxicity of PAP is not due solely to enzymatic activity. Toxicity of PAP appears to be a multistep process that involves possibly different domains of the protein.

Expression of tobacco mosaic virus coat protein and assembly of pseudovirus particles in Escherichia coli

The bidirectional self-assembly of tobacco mosaic virus (TMV, common or U1 strain) has been studied extensively in vitro. Foreign single-stranded RNA molecules containing the TMV origin-of-assembly sequence (OAS, 75-432 nt in length) are also packaged by TMV coat protein (CP) in vitro to form helical pseudovirus particles. To study virus assembly in vivo requires an easily manipulated model system, independent of replication in plants. The TMV assembly machinery also provides a convenient means to protect and recover chimeric gene transcripts of almost any length or sequence for a variety of applications. Native TMV CP expressed in and purified from Escherichia coli formed nonhelical, stacked aggregates after dialysis into pH 5 buffer and was inactive for in vitro assembly with TMV RNA. U1 CP derivatives in which the second amino acid was changed from Ser to Ala or Pro, nonacetylated N termini found in two natural strains of the virus, failed to remediate these anomalous properties. However, in vivo coexpression of CP and single-stranded RNAs (up to approximately 2 kb) containing the TMV OAS gave high yields of helical pseudovirus particles of the predicted length (up to 7.4 +/- 1.4 micrograms/mg of total bacterial protein). If the OAS-containing RNA was first recruited into bacterial polyribosomes, elongation of pseudovirus assembly was blocked. In vivo, E. coli expression of a full-length cDNA clone of the TMV genome (6.4 kb) resulted in high, immunodetectable levels of CP and assembly of sufficient intact genomic RNA to initiate systemic infection of susceptible tobacco plants.

Assembly of tobacco mosaic virus and TMV-like pseudovirus particles in Escherichia coli

High-level expression of plant viral proteins, including coat protein (CP), is possible in Escherichia coli. Native tobacco mosaic virus (TMV) CP expressed in E. coli remains soluble but has a non-acetylated N-terminal Ser residue and following extraction, is unable to package TMV RNA in vitro under standard assembly conditions. Changing the Ser to Ala or Pro by PCR-mutagenesis did not confer assembly competence in vitro, despite these being non-acetylated N-termini present in two natural strains of TMV. All TMV CPs made in E. coli formed stacked cylindrical aggregates in vitro at pH 5.0 and failed to be immunogold-labelled using a mouse monoclonal antibody specific for helically assembled TMV CP. TMV self-assembly has been studied extensively in vitro, and an origin of assembly sequence (OAS) mapped internally on the 6.4 kb ssRNA genome. Pseudovirus particles can be assembled mono- or bi-directionally in vitro using virus-derived CP and chimeric ssRNAs containing the cognate TMV OAS, but otherwise of unlimited length and sequence. Studies on plant virus assembly in vivo would be facilitated by a model system amenable to site-directed mutagenesis and rapid recovery of progeny particles. When chimeric transcripts containing the TMV OAS were co-expressed with TMV CP in vivo for 2-18 h, helical TMV-like ribonucleoprotein particles of the predicted length were formed in high yield (up to 7.4 micrograms/mg total bacterial protein). In addition to providing a rapid, inexpensive and convenient system to produce, protect and recover chimeric gene transcripts of any length or sequence, this E. coli system also offers a rapid approach for studying the molecular requirements for plant virus "self-assembly" in vivo. Transcription of a full-length cDNA clone of TMV RNA also resulted in high levels of CP expression and assembly of sufficient intact genomic RNA to initiate virus infection of susceptible tobacco plants.