cDNA cloning, in vitro transcription and partial sequence analysis of mRNAs from winter wheat (Triticum aestivum L.) with induced resistance to Erysiphe graminis f. sp. tritici

Recognition and defence of plant-infecting fungal pathogens

Attempted infections of plants with fungi result in diverse outcomes ranging from symptom-less resistance to severe disease and even death of infected plants. The deleterious effect on crop yield have led to intense focus on the cellular and molecular mechanisms that explain the difference between resistance and susceptibility. This research has uncovered plant resistance or susceptibility genes that explain either dominant or recessive inheritance of plant resistance with many of them coding for receptors that recognize pathogen invasion. Approaches based on cell biology and phytochemistry have contributed to identifying factors that halt an invading fungal pathogen from further invasion into or between plant cells. Plant chemical defence compounds, antifungal proteins and structural reinforcement of cell walls appear to slow down fungal growth or even prevent fungal penetration in resistant plants. Additionally, the hypersensitive response, in which a few cells undergo a strong local immune reaction, including programmed cell death at the site of infection, stops in particular biotrophic fungi from spreading into surrounding tissue. In this review, we give a general overview of plant recognition and defence of fungal parasites tracing back to the early 20th century with a special focus on Triticeae and on the progress that was made in the last 30 years.

TaWIR1 contributes to post-penetration resistance to Magnaporthe oryzae, but not Blumeria graminis f. sp. tritici, in wheat

Members of the Wheat-Induced Resistance 1 (TaWIR1) gene family are highly induced in response to a wide range of pathogens. Homologues have been identified in barley, but not in Brachypodium, whereas, in rice, only distant WIR1 candidates are known. Phylogenetic analysis placed TaWIR1a and TaWIR1b within a distinct clade of wheat transcripts, whereas TaWIR1c clustered with HvWIR1 genes. Transcripts of all three TaWIR1 genes were strongly induced by a wheat-adapted isolate of Magnaporthe oryzae. Virus-induced gene silencing of the TaWIR1 gene family had no effect on the initial penetration of epidermal cells by M. oryzae. However, following the establishment of an infection site, the fungus was able to grow more extensively within the leaf tissue, relative to control leaves, indicating a role for the TaWIR1 gene family in the cell-to-cell movement of M. oryzae. In contrast, the silencing of TaWIR1 transcripts had no effect on epidermal cell penetration by a wheat-adapted isolate of Blumeria graminis, or on the subsequent growth of hyphae. Differential transcription of TaWIR1 genes was also seen in epidermal peels, relative to the remaining leaf tissue, following inoculation with M. oryzae.

Pathogenesis-associated transcriptional patterns in Triticeae

The Triticeae tribe of the plant Poaceae family contains some of the most important cereal crop plants for nutrition of humans and livestock such as wheat and barley. Despite the agronomical relevance of plant immunity, knowledge on mechanisms of disease or resistance in Triticeae is limited. It is hardly understood what actually stops a microbial invader when restricted by the plant and in how far a susceptible host plant contributes to pathogenesis. Transcriptional reprogramming of the host plant may be involved in both immunity and disease. This paper gives an overview about recent analyses of global pathogenesis-related transcriptional patterns in response of Triticeae to biotrophic or non-biotrophic fungal pathogens and their toxins. It highlights enriched biological functions in association with successful plant defence or disease as well as experiments that successfully translated gene expression data into analysis of gene functions.

Convergent evidence for a role of WIR1 proteins during the interaction of barley with the powdery mildew fungus Blumeria graminis

Pathogen attack triggers a multifaceted defence response in plants that includes the accumulation of pathogenesis-related proteins and their corresponding transcripts. One of these transcripts encodes for WIR1, a small glycine- and proline-rich protein of unknown function that appears to be specific to grass species. Here we describe members of the HvWIR1 multigene family of barley with respect to phylogenetic relationship, transcript regulation, co-localization with quantitative trait loci for resistance to the barley powdery mildew fungus Blumeria graminis (DC.) E.O. Speer f.sp. hordei, the association of single nucleotide polymorphisms or gene haplotypes with resistance, as well as phenotypic effects of gene silencing by RNAi. HvWIR1 is encoded by a multigene family of moderate complexity that splits up into two major clades, one of those being also represented by previously described cDNA sequences from wheat. All analysed WIR1 transcripts accumulated in response to powdery mildew attack in leaves and all mapped WIR1 genes were associated with quantitative trait loci for resistance to B. graminis. Moreover, single nucleotide polymorphisms or haplotypes of WIR1 members were associated with quantitative resistance of barley to B. graminis, and transient WIR1 gene silencing affected the interaction of epidermal cells with the pathogen. The presented data provide convergent evidence for a role of the HvWIR1a gene and possibly other family members, during the interaction of barley with B. graminis.

Tissue-specific expression of a defence-related peroxidase in transgenic wheat potentiates cell death in pathogen-attacked leaf epidermis

Gene technology can offer creative solutions to problems of agronomical relevance, which may not be solved by conventional breeding methods. One of the major problems of wheat cultivation is disease caused by a number of fungal pathogens including the wheat powdery mildew fungus Blumeria graminis f.sp. tritici (Bgt). Transgenic wheat plants that constitutively express the coding sequence of the defence-related wheat peroxidase TaPrx103 (previously TaPERO) in shoot epidermis under the control of the wheat GstA1 promoter were generated and found to exhibit enhanced resistance to Bgt (Altpeter et al., Plant. Mol. Biol. 57, 271-283). Here, I report on physiological and molecular analyses of these plants in order to assess the mode of action of the peroxidase encoded by the TaGstA1:TaPrx103 transgene. Epidermal cells of transgenic lines with enhanced resistance were found to respond to Bgt attack more frequently with hypersensitive cell death and the generation of hydrogen peroxide. By contrast, resistance of epidermal cell walls to degradation by fungal enzymes appeared to be similar in transgenic and wild-type plants. Moreover, the analysis of the abundance of approximately 10,000 wheat transcripts revealed no significant effect of the GstA1i:TaPrx103 transgene on host gene expression in non-inoculated leaves and only a marginal effect in Bgt-challenged leaves, compared with wild-type plants treated in the same manner. The results indicate that the TaPrx103 protein is involved in generating reactive oxygen species specifically in pathogen-attacked cells, which may lead to localized cell death and resistance. I therefore suggest that the transgenic plants presented here can be regarded as substantially equivalent to non-transgenic wheat.

Indução de resistência à brusone em folhas de arroz por isolado avirulento de Magnaporthe oryzae

A resistência a doenças pode ser induzida em plantas tanto por agentes abióticos como por agentes bióticos, por exemplo isolados avirulentos de patógenos. No presente trabalho objetivou-se determinar a concentração de um isolado avirulento (indutor) e o período necessário para induzir resistência em folhas de arroz a um isolado virulento de M. oryzae. Em casa de vegetação, plantas com 18 dias das cultivares Metica-1 e Cica-8 foram pulverizadas com um isolado indutor de resistência, nas concentrações de 0, 10(5), 3x10(5) e 6x10(5) conídios.mL-1 em períodos que antecederam a inoculação do isolado virulento de 24, 48 e 72 horas. A indução da resistência manifestou-se na redução da área foliar afetada e no tipo de lesão. O grau de indução de resistência foi maior na cultivar Metica-1 do que na cultivar Cica-8, em relação a suas respectivas testemunhas. A indução da resistência em Cica-8 foi superior quando o indutor foi aplicado 48 horas antes da aplicação do isolado virulento nas concentrações de 6x10(5) e 3x10(5) conídios.mL-1. Por outro lado, a indução de resistência em Metica-1 foi significativamente maior em todas as concentrações e períodos de aplicações do indutor quando comparados com a testemunha, mas não houve diferença entre os tratamentos de indução.

Genetically engineered resistance to Fusarium head blight in wheat by expression of Arabidopsis NPR1

Fusarium head blight (FHB) is a devastating disease of wheat and barley which causes extensive losses worldwide. Monogenic, gene-for-gene resistance to FHB has not been reported. The best source of resistance to FHB is a complex, quantitative trait derived from the wheat cv. Sumai 3. Here, we show that the Arabidopsis thaliana NPR1 gene (AtNPR1), which regulates the activation of systemic acquired resistance, when expressed in the FHB-susceptible wheat cv. Bobwhite, confers a heritable, type II resistance to FHB caused by Fusarium graminearum. The heightened FHB resistance in the transgenic AtNPRI -expressing wheat is associated with the faster activation of defense response when challenged by the fungus. PR1 expression is induced rapidly to a high level in the fungus-challenged spikes of the AtNPR1-expressing wheat. Furthermore, benzothiadiazole, a functional analog of salicylic acid, induced PR1 expression faster and to a higher level in the AtNPR1-expressing wheat than in the nontransgenic plants. We suggest that FHB resistance in the AtNPR1-expressing wheat is a result of these plants being more responsive to an endogenous activator of plant defense. Our results demonstrate that NPR1 is an effective candidate for controlling FHB.

Plant defence responses: conservation between models and crops

Diseases of plants are a major problem for agriculture world wide. Understanding the mechanisms employed by plants to defend themselves against pathogens may lead to novel strategies to enhance disease resistance in crop plants. Much of the research in this area has been conducted with Arabidopsis as a model system, and this review focuses on how relevant the knowledge generated from this model system will be for increasing resistance in crop plants. In addition, the progress made using other model plant species is discussed. While there appears to be substantial similarity between the defence responses of Arabidopsis and other plants, there are also areas where significant differences are evident. For this reason it is also necessary to increase our understanding of the specific aspects of the defence response that cannot be studied using Arabidopsis as a model.

Stable expression of a defense-related gene in wheat epidermis under transcriptional control of a novel promoter confers pathogen resistance

Tissue-specific or regulated expression of transgenes is desirable in order to prevent pleiotropic side effects of putatively harmful transgene products as well as loss of energy resources due to unnecessary accumulation of transgene products. Epidermis-specific expression would be useful for many defense-related genes directed against attack by fungal pathogens that enter the plant body by direct penetration through the epidermis. In an approach to enhance resistance of wheat to the powdery mildew fungus Blumeria graminis f.sp. tritici, a novel epidermis-specific promoter was developed and used for expression of two defense-related genes. A 2.3 kb fragment of the wheat GstA1 promoter in combination with an intron-containing part of the wheat WIR1a gene was found to drive strong and constitutive transient expression in wheat epidermis. This promoter-intron combination was used for overexpression of oxalate oxidase 9f-2.8 and TaPERO peroxidase, two defense-related wheat genes expressed in inner leaf tissues. Expression studies of several transgenic lines by in situ oxalate-oxidase staining, RNA and protein blot analyses, as well as real-time PCR, demonstrated strong and constitutive transgene expression in the shoot epidermis. Transient as well as stable over-expression of the TaPERO peroxidase gene in wheat epidermis under the control of the GstA1i promoter resulted in enhanced resistance against Blumeria graminis f.sp. tritici, whereas oxalate-oxidase overexpression had no effect in either system. The data suggest that the wheat GstA1 promoter in combination with the WIR1a intron is useful for transgenic approaches to fungal disease resistance in cereals.

Identification of powdery mildew-induced barley genes by cDNA-AFLP: functional assessment of an early expressed MAP kinase

Gene expression analysis by cDNA-AFLP in barley ( Hordeum vulgare L.) after powdery mildew ( Blumeria graminis f.sp. hordei , Bgh ) inoculation revealed 615 (3.7%) of 16 500 screened cDNA fragments being differentially regulated 4 and/or 12 h after inoculation. Of these transcript derived fragments (TDFs), 120 were sequenced, and for 28 out of 29 tested, induction was confirmed via RT-PCR. Most TDFs did not show any homology to sequences with known functions, others showed homology to genes involved in primary and secondary metabolism, pathogen response, redox regulation, and signal transduction. TDFs with homology to a MAP kinase ( PWMK1 ), a WRKY transcription factor, a heparanase, an immunophilin, a cytochrome P450, and a receptor-like protein kinase were isolated as full length cDNAs. Knockdown by RNA interference via biolistic delivery of sequence specific double stranded RNA to leaf segments tagged two of these genes as possible candidates being causally involved in the outcome of the barley- Bgh interaction. Knockdown of the receptor-like protein kinase and the WRKY transcription factor increased resistance to the fungus, while knockdown of PWMK1 only led to a slightly enhanced susceptibility of epidermal cells to Bgh . This suggests that the receptor-like protein kinase and the WRKY protein are candidates for negative regulators of powdery mildew resistance. Based on expression analyses, PWMK1 appears to be more generally involved in stress response.

The germinlike protein GLP4 exhibits superoxide dismutase activity and is an important component of quantitative resistance in wheat and barley

Germinlike proteins (GLP) are encoded in plants by a gene family with proposed functions in plant development and defense. Genes of GLP subfamily 4 of barley (HvGLP4, formerly referred to as HvOxOLP) and the wheat orthologue TaGLP4 (formerly referred to as TaGLP2a) were previously found to be expressed in pathogen-attacked epidermal tissue of barley and wheat leaves, and the corresponding proteins are proposed to accumulate in the apoplast. Here, the role of HvGLP4 and TaGLP4 in the defense of barley and wheat against Blumeria graminis (DC.) E. O. Speer, the cereal powdery mildew fungus, was examined in an epidermal transient expression system and in transgenic Arabidopsis thaliana plants overexpressing His-tagged HvGLP4. Leaf extracts of transgenic Arabidopsis overexpressing HvGLP4 contained a novel His-tagged protein with superoxide dismutase activity and HvGLP4 epitopes. Transient overexpression of TaGLP4 and HvGLP4 enhanced resistance against B. graminis in wheat and barley, whereas transient silencing by RNA interference reduced basal resistance in both cereals. The effect of GLP4 overexpression or silencing was strongly influenced by the genotype of the plant. The data suggest that members of GLP subfamily 4 are components of quantitative resistance in both barley and wheat, acting together with other, as yet unknown, plant components.

Acquired resistance functions in mlo barley, which is hypersusceptible to Magnaporthe grisea

Barley plants carrying a mutation in the Mlo (barley [Hordeum vulgare L.] cultivar Ingrid) locus conferring a durable resistance against powdery mildew are hypersusceptible to the rice blast fungus Magnaporthe grisea. It has been speculated that a functional Mlo gene is required for the expression of basic pathogen resistance and that the loss of Mlo function mediating powdery mildew resistance is an exception for this particular disease. Here, we report that the onset of acquired resistance (AR) after chemical as well as biological treatments is sufficient to overcome the hypersusceptible phenotype of backcross line BCIngridmlo5 (mlo) barley plants against M. grisea. Moreover, even barley plants bearing a functional Mlo gene and thus showing a moderate infection phenotype against rice blast exhibit a further enhanced resistance after induction of AR. Cytological investigations reveal that acquired resistance in mlo genotypes is manifested by the restoration of the ability to form an effective papilla at sites of attempted penetration, similarly to wild-type Mlo plants. In addition, the rate of effective papillae formation in Mlo plants was further enhanced after the onset of AR. These results demonstrate that treatments leading to the AR state in barley function independently of the Mlo/mlo phenotype and suggest that the Mlo protein is not a component of the AR signaling network. Moreover, it seems that only concomitant action of Mlo together with AR permits high level resistance in barley against blast. Higher steady state levels of PR1 and barley chemically induced mRNA correlate with higher disease severity rather than with the degree of resistance observed in this particular interaction.

Engineering pathogen resistance in crop plants

As the world population continues to increase, food supplies must also grow to meet nutritional requirements. One means of ensuring the stability and plentitude of the food supply is to mitigate crop loss caused by plant pathogens. Strategies for combating disease include traditional technologies such as plant breeding and chemical applications; current technologies such as generating transgenic plants that express components of known defense signaling pathways; and the adaptation of newer technologies such as RNA silencing of pathogen and plant transcripts. Breeding has been used to pyramid resistance (R) genes into many different plants including rice. Chemical strategies include application of salicylic acid (SA) analogs to stimulate systemic acquired resistance (SAR) responses. Genetic screens in Arabidopsis have identified genes controlling SAR and these genes have been manipulated and used to engineer crop plants. The diseases caused by plant viruses are being thwarted through the initiation of endogenous RNA silencing mechanisms. Many of these strategies show great promise, some limitations, and exciting opportunities to develop many new tools for combating plant pests.

Transient expression of a vacuolar peroxidase increases susceptibility of epidermal barley cells to powdery mildew

summary The expression of genes encoding the peroxidases, Prx7 and Prx8, is induced in barley leaf tissue after inoculation with the barley powdery mildew fungus, Blumeria graminis f.sp. hordei (DC) Speer (Bgh). The role of these peroxidases in general barley defence responses against fungal attack was investigated using a transient expression system. Colonization frequencies of Bgh on cells transfected with Prx7 or Prx8 expression-, mutant- or fusion-DNA constructs were compared to the frequencies on cells expressing a beta-glucuronidase (GUS) control construct. Twice the number of powdery mildew colonies were observed on cells expressing Prx7 as compared to control cells. Introduction of either mutant or truncated versions of Prx7 showed that decreased resistance against Bgh was dependent on the presence of the C-terminal signal peptide required for correct subcellular targeting, but not affected significantly by mutations in the catalytic centre. No impact on Bgh performance was observed after the introduction of Prx8 or mutant constructs. An enhanced accumulation of the apoplastic Prx8 was verified by immunocytology. These results indicate a more complex role of peroxidases in defence responses than was previously suspected.

Fungal development and induction of defense response genes during early infection of wheat spikes by Fusarium graminearum

Fusarium head blight (FHB) of wheat is a crippling disease that causes severe economic losses in many of the wheat-growing regions of the world. Temporal patterns of fungus development and transcript accumulation of defense response genes were studied in Fusarium graminearum-inoculated wheat spikes within the first 48 to 76 h after inoculation (hai). Microscopy of inoculated glumes revealed that the fungus appeared to penetrate through stomata, exhibited subcuticular growth along stomatal rows, colonized glume parenchyma cells, and sporulated within 48 to 76 hai. No major differences in the timing of these events were found between Sumai 3 (resistant) and Wheaton (susceptible) genotypes. In complementary experiments, RNA was extracted from spikes at several time intervals up to 48 hai and temporal expression patterns were determined for defense response genes encoding peroxidase, PR-1, PR-2 (beta-1,3-glucanase), PR-3 (chitinase), PR-4, and PR-5 (thaumatin-like protein). In both genotypes, transcripts for the six defense response genes accumulated as early as 6 to 12 hai during F. graminearum infection and peaked at 36 to 48 hai. Greater and earlier PR-4 and PR-5 transcript accumulation was observed in Sumai 3, compared with Wheaton. Our results show that the timing of defense response gene induction is correlated with F. graminearum infection.

Transient expression of members of the germin-like gene family in epidermal cells of wheat confers disease resistance

The wheat genome encodes a family of germin-like proteins that differ with respect to regulation and tissue specificity of expression of the corresponding genes. While germin exhibits oxalate oxidase (E.C. 1.2.3.4.) activity, the germin-like proteins (GLPs) have no known enzymatic activity. A role of oxalate oxidase in plant defence has been proposed, based on the capacity of the enzyme to produce H2O2, a reactive oxygen species. The role in defence of germin and other members of the germin-like gene family was functionally assessed in a transient assay system based on particle bombardment of wheat leaves. Transient expression of the pathogen-induced germin gf-2.8 gene, but not of the constitutively expressed HvGLP1 gene, reduced the penetration efficiency of Blumeria (syn. Erysiphe) graminis f.sp. tritici, the causal agent of wheat powdery mildew, on transformed cells. Two engineered germin-gf-2.8 genes and the TaGLP2a gene, which all encoded proteins without oxalate oxidase activity, also reduced the penetration efficiency of the fungus, demonstrating that oxalate oxidase activity is not required for conferring enhanced resistance. Instead, activity tagging experiments showed that in cells transiently expressing the germin gf-2.8 gene, the transgene product became insolubilized at sites of attempted fungal penetration where localised production of H2O2 was observed. Thus, germin and GLPs may play a structural role in cell-wall re-enforcement during pathogen attack.

Wheat genes encoding two types of PR-1 proteins are pathogen inducible, but do not respond to activators of systemic acquired resistance

Wheat cDNAs that encode proteins PR-1.1 and PR-1.2 were cloned. Deduced amino acid sequences were homologous to those of pathogen-induced, basic PR-1 proteins from plants. Although expression of PR1.1 and PR1.2 genes was induced upon infection with either compatible or incompatible isolates of the fungal pathogen Erysiphe graminis, these genes did not respond to activators of systemic acquired resistance (SAR), such as salicylic acid (SA), benzothiadiazole (BTH), or isonicotinic acid (INA).

Differential induction of a peroxidase gene family during infection of rice by Xanthomonas oryzae pv. oryzae

Induction of peroxidase has been correlated with resistant interactions between rice and Xanthomonas oryzae pv. oryzae. To assist in analysis of the role of rice peroxidases in plant defense against the bacterial pathogen, three peroxidase genes, POX22.3, POX8.1, and POX5.1, were identified from a rice cDNA library that was constructed from leaves of plants undergoing a resistant reaction. These genes were highly similar in nucleic acid and amino acid sequences and belonged to a gene family. The three genes showed differential expression in infiltrated rice leaves during pathogen interactions and mechanical stress. Only two peroxidase genes, POX8.1 and POX22.3, were predominantly expressed during resistant interactions. These two genes also were expressed during susceptible interactions, but induction was delayed compared with resistant interactions. POXgX9, a fourth peroxidase gene that was isolated from a genomic library, is adjacent to POX22.3 in the rice genome and has greater than 90% similarity in nucleotide and amino acid sequence identity to POX22.3. Interestingly, POXgX9 was expressed only in the roots of rice plants. While POX22.3 was expressed in both leaves and roots, POX8.1 and POX5.1 were not detected in roots but were induced in leaves by mechanical wounding at different times after treatment. POX22.3, POX8.1, and POX5.1 were estimated to be present in single copies in rice haploid genome. These results indicate that different members of the rice peroxidase gene family are distinctly regulated in response to various environmental cues.

cis-regulatory elements of the peroxidase gene in Arabidopsis thaliana involved in root-specific expression and responsiveness to high-salt stress

The pattern of organ-specific expression of Arabidopsis thaliana peroxidase was similar to that in horseradish. Tobacco plants transformed with the gus gene fused to the -580 bp deletion (Ea-580) of A. thaliana exhibited high GUS expression in roots. Gel retardation and footprinting analyses showed that at least three domains of fragment between -172 and -1 bp have cis-acting element activities. Several physiological functions for plant peroxidases have been suggested; for example, a metabolic adaptation to salinity in the environment can be induced by certain specific elements of the peroxidase gene. The prxEa promoter fragments (Ea-580 and Ea-390) show multiple cis-acting elements in the control of expression in high-salt stress. These data suggest that the DNA-binding factor may be involved in the regulation of gene expression in specific organ and salt stress.

Molecular cloning and expression analysis of peroxidase genes from wheat

A PCR-based screening approach was used to isolate genomic clones from wheat encoding peroxidase isozymes. Three complete genes (pox1, pox2 and pox4) and one truncated gene (pox3) were characterized. The nucleotide sequences predicted mature proteins of 31 kDa, in which all the highly conserved motifs of secreted plant peroxidases were preserved. The coding regions showed 73-83% DNA sequence identity, with the highest level of similarity noted for the tandemly oriented pox2 and pox3. Expression of respective pox genes in various tissues of wheat was assessed by the RT-PCR technique, which showed that all four genes are active. The primary pox1 mRNA was spliced to remove three introns, whereas processing of the other pox transcripts involved only two intervening sequences. Splicing occurred at consensus GU/AG splice sites except for the first introns of pox1, pox2 and pox4 transcripts, where processing took place at unusual GC donor sites. The RNA analysis suggested that the pox1, pox2 and pox4 genes are predominantly expressed in roots. Lower levels of expression were found for pox4 and pox3 in leaves. Infection of wheat by the powdery mildew fungus selectively induced expression of pox2 in leaves.

Characterization and in situ localization of a salt-induced tomato peroxidase mRNA

NaCl treatment of tomato plants in hydroponic culture at concentrations as low as 50 mM resulted in enhanced accumulation of transcripts of TPX1, a full-length cDNA clone that we had isolated from a library of NaCl-treated tomato plants using a peroxidase-specific oligonucleotide probe. Although the overall amino acid sequence identity of TPX1 to other peroxidase genes was less than 45%, there was a very high degree of identity in all of the conserved domains. The deduced amino acid sequence included the presence of a N-terminal signal peptide but not the C-terminal extension present in peroxidases targeted to the vacuole. The mature protein has a theoretical pI value of 7.5. Transcripts that hybridized to TPX1 were detected only in the roots with higher levels of mRNA in epidermal and subepidermal cell layers. Isoelectric focusing of root extracts showed two major bands of peroxidase activity at pI 5.9 and 6.2. Both activities increased with salt treatment. Southern analysis indicated the presence of only a single TPX1 gene in tomato.

Plant antioxidant gene responses to fungal pathogens

Antioxidant defense systems are a prominent element in plant responses to environmental stress. Activated oxygen species have themselves been implicated as both a part of the plant's defense against pathogen attack as well as the phytotoxic component of photosensitizing fungal toxins. Molecular analyses are just beginning to define how plant oxidant and antioxidant genes might integrate with other defense responses to provide effective protection against pathogen attack.

Post-transcriptional transfer of gamma-thio affinity label to RNA in isolated parsley nuclei

As an alternative to soluble plant transcription systems, we examined the reinitiation capacity of isolated parsley nuclei. Nuclear chalcone synthase in vitro transcripts were affinity-labelled with gamma-thio-ATP, gamma-thio-GTP or beta-thio-ATP, and purified by chromatography on a mercury Sepharose affinity column. Primer extension and subsequent PCR amplification of these in vitro transcripts revealed gamma-thio-ATP-dependent, but no beta-thio-ATP-dependent, signals, although affinity labelling of overall in vitro transcripts still occurred with beta-thio-ATP. We conclude that the described plant nuclei reinitiated transcription non-specifically and that post-transcriptional transfer of the gamma-thio affinity label severely interfered with the detection of reinitiated transcripts.