High-level expression of a viscotoxin in Arabidopsis thaliana gives enhanced resistance against Plasmodiophora brassicae

Analysis of structures, functions, and transgenicity of phytopeptides defensin and thionin: a review

Background

Antimicrobial peptides are very primitive innate defense molecules of almost all organisms, from microbes to mammalians and vascular seed-bearing plants. Antimicrobial peptides of plants categorized into cysteine-rich peptides (CRPs) and others and most of the antimicrobial peptides belong to CRPs group. These peptides reported showing the great extent of protecting property against bacteria, fungi, viruses, insect, nematode, and another kind of microbes. To develop a resistant plant against pathogenic fungi, there have been several studies executed to understand the efficiency of transgenicity of these antimicrobial peptides.

Main text

Apart from the intrinsic property of the higher organism for identifying and activating microbial attack defense device, it also involves innate defense mechanism and molecules. In the current review article, apart from the structural and functional characterization of peptides defensin and thionin, we have attempted to provide a succinct overview of the transgenic development of these defense peptides, that are expressed in a constitutive and or over-expressive manner when biotic and abiotic stress inflicted. Transgenic of different peptides show different competence in plants. Most of the transgenic studies made for defensin and thionin revealed the effective transgenic capacity of these peptides.

Conclusion

There have been several studies reported successful development of transgenic plants based on peptides defensin and thionin and observed diverse level of resistance-conferring potency in different plants against phytopathogenic fungi. But due to long regulatory process, there has not been marketed any antimicrobial peptides based transgenic plants yet. However, success report state that possibly in near future transgenic plants of AMPs would be released with devoid of harmful effect, with good efficiency, reproducibility, stability, and least production cost.

Current Status of the Disease-Resistant Gene(s)/QTLs, and Strategies for Improvement in Brassica juncea

Brassica juncea is a major oilseed crop in tropical and subtropical countries, especially in south-east Asia like India, China, Bangladesh, and Pakistan. The widespread cultivation of genetically similar varieties tends to attract fungal pathogens which cause heavy yield losses in the absence of resistant sources. The conventional disease management techniques are often expensive, have limited efficacy, and cause additional harm to the environment. A substantial approach is to identify and use of resistance sources within the Brassica hosts and other non-hosts to ensure sustainable oilseed crop production. In the present review, we discuss six major fungal pathogens of B. juncea: Sclerotinia stem rot (Sclerotinia sclerotiorum), Alternaria blight (Alternaria brassicae), White rust (Albugo candida), Downy mildew (Hyaloperonospora parasitica), Powdery mildew (Erysiphe cruciferarum), and Blackleg (Leptoshaeria maculans). From discussing studies on pathogen prevalence in B. juncea, the review then focuses on highlighting the resistance sources and quantitative trait loci/gene identified so far from Brassicaceae and non-filial sources against these fungal pathogens. The problems in the identification of resistance sources for B. juncea concerning genome complexity in host subpopulation and pathotypes were addressed. Emphasis has been laid on more elaborate and coordinated research to identify and deploy R genes, robust techniques, and research materials. Examples of fully characterized genes conferring resistance have been discussed that can be transformed into B. juncea using advanced genomics tools. Lastly, effective strategies for B. juncea improvement through introgression of novel R genes, development of pre-breeding resistant lines, characterization of pathotypes, and defense-related secondary metabolites have been provided suggesting the plan for the development of resistant B. juncea.

Antimicrobial Peptides - Small but Mighty Weapons for Plants to Fight Phytopathogens

Antimicrobial Peptides (AMPs) have diverse structures, varied modes of actions, and can inhibit the growth of a wide range of pathogens at low concentrations. Plants are constantly under attack by a wide range of phytopathogens causing massive yield losses worldwide. To combat these pathogens, nature has armed plants with a battery of defense responses including Antimicrobial Peptides (AMPs). These peptides form a vital component of the two-tier plant defense system. They are constitutively expressed as part of the pre-existing first line of defense against pathogen entry. When a pathogen overcomes this barrier, it faces the inducible defense system, which responds to specific molecular or effector patterns by launching an arsenal of defense responses including the production of AMPs. This review emphasizes the structural and functional aspects of different plant-derived AMPs, their homology with AMPs from other organisms, and how their biotechnological potential could generate durable resistance in a wide range of crops against different classes of phytopathogens in an environmentally friendly way without phenotypic cost.

Impact of Common Mistletoe (Viscum album L.) on Scots Pine Forests—A Call for Action

Common mistletoe is increasingly mentioned as contributing not only to the decline of deciduous trees at roadside and in city parks, but to conifers in stands. The presence of Viscum in fir stands has been known for many years, but since 2015 has also been the cause of damage to pine. In 2019, mistletoe was observed on 77.5 thousand hectares of Scots pine stands in southern and central Poland. Drought resulting from global climate change is implicated as an important factor conducive to weakening trees and making them more susceptible to the spread of mistletoe and other pests. This paper presents an overview of the latest information on the development of this semi-parasitic plant in Poland, its impact on tree breeding traits and raw material losses, as well as current options for its prevention and eradication.

Arabidopsis thionin-like genes are involved in resistance against the beet-cyst nematode (Heterodera schachtii)

Plants express various antimicrobial peptides including thionins to protect themselves against pathogens. It was recently found that, in addition to four thionin genes, Arabidopsis contains 67 thionin-like (ThiL) genes including six pseudogenes. It is known that thionins have antimicrobial activity and are part of the plant defense system, however, nothing is known about ThiL genes. In this study, we present a bioinformatic analysis of the (ThiL) gene family in Arabidopsis. We identified 15 different motifs which positioned the ThiL peptides in four groups. A comparison of amino acid sequences showed that the ThiL peptides are actually more similar to the acidic domain of thionin proproteins than to the thionin domain. We selected 10 ThiL genes to study the expression and possible function in the Arabidopsis plant. RT-PCR and promoter:GUS fusions showed that most genes were expressed at a very low level but in several organs and at different developmental stages. Some genes were also expressed in syncytia induced by the beet cyst nematode Heterodera schachti in roots while others were downregulated in syncytia. Some overexpression lines supported lower number of nematodes that developed on the roots after inoculation. Two of the genes resulted in a strong hypersensitive response when infiltrated into leaves of Nicotiana benthamiana. These results indicate that ThiL genes might be involved in the response to biotic stress. ThiL genes have been expanded in the Brassicales and specifically the Brassicaceae. The most extreme example is the CRP2460 subfamily that contains 28 very closely related genes from Arabidopsis which are mostly the result of tandem duplications.

Viscothionin purified from mistletoe (Viscum album var. coloratum Ohwi) induces insulin secretion from pancreatic beta cells

ETHNOPHARMACOLOGICAL RELEVANCE

Mistletoe (Viscum album), an evergreen parasitic plant, has been widely used as an oriental phytomedicine to treat diabetes mellitus. However, it is unknown which mistletoe constituent exerts the beneficial effect against the disease. In this study, we examined the hypoglycemic activity of mistletoe and investigated whether the polypeptide viscothionin, purified from mistletoe, was responsible for the activity.

MATERIALS AND METHODS

Mistletoe extracts were prepared by heating mistletoe powder made of leaves and twigs in water for 3, 6, 9, and 12 h. Rat insulinoma RINm5F cells were used to test the cytotoxicity of the extracts and their effects on the secretion of insulin and its precursor, C-peptide. The inhibitory effects of a mistletoe extract on glucose absorption were measured using an α-glucosidase inhibition assay. To determine the component of mistletoe responsible for the observed effects, the mistletoe extract was precipitated with ethanol or hydrolyzed with a protease for further testing. A potential active constituent of mistletoe was isolated by chromatography and molecular weight cut-off fractionation, and its ability to induce insulin secretion was investigated.

RESULTS

A 12-h heat-treated mistletoe extract, showing no cytotoxicity, significantly increased the secretion of insulin and C-peptide by RINm5F cells and enhanced the expression of glucose transporter type 4 (GLUT-4), insulin receptor substrate 1 (IRS-1), and protein kinase B (also known as AKT) in differentiated C2C12 cells. The extract also inhibited α-glucosidase activity. After ethanol precipitation, the extract showed much stronger effects on insulin- and C-peptide-secreting activities of cells, whereas the enzyme-hydrolyzed extract was less effective than the original extract, suggesting that the effect was mediated by a proteinaceous constituent of mistletoe. Subsequent analysis showed that viscothionin, a heat-stable 6-kDa polypeptide isolated from mistletoe, increased the level of insulin secretion by more than 20-fold compared to that induced by the extract.

CONCLUSIONS

Our study indicates that the hypoglycemic effect of mistletoe is mediated by its insulinotropic action and α-glucosidase inhibitory activity, and the effect is due to viscothionin, one of the major bioactive constituents of mistletoe.

The role of thionins in rice defence against root pathogens

Thionins are antimicrobial peptides that are involved in plant defence. Here, we present an in-depth analysis of the role of rice thionin genes in defence responses against two root pathogens: the root-knot nematode Meloidogyne graminicola and the oomycete Pythium graminicola. The expression of rice thionin genes was observed to be differentially regulated by defence-related hormones, whereas all analysed genes were consistently down-regulated in M. graminicola-induced galls, at least until 7 days post-inoculation (dpi). Transgenic lines of Oryza sativa cv. Nipponbare overproducing OsTHI7 revealed decreased susceptibility to M. graminicola infection and P. graminicola colonization. Taken together, these results demonstrate the role of rice thionin genes in defence against two of the most damaging root pathogens attacking rice.

Solid-phase extraction of plant thionins employing aluminum silicate based extraction columns

Thionins belong to a family of cysteine-rich, low-molecular-weight (∼5 KDa) biologically active proteins in the plant kingdom. They display a broad cellular toxicity against a wide range of organisms and eukaryotic cell lines. Thionins protect plants against different pathogens, including bacteria and fungi. A highly selective solid-phase extraction method for plant thionins is reported deploying aluminum silicate (3:2 mullite) powder as a sorbent in extraction columns. Mullite was shown to considerably improve selectivity compared to a previously described zirconium silicate embedded poly(styrene-co-divinylbenzene) monolithic polymer. Due to the presence of aluminum(III), mullite offers electrostatic interactions for the selective isolation of cysteine-rich proteins. In comparison to zirconium(IV) silicate, aluminum(III) silicate showed reduced interactions towards proteins which resulted into superior washings of unspecific compounds while still retaining cysteine-rich thionins. In the presented study, European mistletoe, wheat and barley samples were subjected to solid-phase extraction analysis for isolation of viscotoxins, purothionins and hordothionins, respectively. Matrix-assisted laser desorption/ionization time of flight mass spectroscopy was used for determining the selectivity of the sorbent toward thionins. The selectively retained thionins were quantified by colorimetric detection using the bicinchoninic acid assay. For peptide mass-fingerprint analysis tryptic digests of eluates were examined.

Plant peptides and peptidomics

Extracellular plant peptides perform a large variety of functions, including signalling and defence. Intracellular peptides often have physiological functions or may merely be the products of general proteolysis. Plant peptides have been identified and, in part, functionally characterized through biochemical and genetic studies, which are lengthy and in some cases impractical. Peptidomics is a branch of proteomics that has been developed over the last 5 years, and has been used mainly to study neuropeptides in animals and the degradome of proteases. Peptidomics is a fast, efficient methodology that can detect minute and transient amounts of peptides and identify their post-translational modifications. This review describes known plant peptides and introduces the use of peptidomics for the detection of novel plant peptides.

Disturbance of the Ca(2+)/calmodulin-dependent signalling pathway is responsible for the resistance of Arabidopsis dnd1 against Pectobacterium carotovorum infection

SUMMARY Arabidopsis thaliana wild-type Col-0 and its mutant, 'defence, no death' (dnd) 1-1, were infected with biotrophic Pseudomonas syringae pv. tomato strain DC3000 and necrotrophic Pectobacterium carotovorum strain KACC 10228, and cellular and molecular responses among them were then analysed. Col-0 wild-type was susceptible to both pathogens. By contrast, neither DC3000 nor KACC 10228 infected dnd1-1 (Yu et al., 1998. Proc. Natl. Acad. Sci. USA 95: 7819-7824). Neither of the pathogens triggered cell death or accumulation of active oxygen species in dnd1-1. KACC 10228 induced accelerated transcriptions of PDF1.2 and AtEBP genes in wild-type Col-0, while DC3000-induced transcriptions of them were relatively retarded. Neither of the pathogens modified the constitutive transcription of PR1 in dnd1-1. PDF1.2 and AtEBP transcriptions were not induced by the same treatments. Hydrogen peroxide scavengers, catalase and ascorbic acid, and LaCl(3), an inhibitor of Ca(2+) influx, diminished cell death and protected the wild-type plant from KACC 10228 infection, while EGTA inhibited cell death and pathogen growth. Exogenous Ca(2+) nullified resistance against KACC 10228 challenge in dnd1-1. W-7 and chloropromazine, two calmodulin antagonists, also triggered cell death in dnd1-1 and abolished resistance against KACC 10228. In summary, cell death is correlated with KACC 10228 infection and disease development. Furthermore, the resistance of dnd1-1 against P. carotovorum is dependent on calmodulin and inhibition of cytosolic Ca(2+) increment.

Antifungal effects and mechanism of action of viscotoxin A3

Viscotoxins are cationic proteins, isolated from different mistletoe species, that belong to the group of thionins, a group of basic cysteine-rich peptides of approximately 5 kDa. They have been shown to be cytotoxic to different types of cell, including animal, bacterial and fungal. The aim of this study was to obtain information on the cell targets and the mechanism of action of viscotoxin isoform A3 (VtA3). We describe a detailed study of viscotoxin interaction with fungal-derived model membranes, its location inside spores of Fusarium solani, as well as their induced spore death. We show that VtA3 induces the appearance of ion-channel-like activity, the generation of H2O2, and an increase in cytoplasmic free Ca2+. Moreover, we show that Ca2+ is involved in VtA3-induced spore death and increased H2O2 concentration. The data presented here strongly support the notion that the antifungal activity of VtA3 is due to membrane binding and channel formation, leading to destabilization and disruption of the plasma membrane, thereby supporting a direct role for viscotoxins in the plant defence mechanism.

Production of an engineered killer peptide in Nicotiana benthamiana by using a potato virus X expression system

The decapeptide killer peptide (KP) derived from the sequence of a single-chain, anti-idiotypic antibody acting as a functional internal image of a microbicidal, broad-spectrum yeast killer toxin (KT) was shown to exert a strong microbicidal activity against human pathogens. With the aim to exploit this peptide to confer resistance to plant pathogens, we assayed its antimicrobial activity against a broad spectrum of phytopathogenic bacteria and fungi. Synthetic KP exhibited antimicrobial activity in vitro towards Pseudomonas syringae, Erwinia carotovora, Botrytis cinerea, and Fusarium oxysporum. KP was also expressed in plants by using a Potato virus X (PVX)-derived vector as a fusion to the viral coat protein, yielding chimeric virus particles (CVPs) displaying the heterologous peptide. Purified CVPs showed enhanced antimicrobial activity against the above-mentioned plant pathogens and human pathogens such as Staphylococcus aureus and Candida albicans. Moreover, in vivo assays designed to challenge KP-expressing plants (as CVPs) with Pseudomonas syringae pv. tabaci showed enhanced resistance to bacterial attack. The results indicate that the PVX-based display system is a high-yield, rapid, and efficient method to produce and evaluate antimicrobial peptides in plants, representing a milestone for the large-scale production of high-added-value peptides through molecular farming. Moreover, KP is a promising molecule to be stably engineered in plants to confer broad-spectrum resistance to phytopathogens.

Transgenic tomato plants expressing an Arabidopsis thionin (Thi2.1) driven by fruit-inactive promoter battle against phytopathogenic attack

Tomato is one of the most important crop plants; however, attacks by pathogens can cause serious losses in production. In this report, we explore the potential of using the Arabidopsis thionin (Thi2.1) gene to genetically engineer enhanced resistance to multiple diseases in tomato. Potential thionin toxicity in fruits was negated by the use of a fruit-inactive promoter to drive the Thi2.1 gene. In transgenic lines containing RB7/Thi2.1, constitutive Thi2.1 expression was detected in roots and incidentally in leaves, but not in fruits. Disease assays revealed that the transgenic lines that were tested conferred significant levels of enhanced resistance to bacterial wilt (BW) and Fusarium wilt (FW). Further studies indicated that BW disease progression in transgenic lines was delayed by a systemic suppression of bacterial multiplication. By adopting a safe genetic engineering strategy, the present investigation is another step forward demonstrating thionin practicality in crop protection.

Antimicrobial and insecticidal protein isolated from seeds of Clitoria ternatea, a tropical forage legume

The tropical forage legume Clitoria ternatea (L.) has important agronomic traits such as adaptation to a wide range of soil conditions and resistance to drought. It is resistant to a number of pathogens and pests. These important traits gave us reasons to look more closely at the plant. A highly basic small protein was purified from seeds of C. ternatea to homogeneity by using ultrafiltration with Centricon-3 membrane tubes and preparative granulated-bed isoelectric focusing (IEF). A single protein band was obtained on both sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and IEF gels. The protein, designated 'finotin', has broad and potent inhibitory effect on the growth of various important fungal pathogens of plants, namely Rhizoctonia solani, Fusarium solani, Colletotrichum lindemuthianum, Lasiodiplodia theobromae, Pyricularia grisea, Bipolaris oryzae and Colletotrichum gloeosporioides. It also inhibits the common bean bacterial blight pathogen Xanthomonas axonopodis pv. phaseoli. Moreover, finotin has powerful inhibitory properties against the bean bruchids Zabrotes subfasciatus and Acanthoscelides obtectus.

Mistletoe viscotoxins induce membrane permeabilization and spore death in phytopathogenic fungi

Viscotoxins (Vts) are basic peptides expressed in mistletoe leaves, seeds and stems which have been shown to be cytotoxic to mammalian cells. The aim of this study was to analyse whether Vts were able to control and/or inhibit the growth of phytopathogenic fungi to obtain a clue to their biological function. Incubation of two Vt isoforms, VtA(3) and VtB, at a final concentration of 10 micro M resulted in a complete blockage of the germination of spores from three different pathogenic fungi. It was also shown that lower concentrations than 10 micro M of VtA(3) and VtB inhibit their mycelial growth in a dose-dependent manner. The protein dose required to inhibit the growth of Fusarium solani and Sclerotinia sclerotiorum to a 50% was between 1.5 and 3.75 micro M, which represents a potent activity. No significant differences in the antifungal potency for each Vt isoform, either VtA(3) and VtB, were observed, although they have been shown to exert differential cytotoxicity on mammalian cells. It was also demonstrated that Vts act as fungicidal compounds. To explore the basis of the antifungal activity the ability of VtA(3) to induce changes in membrane permeability and on the oxidative status of F. solani spores was analysed. By using a specific fluorescent probe on intact spores, it was demonstrated that VtA(3) produces rapid changes in fungal membrane permeability. It also induces H(2)O(2) production verified by a histochemical staining. The data presented in this study support a direct role of Vts in the plant defence determined by their lethal effect on fungal pathogens.

Isolation and characterization of a 29-kDa glycoprotein with antifungal activity from bulbs of Urginea indica

In this study an antifungal protein from Urginea indica bulbs was purified to homogeneity by acid precipitation, Diol 300 Gel-filtration, and C(18) reverse phase HPLC. Its molecular mass was estimated to be 29 kDa and periodic acid-Schiff (PAS) staining showed that identified antifungal molecule is a glycoprotein. The neutralization of antifungal activity after periodate oxidation of 29 kDa glycoprotein suggests that the glycan part of the molecule appears to be involved in antifungal activity. N-terminal amino acid sequence of the purified protein was determined as SQLKAXIXDF. This sequence had no sequence similarity with any antifungal proteins. A polyclonal antiserum was raised against purified protein and used in immunolocalization analysis. Results suggest that it is localized to the cell wall of the bulb. Antifungal tests have demonstrated that U. indica protein exerts a fungistatic effect. It completely inhibits the germination of spores and hyphal growth of Fusarium oxysporum.

Interaction of viscotoxins A3 and B with membrane model systems: implications to their mechanism of action

Viscotoxins are small proteins that are thought to interact with biomembranes, displaying different toxic activities against a varied number of cell types, being viscotoxin A(3) (VtA(3)) the most cytotoxic whereas viscotoxin B (VtB) is the less potent. By using infrared and fluorescence spectroscopies, we have studied the interaction of VtA(3) and VtB, both wild and reduced ones, with model membranes containing negatively charged phospholipids. Both VtA(3) and VtB present a high conformational stability, and a similar conformation both in solution and when bound to membranes. In solution, the infrared spectra of the reduced proteins show an increase in bandwidth compared to the nonreduced ones indicating a greater flexibility. VtA(3) and VtB bind with high affinity to membranes containing negatively charged phospholipids and are motional restricted, their binding being dependent on phospholipid composition. Whereas nonreduced proteins maintain their structure when bound to membranes, reduced ones aggregate. Furthermore, leakage experiments show that wild proteins were capable of disrupting membranes whereas reduced proteins were not. The effect of VtA(3) and VtB on membranes having different phospholipid composition is diverse, affecting the cooperativity and fluidity of the membranes. Viscotoxins interact with membranes in a complex way, most likely organizing themselves at the surface inducing the appearance of defects that lead to the destabilization and disruption of the membrane bilayer.

Snakin-2, an antimicrobial peptide from potato whose gene is locally induced by wounding and responds to pathogen infection

The peptide snakin-2 (StSN2) has been isolated from potato (Solanum tuberosum cv Jaerla) tubers and found to be active (EC(50) = 1-20 microM) against fungal and bacterial plant pathogens. It causes a rapid aggregation of both Gram-positive and Gram-negative bacteria. The corresponding StSN2 cDNA encodes a signal sequence followed by a 15-residue acidic sequence that precedes the mature StSN2 peptide, which is basic (isoelectric point = 9.16) and 66 amino acid residues long (molecular weight of 7,025). The StSN2 gene is developmentally expressed in tubers, stems, flowers, shoot apex, and leaves, but not in roots, or stolons, and is locally up-regulated by wounding and by abscisic acid treatment. Expression of this gene is also up-regulated after infection of potato tubers with the compatible fungus Botritys cinerea and down-regulated by the virulent bacteria Ralstonia solanacearum and Erwinia chrysanthemi. These observations are congruent with the hypothesis that the StSN2 is a component of both constitutive and inducible defense barriers.

Antibiotic activities of peptides, hydrogen peroxide and peroxynitrite in plant defence

Genes encoding plant antibiotic peptides show expression patterns that are consistent with a defence role. Transgenic over-expression of defence peptide genes is potentially useful to engineer resistance of plants to relevant pathogens. Pathogen mutants that are sensitive to plant peptides in vitro have been obtained and a decrease of their virulence in planta has been observed, which is consistent with their hypothetical defence role. A similar approach has been followed to elucidate the potential direct anti-microbial role of hydrogen peroxide. Additionally, a scavenger of peroxynitrite has been used to investigate its involvement in plant defence.

Plant defense peptides

Eight families of antimicrobial peptides, ranging in size from 2 to 9 kD, have been identified in plants. These are thionins, defensins, so-called lipid transfer proteins, hevein- and knottin-like peptides, MBP1, IbAMP, and the recently reported snakins. All of them have compact structures that are stabilized by 2-6 disulfide bridges. They are part of both permanent and inducible defense barriers. Transgenic overexpression of the corresponding genes leads to enhanced tolerance to pathogens, and peptide-sensitive pathogen mutants have reduced virulence.

[Kohlhernie - neue Ansätze zur Bekämpfung der gefürchteten Kohlerkrankung]

Durch Pflanzenkrankheiten entstehen weltweit hohe Ernteverluste. Eine der häufigsten Infektionen in der Familie der Kreuzb&luml;tengewächse wird durch den Pilz Plasmodiophora brassicae verursacht. Die Krankheit äußert sich in Form von Wurzeltumoren, den "Kohlherniegallen". Da es auf verseuchten Böden zu hohen Ernteausfällen kommt, besteht ein enormes Interesse an der Aufklärung der Vorgänge, die zu diesem Krankheitsbild führen.

Wounding and chemicals induce expression of the Arabidopsis thaliana gene Thi2.1, encoding a fungal defense thionin, via the octadecanoid pathway

In seedlings of Arabidopsis thaliana the thionin gene Thi2.1 is inducible by methyl jasmonate, wounding, silver nitrate, coronatine, and sorbitol. We have used a biochemical and genetic approach to test the signal transduction of these different inducers. Both exogenously applied jasmonates and jasmonates produced endogenously upon stress induction, lead to GUS expression in a Thi2.1 promoter-uidA transgenic line. No GUS expression was observed in a coil mutant background which lacks jasmonate perception whereas methyl jasmonate and coronatine but not the other inducers were able to overcome the block in jasmonic acid production in a fad3-2 fad7-2 fad8 mutant background. Our results show conclusively that all these inducers regulate Thi2-1 gene expression via the octadecanoid pathway.

Systemic and local induction of an Arabidopsis thionin gene by wounding and pathogens

The Arabidopsis Thi2.1 thionin gene was cloned and sequenced. The promoter was fused to the uidA gene and stably transformed into Arabidopsis to study its regulation. GUS expression levels correlated with the steady-state levels of Thi2.1 mRNA, thus demonstrating that the promoter is sufficient for the regulation of the Thi2.1 gene. The sensitivity of the Thi2.1 gene to methyl jasmonate was found to be developmentally determined. Systemic and local expression could be induced by wounding and inoculation with Fusarium oxysporum f sp. matthiolae. A deletion analysis of the promoter identified a fragment of 325 bp upstream of the start codon, which appears to contain all the elements necessary for the regulation of the Thi2.1 gene. These results support the view that thionins are defence proteins, and indicate the possibility that resistance of Arabidopsis plants to necrotrophic fungal pathogens is mediated through the octadecanoid pathway.