Regulation of the wound-induced myrosinase-associated protein transcript in Brassica napus plants

S-nitrosylation analysis in Brassica juncea apoplast highlights the importance of nitric oxide in cold-stress signaling

Reactive nitrogen species (RNS) including nitric oxide (NO) are important components of stress signaling. However, RNS-mediated signaling in the apoplast remains largely unknown. NO production measured in the shoot apoplast of Brassica juncea seedlings showed nonenzymatic nitrite reduction to NO. Thiol pool quantification showed cold-induced increase in the protein (including S-nitrosothiols) as well as non protein thiols. Proteins from the apoplast were resolved as 109 spots on the 2-D gel, while S-nitrosoglutathione-treated (a NO donor), neutravidin-agarose affinity chromatography-purified S-nitrosylated proteins were resolved as 52 spots. Functional categorization after MALDI-TOF/TOF identification showed 41 and 38% targets to be metabolic/cell-wall-modifying and stress-related, respectively, suggesting the potential role(s) of S-nitrosylation in regulating these responses. Additionally, identification of cold-stress-modulated putative S-nitrosylated proteins by nLC-MS/MS showed that only 38.4% targets with increased S-nitrosylation were secreted by classical pathway, while the majority (61.6%) of these were secreted by unknown/nonclassical pathways. Cold-stress-increased dehydroascorbate reductase and glutathione S-transferase activity via S-nitrosylation and promoted ROS detoxification by ascorbate regeneration and hydrogen peroxide detoxification. Taken together, cold-mediated NO production, thiol pool enrichment, and identification of the 48 putative S-nitrosylated proteins, including 25 novel targets, provided the preview of RNS-mediated cold-stress signaling in the apoplast.

Cloning and functional analysis of three genes encoding polygalacturonase-inhibiting proteins from Capsicum annuum and transgenic CaPGIP1 in tobacco in relation to increased resistance to two fungal pathogens

Polygalacturonase-inhibiting proteins (PGIPs) are plant cell wall glycoproteins that can inhibit fungal endopolygalacturonases (PGs). The PGIPs directly reduce the aggressive potential of PGs. Here, we isolated and functionally characterized three members of the pepper (Capsicum annuum) PGIP gene family. Each was up-regulated at a different time following stimulation of the pepper leaves by Phytophthora capcisi and abiotic stresses including salicylic acid, methyl jasmonate, abscisic acid, wounding and cold treatment. Purified recombinant proteins individually inhibited activity of PGs produced by Alternaria alternata and Colletotrichum nicotianae, respectively, and virus-induced gene silencing in pepper conferred enhanced susceptibility to P. capsici. Because three PGIP genes acted similarily in conferring resistance to infection by P. capsici, and because individually purified proteins showed consistent inhibition against PG activity of both pathogens, CaPGIP1 was selected for manipulating transgenic tobacco. The crude proteins from transgenic tobacco exhibited distinct enhanced resistance to PG activity of both fungi. Moreover, the transgenic tobacco showed effective resistance to infection and a significant reduction in the number of infection sites, number of lesions and average size of lesions in the leaves. All results suggest that CaPGIPs may be involved in plant defense response and play an important role in a plant's resistance to disease.

Engineering glucosinolates in plants: current knowledge and potential uses

Glucosinolates (GSL) and their derivatives are well known for the characteristic roles they play in plant defense as signaling molecules and as bioactive compounds for human health. More than 130 GSLs have been reported so far, and most of them belong to the Brassicaceae family. Several enzymes and transcription factors involved in the GSL biosynthesis have been studied in the model plant, Arabidopsis, and in a few other Brassica crop species. Recent studies in GSL research have defined the regulation, distribution, and degradation of GSL biosynthetic pathways; however, the underlying mechanism behind transportation of GSLs in plants is still largely unknown. This review highlights the recent advances in the metabolic engineering of GSLs in plants and discusses their potential applications.

Evolution of jasmonate and salicylate signal crosstalk

The evolution of land plants approximately 470 million years ago created a new adaptive zone for natural enemies (attackers) of plants. In response to attack, plants evolved highly effective, inducible defense systems. Two plant hormones modulating inducible defenses are salicylic acid (SA) and jasmonic acid (JA). Current thinking is that SA induces resistance against biotrophic pathogens and some phloem feeding insects and JA induces resistance against necrotrophic pathogens, some phloem feeding insects and chewing herbivores. Signaling crosstalk between SA and JA commonly manifests as a reciprocal antagonism and may be adaptive, but this remains speculative. We examine evidence for and against adaptive explanations for antagonistic crosstalk, trace its phylogenetic origins and provide a hypothesis-testing framework for future research on the adaptive significance of SA-JA crosstalk.

Proteomic alterations of Brassica napus root in response to boron deficiency

Boron (B) deficiency is a worldwide problem, and Brassica napus is one of the most sensitive crops to B deficiency. To better understand the B starvation response of Brassica napus, we conducted a comparative proteomic analysis of seedling stage Brassica napus root between B-sufficient and B-limited conditions: 45 differentially expressed proteins were successfully identified by 2-DE coupled with MALDI-TOF/TOF-MS and LTQ-ESI-MS/MS analysis. Among these proteins, 10 were down-regulated and 35 were up-regulated under B-limited condition. Combining GO and KEGG analyses with data from previous reports, proteins were categorized into several functional groups, including antioxidant and detoxification, defense-related proteins, signaling and regulation, carbohydrate and energy metabolism, amino acid and fatty acid metabolism, protein translation and degradation, cell wall structure, and transporter. The genes of selected proteins were analyzed by quantitative RT-PCR. Our results provide novel information for better understanding the physiological and biochemical responses to B deficiency in plants.

beta-Glucosidases as detonators of plant chemical defense

Some plant secondary metabolites are classified as phytoanticipins. When plant tissue in which they are present is disrupted, the phytoanticipins are bio-activated by the action of beta-glucosidases. These binary systems--two sets of components that when separated are relatively inert--provide plants with an immediate chemical defense against protruding herbivores and pathogens. This review provides an update on our knowledge of the beta-glucosidases involved in activation of the four major classes of phytoanticipins: cyanogenic glucosides, benzoxazinoid glucosides, avenacosides and glucosinolates. New aspects of the role of specific proteins that either control oligomerization of the beta-glucosidases or modulate their product specificity are discussed in an evolutionary perspective.

PYK10, a beta-glucosidase located in the endoplasmatic reticulum, is crucial for the beneficial interaction between Arabidopsis thaliana and the endophytic fungus Piriformospora indica

Piriformospora indica, an endophyte of the Sebacinaceae family, promotes growth and seed production of many plant species, including Arabidopsis. Growth of a T-DNA insertion line in PYK10 is not promoted and the plants do not produce more seeds in the presence of P. indica, although their roots are more colonized by the fungus than wild-type roots. Overexpression of PYK10 mRNA did not affect root colonization and the response to the fungus. PYK10 codes for a root- and hypocotyl-specific beta-glucosidase/myrosinase, which is implicated to be involved in plant defences against herbivores and pathogens. Expression of PYK10 is activated by the basic helix-loop-helix domain containing transcription factor NAI1, and two Arabidopsis lines with mutations in the NAI1 gene show the same response to P. indica as the PYK10 insertion line. PYK10 transcript and PYK10 protein levels are severely reduced in a NAI1 mutant, indicating that PYK10 and not the transcription factor NAI1 is responsible for the response to the fungus. In wild-type roots, the message level for a leucine-rich repeat protein LRR1, but not for plant defensin 1.2 (PDF1.2), is upregulated in the presence of P. indica. In contrast, in lines with reduced PYK10 levels the PDF1.2, but not LRR1, message level is upregulated in the presence of the fungus. We propose that PYK10 restricts root colonization by P. indica, which results in the repression of defence responses and the upregulation of responses leading to a mutualistic interaction between the two symbiotic partners.

Overexpression of Arabidopsis thaliana LTL1, a salt-induced gene encoding a GDSL-motif lipase, increases salt tolerance in yeast and transgenic plants

Genes involved in the mechanisms of plant responses to salt stress may be used as biotechnological tools for the genetic improvement of salt tolerance in crop plants. This would help alleviate the increasing problem of salinization of lands cultivated under irrigation in arid and semi-arid regions. We have isolated a novel halotolerance gene from Arabidopsis thaliana, A. thaliana Li-tolerant lipase 1 (AtLTL1), on the basis of the phenotype of tolerance to LiCl conferred by its expression in yeast. AtLTL1 encodes a putative lipase of the GDSL-motif family, which includes bacterial and a very large number of plant proteins. In Arabidopsis, AtLTL1 expression is rapidly induced by LiCl or NaCl, but not by other abiotic stresses. Overexpression of AtLTL1 increases salt tolerance in transgenic Arabidopsis plants, compared to non-transformed controls, allowing germination of seeds in the presence of toxic concentrations of LiCl and NaCl, and stimulating vegetative growth, flowering and seed set in the presence of NaCl. These results clearly point to a role of AtLTL1 in the mechanisms of salt tolerance. In addition, we show that AtLTL1 expression is also activated, although only transiently, by salicylic acid (SA), suggesting that the lipase could also be involved in defence reactions against pathogens.

The gene controlling the quantitative trait locus EPITHIOSPECIFIER MODIFIER1 alters glucosinolate hydrolysis and insect resistance in Arabidopsis

Glucosinolates are sulfur-rich plant secondary metabolites whose breakdown products have a wide range of biological activities in plant-herbivore and plant-pathogen interactions and anticarcinogenic properties. In Arabidopsis thaliana, hydrolysis by the enzyme, myrosinase, produces bioactive nitriles, epithionitriles, or isothiocyanates depending upon the plant's genotype and the glucosinolate's structure. A major determinant of this structural specificity is the epithiospecifier locus (ESP), whose protein causes the formation of epithionitriles and nitriles. A quantitative trait locus (QTL) on chromosome 3 epistatically affects nitrile formation in combination with ESP; this QTL has been termed EPITHIOSPECIFIER MODIFIER1 (ESM1). We identified a myrosinase-associated protein as the ESM1 QTL in Arabidopsis using map-based cloning with recombinant inbred lines, natural variation transcriptomic analysis, and metabolic profiling. In planta and in vitro analyses with natural ESM1 alleles, ESM1 knockouts, and overexpression lines show that ESM1 represses nitrile formation and favors isothiocyanate production. The glucosinolate hydrolysis profile change influenced by ESM1 is associated with the ability to deter herbivory by Trichoplusia ni. This gene could provide unique approaches toward improving human nutrition.

Arabidopsis myrosinases TGG1 and TGG2 have redundant function in glucosinolate breakdown and insect defense

In Arabidopsis and other Brassicaceae, the enzyme myrosinase (beta-thioglucoside glucohydrolase, TGG) degrades glucosinolates to produce toxins that deter herbivory. A broadly applicable selection for meiotic recombination between tightly linked T-DNA insertions was developed to generate Arabidopsis tgg1tgg2 double mutants and study myrosinase function. Glucosinolate breakdown in crushed leaves of tgg1 or tgg2 single mutants was comparable to that of wild-type, indicating redundant enzyme function. In contrast, leaf extracts of tgg1tgg2 double mutants had undetectable myrosinase activity in vitro, and damage-induced breakdown of endogenous glucosinolates was apparently absent for aliphatic and greatly slowed for indole glucosinolates. Maturing leaves of myrosinase mutants had significantly increased glucosinolate levels. However, developmental decreases in glucosinolate content during senescence and germination were unaffected, showing that these processes occur independently of TGG1 and TGG2. Insect herbivores with different host plant preferences and feeding styles varied in their responses to myrosinase mutations. Weight gain of two Lepidoptera, the generalist Trichoplusia ni and the facultative Solanaceae-specialist Manduca sexta, was significantly increased on tgg1tgg2 double mutants. Two crucifer-specialist Lepidoptera had differing responses. Whereas Plutella xylostella was unaffected by myrosinase mutations, Pieris rapae performed better on wild-type, perhaps due to reduced feeding stimulants in tgg1tgg2 mutants. Reproduction of two Homoptera, Myzus persicae and Brevicoryne brassicae, was unaffected by myrosinase mutations.

Molecular cloning and immunoglobulin E reactivity of a natural rubber latex lecithinase homologue, the major allergenic component of Hev b 4

BACKGROUND

Hev b 4 is an allergenic natural rubber latex (NRL) protein complex that is reactive in skin prick tests and in vitro immunoassays. On SDS-polyacrylamide gel electrophoresis (SDS-PAGE), Hev b 4 is discerned predominantly at 53-55 kDa together with a 57 kDa minor component previously identified as a cyanogenic glucosidase. Of the 13 NRL allergens recognized by the International Union of Immunological Societies, the 53-55 kDa Hev b 4 major protein is the only candidate that lacks complete cDNA and protein sequence information.

OBJECTIVE

We sought to clone the transcript encoding the Hev b 4 major protein, and characterize the native protein and its recombinant form in relation to IgE binding.

METHODS

The 5'/3' rapid amplification of cDNA ends method was employed to obtain the complete cDNA of the Hev b 4 major protein. A recombinant form of the protein was over-expressed in Escherichia coli. The native Hev b 4 major protein was deglycosylated by trifluoromethane sulphonic acid. Western immunoblots of the native, deglycosylated and recombinant proteins were performed using both polyclonal antibodies and sera from latex-allergic patients.

RESULTS

The cDNA encoding the Hev b 4 major protein was cloned. Its open reading frame matched lecithinases in the conserved domain database and contained 10 predicted glycosylation sites. Detection of glycans on the Hev b 4 lecithinase homologue confirmed it to be a glycoprotein. The deglycosylated lecithinase homologue was discerned at 40 kDa on SDS-PAGE, this being comparable to the 38.53 kDa mass predicted by its cDNA. Deglycosylation of the lecithinase homologue resulted in the loss of IgE recognition, although reactivity to polyclonal rabbit anti-Hev b 4 was retained. IgE from latex-allergic patients also failed to recognize the non-glycosylated E. coli recombinant lecithinase homologue.

CONCLUSION

The IgE epitopes of the Hev b 4 lecithinase homologue reside mainly in its carbohydrate moiety, which also account for the discrepancy between the observed molecular weight of the protein and the value calculated from its cDNA.

An expression and bioinformatics analysis of the Arabidopsis serine carboxypeptidase-like gene family

The Arabidopsis (Arabidopsis thaliana) genome encodes a family of 51 proteins that are homologous to known serine carboxypeptidases. Based on their sequences, these serine carboxypeptidase-like (SCPL) proteins can be divided into several major clades. The first group consists of 21 proteins which, despite the function implied by their annotation, includes two that have been shown to function as acyltransferases in plant secondary metabolism: sinapoylglucose:malate sinapoyltransferase and sinapoylglucose:choline sinapoyltransferase. A second group comprises 25 SCPL proteins whose biochemical functions have not been clearly defined. Genes encoding representatives from both of these clades can be found in many plants, but have not yet been identified in other phyla. In contrast, the remaining SCPL proteins include five members that are similar to serine carboxypeptidases from a variety of organisms, including fungi and animals. Reverse transcription PCR results suggest that some SCPL genes are expressed in a highly tissue-specific fashion, whereas others are transcribed in a wide range of tissue types. Taken together, these data suggest that the Arabidopsis SCPL gene family encodes a diverse group of enzymes whose functions are likely to extend beyond protein degradation and processing to include activities such as the production of secondary metabolites.

The potassium-dependent transcriptome of Arabidopsis reveals a prominent role of jasmonic acid in nutrient signaling

Full genome microarrays were used to assess transcriptional responses of Arabidopsis seedlings to changing external supply of the essential macronutrient potassium (K(+)). Rank product statistics and iterative group analysis were employed to identify differentially regulated genes and statistically significant coregulated sets of functionally related genes. The most prominent response was found for genes linked to the phytohormone jasmonic acid (JA). Transcript levels for the JA biosynthetic enzymes lipoxygenase, allene oxide synthase, and allene oxide cyclase were strongly increased during K(+) starvation and quickly decreased after K(+) resupply. A large number of well-known JA responsive genes showed the same expression profile, including genes involved in storage of amino acids (VSP), glucosinolate production (CYP79), polyamine biosynthesis (ADC2), and defense (PDF1.2). Our findings highlight a novel role of JA in nutrient signaling and stress management through a variety of physiological processes such as nutrient storage, recycling, and reallocation. Other highly significant K(+)-responsive genes discovered in our study encoded cell wall proteins (e.g. extensins and arabinogalactans) and ion transporters (e.g. the high-affinity K(+) transporter HAK5 and the nitrate transporter NRT2.1) as well as proteins with a putative role in Ca(2+) signaling (e.g. calmodulins). On the basis of our results, we propose candidate genes involved in K(+) perception and signaling as well as a network of molecular processes underlying plant adaptation to K(+) deficiency.

Salicylic acid inhibits jasmonic acid-induced resistance of Arabidopsis thaliana to Spodoptera exigua

The role of salicylic acid (SA) in plant responses to pathogens has been well documented, but its direct and indirect effects on plant responses to insects are not so well understood. We examined the effects of SA, alone and in combination with jasmonic acid (JA), on the performance of the generalist herbivore, Spodoptera exigua, in wild-type and mutant Arabidopsis thaliana genotypes that varied genetically in their ability to mount SA- and JA-mediated defence responses. In one experiment, growth of S. exigua larvae was highest on the Wassilewskija wild-type, intermediate on the Columbia wild-type and the JA-deficient fad mutant, and lowest on the nim1-1 and jar1-mutants, which are defective in the SA and JA pathways, respectively. Activity of guaiacol peroxidase, polyphenoloxidase, n-acetylglucosaminidase, and trypsin inhibitor varied by genotype but did not correlate with insect performance. SA treatment increased growth of S. exigua larvae by approximately 35% over all genotypes, but had no discernable effect on activities of the four defence proteins. In a second experiment, growth of S. exigua was highest across treatments on the cep1 mutant, a constitutive expressor of high SA levels and systemic acquired resistance, and lowest on the fad mutant, which is JA-deficient. JA treatment generally increased activity of all four defence proteins, increased total glucosinolate levels and reduced insect growth by approximately 25% over all genotypes. SA generally inhibited expression of JA-induced resistance to S. exigua when both hormones were applied simultaneously. Across genotypes and treatments, larval mass was negatively correlated with the activity of trypsin inhibitor and polyphenoloxidase and with total glucosinolate levels, and insect damage was negatively correlated with the activity of polyphenoloxidase. SA had little effect on the induction of defence protein activity by JA. However, SA attenuated the induction of glucosinolates by JA and therefore may explain better the interactive effects of SA and JA on insect performance. This study illustrates that direct and indirect cross-effects of SA on resistance to S. exigua can occur in A. thaliana. Effects of SA may be mediated through effects on plant defence chemistry or other aspects of the suitability of foliage for insect feeding and growth.

Isolation and characterization of the early nodule-specific protein homologue (Hev b 13), an allergenic lipolytic esterase from Hevea brasiliensis latex

Recurring reports of a highly allergenic 42-46-kDa protein in Hevea brasiliensis latex appeared to have been resolved with the discovery of a 43-kDa allergenic latex protein that was a homologue to patatin. However, the low to moderate prevalence of sensitization to the protein, designated Hev b 7, among latex-allergic patients could not adequately explain the frequent observations of the 42-46-kDa allergen. This led to the hypothesis that another, more allergenic protein of a similar molecular mass existed in Hevea latex. We report the isolation and purification of a 42.98-kDa latex glycoprotein showing homology to the early nodule-specific protein (ENSP) of the legumes Medicago sativa, Medicago truncatula, and Glycine max. The protein is allergenic, being recognized by immunoglobulin E (IgE) in sera from latex-allergic patients. The IgE epitope resides on the carbohydrate moiety of the protein, and the presence of a similar carbohydrate component on potato tuber patatin enables the latter to inhibit IgE binding to the ENSP homologue. The cDNA encoding the ENSP homologue was isolated by reverse transcription-PCR and cloned. The protein predicted from the cDNA sequence has 391 amino acids, the first 26 of which constitute a putative signal peptide. The deduced molecular mass of the mature protein is 40.40 kDa, while its isoelectric point is estimated at 5.0. The discrepancy between the predicted and observed molecular mass might be due to glycosylation, for which three N-sites on the protein are predicted. The purified protein showed lipase and esterase activities and may be involved in plant defense.

Interactions between aboveground and belowground induction of glucosinolates in two wild Brassica species

•  Interactions between shoot and root induction of glucosinolates in two crucifers, Brassica oleracea and B. nigra, were studied by applying the signalling hormones jasmonic acid (JA) and salicylic acid (SA). •  JA application increased total shoot glucosinolate levels 1.5-3 times, but total root levels did not increase. Only root JA-application yielded a systemic response. In B. oleracea it mattered where JA was applied: root application increased aliphatic glucosinolates in the shoot, whereas shoot application increased indole glucosinolates. Plants treated with JA to both organs had profiles similar to shoot-treated plants. SA-application did not disturb the organ-specific response to JA. Increases in glucosinolate levels did not reduce plant biomass. •  A applications reduced root glucosinolates in root-treated plants. SA root-application in B. nigra resulted in lesions on the leaves and shoot-application caused a trichome response. •  lants thus respond specifically, depending on the organ that is induced and the hormone that is applied. We find a large potential for root-feeders to affect shoot-feeders. Glucosinolate induction in one organ is not constrained by induction in the other organ.

Characterization of a Salicylic Acid- and Pathogen-induced Lipase-like Gene in Chinese Cabbage

A cDNA clone for a salicylic acid-induced gene in Chinese cabbage (Brassica rapa subsp. pekinensis) was isolated and characterized. The cabbage gene, designated Br-sil1 (for Brassica rapa salicylate-induced lipase-like 1 gene), encodes a putative lipase that has the family II lipase motif GDSxxDxG around the active site serine. A database search showed that plant genomes have a large number of genes that contain the family II lipase motif. The lipase-like proteins include a myrosinase-associated protein, an anther-specific proline-rich protein APG, a pollen coat protein EXL, and an early nodule-specific protein. The Br-sil1 gene is strongly induced by salicylic acid and a nonhost pathogen, Pseudomonas syringae pv. tomato, that elicits a hypersensitive response in Chinese cabbage. Treatment of the cabbage leaves with BTH, methyl jasmonate, or ethephon showed that the Br-sil1 gene expression is induced by BTH, but not by methyl jasmonate or ethylene. This indicates that the cabbage gene is activated via a salicylic acid-dependent signaling pathway. An examination of the tissue-specific expression revealed that the induction of the Br-sil1 gene expression by BTH occurs in leaves and stems, but not in roots and flowers. Without the BTH treatment, however, the Br-sil1 gene is not expressed in any of the tissues that were examined.

Two Brassica napus polygalacturonase inhibitory protein genes are expressed at different levels in response to biotic and abiotic stresses

Plants encode a distinct set of polygalacturonase inhibitory proteins (PGIPs) that function to inhibit polygalacturonase enzymes produced by soft-rot fungal pathogens. We characterized two PGIP-encoding genes ( Bnpgip1 and Bnpgip2) from Brassica napus DH12075 (a double-haploid line derived from a cross between 'Crésor' and 'Westar'). The two proteins exhibit 67.4% identity at the amino acid level and contain 10 imperfect leucine-rich repeats. The pgip genes are present as a small multigene family in B. napus with at least four members. Bnpgip1 and Bnpgip2 are constitutively expressed in roots, stems, flower buds and open flowers. In mature leaf tissue, different levels of induction were observed in response to biotic and abiotic stresses. Bnpgip1 expression was highly responsive to flea beetle feeding and mechanical wounding, weakly responsive to Sclerotinia sclerotiorum infection and exposure to cold but not to dehydration. Conversely, Bnpgip2 expression was strongly induced by S. sclerotiorum infection and to a lesser degree by wounding but not by flea beetle feeding. Application of jasmonic acid to leaves induced both Bnpgip1 and Bnpgip2 gene expression; however, salicylic acid did not activate either gene. Taken together, these results suggest that separate pathways regulate Bnpgip1 and Bnpgip2, and that their roles in plant development or resistance to biotic and abiotic stress differ.

Complex formation of myrosinase isoenzymes in oilseed rape seeds are dependent on the presence of myrosinase-binding proteins

The enzyme myrosinase (EC 3.2.3.1) degrades the secondary compounds glucosinolates upon wounding and serves as a defense to generalist pests in Capparales. Certain myrosinases are present in complexes together with other proteins such as myrosinase-binding proteins (MBP) in extracts of oilseed rape (Brassica napus) seeds. Immunhistochemical analysis of wild-type seeds showed that MBPs were present in most cells but not in the myrosin cells, indicating that the complex formation observed in extracts is initiated upon tissue disruption. To study the role of MBP in complex formation and defense, oilseed rape antisense plants lacking the seed MBPs were produced. Western blotting and immunohistochemical staining confirmed depletion of MBP in the transgenic seeds. The exclusive expression of myrosinase in idioblasts (myrosin cells) of the seed was not affected by the down-regulation of MBP. Using size-exclusion chromatography, we have shown that myrosinases with subunit molecular masses of 62 to 70 kD were present as free dimers from the antisense seed extract, whereas in the wild type, they formed complexes. In accordance with this, MBPs are necessary for myrosinase complex formation of the 62- to 70-kD myrosinases. The product formed from sinalbin hydrolysis by myrosinase was the same whether MBP was present or not. The performance of a common beetle generalist (Tenebrio molitor) fed with seeds, herbivory by flea beetles (Phyllotreta undulata) on cotyledons, or growth rate of the Brassica fungal pathogens Alternaria brassicae or Lepthosphaeria maculans in the presence of seed extracts were not affected by the down-regulation of MBP, leaving the physiological function of this protein family open.

Characterization of a Brassica napus myrosinase expressed and secreted by Pichia pastoris

In Brassica napus three different gene families with different temporal and tissue-specific expression and distribution patterns encode myrosinases (thioglucoside glucohydrolases, EC 3.2.3.1). Myrosinases encoded by the MA gene family are found as free and soluble dimers, while myrosinases encoded by the MB and MC gene families are mainly found in large insoluble complexes associated with myrosinase-binding proteins and myrosinase-associated proteins. These large complexes impede purification and characterization of MB and MC myrosinases from the plant. We used Pichia pastoris to express and secrete functional recombinant MYR1 myrosinase from B. napus to allow further characterization of myrosinase belonging to the MB gene family. The purified recombinant myrosinase hydrolyzes sinigrin with a K(m) of 1.0 mM; the specific activity and calculated k(cat)/K(m) were 175 U/mg and 1.9 x 10(5) s(-1) M(-1), respectively. A novel in-gel staining method for myrosinase activity is presented.

The myrosinase-glucosinolate system in the interaction between Leptosphaeria maculans and Brassica napus

summary Leptosphaeria maculans causes blackleg disease, and resistance to this fungal pathogen is an important trait in the breeding of oilseed rape. A better comprehension of the role of the myrosinase-glucosinolate system in this context is of great value. The present study is the first to address effects on multiple components of this complex system, including concentrations of individual glucosinolates, product formation, myrosinase isoform distribution and activity, and levels of myrosinase binding proteins during the infection process. One resistant B. napus cultivar (Maluka) and one susceptible cultivar (Westar) were compared in the investigation. Our results show that the two cultivars had the same histological distribution, isoform expression, and activity of the myrosinase enzymes. The glucosinolate levels were also similar, with the exception of glucobrassicin and neoglucobrassicin, which were significantly lower in the resistant cultivar at 11 days post-infection. Growth of the fungus on the plant tissues did not alter glucosinolate levels, suggesting that L. maculans does not degrade these compounds. When the plants were starved of sulphur, and thereby depleted of glucosinolates, no increased susceptibility was observed. Hence, we suggest that the myrosinase-glucosinolate system does not determine the outcome of the interaction between B. napus and L. maculans.

Arabidopsis map kinase 4 negatively regulates systemic acquired resistance

Transposon inactivation of Arabidopsis MAP kinase 4 produced the mpk4 mutant exhibiting constitutive systemic acquired resistance (SAR) including elevated salicylic acid (SA) levels, increased resistance to virulent pathogens, and constitutive pathogenesis-related gene expression shown by Northern and microarray hybridizations. MPK4 kinase activity is required to repress SAR, as an inactive MPK4 form failed to complement mpk4. Analysis of mpk4 expressing the SA hydroxylase NahG and of mpk4/npr1 double mutants indicated that SAR expression in mpk4 is dependent upon elevated SA levels but is independent of NPR1. PDF1.2 and THI2.1 gene induction by jasmonate was blocked in mpk4 expressing NahG, suggesting that MPK4 is required for jasmonic acid-responsive gene expression.

Myrosinase: gene family evolution and herbivore defense in Brassicaceae

Glucosinolates are a category of secondary products present primarily in species of the order Capparales. When tissue is damaged, for example by herbivory, glucosinolates are degraded in a reaction catalyzed by thioglucosidases, denoted myrosinases, also present in these species. Thereby, toxic compounds such as nitriles, isothiocyanates, epithionitriles and thiocyanates are released. The glucosinolate-myrosinase system is generally believed to be part of the plant's defense against insects, and possibly also against pathogens. In this review, the evolution of the system and its impact on the interaction between plants and insects are discussed. Further, data suggesting additional functions in the defense against pathogens and in sulfur metabolism are reviewed.

The myrosinase-binding protein from Brassica napus seeds possesses lectin activity and has a highly similar vegetatively expressed wound-inducible counterpart

This communication demonstrates that proteins in the family of myrosinase-binding proteins (MBP) present in seeds of Brassica napus possess lectin activity, binding most efficiently to p-aminophenyl alpha-D-mannopyranoside-agarose, and to some extent to N-acetylglucosamine-agarose. A cDNA encoding a vegetatively expressed, wound-inducible counterpart to these seed MBP was isolated and characterised. Upon wounding, this MBP transcript accumulated in old and young leaves, and was systemically expressed in the young plant. Additionally, the wound-induced MBP transcript increased in abundance after treating the young plants with methyl jasmonate (MeJA), jasmonic acid (JA) or abscisic acid (ABA), and to some extent in response to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. Expression induced by wounding, ABA or JA was antagonised by simultaneous feeding of the plants with salicylic acid. MBP polypeptides accumulated in MeJA-treated plants. The myrosinases redistributed from the soluble fraction into the insoluble fraction of a tissue extract after induction. The most abundant MBP (94 kDa) partitioned in the insoluble fraction, while two larger MBP (103 kDa and 108 kDa) were present only in the soluble fraction of extracts obtained from the control or MeJA-treated plant tissues.