Lipid transfer proteins and protease inhibitors as key factors in the priming of barley responses to Fusarium head blight disease by a biocontrol strain of Pseudomonas fluorescens

TcSERPIN, an inhibitor that interacts with cocoa defense proteins and has biotechnological potential against human pathogens

In plants, serpins are a superfamily of serine and cysteine protease inhibitors involved in stress and defense mechanisms, with potential for controlling agricultural pests, making them important biotechnological tools. The objective of this study was to characterize a serpin from Theobroma cacao, called TcSERPIN, to identify its endogenous targets and determine its function and biotechnological potential. TcSERPIN has 390 amino acid residues and shows conservation of the main active site, RCL. Cis-elements related to light, stress, hormones, anaerobic induction, cell cycle regulation and defense have been identified in the gene's regulatory region. TcSERPIN transcripts are accumulated in different tissues of Theobroma cacao. Furthermore, in plants infected with Moniliophtora perniciosa and Phytophthora palmivora, the expression of TcSERPIN was positively regulated. The protein spectrum, rTcSERPIN, reveals a typical β-sheet pattern and is thermostable at pH 8, but loses its structure with temperature increases above 66°C at pH 7. At the molar ratios of 0.65 and 0.49, rTcSERPIN inhibited 55 and 28% of the activity of papain from Carica papaya and trypsin from Sus scrofa, respectively. The protease trap containing immobilized rTcSERPIN captured endogenous defense proteins from cocoa extracts that are related to metabolic pathways, stress and defense. The evaluation of the biotechnological potential against geohelminth larvae showed that rTcSERPIN and rTcCYS4 (Theobroma cacao cystatin 4) reduced the movement of larvae after 24 hours. The results of this work show that TcSERPIN has ideal biochemical characteristics for biotechnological applications, as well as potential for studies of resistance to phytopathogens of agricultural crops.

Microbial diversity in soils suppressive to Fusarium diseases

Fusarium species are cosmopolitan soil phytopathogens from the division Ascomycota, which produce mycotoxins and cause significant economic losses of crop plants. However, soils suppressive to Fusarium diseases are known to occur, and recent knowledge on microbial diversity in these soils has shed new lights on phytoprotection effects. In this review, we synthesize current knowledge on soils suppressive to Fusarium diseases and the role of their rhizosphere microbiota in phytoprotection. This is an important issue, as disease does not develop significantly in suppressive soils even though pathogenic Fusarium and susceptible host plant are present, and weather conditions are suitable for disease. Soils suppressive to Fusarium diseases are documented in different regions of the world. They contain biocontrol microorganisms, which act by inducing plants' resistance to the pathogen, competing with or inhibiting the pathogen, or parasitizing the pathogen. In particular, some of the Bacillus, Pseudomonas, Paenibacillus and Streptomyces species are involved in plant protection from Fusarium diseases. Besides specific bacterial populations involved in disease suppression, next-generation sequencing and ecological networks have largely contributed to the understanding of microbial communities in soils suppressive or not to Fusarium diseases, revealing different microbial community patterns and differences for a notable number of taxa, according to the Fusarium pathosystem, the host plant and the origin of the soil. Agricultural practices can significantly influence soil suppressiveness to Fusarium diseases by influencing soil microbiota ecology. Research on microbial modes of action and diversity in suppressive soils should help guide the development of effective farming practices for Fusarium disease management in sustainable agriculture.

Plant Serpins: Potential Inhibitors of Serine and Cysteine Proteases with Multiple Functions

Plant serpins are a superfamily of protein inhibitors that have been continuously studied in different species and have great biotechnological potential. However, despite ongoing studies with these inhibitors, the biological role of this family in the plant kingdom has not yet been fully clarified. In order to obtain new insights into the potential of plant serpins, this study presents the first systematic review of the topic, whose main objective was to scrutinize the published literature to increase knowledge about this superfamily. Using keywords and the eligibility criteria defined in the protocol, we selected studies from the Scopus, PubMed, and Web of Science databases. According to the eligible studies, serpins inhibit different serine and non-serine proteases from plants, animals, and pathogens, and their expression is affected by biotic and abiotic stresses. Moreover, serpins like AtSerpin1, OSP-LRS, MtSer6, AtSRP4, AtSRP5, and MtPiI4, act in resistance and are involved in stress-induced cell death in the plant. Also, the system biology analysis demonstrates that serpins are related to proteolysis control, cell regulation, pollen development, catabolism, and protein dephosphorylation. The information systematized here contributes to the design of new studies of plant serpins, especially those aimed at exploring their biotechnological potential.

Plant Beneficial Bacteria as Bioprotectants against Wheat and Barley Diseases

Wheat and barley are the main cereal crops cultivated worldwide and serve as staple food for a third of the world's population. However, due to enormous biotic stresses, the annual production has significantly reduced by 30-70%. Recently, the accelerated use of beneficial bacteria in the control of wheat and barley pathogens has gained prominence. In this review, we synthesized information about beneficial bacteria with demonstrated protection capacity against major barley and wheat pathogens including Fusarium graminearum, Zymoseptoria tritici and Pyrenophora teres. By summarizing the general insights into molecular factors involved in plant-pathogen interactions, we show to an extent, the means by which beneficial bacteria are implicated in plant defense against wheat and barley diseases. On wheat, many Bacillus strains predominantly reduced the disease incidence of F. graminearum and Z. tritici. In contrast, on barley, the efficacy of a few Pseudomonas, Bacillus and Paraburkholderia spp. has been established against P. teres. Although several modes of action were described for these strains, we have highlighted the role of Bacillus and Pseudomonas secondary metabolites in mediating direct antagonism and induced resistance against these pathogens. Furthermore, we advance a need to ascertain the mode of action of beneficial bacteria/molecules to enhance a solution-based crop protection strategy. Moreover, an apparent disjoint exists between numerous experiments that have demonstrated disease-suppressive effects and the translation of these successes to commercial products and applications. Clearly, the field of cereal disease protection leaves a lot to be explored and uncovered.

Characteristics, expression profile, and function of non-specific lipid transfer proteins of Populus trichocarpa

Plant non-specific lipid transfer proteins (nsLTPs) are involved in various physiological processes. However, the characteristics and function of LTPs in Populus trichocarpa are unclear. Here, we report the functional properties of type IV, V, and VI P. trichocarpa nsLTPs (PtLTPs). The IV, V, and VI PtLTPs clustered in the same clade shared similar gene structures and motif and distributions. Also, collinearity analysis revealed 2 and 7 gene pairs have tandem duplication and segmental duplication events, respectively. The expression patterns of type IV, V, and VI PtLTPs differed among poplar tissues. We investigated the effects of various stresses on the Potri.010G100600, Potri.010G196300, and Potri.016G104300 (type V LTPs) mRNA levels, and type V LTPs can respond to multiple stresses. Potri.008G061800 was localized to the cell wall, extracellular space, and plasma membrane. Glutathione-S-transferase-Potri.008G061800 obtained by prokaryotic expression had weakly inhibited the growth of Septotis populiperda in vitro. Taken together, our data show that type IV, V, and VI PtLTPs may be thought as novel regulators of plant stresses. They could be considered an effective genetic resource for molecular breeding in poplar.

Transcriptome Alterations of an in vitro-Selected, Moderately Resistant, Two-Row Malting Barley in Response to 3ADON, 15ADON, and NIV Chemotypes of Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum is a devastating disease of malting barley. Mycotoxins associated with contaminated grain can be transferred from malt to beer and pose a health risk to consumers. In western Canada, F. graminearum has undergone an adaptive shift from 15ADON constituency to dominance by virulent 3ADON-producers; likewise, NIV-producers have established in regions of southern United States. Lack of adapted resistance sources with adequate malting quality has promoted the use of alternative breeding methodologies, such as in vitro selection. We studied the low-deoxynivalenol characteristic of in vitro selected, two-row malting barley variety "Norman" by RNAseq in contrast to its parental line "CDC Kendall," when infected by 15ADON-, 3ADON-, and NIV-producing isolates of F. graminearum. The current study documents higher mycotoxin accumulation by 3ADON isolates, thereby representing increased threat to barley production. At 72-96-h post infection, significant alterations in transcription patterns were observed in both varieties with pronounced upregulation of the phenylpropanoid pathway and detoxification gene categories (UGT, GST, CyP450, and ABC), particularly in 3ADON treatment. Defense response was multitiered, where differential expression in "Norman" associated with antimicrobial peptides (thionin 2.1, defensing, non-specific lipid-transfer protein) and stress-related proteins, such as late embryogenesis abundant proteins, heat-shock, desiccation related, and a peroxidase (HvPrx5). Several gene targets identified in "Norman" would be useful for application of breeding varieties with reduced deoxynivalenol content.

An Arabidopsis DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 is required for resistance against various phytopathogens and tolerance to salt stress

Synchronous and timely regulation of multiple genes results in an effective defense response that decides the fate of the host when challenged with pathogens or unexpected changes in environmental conditions. One such gene, which is downregulated in response to multiple bacterial pathogens, is a putative nonspecific lipid transfer protein (nsLTP) of unknown function that we have named DISEASE RELATED NONSPECIFIC LIPID TRANSFER PROTEIN 1 (DRN1). We show that upon pathogen challenge, DRN1 is strongly downregulated, while a putative DRN1-targeting novel microRNA (miRNA) named DRN1 Regulating miRNA (DmiR) is reciprocally upregulated. Furthermore, we provide evidence that DRN1 is required for defense against bacterial and fungal pathogens as well as for normal seedling growth under salinity stress. Although nsLTP family members from different plant species are known to be a significant source of food allergens and are often associated with antimicrobial properties, our knowledge on the biological functions and regulation of this gene family is limited. Our current work not only sheds light on the mechanism of regulation but also helps in the functional characterization of DRN1, a putative nsLTP family member of hitherto unknown function.

A coupled role for CsMYB75 and CsGSTF1 in anthocyanin hyperaccumulation in purple tea

Cultivars of purple tea (Camellia sinensis) that accumulate anthocyanins in place of catechins are currently attracting global interest in their use as functional health beverages. RNA-seq of normal (LJ43) and purple Zijuan (ZJ) cultivars identified the transcription factor CsMYB75 and phi (F) class glutathione transferase CsGSTF1 as being associated with anthocyanin hyperaccumulation. Both genes mapped as a quantitative trait locus (QTL) to the purple bud leaf color (BLC) trait in F1 populations, with CsMYB75 promoting the expression of CsGSTF1 in transgenic tobacco (Nicotiana tabacum). Although CsMYB75 elevates the biosynthesis of both catechins and anthocyanins, only anthocyanins accumulate in purple tea, indicating selective downstream regulation. As glutathione transferases in other plants are known to act as transporters (ligandins) of flavonoids, directing them for vacuolar deposition, the role of CsGSTF1 in selective anthocyanin accumulation was investigated. In tea, anthocyanins accumulate in multiple vesicles, with the expression of CsGSTF1 correlated with BLC, but not with catechin content, in diverse germplasm. Complementation of the Arabidopsis tt19-8 mutant, which is unable to express the orthologous ligandin AtGSTF12, restored anthocyanin accumulation, but did not rescue the transparent testa phenotype, confirming that CsGSTF1 did not function in catechin accumulation. Consistent with a ligandin function, transient expression of CsGSTF1 in Nicotiana occurred in the nucleus, cytoplasm and membrane. Furthermore, RNA-Seq of the complemented mutants exposed to 2% sucrose as a stress treatment showed unexpected roles for anthocyanin accumulation in affecting the expression of genes involved in redox responses, phosphate homeostasis and the biogenesis of photosynthetic components, as compared with non-complemented plants.

Induced Systemic Resistance Against Citrus Canker Disease by Rhizobacteria

Citrus canker, caused by Xanthomonas citri subsp. citri, is an important citrus disease that causes significant economic losses worldwide. All commercial citrus varieties are susceptible to citrus canker. Currently, chemical control with copper based products is the main approach to control X. citri subsp. citri dispersal and plant colonization. However, extensive use of copper compounds can result in copper-resistant strains and cause adverse effects on the environment. Alternatives to chemical control involve the activation of citrus immunity to control the disease. Here, we investigated the ability of multiple rhizobacteria to induce a systemic defense response in cultivar Duncan grapefruit. Burkholderia territorii strain A63, Burkholderia metallica strain A53, and Pseudomonas geniculata strain 95 were found to effectively activate plant defense and significantly reduce symptom development in leaves challenged with X. citri subsp. citri. In the priming phase, root application of P. geniculata induced the expression of salicylic acid (SA)-signaling pathway marker genes (PR1, PR2, PR5, and salicylic acid carboxyl methyltransferase [SAM-SACM]). Gene expression analyses after X. citri subsp. citri challenge showed that root inoculation with P. geniculata strain 95 increased the relative levels of phenylalanine ammonia lyase 1 and SAM-SACM, two genes involved in the phenylpropanoid pathway as well as the biosynthesis of SA and methyl salicylate (MeSA), respectively. However, hormone analyses by UPLC-MS/MS showed no significant difference between SA in P. geniculata-treated plants and control plants at 8 days post-beneficial bacteria root inoculation. Moreover, P. geniculata root-treated plants contained higher reactive oxygen species levels in aerial tissues than control plants 8 days post-treatment application. This study demonstrates that rhizobacteria can modulate citrus immunity resulting in a systemic defense response against X. citri subsp. citri under greenhouse conditions.

Microbial Inhibition of Fusarium Pathogens and Biological Modification of Trichothecenes in Cereal Grains

Fungi of the genus Fusarium infect cereal crops during the growing season and cause head blight and other diseases. Their toxic secondary metabolites (mycotoxins) contaminate grains. Several dozen toxic compounds produced by fungal pathogens have been identified to date. Type B trichothecenes—deoxynivalenol, its acetyl derivatives and nivalenol (produced mainly by F. graminearum and F. culmorum)—are most commonly detected in cereal grains. “T-2 toxin” (produced by, among others, F. sporotrichioides) belongs to type-A trichothecenes which are more toxic than other trichothecenes. Antagonistic bacteria and fungi can affect pathogens of the genus Fusarium via different modes of action: direct (mycoparasitism or hyperparasitism), mixed-path (antibiotic secretion, production of lytic enzymes) and indirect (induction of host defense responses). Microbial modification of trichothecenes involves acetylation, deacetylation, oxidation, de-epoxidation, and epimerization, and it lowers the pathogenic potential of fungi of the genus Fusarium. Other modifing mechanisms described in the paper involve the physical adsorption of mycotoxins in bacterial cells and the conjugation of mycotoxins to glucose and other compounds in plant and fungal cells. The development of several patents supports the commercialization and wider application of microorganisms biodegrading mycotoxins in grains and, consequently, in feed additives.

RNA-Seq analysis of resistant and susceptible sub-tropical maize lines reveals a role for kauralexins in resistance to grey leaf spot disease, caused by Cercospora zeina

BACKGROUND

Cercospora zeina is a foliar pathogen responsible for maize grey leaf spot in southern Africa that negatively impacts maize production. Plants use a variety of chemical and structural mechanisms to defend themselves against invading pathogens such as C. zeina, including the production of secondary metabolites with antimicrobial properties. In maize, a variety of biotic and abiotic stressors induce the accumulation of the terpenoid phytoalexins, zealexins and kauralexins.

RESULTS

C. zeina-susceptible line displayed pervasive rectangular grey leaf spot lesions, running parallel with the leaf veins in contrast to C. zeina-resistant line that had restricted disease symptoms. Analysis of the transcriptome of both lines indicated that genes involved in primary and secondary metabolism were up-regualted, and although different pathways were prioritized in each line, production of terpenoid compounds were common to both. Targeted phytoalexin analysis revealed that C. zeina-inoculated leaves accumulated zealexins and kauralexins. The resistant line shows a propensity toward accumulation of the kauralexin B series metabolites in response to infection, which contrasts with the susceptible line that preferentially accumulates the kauralexin A series. Kauralexin accumulation was correlated to expression of the kauralexin biosynthetic gene, ZmAn2 and a candidate biosynthetic gene, ZmKSL2. We report the expression of a putative copalyl diphosphate synthase gene that is induced by C. zeina in the resistant line exclusively.

DISCUSSION

This study shows that zealexins and kauralexins, and expression of their biosynthetic genes, are induced by C. zeina in both resistant and susceptible germplasm adapted to the southern African climate. The data presented here indicates that different forms of kauralexins accumulate in the resistant and susceptible maize lines in response to C. zeina, with the accumulation of kauralexin B compounds in a resistant maize line and kauralexin A compounds accumulating in the susceptible line.

Screening of wheat endophytes as biological control agents against Fusarium head blight using two different in vitro tests

In order to find biological control agents (BCAs) for the management of Fusarium head blight (FHB), a major disease on wheat crops worldwide, 86 microorganisms isolated from inner tissues of wheat plants were discriminated for their ability to inhibit the growth of Fusarium graminearum and Fusarium culmorum by in vitro dual culture assays. A group of 22 strains appeared very effective to inhibit F. graminearum (inhibition of 30-51%) and they were also globally effective in controlling F. culmorum (inhibition of 15-53%). Further evaluation of a subselection of strains by screening on detached spikelets in vitro confirmed three species, namely Phoma glomerata, Aureobasidium proteae and Sarocladium kiliense, that have not yet been reported for their efficacy against Fusarium spp., indicating that looking for BCAs toward FHB among wheat endophytes proved to be promising. The efficacy of some strains turned out different between both in vitro screening approaches, raising the importance of finding the most appropriate screening approach for the search of BCAs. This study pointed out the interest of the test on detached wheat spikelets that provided information about a potential pathogenicity, the growth capacity and efficacy of the endophyte strains on the targeted plant, before testing them on whole plants.

Transcriptome- Assisted Label-Free Quantitative Proteomics Analysis Reveals Novel Insights into Piper nigrum-Phytophthora capsici Phytopathosystem

Black pepper (Piper nigrum L.), a tropical spice crop of global acclaim, is susceptible to Phytophthora capsici, an oomycete pathogen which causes the highly destructive foot rot disease. A systematic understanding of this phytopathosystem has not been possible owing to lack of genome or proteome information. In this study, we explain an integrated transcriptome-assisted label-free quantitative proteomics pipeline to study the basal immune components of black pepper when challenged with P. capsici. We report a global identification of 532 novel leaf proteins from black pepper, of which 518 proteins were functionally annotated using BLAST2GO tool. A label-free quantitation of the protein datasets revealed 194 proteins common to diseased and control protein datasets of which 22 proteins showed significant up-regulation and 134 showed significant down-regulation. Ninety-three proteins were identified exclusively on P. capsici infected leaf tissues and 245 were expressed only in mock (control) infected samples. In-depth analysis of our data gives novel insights into the regulatory pathways of black pepper which are compromised during the infection. Differential down-regulation was observed in a number of critical pathways like carbon fixation in photosynthetic organism, cyano-amino acid metabolism, fructose, and mannose metabolism, glutathione metabolism, and phenylpropanoid biosynthesis. The proteomics results were validated with real-time qRT-PCR analysis. We were also able to identify the complete coding sequences for all the proteins of which few selected genes were cloned and sequence characterized for further confirmation. Our study is the first report of a quantitative proteomics dataset in black pepper which provides convincing evidence on the effectiveness of a transcriptome-based label-free proteomics approach for elucidating the host response to biotic stress in a non-model spice crop like P. nigrum, for which genome information is unavailable. Our dataset will serve as a useful resource for future studies in this plant. Data are available via ProteomeXchange with identifier PXD003887.

Functional Agents to Biologically Control Deoxynivalenol Contamination in Cereal Grains

Mycotoxins, as microbial secondary metabolites, frequently contaminate cereal grains and pose a serious threat to human and animal health around the globe. Deoxynivalenol (DON), a commonly detected Fusarium mycotoxin, has drawn utmost attention due to high exposure levels and contamination frequency in the food chain. Biological control is emerging as a promising technology for the management of DON contamination. Functional biological control agents (BCAs), which include antagonistic microbes, natural fungicides derived from plants and detoxification enzymes, can be used to control DON contamination at different stages of grain production. In this review, studies regarding different biological agents for DON control in recent years are summarized for the first time. Furthermore, this article highlights the significance of BCAs for controlling DON contamination, as well as the need for more practical and efficient BCAs concerning food safety.

Genes related to antioxidant metabolism are involved in Methylobacterium mesophilicum-soybean interaction

The genus Methylobacterium is composed of pink-pigmented methylotrophic bacterial species that are widespread in natural environments, such as soils, stream water and plants. When in association with plants, this genus colonizes the host plant epiphytically and/or endophytically. This association is known to promote plant growth, induce plant systemic resistance and inhibit plant infection by phytopathogens. In the present study, we focused on evaluating the colonization of soybean seedling-roots by Methylobacterium mesophilicum strain SR1.6/6. We focused on the identification of the key genes involved in the initial step of soybean colonization by methylotrophic bacteria, which includes the plant exudate recognition and adaptation by planktonic bacteria. Visualization by scanning electron microscopy revealed that M. mesophilicum SR1.6/6 colonizes soybean roots surface effectively at 48 h after inoculation, suggesting a mechanism for root recognition and adaptation before this period. The colonization proceeds by the development of a mature biofilm on roots at 96 h after inoculation. Transcriptomic analysis of the planktonic bacteria (with plant) revealed the expression of several genes involved in membrane transport, thus confirming an initial metabolic activation of bacterial responses when in the presence of plant root exudates. Moreover, antioxidant genes were mostly expressed during the interaction with the plant exudates. Further evaluation of stress- and methylotrophic-related genes expression by qPCR showed that glutathione peroxidase and glutathione synthetase genes were up-regulated during the Methylobacterium-soybean interaction. These findings support that glutathione (GSH) is potentially a key molecule involved in cellular detoxification during plant root colonization. In addition to methylotrophic metabolism, antioxidant genes, mainly glutathione-related genes, play a key role during soybean exudate recognition and adaptation, the first step in bacterial colonization.

The 'prime-ome': towards a holistic approach to priming

Plants can be primed to respond faster and more strongly to stress and multiple pathways, specific for the encountered challenge, are involved in priming. This adaptability of priming makes it difficult to pinpoint an exact mechanism: the same phenotypic observation might be the consequence of unrelated underlying events. Recently, details of the molecular aspects of establishing a primed state and its transfer to offspring have come to light. Advances in techniques for detection and quantification of elements spanning the fields of transcriptomics, proteomics, and metabolomics, together with adequate bioinformatics tools, will soon allow us to take a holistic approach to plant defence. This review highlights the state of the art of new strategies to study defence priming in plants and provides perspectives towards 'prime-omics'.

Components of priming-induced resistance to Fusarium head blight in wheat revealed by two distinct mutants of Fusarium graminearum

Two mutants (tri6Δ and noxABΔ) of the fungal pathogen Fusarium graminearum were assessed for their ability to prime immune responses in wheat (cv. Roblin) against challenge with pathogenic F. graminearum. Priming treatments generated Fusarium head blight (FHB)-resistant wheat phenotypes and reduced the accumulation of fungal mycotoxins in infected tissues. Microarray analysis identified 260 transcripts that were differentially expressed during the priming period. Expression changes were observed in genes associated with immune surveillance systems, signalling cascades, antimicrobial compound production, oxidative burst, secondary metabolism, and detoxification and transport. Specifically, genes related to jasmonate, gibberellin and ethylene biosynthesis exhibited differential expression during priming. In addition, the induction of the phenylpropanoid pathways that lead to flavonoid, coumarin and hydroxycinnamic acid amide accumulation was also observed. This study highlights the utility of nonpathogenic mutants to both elicit and delineate stages of defence responses in wheat.

Sorghum mutant RG displays antithetic leaf shoot lignin accumulation resulting in improved stem saccharification properties

BACKGROUND

Improving saccharification efficiency in bioenergy crop species remains an important challenge. Here, we report the characterization of a Sorghum (Sorghum bicolor L.) mutant, named REDforGREEN (RG), as a bioenergy feedstock.

RESULTS

It was found that RG displayed increased accumulation of lignin in leaves and depletion in the stems, antithetic to the trend observed in wild type. Consistent with these measurements, the RG leaf tissue displayed reduced saccharification efficiency whereas the stem saccharification efficiency increased relative to wild type. Reduced lignin was linked to improved saccharification in RG stems, but a chemical shift to greater S:G ratios in RG stem lignin was also observed. Similarities in cellulose content and structure by XRD-analysis support the correlation between increased saccharification properties and reduced lignin instead of changes in the cellulose composition and/or structure.

CONCLUSION

Antithetic lignin accumulation was observed in the RG mutant leaf-and stem-tissue, which resulted in greater saccharification efficiency in the RG stem and differential thermochemical product yield in high lignin leaves. Thus, the red leaf coloration of the RG mutant represents a potential marker for improved conversion of stem cellulose to fermentable sugars in the C4 grass Sorghum.

On the move: induced resistance in monocots

Although plants possess an arsenal of constitutive defences such as structural barriers and preformed antimicrobial defences, many attackers are able to overcome the pre-existing defence layers. In response, a range of inducible plant defences is set up to battle these pathogens. These mechanisms, commonly integrated as induced resistance (IR), control pathogens and pests by the activation of specific defence pathways. IR mechanisms have been extensively studied in the Dicotyledoneae, whereas knowledge of IR in monocotyledonous plants, including the globally important graminaceous crop plants, is elusive. Considering the potential of IR for sustainable agriculture and the recent advances in monocot genomics and biotechnology, IR in monocots is an emerging research field. In the following, current facts and trends concerning basal immunity, and systemic acquired/induced systemic resistance in the defence of monocots against pathogens and herbivores will be summarized.

Auxin as a player in the biocontrol of Fusarium head blight disease of barley and its potential as a disease control agent

BACKGROUND

Mechanisms involved in the biological control of plant diseases are varied and complex. Hormones, including the auxin indole acetic acid (IAA) and abscisic acid (ABA), are essential regulators of a multitude of biological functions, including plant responses to biotic and abiotic stressors. This study set out to determine what hormones might play a role in Pseudomonas fluorescens -mediated control of Fusarium head blight (FHB) disease of barley and to determine if biocontrol-associated hormones directly affect disease development.

RESULTS

A previous study distinguished bacterium-responsive genes from bacterium-primed genes, distinguished by the fact that the latter are only up-regulated when both P. fluorescens and the pathogen Fusarium culmorum are present. In silico analysis of the promoter sequences available for a subset of the bacterium-primed genes identified several hormones, including IAA and ABA as potential regulators of transcription. Treatment with the bacterium or pathogen resulted in increased IAA and ABA levels in head tissue; both microbes had additive effects on the accumulation of IAA but not of ABA. The microbe-induced accumulation of ABA preceded that of IAA. Gene expression analysis showed that both hormones up-regulated the accumulation of bacterium-primed genes. But IAA, more than ABA up-regulated the transcription of the ABA biosynthesis gene NCED or the signalling gene Pi2, both of which were previously shown to be bacterium-responsive rather than primed. Application of IAA, but not of ABA reduced both disease severity and yield loss caused by F. culmorum, but neither hormone affect in vitro fungal growth.

CONCLUSIONS

Both IAA and ABA are involved in the P. fluorescens-mediated control of FHB disease of barley. Gene expression studies also support the hypothesis that IAA plays a role in the primed response to F. culmorum. This hypothesis was validated by the fact that pre-application of IAA reduced both symptoms and yield loss asssociated with the disease. This is the first evidence that IAA plays a role in the control of FHB disease and in the bacterial priming of host defences.

On the trail of a cereal killer: recent advances in Fusarium graminearum pathogenomics and host resistance

The ascomycete fungal pathogen Fusarium graminearum (sexual stage: Gibberella zeae) causes the devastating head blight or scab disease on wheat and barley, and cob or ear rot disease on maize. Fusarium graminearum infection causes significant crop and quality losses. In addition to roles as virulence factors during pathogenesis, trichothecene mycotoxins (e.g. deoxynivalenol) produced by this pathogen constitute a significant threat to human and animal health if consumed in respective food or feed products. In the last few years, significant progress has been made towards a better understanding of the processes involved in F. graminearum pathogenesis, toxin biosynthesis and host resistance mechanisms through the use of high-throughput genomic and phenomic technologies. In this article, we briefly review these new advances and also discuss how future research can contribute to the development of sustainable plant protection strategies against this important plant pathogen.