Omics for understanding synergistic action of validamycin A and Trichoderma asperellum GDFS1009 against maize sheath blight pathogen

Bioinspired total synthesis and biological activity of Pegaharine A

BACKGROUND

Phytopathogens cause various diseases by parasitizing crops, reducing crop yield and resulting in substantial economic losses in agricultural production. A novel type isolated from the perennial herbaceous Peganum harmala L. seeds, β-carboline alkaloids pegaharine A (PA), has become a hot topic in developing plant-originated green pesticides owing to their significant physiological activities.

RESULTS

A scalable bioinspired total synthesis of PA is accomplished in the present work. The systematical biological assay study showed that PA exhibited moderate inhibitory activity against nine tested plant pathogenic fungi and showed significant inhibitory activity in vitro against the three tested plant pathogenic bacteria. Most noteworthy is the inhibitory rates of PA on Xanthomonas oryzae pv. oryzae (Xoo), X. oryzae pv. oryzicola (Xoc) and X. axonopodis pv. citri (Xac) of 93.6%, 92.1% and 86.1%, respectively, which are better than the control drug, bismerthiazol (63.4%, 61.2% and 53.7% at 100 μg mL-1 concentration). Furthermore, the EC50 value of PA against Xoo, Xoc and Xac was 52.2, 60.0 and 65.1 μg mL-1 , respectively, superior to 72.9, 64.2 and 70.1 μg mL-1 of the control drug. Moreover, the anti-Xoo mechanistic studies revealed that PA exerted its antibacterial effects by increasing the permeability of the bacterial membrane, reducing the extracellular polysaccharide content and inducing morphological changes in bacterial cells.

CONCLUSION

A novel β-carboline alkaloid, PA, was prepared by biomimetic total synthesis. Its significant antibacterial activity was closely related to the permeation of bacterial cell membranes, which was confirmed by anti-Xoo mechanistic studies. More importantly, the structure could be regarded as a model for developing novel bactericides. © 2023 Society of Chemical Industry.

Utilizing Two Populations Derived from Tropical Maize for Genome-Wide Association Analysis of Banded Leaf and Sheath Blight Resistance

Banded leaf and sheath blight (BLSB) in maize is a soil-borne fungal disease caused by Rhizoctonia solani Kühn, resulting in significant yield losses. Investigating the genes responsible for regulating resistance to BLSB is crucial for yield enhancement. In this study, a multiparent maize population was developed, comprising two recombinant inbred line (RIL) populations totaling 442 F8RILs. The populations were generated by crossing two tropical inbred lines, CML444 and NK40-1, known for their BLSB resistance, as female parents, with the high-yielding but BLSB-susceptible inbred line Ye107 serving as the common male parent. Subsequently, we utilized 562,212 high-quality single nucleotide polymorphisms (SNPs) generated through genotyping-by-sequencing (GBS) for a comprehensive genome-wide association study (GWAS) aimed at identifying genes responsible for BLSB resistance. The objectives of this study were to (1) identify SNPs associated with BLSB resistance through genome-wide association analyses, (2) explore candidate genes regulating BLSB resistance in maize, and (3) investigate pathways involved in BLSB resistance and discover key candidate genes through Gene Ontology (GO) analysis. The GWAS analysis revealed nineteen SNPs significantly associated with BLSB that were consistently identified across four environments in the GWAS, with phenotypic variation explained (PVE) ranging from 2.48% to 11.71%. Screening a 40 kb region upstream and downstream of the significant SNPs revealed several potential candidate genes. By integrating information from maize GDB and the NCBI, we identified five novel candidate genes, namely, Zm00001d009723, Zm00001d009975, Zm00001d009566, Zm00001d009567, located on chromosome 8, and Zm00001d026376, on chromosome 10, related to BLSB resistance. These candidate genes exhibit association with various aspects, including maize cell membrane proteins and cell immune proteins, as well as connections to cell metabolism, transport, transcriptional regulation, and structural proteins. These proteins and biochemical processes play crucial roles in maize defense against BLSB. When Rhizoctonia solani invades maize plants, it induces the expression of genes encoding specific proteins and regulates corresponding metabolic pathways to thwart the invasion of this fungus. The present study significantly contributes to our understanding of the genetic basis of BLSB resistance in maize, offering valuable insights into novel candidate genes that could be instrumental in future breeding efforts to develop maize varieties with enhanced BLSB resistance.

Streptomyces Strains and Their Metabolites for Biocontrol of Phytopathogens in Agriculture

Sustainable agriculture is increasingly linked to biological pesticides as alternatives to agro-chemicals. Streptomyces species suppress plant diseases through their unique traits and numerous metabolites. Although many Streptomyces strains have been developed into commercial products, their roles in the biocontrol of phytopathogens and mechanisms of functional metabolite synthesis remain poorly understood. In this review, biocontrol of plant diseases by Streptomyces is summarized on the basis of classification of fungal and bacterial diseases and secondary metabolites produced by Streptomyces that act on phytopathogenic microorganisms are discussed. The associated non-ribosomal peptide synthetases and polyketide synthetases responsible for biosynthesis of these secondary metabolites are also investigated, and advances in fermentation of Streptomyces are described. Finally, the need to develop precise and effective biocontrol methods for plant diseases is highlighted.

The Endophyte Trichoderma asperellum M2RT4 Induces the Systemic Release of Methyl Salicylate and (Z)-jasmone in Tomato Plant Affecting Host Location and Herbivory of Tuta absoluta

The use of endophytic fungi has dramatically increased plant performance through the enhancement of plant protection against abiotic and biotic stressors. We previously demonstrated that the endophytic fungus Trichoderma asperellum M2RT4 improves tomato defenses against the tomato leafminer Tuta absoluta through the reduction of oviposition, leafmining, pupation, and adult emergence. However, the underlying mechanism by which the presence of this endophytic fungus within tomato host plant affects T. absoluta host selection and life-history traits is unknown. We tested the behavioral responses of T. absoluta in Y-tube olfactometer bioassays and found that females preferred non-inoculated tomato plants against those inoculated by endophytes. Additionally, T. absoluta females were not attracted to non-inoculated infested nor to inoculated-infested tomato plants. Chemical analysis revealed the emission of methyl salicylate in inoculated tomato plant and an increase in the amounts of monoterpenes emitted from non-inoculated infested plants. Additionally, we found that upon herbivory, T. asperellum M2RT4 modulates tomato plant chemistry through the production of (Z)-jasmone thus activating both salicylic and jasmonic acid defense pathways. Further, T. absoluta females were attracted to monoterpernes including α-pinene, 2-carene, and β-phellandrene but repelled by methyl salicylate. Methyl salicylate could therefore be considered as a good semiochemical-based candidate for sustainable T. absoluta management using a "push-pull" approach. However, in dose-response bioassays, females of T. absoluta did not show any preference to the four component-blend (α-pinene, 2-carene, β-phellandrene, and methyl salicylate). (Z)-jasmone-treated tomato leaflets significantly reduced the leafmining activity of the pest at the concentration of 10 ng/μL and causing the highest larval mortality rate (83%) with the shortest LT₅₀ (1.73 days) 7 days post-treatment. T. asperellum M2RT4 effect on herbivore performance was then (Z)-jasmone-mediated. These findings expand our understanding of how the endophytic fungus T. asperellum M2RT4 could mediate chemical interactions between T. absoluta and its host plant which are potentially important for development of environmentally friendly T. absoluta management programs.

Role of cytochrome P450 genes of Trichoderma atroviride T23 on the resistance and degradation of dichlorvos

The Trichoderma has been extensively used to degrade the xenobiotics. In the present study, thirty-nine open reading frames of cytochrome P450 genes from T. atroviride T23 genome was cloned and it was found to be distributed in 29 families under 21 clades. Among them, 21 cytochrome P450 genes were involved in the degradation of xenobiotics. The quantitative expression of P450 genes in the presence of dichlorvos at 24 h showed 7 different expression patterns in the presence of 100 μg/mL, 300 μg/mL, 500 μg/mL and 1000 μg/mL of dichlorvos. The relative expression of P450 genes belongs to the family of TaCyp548, TaCyp620, TaCyp52, TaCyp528, TaCyp504 were upregulated at least 1-fold compared to the control. Significantly, the deletion of TaCyp548-2 reduced the concentration of 2,2-dichloroethanol. Further, it was observed that TaCyp548-2 belongs to the ω-hydroxylase family was responsible for fatty acid oxidation and the production of acetic acid, propionic acid, isobutyric acid and dibutyric acid to convert the 2,2-dichloroethanol to 2,2-dichloroethanolacetate. This study evidenced the involvement of Trichoderma P450 genes on dichlorvos degradation as an environmentally significant Biological control agent for the sustainable agriculture.

Mining of the Catharanthus roseus Genome Leads to Identification of a Biosynthetic Gene Cluster for Fungicidal Sesquiterpenes

Characterization of cryptic biosynthetic gene clusters (BGCs) from microbial genomes has been proven to be a powerful approach to the discovery of new natural products. However, such a genome mining approach to the discovery of bioactive plant metabolites has been muted. The plant BGCs characterized to date encode pathways for antibiotics important in plant defense against microbial pathogens, providing a means to discover such phytoalexins by mining plant genomes. Here is reported the discovery and characterization of a minimal BGC from the medicinal plant Catharanthus roseus, consisting of an adjacent pair of genes encoding a terpene synthase (CrTPS18) and cytochrome P450 (CYP71D349). These two enzymes act sequentially, with CrTPS18 acting as a sesquiterpene synthase, producing 5-epi-jinkoheremol (1), which CYP71D349 further hydroxylates to debneyol (2). Infection studies with maize revealed that 1 and 2 exhibit more potent fungicidal activity than validamycin. Accordingly, this study demonstrates that characterization of such cryptic plant BGCs is a promising strategy for the discovery of potential agrochemical leads. Moreover, despite the observed absence of 1 and 2 in C. roseus, the observed transcriptional regulation is consistent with their differential fungicidal activity, suggesting that such conditional coexpression may be sufficient to drive BGC assembly in plants.

Heterokaryotic state of a point mutation (H249Y) in SDHB protein drives the evolution of thifluzamide resistance in Rhizoctonia solani

BACKGROUND

Sheath blight, caused by Rhizoctonia solani, can be effectively controlled by application of the succinate dehydrogenase inhibitor thifluzamide. Although the risk of resistance to thifluzamide in R. solani had been reported, the thifluzamide-resistance mechanism and the evolution of thifluzamide-resistance in R. solani have not been investigated in detail.

RESULTS

No differences were found between the sequences of proteins SDHA, SDHC, and SDHD in thifluzamide-sensitive isolates and thifluzamide-resistant mutants, but a single point mutation H249Y was found in SDHB. Two different types of thifluzamide-resistant R. solani mutants were characterized: homokaryotic, carrying only the resistance allele; and heterokaryotic, retaining the wild-type allele in addition to the resistance allele. The resistance level differed according to the nuclear composition at codon 249 in the sdhB gene. Molecular docking results suggested that the point mutation (H249Y) might significantly alter the affinity of thifluzamide and SDHB protein. Heterokaryotic mutants were able to evolve into a homokaryon when repeatedly cultured on agar media or rice plants in the presence of thifluzamide, but thifluzamide treatment had no effect on the genotypes of homokaryotic mutants or sensitive isolates.

CONCLUSION

This study showed that H249Y in SDHB protein could cause thifluzamide resistance in R. solani. Fungicide application could promote heterokaryotic mutants to evolve into a homokaryon. © 2020 Society of Chemical Industry.

Biocontrol and growth-promoting effect of Trichoderma asperellum TaspHu1 isolate from Juglans mandshurica rhizosphere soil

To better apply the biocontrol agent Trichoderma spp. in Northeast China, collecting and screening more suitable native Trichoderma strains is necessary. In the present study, 10 isolates were obtained from Juglans mandshurica rhizosphere soils in Heilongjiang Province, and were identified as T. asperellum (four isolates), T. harzianum (four), T. hamatum (one), T. atroviride (one). The fastest-growing isolate per species on potato dextrose agar medium were further evaluated in stress tolerance tests (salt, alkali, nutritional stress, and low temperature) and confrontation assays (eight pathogens), which showed that T. asperellum TaspHu1 possessed the best adaptation and biological control ability. Then, Solanum lycopersicum (tomato) seeds were sown and treated with a series of concentrations of TaspHu1 spore suspension, as was unsown soil. Tomato seedlings treated by TaspHu1 had a significantly greater height, stem diameter, soluble protein content and soluble sugar content. Furthermore, their nitrate reductase activity and catalase activity were significantly increased, and these promoting effects depended on the concentration of the spore suspension. Meanwhile, a decrease in chlorophyll content was observed in the tomato seedlings treated with TaspHu1. In addition, strain TaspHu1 enhanced the tomato seedlings' absorption of available nitrogen, but did not influence the soil available nitrogen content. Furthermore, the resistance of tomato seedlings against Alternaria alternata was enhanced by TaspHu1 (smaller, fewer leaf spots), the seedlings' hormone signal transduction genes JAR1, MYC2, NPR1, PR1, and GH3.2 were highly expressed. Thus, TaspHu1 is a promising biocontrol candidate for use in agriculture and forestry.

ROS-Responsive Polymeric Micelle for Improving Pesticides Efficiency and Intelligent Release

The low utilization rate of pesticides causes serious problems such as food safety and environmental pollution. Stimulus-responsive release can effectively improve the utilization rate of pesticides. Reactive oxygen species (ROS) burst, as an early event of plant-pathogen interaction, can stimulate the release of pesticides. In this work, a polymeric micelle with ROS-responsive was prepared and then Validamycin (Vail) was loaded into polymeric micelle to prepare Vail-loaded polymeric micelle. The Vail-loaded polymeric micelle displayed excellent ROS-dependent release kinetics. In vitro and in vivo antifungal experiments confirmed that the Vail-loaded polymeric micelle could improve antifungal efficacy against Rhizoctonia solani than with the Vail reagent. Therefore, as a biostimulation and controlled release system, ROS-responsive polymeric micelles can improve the utilization rate of pesticides and alleviate the problem of food safety and environmental pollution.

The Inhibitory Effect of Validamycin A on Aspergillus flavus

Aspergillus flavus is one of the most common isolates from patients with fungal infections. Aspergillus infection is usually treated with antifungal agents, but side effects of these agents are common. Trehalase is an essential enzyme involved in fungal metabolism, and the trehalase inhibitor, validamycin A, has been used to prevent fungal infections in agricultural products. In this study, we observed that validamycin A significantly increased trehalose levels in A. flavus conidia and delayed germination, including decreased fungal adherence. In addition, validamycin A and amphotericin B showed a combinatorial effect on A. flavus ATCC204304 and clinical isolates with high minimum inhibitory concentrations (MICs) of amphotericin B using checkerboard assays. We observed that validamycin A and amphotericin B had a synergistic effect on A. flavus strains resistant to amphotericin B. The MICs in the combination of validamycin A and amphotericin B were at 0.125 μg/mL and 2 μg/mL, respectively. The FICI of validamycin A and amphotericin B of these clinical isolates was about 0.25-0.28 with synergistic effects. No drug cytotoxicity was observed in human bronchial epithelial cells treated with validamycin A using LDH-cytotoxicity assays. In conclusion, this study demonstrated that validamycin A inhibited the growth of A. flavus and delayed conidial germination. Furthermore, the combined effect of validamycin A with amphotericin B increased A. flavus killing, without significant cytotoxicity to human bronchial epithelial cells. We propose that validamycin A could potentially be used in vivo as an alternative treatment for A. flavus infections.

Proteomic analysis of the processes leading to Madurella mycetomatis grain formation in Galleria mellonella larvae

Mycetoma is a neglected chronic and granulomatous infection primarily associated with the fungal pathogen Madurella mycetomatis. Characteristic of this infection is the formation of grains. However, the processes leading to grain formation are not known. In this study, we employed a proteomic approach to characterise M. mycetomatis grain formation in Galleria mellonella larvae and map the processes leading to grain formation over time. For this, at 1 day, 3 days and 7 days post-inoculation, proteins from grains and hemolymph were extracted and analysed by label-free mass spectrometry. A total of 87, 51 and 48 M. mycetomatis proteins and 713, 997, 18 G. mellonella proteins were found in grains on day 1, 3 and 7 post-inoculation respectively. M. mycetomatis proteins were mainly involved in cellular metabolic processes and numerous enzymes were encountered. G. mellonella proteins were primarily involved in the nodulation process. The proteins identified were linked to nodulation and grain formation and four steps of grain formation were identified. The results of this proteomic approach could in the future be used to design novel strategies to interfere with mycetoma grain formation and to combat this difficult to treat infection.

Although grain formation is the hallmark of mycetoma, so far the pathways leading to grain formation were not studied. Since our hypothesis is that both host and pathogen play a role in this process, we aimed to study this process in a model system. Grains can be formed in the invertebrate Galleria mellonella and different stages of grain formation can be noted within the larvae. We therefore infected G. mellonella with the mycetoma causative agent Madurella mycetomatis, and monitored grain formation over time. At day 1, day 3 and day 7 post-inoculation, grains and hemolymph were obtained from infected larvae. Proteins were isolated and identified by label-free mass spectrometry. By analyzing the proteins found in both host and pathogen on the different time points, we were able to develop a grain model over time. This grain model can in the future be used to identify novel treatments for this difficult to treat infection.

Seed Biopriming with Microbial Inoculant Triggers Local and Systemic Defense Responses against Rhizoctonia solani Causing Banded Leaf and Sheath Blight in Maize (Zea mays L.)

Plant growth promoting rhizobacteria Pseudomonas aeruginosa strain MF-30 isolated from maize rhizosphere was characterized for several plant growth stimulating attributes. The strain MF-30 was also evaluated for antifungal properties against Rhizoctonia solani causing banded leaf and sheath blight in maize (Zea mays L.) under in vitro conditions and was found to have higher mycelial growth suppression in the culture suspension (67.41%) followed by volatile organic compounds (62.66%) and crude extract (51.20%) in a dual plate assay. The endophytic and epiphytic colonization ability was tested using Green Fluorescent Protein (GFP)-tagging. Visualization through confocal scanning laser microscope clearly indicated that strain MF-30 colonizes the root and foliar parts of the plants. Further, the effects of seed bio-priming with P. aeruginosa MF-30 was evaluated in the induction and bioaccumulation of defense-related biomolecules, enzymes, natural antioxidants, and other changes in maize under pot trial. This not only provided protection from R. solani but also ensured growth promotion under pathogenic stress conditions in maize. The maximum concentration of hydrogen peroxide (H2O2) was reported in the root and shoot of the plants treated with R. solani alone (8.47 and 17.50 mmol mg-1 protein, respectively) compared to bioagent, P. aeruginosa MF-30 bio-primed plants (3.49 and 7.50 mmol mg-1 protein, respectively). Effects on total soluble sugar content, total protein, and total proline were also found to enhanced significantly due to inoculation of P. aeruginosa MF-30. The activities of anti-oxidative defense enzymes phenylalanine ammonia lyase (PAL), ascorbate peroxidase, peroxidase, superoxide dismutase, and catalase increased significantly in the plants bio-primed with P. aeruginosa MF-30 and subsequent foliar spray of culture suspension of MF-30 compared to pathogen alone inoculated plants. qRT-PCR analysis revealed that seed bio-priming and foliar application of P. aeruginosa MF-30 significantly increased the expression of PR-1 and PR-10 genes with the simultaneous decrease in the disease severity and lesion length in the maize plants under pathogenic stress conditions. A significant enhancement of shoot and root biomass was recorded in MF-30 bio-primed plants as compared to untreated control (p < 0.05). Significant increase in plant growth and antioxidant content, as well as decreased disease severity in the P. aeruginosa MF-30 bio-primed plants, suggested the possibility of an eco-friendly and economical means of achieving antioxidants-rich, healthier maize plants.

Molecular tagging of biocontrol fungus Trichoderma asperellum and its colonization in soil

AIMS

To conduct molecular tagging of the biocontrol fungus Trichoderma asperellum strain T₄ and elucidate its colonization patterns in soil.

METHODS AND RESULTS

We constructed an expression vector harbouring a hygromycin B-resistant gene (hph) and an efficient green fluorescent protein (egfp) gene. By applying Agrobacterium AGL-1-mediated genetic transformation technology, we conducted molecular tagging of T. asperellum and monitored the colonization dynamics of T. asperellum in soil. The results of tracking five independent transformants of T. asperellum indicated that its expansion rates ranged from 4·7 to 6·8 cm week^-1 . After inoculation in soil, the quantities of T. asperellum could be maintained at over 10 × 10⁴  CFU per gram soil in the first year. In the third year after inoculation, the quantities of T. asperellum in soil were still higher than 1 × 10³  CFU per gram soil. In addition, molecularly tagged T. asperellum in soil in the second year (i.e. 12 months) after inoculation could still reach the biocontrol effect on cucumber Rhizoctonia rot by more than 74%.

CONCLUSION

Trichoderma asperellum strain T₄ is capable of effectively colonizing in soil and surviving for more than 1 year.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has provided the scientific basis for applying T. asperellum as the biocontrol fungus for prevention and control of plant diseases.

Co-cultivation of Trichoderma asperellum GDFS1009 and Bacillus amyloliquefaciens 1841 Causes Differential Gene Expression and Improvement in the Wheat Growth and Biocontrol Activity

In an effort to balance the demands of plant growth promoting and biological control agents in a single product, the technology on the co-cultivation of two microbes, Trichoderma asperellum GDFS1009 and Bacillus amyloliquefaciens 1841 has been developed and demonstrated its effectiveness in synergistic interactions and its impact on the plant growth and biocontrol potential. In this study, optimization of T. asperellum and B. amyloliquefaciens growth in a single medium was carried out using response surface methodology (RSM). The optimal medium for enhanced growth was estimated as 2% yeast extract, 2% molasses and 2% corn gluten meal. T. asperellum evolved the complicated molecular mechanisms in the co-culture by the induction of BLR-1/BLR-2, VELVET, and NADPH oxidases genes. In performance with these genes, conserved signaling pathways, such as heterotrimeric G proteins and mitogen-activated protein kinases (MAPKs) had also involved in this molecular orchestration. The co-cultivation induced the expression of T. asperellum genes related to secondary metabolism, mycoparasitism, antioxidants and plant growth. On the other hand, the competition during co-cultivation induced the production of new compounds that are not detected in axenic cultures. In addition, the co-culture significantly enhanced the plant growth and protection against Fusarium graminearum. The present study demonstrated the potential of co-cultivation technology could be a used to grow the T. asperellum GDFS1009 and B. amyloliquefaciens 1841 synergistically to improve the production of mycoparasitism related enzymes, secondary metabolites, and plant growth promoting compounds to significantly enhance the plant growth and protection against plant pathogens.

Analysis of metabolic changes in Trichoderma asperellum TJ01 at different fermentation time-points by LC-QQQ-MS

Trichoderma spp. are among the most widely recognized biocontrol fungi used to inhibit pathogens and promote plant growth. These functions are related to primary and secondary metabolites. This study investigated the different metabolites in Trichoderma asperellum TJ01 cultured for 24 and 72 h using liquid chromatography with triple-quadrupole mass spectrometry. Compared to the 24 h culture of T. asperellum TJ01, the 72 h culture with amino acid metabolism tended to decrease while sugar and lipid metabolisms tended to increase. Furthermore, the 72 h culture had a higher proportion of upregulated flavonoids, in combination with a higher proportion of downregulated alkaloids, and equal proportions of upregulated and downregulated polyphenols and hormones. This study also identified a few valuable medicinal substances such as trigonelline and 5-hydroxytryptophan in T. asperellum TJ01 fermentation cultures.

Mechanistic insights into enzymatic catalysis by trehalase from the insect gut endosymbiont Enterobacter cloacae

Energy metabolism in the diamondback moth Plutella xylostella is facilitated by trehalase, an enzyme which assists in trehalose hydrolysis, from the predominant gut bacterium Enterobacter cloacae. We report the biochemical and structural characterization of recombinant trehalase from E. cloacae (Px_EclTre). Px_EclTre showed K_M of 1.47 (±0.05) mm, k_cat of 6254.72 min^-1 and V_max 0.2 (±0.002) mm·min^-1 at 55 °C and acidic pH. Crystal structures of Px_EclTre were determined in the ligand-free form and bound to the inhibitor Validoxylamine A. The crystal structure of the ligand-free form, unavailable until now for any other bacterial trehalases, enabled us to delineate the conformational changes accompanying ligand binding in trehalases. Multiple salt bridges were identified that potentially facilitated closure of a hood over the substrate-binding site. A cluster of five tryptophans lined the -1 substrate-binding subsite, interacted with crucial active site residues and contributed to both trehalase activity and stability. The importance of these residues in enzyme activity was further validated by mutagenesis studies. Many of these identified residues form part of signature motifs and other conserved sequences in trehalases. The structure analysis thus led to the assignment of the functional role to these conserved residues. This information can be further explored for the design of effective inhibitors against trehalases.

Pyramiding of nine transgenes in maize generates high-level resistance against necrotrophic maize pathogens

Key message Nine transgenes from different categories, viz. plant defense response genes and anti-apoptosis genes, played combined roles in maize to inhibit the necrotrophic pathogens Rhizoctonia solani and Bipolaris maydis. Maize sheath blight and southern corn leaf blight are major global threats to maize production. The management of these necrotrophic pathogens has encountered limited success due to the characteristics of their lifestyle. Here, we presented a transgenic pyramiding breeding strategy to achieve nine different resistance genes integrated in one transgenic maize line to combat different aspects of necrotrophic pathogens. These nine genes, selected from two different categories, plant defense response genes (Chi, Glu, Ace-AMP1, Tlp, Rs-AFP2, ZmPROPEP1 and Pti4), and anti-apoptosis genes (Iap and p35), were successfully transferred into maize and further implicated in resistance against the necrotrophic pathogens Rhizoctonia solani and Bipolaris maydis. Furthermore, the transgenic maize line 910, with high expression levels of the nine integrated genes, was selected from 49 lines. Under greenhouse and field trial conditions, line 910 showed significant resistance against maize sheath blight and southern corn leaf blight diseases. Higher-level resistance was obtained after the pyramiding of more resistance transgenes from different categories that function via different mechanisms. The present study provides a successful strategy for the management of necrotrophic pathogens.

Pyramiding of nine transgenes in maize generates high-level resistance against necrotrophic maize pathogens

Key message Nine transgenes from different categories, viz. plant defense response genes and anti-apoptosis genes, played combined roles in maize to inhibit the necrotrophic pathogens Rhizoctonia solani and Bipolaris maydis. Maize sheath blight and southern corn leaf blight are major global threats to maize production. The management of these necrotrophic pathogens has encountered limited success due to the characteristics of their lifestyle. Here, we presented a transgenic pyramiding breeding strategy to achieve nine different resistance genes integrated in one transgenic maize line to combat different aspects of necrotrophic pathogens. These nine genes, selected from two different categories, plant defense response genes (Chi, Glu, Ace-AMP1, Tlp, Rs-AFP2, ZmPROPEP1 and Pti4), and anti-apoptosis genes (Iap and p35), were successfully transferred into maize and further implicated in resistance against the necrotrophic pathogens Rhizoctonia solani and Bipolaris maydis. Furthermore, the transgenic maize line 910, with high expression levels of the nine integrated genes, was selected from 49 lines. Under greenhouse and field trial conditions, line 910 showed significant resistance against maize sheath blight and southern corn leaf blight diseases. Higher-level resistance was obtained after the pyramiding of more resistance transgenes from different categories that function via different mechanisms. The present study provides a successful strategy for the management of necrotrophic pathogens.

Omics for understanding the tolerant mechanism of Trichoderma asperellum TJ01 to organophosphorus pesticide dichlorvos

BACKGROUD

Though it is toxic to humans, dichlorvos is a widely used chemical pesticide and plays an important role in the control of plant pests. The application of a combination of the biocontrol agent Trichoderma with dichlorvos may reduce the need for chemical pesticides. Therefore, revealing the specific molecular mechanism of Trichoderma tolerance to dichlorvos has become particularly important.

RESULTS

In this study, using transcriptome and metabolome analyses, changes in primary and secondary metabolisms in Trichoderma asperellum TJ01 were comprehensively studied in the presence of dichlorvos. A novel C₂H₂ zinc finger protein gene, zinc finger chimera 1 (zfc1), was discovered to be upregulated, along with a large number of oxidoreductase genes and ABC transporter genes under dichlorvos stress. In addition, gas chromatography-mass spectrometry (GC-TOF-MS), and liquid chromatography-mass spectrometry (LC-QQQ-MS) data revealed the global primary and secondary metabolic changes that occur in T. asperellum TJ01 under dichlorvos stress.

CONCLUSIONS

The tolerance mechanism of T. asperellum TJ01 to dichlorvos was proposed. In addition, the absorption and residue of dichlorvos were analyzed, laying the foundation for elucidation of the mechanism by which T. asperellum TJ01 degrades pesticide residues.

Metabolome- and genome-scale model analyses for engineering of Aureobasidium pullulans to enhance polymalic acid and malic acid production from sugarcane molasses

BACKGROUND

Polymalic acid (PMA) is a water-soluble biopolymer with many attractive properties for food and pharmaceutical applications mainly produced by the yeast-like fungus Aureobasidium pullulans. Acid hydrolysis of PMA, resulting in release of the monomer l-malic acid (MA), which is widely used in the food and chemical industry, is a competitive process for producing bio-based platform chemicals.

RESULTS

In this study, the production of PMA and MA from sucrose and sugarcane molasses by A. pullulans was studied in shake flasks and bioreactors. Comparative metabolome analysis of sucrose- and glucose-based fermentation identified 81 intracellular metabolites and demonstrated that pyruvate from the glycolysis pathway may be a key metabolite affecting PMA synthesis. In silico simulation of a genome-scale metabolic model (iZX637) further verified that pyruvate carboxylase (pyc) via the reductive tricarboxylic acid cycle strengthened carbon flux for PMA synthesis. Therefore, an engineered strain, FJ-PYC, was constructed by overexpressing the pyc gene, which increased the PMA titer by 15.1% compared with that from the wild-type strain in a 5-L stirred-tank fermentor. Sugarcane molasses can be used as an economical substrate without any pretreatment or nutrient supplementation. Using fed-batch fermentation of FJ-PYC, we obtained the highest PMA titers (81.5, 94.2 g/L of MA after hydrolysis) in 140 h with a corresponding MA yield of 0.62 g/g and productivity of 0.67 g/L h.

CONCLUSIONS

We showed that integrated metabolome- and genome-scale model analyses were an effective approach for engineering the metabolic node for PMA synthesis, and also developed an economical and green process for PMA and MA production from renewable biomass feedstocks.