Overexpression of the chitinase gene CmCH1 from Coniothyrium minitans renders enhanced resistance to Sclerotinia sclerotiorum in soybean

Expression of endochitinase and exochitinase in lettuce chloroplasts increases plant biomass and kills fungal pathogen Candida albicans

Lettuce (Lactuca sativa) is a popular leafy vegetable with global production of ~28 million Mt, cultivated >1 million hectares, with a market value of US$ 4 billion in 2022. However, lettuce is highly susceptible to fungal pathogens that drastically reduce biomass and quality due to spoilage/rot. Therefore, in this study, we investigated the expression of chitinase genes via the lettuce chloroplast genome to enhance biomass and disease resistance. Site-specific integration of the expression cassette into chloroplast genomes was confirmed using two sets of PCR primers. Homoplasmy in transplastomic lines was confirmed in Southern blots by the absence of untransformed genomes. Maternal inheritance of transgenes was confirmed by the lack of segregation when seedlings were germinated in the selection medium. Chitinases expressed in chloroplasts are active in a broad range of pH (5-9) and temperatures (20-50 °C). Exochitinase expression significantly increased the number of leaves, root or shoot length and biomass throughout the growth cycle. Endochitinase expression reduced root/shoot biomass at early stages but recovered in older plants. Plant extracts expressing endochitinase/exochitinase showed activities as high as purified commercial enzymes. Antifungal activity in Candida albicans cultures inhibited growth up to 87%. A novel Carbotrace 680™ Optotracer binding to the ß-1,4 linkages of chitin, evaluated for the first time in plant systems, is highly sensitive to measure chitinase activity. To the best of our knowledge, this is the first report of chitinase expression via the chloroplast genomes of an edible plant, to confer desired agronomic traits or for biomedical applications.

The function and regulatory network of sugarcane chitinase gene ScChiIV1 in response to pathogen stress

Plant chitinase is a pathogenesis-related protein that can hydrolyze chitin, the main component of fungal cell walls, and plays an important role in plant disease defense responses. Our previous study found the sugarcane class IV chitinase gene ScChiIV1 (GenBank Accession No. KP165001) was responding positively to smut pathogen Sporisorium scitamineum stress, but its disease resistance function and mechanism were unclear. Here, the upstream promoter of the ScChiIV1 gene (pro-ScChiIV1) with a length of 1696 bp was cloned which contained cis-acting elements related to hormone and stress response. Transient overexpression of the pro-ScChiIV1 in Nicotiana benthamiana showed inducible transcriptional levels by ABA, Fusarium solani var. coeruleum, and Alternaria longipes stimuli. Furthermore, stable overexpression of the ScChiIV1 gene in N. benthamiana enhanced the resistance of transgenic plants against F. solani var. coeruleum and S. scitamineum. Phenotypic monitoring, relevant physiological indicators, immune-related gene expression, and transcriptome analyses revealed that ScChiIV1 may activate potential TFs and PKs by inducing Ca2+ influx, ROS generation, and MAPK activation, thereby increasing the expression level of genes related to hormone signaling pathways, hypersensitive response (HR), and reactive oxygen species (ROS), as well as the activities of chitinase, superoxide dismutase (SOD), and catalase (CAT). In addition, ScChiIV1 reduced the contents of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in transgenic plants, ultimately increasing disease resistance. This study provides novel insights into the molecular mechanism of the early response of the ScChiIV1 gene to pathogen stress and offers an excellent genetic resource for sugarcane disease resistant breeding.

SsNEP2 Plays a Role in the Interaction Between Sclerotinia sclerotiorum and Coniothyrium minitans

Sclerotinia sclerotiorum, a fungal pathogen that is spread worldwide and causes serious diseases on crops, can be parasitized specifically by the mycoparasite Coniothyrium minitans. SsNEP2, encoding a necrosis-inducing protein in S. sclerotiorum, was previously inferred to play a role in the virulence to host plants. In this study, silencing of SsNEP2 in S. sclerotiorum had no significant (p < 0.01) influence on mycelial morphology, while overexpression led to lower mycelial growth and more branches. When amended with the fermentation broth of the SsNEP2 silencing mutants, conidial germination of C. minitans was promoted, while conidial production decreased. When parasitized by C. minitans, enhanced resistance of the SsNEP2 silencing mutants and weaker resistance of the overexpressed transformants were observed compared to the wild-type S. sclerotiorum strain 1980. In addition, the expression of SsNEP2 in C. minitans enhanced mycelial parasitism on S. sclerotiorum and restored the effect of silencing SsNEP2 in S. sclerotiorum on mycoparasitism. Thus, we highlight the role of SsNEP2 as a PAMP-like protein in the mycoparasitism between C. minitans and its host fungus S. sclerotiorum. SsNEP2 can be used to promote the biological potential of C. minitans.

White Mold: A Global Threat to Crops and Key Strategies for Its Sustainable Management

White mold, caused by the fungal pathogen Sclerotinia sclerotiorum (Lib.) de Bary, is a significant biotic stress impacting horticultural and field crops worldwide. This disease causes plants to wilt and ultimately die, resulting in considerable yield losses. This monocyclic disease progresses through a single infection cycle involving basal infections from myceliogenically germinated sclerotia or aerial infections initiated by ascospores from carpogenically germinated sclerotia. The pathogen has a homothallic mating system with a weak population structure. Relatively cool temperatures and extended wetness are typical conditions for spreading the disease. Each stage of infection triggers a cascade of molecular and physiological events that underpin defense responses against S. sclerotiorum. Molecular markers can help rapid diagnosis of this disease in plants. Effective management strategies encompass altering the crop microclimate, applying fungicides, reducing inoculum sources, and developing resistant plant varieties. Integrated approaches combining those strategies often yield the best results. This review discusses the latest insights into the biology, epidemiology, infection mechanisms, and early detection of white mold. This review also aims to provide comprehensive guidelines for sustainable management of this destructive disease while reducing the use of excessive pesticides in crop fields.

Biocontrol Methods for the Management of Sclerotinia sclerotiorum in Legumes: A Review

Sclerotinia sclerotiorum is an economically damaging fungal pathogen that causes Sclerotinia stem rot in legumes, producing enormous yield losses. This pathogen is difficult to control due to its wide host spectrum and ability to produce sclerotia, which are resistant bodies that can remain active for long periods under harsh environmental conditions. Here, the biocontrol methods for the management of S. sclerotiorum in legumes are reviewed. Bacillus strains, which synthesized lipopeptides and volatile organic compounds, showed high efficacies in soybean plants, whereas the highest efficacies for the control of the pathogen in alfalfa and common bean were observed when using Coniothyrium minitans and Streptomyces spp., respectively. The biocontrol efficacies in fields were under 65%, highlighting the lack of strategies to achieve a complete control. Overall, although most studies involved extensive screenings using different biocontrol agent concentrations and application conditions, there is a lack of knowledge regarding the specific antifungal mechanisms, which limits the optimization of the reported methods.

Cloning of maize chitinase 1 gene and its expression in genetically transformed rice to confer resistance against rice blast caused by Pyricularia oryzae

Fungal pathogens are one of the major reasons for biotic stress on rice (Oryza sativa L.), causing severe productivity losses every year. Breeding for host resistance is a mainstay of rice disease management, but conventional development of commercial resistant varieties is often slow. In contrast, the development of disease resistance by targeted genome manipulation has the potential to deliver resistant varieties more rapidly. The present study reports the first cloning of a synthetic maize chitinase 1 gene and its insertion in rice cv. (Basmati 385) via Agrobacterium-mediated transformation to confer resistance to the rice blast pathogen, Pyricularia oryzae. Several factors for transformation were optimized; we found that 4-week-old calli and an infection time of 15 minutes with Agrobacterium before colonization on co-cultivation media were the best-suited conditions. Moreover, 300 μM of acetosyringone in co-cultivation media for two days was exceptional in achieving the highest callus transformation frequency. Transgenic lines were analyzed using molecular and functional techniques. Successful integration of the gene into rice lines was confirmed by polymerase chain reaction with primer sets specific to chitinase and hpt genes. Furthermore, real-time PCR analysis of transformants indicated a strong association between transgene expression and elevated levels of resistance to rice blast. Functional validation of the integrated gene was performed by a detached leaf bioassay, which validated the efficacy of chitinase-mediated resistance in all transgenic Basmati 385 plants with variable levels of enhanced resistance against the P. oryzae. We concluded that overexpression of the maize chitinase 1 gene in Basmati 385 improved resistance against the pathogen. These findings will add new options to resistant germplasm resources for disease resistance breeding. The maize chitinase 1 gene demonstrated potential for genetic improvement of rice varieties against biotic stresses in future transformation programs.

Physiological and metabolic analyses provide insight into soybean seed resistance to fusarium fujikuroi causing seed decay

Seed-borne pathogens cause diverse diseases at the growth, pre- and post-harvest stage of soybean resulting in a large reduction in yield and quality. The physiological and metabolic aspects of seeds are closely related to their defense against pathogens. Recently, Fusarium fujikuroi has been identified as the dominant seed-borne fungi of soybean seed decay, but little information on the responses of soybean seeds induced by F. fujikuroi is available. In this study, a time-course symptom development of seed decay was observed after F. fujikuroi inoculation through spore suspension soaking. The germination rate and the contents of soluble sugar and soluble protein were significantly altered over time. Both chitinase and β-1,3-glucanase as important fungal cell wall-degrading enzymes of soybean seeds were also rapidly and transiently activated upon the early infection of F. fujikuroi. Metabolic profile analysis showed that the metabolites in glycine, serine, and threonine metabolism and tryptophan metabolism were clearly induced by F. fujikuroi, but different metabolites were mostly enriched in isoflavone biosynthesis, flavone biosynthesis, and galactose pathways. Interestingly, glycitein and glycitin were dramatically upregulated while daidzein, genistein, genistin, and daidzin were largely downregulated. These results indicate a combination of physiological responses, cell wall-related defense, and the complicated metabolites of soybean seeds contributes to soybean seed resistance against F. fujikuroi, which are useful for soybean resistance breeding.

Genome-Wide Identification and Expression Analyses of the Chitinase Gene Family in Response to White Mold and Drought Stress in Soybean (Glycine max)

Chitinases are enzymes catalyzing the hydrolysis of chitin that are present on the cell wall of fungal pathogens. Here, we identified and characterized the chitinase gene family in cultivated soybean (Glycine max L.) across the whole genome. A total of 38 chitinase genes were identified in the whole genome of soybean. Phylogenetic analysis of these chitinases classified them into five separate clusters, I–V. From a broader view, the I–V classes of chitinases are basically divided into two mega-groups (X and Y), and these two big groups have evolved independently. In addition, the chitinases were unevenly and randomly distributed in 17 of the total 20 chromosomes of soybean, and the majority of these chitinase genes contained few introns (≤2). Synteny and duplication analysis showed the major role of tandem duplication in the expansion of the chitinase gene family in soybean. Promoter analysis identified multiple cis-regulatory elements involved in the biotic and abiotic stress response in the upstream regions (1.5 kb) of chitinase genes. Furthermore, qRT-PCR analysis showed that pathogenic and drought stress treatment significantly induces the up-regulation of chitinase genes belonging to specific classes at different time intervals, which further verifies their function in the plant stress response. Hence, both in silico and qRT-PCR analysis revealed the important role of the chitinases in multiple plant defense responses. However, there is a need for extensive research efforts to elucidate the detailed function of chitinase in various plant stresses. In conclusion, our investigation is a detailed and systematic report of whole genome characterization of the chitinase family in soybean.

Analysis of Tissue-Specific Defense Responses to Sclerotinia sclerotiorum in Brassica napus

Sclerotinia stem rot (SSR) caused by Sclerotinia sclerotiorum (S. sclerotiorum) is the main disease threat of oilseed rape (Brassica napus), resulting in huge economic losses every year. SSR resistance manifests as quantitative disease resistance (QDR), and no gene with complete SSR resistance has been cloned or reported so far. Transcriptome analysis has revealed a large number of defense-related genes and response processes. However, the similarities and differences in the defense responses of different tissues are rarely reported. In this study, we analyzed the similarities and differences of different tissues in response to S. sclerotiorum at 24 h post inoculation (hpi) by using the published transcriptome data for respective leaf and stem inoculation. At 24 hpi, large differences in gene expression exist in leaf and stem, and there are more differentially expressed genes and larger expression differences in leaf. The leaf is more sensitive to S. sclerotiorum and shows a stronger response than stem. Different defense responses appear in the leaf and stem, and the biosynthesis of lignin, callose, lectin, chitinase, PGIP, and PR protein is activated in leaf. In the stem, lipid metabolism-mediated defense responses are obviously enhanced. For the common defense responses in both leaf and stem, the chain reactions resulting from signal transduction and biological process take the primary responsibility. This research will be beneficial to exploit the potential of different tissues in plant defense and find higher resistance levels of genotypic variability in different environments. Our results are significant in the identification of resistance genes and analysis of defense mechanisms.

A Contemporary Appraisal on Impending Industrial and Agricultural Applications of Thermophilic-Recombinant Chitinolytic Enzymes from Microbial Sources

The ability of chitinases to degrade the second most abundant polymer, chitin, into potentially useful chitooligomers and chitin derivatives has not only rendered them fit for chitinous waste management but has also made them important from industrial point of view. At the same time, they have also been recognized to have an imperative role as promising biocontrol agents for controlling plant diseases. As thermostability is an important property for an industrially important enzyme, various bacterial and fungal sources are being exploited to obtain such stable enzymes. These stable enzymes can also play a role in agriculture by maintaining their stability under adverse environmental conditions for longer time duration when used as biocontrol agent. Biotechnology has also played its role in the development of recombinant chitinases with enhanced activity, thermostability, fungicidal and insecticidal activity via recombinant DNA techniques. Furthermore, a relatively new approach of generating pathogen-resistant transgenic plants has opened new ways for sustainable agriculture by minimizing the yield loss of valuable crops and plants. This review focuses on the potential applications of thermostable and recombinant microbial chitinases in industry and agriculture.

Progress in Soybean Genetic Transformation Over the Last Decade

Soybean is one of the important food, feed, and biofuel crops in the world. Soybean genome modification by genetic transformation has been carried out for trait improvement for more than 4 decades. However, compared to other major crops such as rice, soybean is still recalcitrant to genetic transformation, and transgenic soybean production has been hampered by limitations such as low transformation efficiency and genotype specificity, and prolonged and tedious protocols. The primary goal in soybean transformation over the last decade is to achieve high efficiency and genotype flexibility. Soybean transformation has been improved by modifying tissue culture conditions such as selection of explant types, adjustment of culture medium components and choice of selection reagents, as well as better understanding the transformation mechanisms of specific approaches such as Agrobacterium infection. Transgenesis-based breeding of soybean varieties with new traits is now possible by development of improved protocols. In this review, we summarize the developments in soybean genetic transformation to date, especially focusing on the progress made using Agrobacterium-mediated methods and biolistic methods over the past decade. We also discuss current challenges and future directions.

Overexpression of chitinase in the endophyte Phomopsis liquidambaris enhances wheat resistance to Fusarium graminearum

Fusarium head blight (FHB) is a disease that affects wheat crops worldwide and is caused by Fusarium graminearum. Effective and safe strategies for the prevention and treatment of the disease are very limited. Phomopsis liquidambaris, a universal endophyte, can colonize wheat. Two engineered strains, Phomopsis liquidambaris OE-Chi and IN-Chi, were constructed by transformation with a plasmid and integration of a chitinase into the genome, respectively. The OE-Chi and IN-Chi strains could inhibit the expansion of Fusarium sp. in plate confrontation assays in vitro. Colonization of the OE-Chi strain in wheat showed better effects than colonization of the IN-Chi strain and alleviated the inhibition of wheat growth caused by F. graminearum. The shoot length, root length and fresh weight of infected wheat increased by 164.9%, 115.4%, and 190.7%, respectively, when the plants were inoculated with the OE-Chi strain. The peroxidase (POD) activity in the wheat root increased by 38.0%, and it was maintained at a high level in the shoot, which suggested that the OE-Chi strain could enhance the resistance of wheat to F. graminearum. The root and shoot superoxide dismutase (SOD) activities were decreased by 11.8% and 19.0%, respectively, which may be helpful for colonization by the OE-Chi strain. These results suggested that the Phomopsis liquidambaris OE-Chi strain may be a potential endophyte in the biocontrol of FHB.

Genome-Wide Identification and Expression of Chitinase Class I Genes in Garlic (Allium sativum L.) Cultivars Resistant and Susceptible to Fusarium proliferatum

Vegetables of the Allium genus are prone to infection by Fusarium fungi. Chitinases of the GH19 family are pathogenesis-related proteins inhibiting fungal growth through the hydrolysis of cell wall chitin; however, the information on garlic (Allium sativum L.) chitinases is limited. In the present study, we identified seven class I chitinase genes, AsCHI1–7, in the A. sativum cv. Ershuizao genome, which may have a conserved function in the garlic defense against Fusarium attack. The AsCHI1–7 promoters contained jasmonic acid-, salicylic acid-, gibberellins-, abscisic acid-, auxin-, ethylene-, and stress-responsive elements associated with defense against pathogens. The expression of AsCHI2, AsCHI3, and AsCHI7 genes was constitutive in Fusarium-resistant and -susceptible garlic cultivars and was mostly induced at the early stage of F. proliferatum infection. In roots, AsCHI2 and AsCHI3 mRNA levels were increased in the susceptible and decreased in the resistant cultivar, whereas in cloves, AsCHI7 and AsCHI5 expression was decreased in the susceptible but increased in the resistant plants, suggesting that these genes are involved in the garlic response to Fusarium proliferatum attack. Our results provide insights into the role of chitinases in garlic and may be useful for breeding programs to increase the resistance of Allium crops to Fusarium infections.

Recent advances in the bioprospection and applications of chitinolytic bacteria for valorization of waste chitin

One of the most abundant natural polymers on earth, chitin is a fibrous and structural polysaccharide, composed of N-acetyl-D-glucosamine. The biopolymer is the major structural constituent of fungi, arthropods, mollusks, nematodes, and some algae. The biodegradation of chitin is largely manifested by chitinolytic enzyme secreting organisms including bacteria, insects, and plants. Among them, bacterial chitinases represent the most promising, inexpensive, and sustainable source of proteins that can be employed for industrial-scale applications. To this end, the presented review comes at a timely moment to highlight the major sources of chitinolytic bacteria. It also discusses the potential pros and cons of prospecting bacterial chitinases that can be easily manipulated through genetic engineering. Additionally, we have elaborated the recent applications of the chitin thereby branding chitinases as potential candidates for biorefinery and biomedical research for eco-friendly and sustainable management of chitin waste in the environment.

Tackling Control of a Cosmopolitan Phytopathogen: Sclerotinia

Phytopathogenic members of the Sclerotinia genus cause widespread disease across a broad range of economically important crops. In particular, Sclerotinia sclerotiorum is considered one of the most destructive and cosmopolitan of plant pathogens. Here, were review the epidemiology of the pathogen, its economic impact on agricultural production, and measures employed toward control of disease. We review the broad approaches required to tackle Sclerotinia diseases and include cultural practices, crop genetic resistance, chemical fungicides, and biological controls. We highlight the benefits and drawbacks of each approach along with recent advances within these controls and future strategies.

Genotype-Specific Antioxidant Responses and Assessment of Resistance Against Sclerotinia sclerotiorum Causing Sclerotinia Rot in Indian Mustard

Productivity of Indian mustard, an important oilseed crop of India, is affected by several pathogens. Among them, the hemibiotroph Sclerotinia sclerotiorum, which causes sclerotinia rot disease, is the most devastating fungal pathogen causing up to 90% yield losses. The availability of host resistance is the only efficient approach to control and understand the host-pathogen interaction. Therefore, the present investigation was carried out using six Indian mustard genotypes with contrasting behavior towards sclerotinia rot to study the antioxidant resistance mechanism against S. sclerotiorum. The plants at post-flowering stage were inoculated with five-day-old pure culture of S. sclerotiorum using artificial stem inoculation method. Disease evaluation revealed significant genotypic differences for mean lesion length among the tested genotypes, where genotype DRMR 2035 was found highly resistant, while genotypes RH 1569 and RH 1633 were found highly susceptible. The resistant genotypes had more phenolics and higher activities of peroxidase, catalase and polyphenol oxidase which provide them more efficient and strong antioxidant systems as compared with susceptible genotypes. Studies of antioxidative mechanisms validate the results of disease responses.