Molecular diagnostics on the toxigenic potential of Fusarium spp. plant pathogens

The Effects of Growth Modification on Pollen Development in Spring Barley (Hordeum vulgare L.) Genotypes with Contrasting Drought Tolerance

Drought stress inducing pollen sterility can reduce crop yield worldwide. The regulatory crosstalk associated with the effects of drought on pollen formation at the cellular level has not been explored in detail so far. In this study, we performed morphological and cytoembryological analysis of anther perturbations and examined pollen development in two spring barley genotypes that differ in earliness and drought tolerance. The Syrian breeding line CamB (drought-tolerant) and the European cultivar Lubuski (drought-sensitive) were used as experimental materials to analyze the drought-induced changes in yield performance, chlorophyll fluorescence kinetics, the pollen grain micromorphology and ultrastructure during critical stages of plant development. In addition, fluctuations in HvGAMYB expression were studied, as this transcription factor is closely associated with the development of the anther. In the experiments, the studied plants were affected by drought, as was confirmed by the analyses of yield performance and chlorophyll fluorescence kinetics. However, contrary to our expectations, the pollen development of plants grown under specific conditions was not severely affected. The results also suggest that growth modification, as well as the perturbation in light distribution, can affect the HvGAMYB expression. This study demonstrated that the duration of the vegetation period can influence plant drought responses and, as a consequence, the processes associated with pollen development as every growth modification changes the dynamics of drought effects as well as the duration of plant exposition to drought.

The effects of heading time on yield performance and HvGAMYB expression in spring barley subjected to drought

In the lifetime of a plant, flowering is not only an essential part of the reproductive process but also a critical developmental stage that can be vulnerable to environmental stresses. To ensure survival during drought, plants accelerate the flowering process, and this response is known as "drought escape." HvGAMYB-transcription factor associated, among others, with flowering process and anther development in barley-has also an important role in developmental modification and yield performance in plants subjected to stressed conditions. Due to the fact that information about the mechanisms associated both with the flowering acceleration and the anther or pollen disruption is limited, the exploration of the potential HvGAMYB role in flower development may shed light on pollen and spike morphology formations in plants grown under unfavorable water conditions. The aim of this study was to characterize differences in responses to drought among early- and late-heading barley genotypes. These two subgroups of plants-differentiated in terms of phenology-were analyzed, and traits linked to plant phenotype, physiology, and yield were investigated. In our study, the drought stress reactions of two barley subgroups showed a wide range of diversity in terms of yield performance, anther morphology, chlorophyll fluorescence kinetics, and pollen viability. The studied plants exhibited different yield performances under control and drought conditions. Moreover, the random distribution of genotypes on the biplot showing variability of OJIP parameters in the second developmental point of our investigation revealed that prolonged drought stress caused that among early- and late-heading plants, the studied genotypes exhibited different responses to applied stress conditions. The results of this study also showed that the HvGAMYB expression level was correlated positively with traits associated with lateral spike morphology in the second developmental point of this investigation, which showed that this association occurred only under prolonged drought and highlighted the drought stress duration effect on the HvGAMYB expression level.

Distribution, Function, and Evolution of a Gene Essential for Trichothecene Toxin Biosynthesis in Trichoderma

Trichothecenes are terpenoid toxins produced by species in 10 fungal genera, including species of Trichoderma. The trichothecene biosynthetic gene (tri) cluster typically includes the tri5 gene, which encodes a terpene synthase that catalyzes formation of trichodiene, the parent compound of all trichothecenes. The two Trichoderma species, Trichoderma arundinaceum and T. brevicompactum, that have been examined are unique in that tri5 is located outside the tri cluster in a genomic region that does not include other known tri genes. In the current study, analysis of 35 species representing a wide range of the phylogenetic diversity of Trichoderma revealed that 22 species had tri5, but only 13 species had both tri5 and the tri cluster. tri5 was not located in the cluster in any species. Using complementation analysis of a T. arundinaceum tri5 deletion mutant, we demonstrated that some tri5 homologs from species that lack a tri cluster are functional, but others are not. Phylogenetic analyses suggest that Trichoderma tri5 was under positive selection following its divergence from homologs in other fungi but before Trichoderma species began diverging from one another. We propose two models to explain these diverse observations. One model proposes that the location of tri5 outside the tri cluster resulted from loss of tri5 from the cluster in an ancestral species followed by reacquisition via horizontal transfer. The other model proposes that in species that have a functional tri5 but lack the tri cluster, trichodiene production provides a competitive advantage.

Fusarium cerealis causing Fusarium head blight of durum wheat and its associated mycotoxins

Fusarium Head Blight (FHB) is a very important fungal disease that affects small grain cereals worldwide. This disease not only causes yield loses but also crops contamination with mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Species within the Fusarium graminearum species complex have been described as the main causal agents of this disease, however lately there have been few reports of Fusarium cerealis causing the disease in wheat and barley in different parts of the world. This study evaluated the aggressiveness of F. cerealis to durum wheat cultivars and also mycotoxin production in planta. Moreover, the mycotoxin profile of F. cerealis strains was characterized molecularly and chemically. All durum wheat cultivars showed typical FHB symptoms but the disease severity varied among them in levels up to 66%. In addition, seventeen different compounds were detected in the infected heads including DON, NIV and nivalenol-3-β-d-glucose (NIV3G). NIV was detected in all cultivars and was the most produced mycotoxin with levels ranging from 1.04 to 6.8 mg/kg. On the other hand, the molecular analysis of F. cerealis strains showed that all of them possessed NIV genotype while the chemical assessment showed that the strains were able to produce not only this toxin in vitro but also DON, zearalenone and other twenty-one secondary metabolites. The increasing incidence of F. cerealis and the possible contamination of crops with the mycotoxins that it produces are of great concern for food security and world cereal trade since it has been reported that NIV is more toxic for humans and animals than DON.

Efflux pumps as an additional source of resistance to trichothecenes in Fusarium proliferatum and Fusarium oxysporum isolates

Role of efflux-mediated toxin resistance to trichothecenes is known in trichothecene-producing species. However, the role of trichothecene efflux pump homologues in non-producing fusaria such as F. oxysporum and F. proliferatum was not investigated in detail. Analysis of the homologues of trichothecene efflux pump from multiple fungal species allowed us to uncover and catalogue functional gene copies of conserved structure. Putative Tri12 candidates in Fusarium oxysporum and F. proliferatum were characterised via expression profiling in response to different trigger compounds, providing supporting evidence for role of Tri12 homologues in the resistance to trichothecenes. Our analysis of Tri12 phylogeny also suggests that efflux-mediated trichothecene resistance is likely to predate the divergence of Trichoderma and Fusarium species. On the regulatory level, we posit that the increased tolerance of trichothecenes by F. oxysporum is possibly related to the decoupling of Tri12 homologue expression from pH, due to the deletion of PACC/RIM101 transcription factor binding site in its promoter region.

Development of Indirect Competitive Enzyme-Linked Immunosorbent Assay to Detect Fusarium verticillioides in Poultry Feed Samples

Fumonisins are a group of toxic secondary metabolites that are produced by Fusarium verticillioides which are associated with poultry health hazard and great economic losses. The objective of the present study was to develop an immunological method to detect F. verticillioides in poultry feed samples. An indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) based on a polyclonal antibody against 67 kDa protein of the F. verticillioides 97K exoantigen was developed to detect this fungus. Antibody anti-67 kDa protein showed cross-reactivity against F. graminearum (2⁻7%) and F. sporotrichioides (10%), but no or low cross-reactivity against Aspergillus sp. and Penicillium sp. exoantigens. The detection limit for the 67 kDa protein of F. verticillioides was 29 ng/mL. Eighty-one poultry feed samples were analyzed for Fusarium sp. count, 67 kDa protein of F. verticillioides and fumonisin concentrations. Eighty of the 81 feed samples (98.6%) showed Fusarium sp. contamination (mean 6.2 x 10⁴ CFU/g). Mean 67 kDa protein and fumonisin concentration in the poultry feed samples was 21.0 µg/g and 1.02 µg/g, respectively. The concentration of 67 kDa protein, as determined by ic-ELISA correlated positively (p < 0.05) with fumonisin levels (r = 0.76). These results suggest that this ic-ELISA has potential to detect F. verticillioides and predict fumonisin contamination in poultry feed samples.

Augmentation of crop productivity through interventions of omics technologies in India: challenges and opportunities

With the continuous increase in the population of developing countries and decline of natural resources, there is an urgent need to qualitatively and quantitatively augment crop productivity by using new tools and technologies for improvement of agriculturally important traits. The new scientific and technological omics-based approaches have enabled us to deal with several issues and challenges faced by modern agricultural system and provided us novel opportunities for ensuring food and nutritional security. Recent developments in sequencing techniques have made available huge amount of genomic and transcriptomic data on model and cultivated crop plants including Arabidopsis thaliana, Oryza sativa, Triticum aestivum etc. The sequencing data along with other data generated through several omics platforms have significantly influenced the disciplines of crop sciences. Gene discovery and expression profiling-based technologies are offering enormous opportunities to the scientific community which can now apply marker-assisted selection technology to assess and enhance diversity in their collected germplasm, introgress essential traits from new sources and investigate genes that control key traits of crop plants. Utilization of omics science and technologies for crop productivity, protection and management has recently been receiving a lot of attention; the majority of the efforts have been put into signifying the possible applications of various omics technologies in crop plant sciences. This article highlights the background of challenges and opportunities for augmentation of crop productivity through interventions of omics technologies in India.

Detection of Fusarium verticillioides by PCR-ELISA based on FUM21 gene

Fusarium verticillioides is a primary corn pathogen and fumonisin producer which is associated with toxic effects in humans and animals. The traditional methods for detection of fungal contamination based on morphological characteristics are time-consuming and show low sensitivity and specificity. Therefore, the objective of this study was to develop a PCR-ELISA based on the FUM21 gene for F. verticillioides detection. The DNA of the F. verticillioides, Fusarium sp., Aspergillus sp. and Penicillium sp. isolates was analyzed by conventional PCR and PCR-ELISA to determine the specificity. The PCR-ELISA was specific to F. verticillioides isolates, showed a 2.5 pg detection limit and was 100-fold more sensitive than conventional PCR. In corn samples inoculated with F. verticillioides conidia, the detection limit of the PCR-ELISA was 1 × 10⁴ conidia/g and was also 100-fold more sensitive than conventional PCR. Naturally contaminated corn samples were analyzed by PCR-ELISA based on the FUM21 gene and PCR-ELISA absorbance values correlated positively (p < 0.05) with Fusarium sp. counts (CFU/g). These results suggest that the PCR-ELISA developed in this study can be useful for F. verticillioides detection in corn samples.

Assessing contamination of microalgal astaxanthin producer Haematococcus cultures with high-resolution melting curve analysis

Due to its superior antioxidant capabilities and higher activity than other carotenoids, astaxanthin is used widely in the nutraceutical and medicine industries. The most prolific natural producer of astaxanthin is the unicellular green microalga Haematococcus pluvialis. The correct identification of any contaminants in H. pluvialis cultures is both essential and nontrivial for several reasons. Firstly, while it is possible to distinguish the main microalgal contaminant Coelastrella sp. (in H. pluvialis cultures), in practice, it is frequently a daunting and error-prone task for personnel without extensive experience in the microscopic identification of algal species. Secondly, the undetected contaminants may decrease or stop production of astaxanthin. Lastly, the presence of other contaminants such as fungi can eventually infect and destroy the whole algae collection. In this study, high-resolution melting (HRM) analysis was developed to detect microalgal and fungal contamination. The developed diagnostic procedure allowed to distinguish pure H. pluvialis samples from cultures contaminated with low amounts (1.25 ng/ml) of microalgal DNA and fungal DNA (2.5 ng/ml). Such discrimination is not possible with the use of microscopy observations and allows fast and efficient collection testing.

Molecular strategies for detection and quantification of mycotoxin-producing Fusarium species: a review

Fusarium contamination is considered a major agricultural problem, which could not only significantly reduce yield and quality of agricultural products, but produce mycotoxins that are virulence factors responsible for many diseases of humans and farm animals. One strategy to identify toxigenic Fusarium species is the use of modern molecular methods, which include the analysis of DNA target regions for differentiation of the Fusarium species, particularly the mycotoxin-producing Fusarium species such as F. verticillioides and F. graminearum. Additionally, polymerase chain reaction assays are used to determine the genes involved in the biosynthesis of the toxins in order to facilitate a qualitative and quantitative detection of Fusarium-producing mycotoxins. Also, it is worth mentioning that some factors that modulate the biosynthesis of mycotoxins are not only determined by their biosynthetic gene clusters, but also by environmental conditions. Therefore, all of the aforementioned factors which may affect the molecular diagnosis of mycotoxins will be reviewed and discussed in this paper.