The transcriptome of Fusarium graminearum during the infection of wheat

Fusarium graminearum causes head blight disease in wheat and barley. To help understand the infection process on wheat, we studied global gene expression of F. graminearum in a time series from 24 to 196 h after inoculation, compared with a noninoculated control. The infection was rapid and, after 48 h, over 4,000 fungal genes were expressed. The number of genes expressed increased over time up to 96 h (>8,000 genes), and then declined at the 144- and 192-h post-inoculation time points. After subtraction of genes found expressed on complete medium, during carbon or nitrogen starvation, and on barley, only 355 were found exclusively expressed in wheat, mostly genes with unknown function (72.6%). These genes were mainly found in single-nucleotide polymorphism-enriched islands on the chromosomes, suggesting a higher evolutionary selection pressure. The annotated genes were enriched in functional groups predicted to be involved in allantoin and allantoate transport, detoxification, nitrogen, sulfur and selenium metabolism, secondary metabolism, carbohydrate metabolism, and degradation of polysaccharides and ester compounds. Several putative secreted virulence factors were also found expressed in wheat.     

Genotypic variation in zinc efficiency and resistance to crown rot disease (Fusarium graminearum Schw. Group 1) in wheat

A crown rot disease in wheat caused by the fungusFusarium graminearum Schw. Group 1 is a widespread problem in chronically Zn-deficient Australian soils. A link between crown rot and Zn deficiency was established by Sparrow and Graham (1988). This paper reports a test of a further hypothesis, that wheat genotypes more efficient at extracting zinc from low-zinc soils are more resistant to infection by this pathogen. Three wheat cultivars (Excalibur, Songlen and Durati) of differential Zn efficiency were tested at three zinc levels (0.05, 0.5 and 2.0 mg Zn kg⁻¹ of soil) and three levels ofF. graminearum S. Group 1 inoculum (0.1 g and 0.3 g kg⁻¹ live chaff-inoculum and control having 0.1 g kg⁻¹ dead chaff inoculum). Six weeks after sowing dry matter production of shoots and roots was decreased byFusarium inoculation at 0.05 mg and 0.5 mg kg⁻¹ applied Zn.Fusarium inoculum at 0.1 g was as effective as 0.3 g kg⁻¹ for infection and decreasing dry matter. The infection at the basal part of culm decreased significantly by increasing the rate of Zn application. Excalibur, a Zn-efficient cultivar (tolerant to Zn deficiency) produced significantly more shoot and root dry matter, and showed less disease infection compared with Zn-inefficient cultivars (Durati and Songlen) at low (0.05 mg Zn kg⁻¹ soil) and medium (0.5 mg Zn kg⁻¹ soil) Zn fertilization rates. Higher rate of Zn fertilization (2.0 mg Zn kg⁻¹ soil) reduced the disease level in Durati to the level of Excalibur but the disease level of Songlen was still high, indicating its high Zn requirement and or sensitivity to crown rot. The data on Zn uptake show that Excalibur, being Zn-efficient, was able to scavenge enough Zn from Zn-deficient soil, we suggest that besides sustaining growth Excalibur was able to build and maintain resistance to the pathogen; inefficient cultivars needed extra Zn fertilization to achieve performance comparable to that of Excalibur. The present study indicates that growing Zn-efficient cultivars of wheat along with judicious use of Zn fertilizer in Zn-deficient areas where crown rot is a problem may sustain wheat production by reducing the severity of the disease as well as by increasing the plant vigour through improved Zn nutrition. ei]Section editor: R Rodriques-Kalana     

BDM1, a phosducin-like gene of Fusarium graminearum, is involved in virulence during infection of wheat and maize

Fusarium graminearum is a common pathogen of wheat and maize throughout the world. Despite recent advances in the elucidation of the genetic basis of virulence, significant gaps in the regulatory network underlying pathogenesis remain to be filled. In particular, little is known at the molecular level about the overlap among mechanisms of pathogenicity on maize and wheat. G-protein signalling has been implicated in pathogenesis in F. graminearum, although the underlying mechanisms are not fully understood. In this study, we investigated the involvement of a putative phosducin-like gene (BDM1) in growth, development and pathogenesis in F. graminearum. Targeted deletion of BDM1 revealed roles in sexual and asexual sporulation, germ tube development, hyphal branching and mycelial morphology. During pathogenesis, BDM1 is required for wild-type levels of colonization of maize silk tissue and stalks, but is dispensable for the colonization of kernels. The deletion of BDM1 also reduced the virulence of F. graminearum during the infection of wheat seedlings and heads, resulting in a significant reduction in fungal biomass and a delayed spread of visual symptom expression (i.e. bleaching in heads). Furthermore, BDM1 is required for wild-type levels of deoxynivalenol biosynthesis during the infection of wheat heads and maize silks. In summation, BDM1 is one of the few genes characterized to date in F. graminearum involved in virulence during infection of both maize and wheat. Thus, the functional characterization of BDM1 has established a new regulatory link between pathogenesis in maize and wheat, and provides a genetic resource through which the regulatory networks underlying virulence in F. graminearum can be further elucidated.     

Identification and characterization of a novel Iraqi isolate of Fusarium pseudograminearum causing crown rot in wheat

Crown rot is one of the main important fungal diseases affecting wheat in many areas of the world, including Australia, USA, and Iran. Until now, there had been no report of this pathogen in Iraq. Plants displaying crown rot symptoms were observed in Shaat Alarab (Basra, Iraq); we investigated the causal agent of the disease. Samples were surface-sterilized in bleach (1% available chlorine) and cultured on quarter-strength potato dextrose agar plates. DNA was extracted from fungal mycelia, using a modified CTAB protocol. The ITS/5.8S regions were amplified using primer pair ITS1 and ITS4. PCR products purified using a gel extraction kit were sequenced. The sequence that was detected was used to BLAST against NCBI data. The most similar sequence was the ITS/5.8S rDNA region of Fusarium pseudograminearum (strain NRRL28062), showing 97.95% identity. This species normally causes crown rot, resulting in severe damage under dry spring conditions. A pathogenicity test employed to assess the disease-causing ability of the strain showed significant disease symptoms up to 57% infected spikelets. The results confirmed the presence of F. pseudograminearum as a causal agent of wheat crown rot in Iraq. The presence of this pathogen demands further investigations to develop resistant cultivars and/or mechanical control.     

FcRav2, a gene with a ROGDI domain involved in Fusarium head blight and crown rot on durum wheat caused by Fusarium culmorum

Fusarium culmorum is a soil‐borne fungal pathogen which causes foot and root rot and Fusarium head blight on small‐grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in the contamination of kernels with type B trichothecene mycotoxins. Our knowledge of the pathogenicity factors of this fungus is still limited. A transposon tagging approach based on the mimp1/impala double‐component system has allowed us to select a mutant altered in multiple metabolic and morphological processes, trichothecene production and virulence. The flanking regions of mimp1 were used to seek homologies in the F. culmorum genome, and revealed that mimp1 had reinserted within the last exon of a gene encoding a hypothetical protein of 318 amino acids which contains a ROGDI‐like leucine zipper domain, supposedly playing a protein–protein interaction or regulatory role. By functional complementation and bioinformatic analysis, we characterized the gene as the yeast Rav2 homologue, confirming the high level of divergence in multicellular fungi. Deletion of FcRav2 or its orthologous gene in F. graminearum highlighted its ability to influence a number of functions, including virulence, trichothecene type B biosynthesis, resistance to azoles and resistance to osmotic and oxidative stress. Our results indicate that the FcRav2 protein (and possibly the RAVE complex as a whole) may become a suitable target for new antifungal drug development or the plant‐mediated resistance response in filamentous fungi of agricultural interest.     

Induction of systemic resistance against Fusarium crown and root rot disease by blast processing

The effect of fan-forced wind on the severity and growth of Fusarium oxysporum f. sp. radicis-lycopersici (FORL) was examined in this study. The discoloration severity of the total root system was significantly reduced in plants treated with air blasting for 30?min at a wind speed of 4?m/s compared with the control. In addition, the number of colony-forming units of FORL per gram of fresh root weight was significantly reduced (p?≤?0.05) in plants treated with air blasting at a wind speed of 4?m/s for 30?min, and the root extracts of these plants had a significantly lower production of FORL budding cells. Booster wind treatments significantly reduced the severity and growth of FORL compared with single and control treatments. Furthermore, RT-PCR analysis indicated that the expression of defense-related genes was induced in the leaves of seedlings treated with air blasting at a wind speed of 4?m/s.     

Overexpression of wheat lipid transfer protein gene TaLTP5 increases resistances to Cochliobolus sativus and Fusarium graminearum in transgenic wheat

The fungus Cochliobolus sativus is the main pathogen of common root rot, a serious soil-borne disease of wheat (Triticum aestivum L.). The fungus Fusarium graminearum is the primary pathogen of Fusarium head blight, a devastating disease of wheat worldwide. In this study, the wheat lipid transfer protein gene, TaLTP5, was cloned and evaluated for its ability to suppress disease development in transgenic wheat. TaLTP5 expression was induced after C. sativus infection. The TaLTP5 expression vector, pA25-TaLTP5, was constructed and bombarded into Chinese wheat variety Yangmai 18. Six TaLTP5 transgenic wheat lines were established and characterized. PCR and Southern blot analyses indicated that the introduced TaLTP5 gene was integrated into the genomes of six transgenic wheat lines by distinct patterns, and heritable. RT-PCR and real-time quantitative RT-PCR revealed that the TaLTP5 gene was over-expressed in the transgenic wheat lines compared to segregants lacking the transgene and wild-type wheat plants. Following challenge with C. sativus or F. graminearum, all six transgenic lines overexpressing TaLTP5 exhibited significantly enhanced resistance to both common root rot and Fusarium head blight compared to the untransformed wheat Yangmai 18.     

Transgenic wheat expressing a barley class II chitinase gene has enhanced resistance against Fusarium graminearum

Fusarium head blight (FHB; scab), primarily caused by Fusarium graminearum, is a devastating disease of wheat worldwide. FHB causes yield reductions and contamination of grains with trichothecene mycotoxins such as deoxynivalenol (DON). The genetic variation in existing wheat germplasm pools for FHB resistance is low and may not provide sufficient resistance to develop cultivars through traditional breeding approaches. Thus, genetic engineering provides an additional approach to enhance FHB resistance. The objectives of this study were to develop transgenic wheat expressing a barley class II chitinase and to test the transgenic lines against F. graminearum infection under greenhouse and field conditions. A barley class II chitinase gene was introduced into the spring wheat cultivar, Bobwhite, by biolistic bombardment. Seven transgenic lines were identified that expressed the chitinase transgene and exhibited enhanced Type II resistance in the greenhouse evaluations. These seven transgenic lines were tested under field conditions for percentage FHB severity, percentage visually scabby kernels (VSK), and DON accumulation. Two lines (C8 and C17) that exhibited high chitinase protein levels also showed reduced FHB severity and VSK compared to Bobwhite. One of the lines (C8) also exhibited reduced DON concentration compared with Bobwhite. These results showed that transgenic wheat expressing a barley class II chitinase exhibited enhanced resistance against F. graminearum in greenhouse and field conditions.     

Pyramiding QTL increases seedling resistance to crown rot (Fusarium pseudograminearum) of wheat (Triticum aestivum)

Crown rot of wheat (Triticum aestivum), predominantly caused by the fungus Fusarium pseudograminearum, has become an increasingly important disease constraint in many winter cereal production regions in Australia. Our group has previously identified a range of quantitative trait loci (QTL) for partial resistance to crown rot in various bread wheat sources. Here, we report on work that has assessed the effectiveness of pyramiding QTL to improve resistance to crown rot. Two doubled haploid populations were analysed—one from a cross between two previously characterised sources of partial seedling resistance (2-49 and W21MMT70; n = 208) and one from a cross between 2-49 and the commercial variety Sunco, a source of adult field resistance (n = 134). Both populations were phenotyped for seedling resistance to crown rot. Microsatellite and DArT markers were used to construct whole genome linkage maps for use in composite interval mapping (CIM) to identify QTL. Three QTL were detected in both trials conducted on the 2-49/W21MMT70 population. These were located on chromosomes 1D (QCr.usq-1D.1), 3B (QCr.usq-3B.1) and 7A. QCr.usq-1D.1 and the previously undetected 7A QTL were inherited from 2-49. QCr.usq-3B.1, inherited from W21MMT70, was the most significant of the QTL, explaining up to 40.5% of the phenotypic variance. Three QTL were identified in multiple trials of the Sunco/2-49 population. These were located on chromosomes 1D (QCr.usq-1D.1), 2B (QCr.usq-2B.2) and 4B (QCr.usq-4B.1). Only QCr.usq-2B.2 was inherited from Sunco. QCr.usq-4B.1 was the most significant of these QTL, explaining up to 19.1% of the phenotypic variance. In the 2-49/W21MMT70 population, several DH lines performed significantly better than either parent, with the best recording an average disease severity rating of only 3.8% of that scored by the susceptible check cultivar Puseas. These lines represent a new level of seedling crown rot resistance in wheat.     

Augmentation of wheat common root rot by Fusarium acuminatum

Wheat was inoculated with Bipolaris sorokiniana and Fusarium acuminatum individually and in combination under controlled conditions. Only B. sorokininana produced significant disease when used alone; however, F. acuminarum significantly augmented the effects of B. sorokiniana when plants are inoculated with both fungi.     

Genetic relationships between resistances to Fusarium head blight and crown rot in bread wheat (Triticum aestivum L.)

Fusarium head blight (FHB) and crown rot (CR) are two wheat diseases caused by the same Fusarium pathogens. Progress towards CR resistance could benefit from FHB-resistant germplasm if the same genes are involved in resistance to these two different diseases. Two independent studies were conducted to investigate the relationship between host resistances to these two diseases. In the first study 32 genotypes were assessed and no significant correlation between their reactions to FHB and CR was detected. The second study was based on a QTL analysis of a doubled haploid population derived from a variety with resistance to both diseases. Results from this study showed that loci conferring resistance to FHB and CR are located on different chromosomes. Together, these results suggest that, despite a common aetiology, different host genes are involved in the resistance against FHB and CR in wheat. Thus, although it is possible that genes affecting both diseases may exist in other germplasm or under different conditions, separate screening seems to be needed in identifying sources of CR resistance.     

Transgenic expression of polygalacturonase-inhibiting proteins in Arabidopsis and wheat increases resistance to the flower pathogen Fusarium graminearum

Fusarium head blight (FHB), caused by Fusarium graminearum, is one of the most important diseases of wheat worldwide, resulting in yield losses and mycotoxin contamination. The molecular mechanisms regulating Fusarium penetration and infection are poorly understood. Beside mycotoxin production, cell wall degradation may play a role in the development of FHB. Many fungal pathogens secrete polygalacturonases (PGs) during the early stages of infection, and plants have evolved polygalacturonase-inhibiting proteins (PGIPs) to restrict pectin degradation during fungal infection. To investigate the role of plant PGIPs in restricting the development of FHB symptoms, we first used Arabidopsis thaliana, whose genome encodes two PGIPs (AtPGIP1 and AtPGIP2). Arabidopsis transgenic plants expressing either of these PGIPs under control of the CaMV 35S promoter accumulate inhibitory activity against F.?graminearum PG in their inflorescences, and show increased resistance to FHB. Second, transgenic wheat plants expressing the bean PvPGIP2 in their flowers also had a significant reduction of symptoms when infected with F.?graminearum. Our data suggest that PGs likely play a role in F.?graminearum infection of floral tissues, and that PGIPs incorporated into wheat may be important for increased resistance to FHB.