Genome-Wide Analysis of Genes Induced by <Emphasis Type="Italic">Fusarium graminearum</Emphasis> Infection in Resistant and Susceptible Wheat Cultivars

Fusarium head blight (FHB) caused by Fusarium graminearum is one of the most serious diseases in wheat (Triticum aestivum) and barley (Hordeum vulgare). Dahongmil is an elite Korean wheat cultivar with relatively high resistance to FHB. To identify differentially expressed genes in the resistant cultivar Dahongmil and the susceptible cultivar Urimil after inoculation of F. graminearum, we used the Affymetrix GeneChip® Wheat Genome Array to identify 328 ESTs that were differentially expressed in inoculated seedling tissues of the two cultivars. From these, we selected 16 induced genes and found that they have defense functions, such as genes encoding pathogen resistance proteins, oxidative stress-related proteins, metabolism, and proteins involved in defense mechanisms. To verify the DNA microarray results, we tested seven of these genes by semiquantitative RT-PCR and confirmed that these defense- and stress-related genes were expressed at much higher levels in the resistant Dahongmil cultivar. We next developed a hypothetical functional gene network and identified 89 interaction pairs mediated by four of the differentially expressed genes in the hypothetical network. We further refined the network by identifying nine genes showing significant up- or down-regulation after FHB challenge in the resistant cultivar and two genes having multiple interactions with queried proteins. We hope that the set of induced genes identified in this study can be used for development of new wheat and barley cultivars with improved resistance to FHB.     

Genetically engineered resistance to Fusarium head blight in wheat by expression of Arabidopsis NPR1

Fusarium head blight (FHB) is a devastating disease of wheat and barley which causes extensive losses worldwide. Monogenic, gene-for-gene resistance to FHB has not been reported. The best source of resistance to FHB is a complex, quantitative trait derived from the wheat cv. Sumai 3. Here, we show that the Arabidopsis thaliana NPR1 gene (AtNPR1), which regulates the activation of systemic acquired resistance, when expressed in the FHB-susceptible wheat cv. Bobwhite, confers a heritable, type II resistance to FHB caused by Fusarium graminearum. The heightened FHB resistance in the transgenic AtNPRI -expressing wheat is associated with the faster activation of defense response when challenged by the fungus. PR1 expression is induced rapidly to a high level in the fungus-challenged spikes of the AtNPR1-expressing wheat. Furthermore, benzothiadiazole, a functional analog of salicylic acid, induced PR1 expression faster and to a higher level in the AtNPR1-expressing wheat than in the nontransgenic plants. We suggest that FHB resistance in the AtNPR1-expressing wheat is a result of these plants being more responsive to an endogenous activator of plant defense. Our results demonstrate that NPR1 is an effective candidate for controlling FHB.     

Salicylic acid regulates basal resistance to Fusarium head blight in wheat

Fusarium head blight (FHB) is a destructive disease of cereal crops such as wheat and barley. Previously, expression in wheat of the Arabidopsis NPR1 gene (AtNPR1), which encodes a key regulator of salicylic acid (SA) signaling, was shown to reduce severity of FHB caused by Fusarium graminearum. It was hypothesized that SA signaling contributes to wheat defense against F. graminearum. Here, we show that increased accumulation of SA in fungus-infected spikes correlated with elevated expression of the SA-inducible pathogenesis-related 1 (PR1) gene and FHB resistance. In addition, FHB severity and mycotoxin accumulation were curtailed in wheat plants treated with SA and in AtNPR1 wheat, which is hyper-responsive to SA. In support of a critical role for SA in basal resistance to FHB, disease severity was higher in wheat expressing the NahG-encoded salicylate hydroxylase, which metabolizes SA. The FHB-promoting effect of NahG was overcome by application of benzo (1,2,3), thiadiazole-7 carbothioic acid S-methyl ester, a synthetic functional analog of SA, thus confirming an important role for SA signaling in basal resistance to FHB. We further demonstrate that jasmonate signaling has a dichotomous role in wheat interaction with F. graminearum, constraining activation of SA signaling during early stages of infection and promoting resistance during the later stages of infection.     

AFLP and STS tagging of a major QTL for Fusarium head blight resistance in wheat

Large-scale field screening for Fusarium head blight (FHB) resistance in wheat is difficult because environmental factors strongly influences the expression of resistance genes. Marker-assisted selection (MAS) may provide a powerful alternative. Conversion of amplified fragment length polymorphism (AFLP) markers into sequence-tagged site (STS) markers can generate breeder-friendly markers for MAS. In a previous study, one major quantitative trait locus (QTL) on chromosome 3BS was identified by using EcoRI-AFLP and a recombinant inbred population derived from the cross Ning 7840/Clark. Further mapping with PstI-AFLPs identified five markers that were significantly associated with the QTL. Three of them individually explained 38% to 50% of the phenotypic variation for FHB resistance. Two of them (pAGT/mCTG57, pACT/mCTG136) were linked to the QTL in coupling, and another (pAG/mCAA244) was linked to the QTL in repulsion. Successful conversion of one AFLP marker (pAG/mCAA244) yielded a co-dominant STS marker that explains about 50% of the phenotypic variation for FHB resistance in the population. The STS was validated in 14 other cultivars and is the first STS marker for a FHB resistance QTL converted from an AFLP marker.     

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.     

Overexpression of defense response genes in transgenic wheat enhances resistance to Fusarium head blight

Fusarium head blight (FHB) of wheat, caused by Fusarium graminearum and other Fusarium species, is a major disease problem for wheat production worldwide. To combat this problem, large-scale breeding efforts have been established. Although progress has been made through standard breeding approaches, the level of resistance attained is insufficient to withstand epidemic conditions. Genetic engineering provides an alternative approach to enhance the level of resistance. Many defense response genes are induced in wheat during F. graminearum infection and may play a role in reducing FHB. The objectives of this study were (1) to develop transgenic wheat overexpressing the defense response genes α-1-purothionin, thaumatin-like protein 1 (tlp-1), and β-1,3-glucanase; and (2) to test the resultant transgenic wheat lines against F. graminearum infection under greenhouse and field conditions. Using the wheat cultivar Bobwhite, we developed one, two, and four lines carrying the α-1-purothionin, tlp-1, and β-1,3-glucanase transgenes, respectively, that had statistically significant reductions in FHB severity in greenhouse evaluations. We tested these seven transgenic lines under field conditions for percent FHB disease severity, deoxynivalenol (DON) mycotoxin accumulation, and percent visually scabby kernels (VSK). Six of the seven lines differed from the nontransgenic parental Bobwhite line for at least one of the disease traits. A β-1,3-glucanase transgenic line had enhanced resistance, showing lower FHB severity, DON concentration, and percent VSK compared to Bobwhite. Taken together, the results showed that overexpression of defense response genes in wheat could enhance the FHB resistance in both greenhouse and field conditions.     

Differential proteomic analysis of proteins in wheat spikes induced by Fusarium graminearum

Scab, caused by Fusarium graminearum, is a serious spike disease in wheat. To identify proteins in resistant wheat cultivar Wangshuibai induced by F. graminearum infection, proteins extracted from spikes 6, 12 and 24 h after inoculation were separated by 2-DE. Thirty protein spots showing 3-fold change in abundance when compared with treatment without inoculation were characterized by MALDI-TOF MS and matched to proteins by querying the mass spectra in protein databases or the Triticeae EST translation database. Based on their volume profiles, these proteins were classified into four categories. The first one fell off rapidly at the initial inoculation and then rose at 12 or 24 hai, the second one decreased considerably after inoculation and remained at low level, the third one rose at the initial inoculation and then declined at 12 or 24 hai, the forth one showed steady increase after inoculation and maintained at a high level. Many of the proteins identified in the first two categories are related to carbon metabolism and photosynthesis. While most of proteins identified in the last two categories are related to stress defense of plants, indicating that proteins associated with the defense reactions were activated or translated shortly after inoculation.     

Differentially Expressed Proteins Associated with Fusarium Head Blight Resistance in Wheat

Background

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, substantially reduces wheat grain yield and quality worldwide. Proteins play important roles in defense against the fungal infection. This study characterized differentially expressed proteins between near-isogenic lines (NILs) contrasting in alleles of Fhb1, a major FHB resistance gene in wheat, to identify proteins underlining FHB resistance of Fhb1.

Methods

The two-dimensional protein profiles were compared between the Fusarium-inoculated spikes of the two NILs collected 72 h after inoculation. The protein profiles of mock- and Fusarium-inoculated Fhb1⁺NIL were also compared to identify pathogen-responsive proteins.

Results

Eight proteins were either induced or upregulated in inoculated Fhb1⁺NIL when compared with mock-inoculated Fhb1⁺NIL; nine proteins were either induced or upregulated in the Fusarium-inoculated Fhb1⁺NIL when compared with Fusarium-inoculated Fhb1⁻NIL. Proteins that were differentially expressed in the Fhb1⁺NIL, not in the Fhb1⁻NIL, after Fusarium inoculation included wheat proteins for defending fungal penetration, photosynthesis, energy metabolism, and detoxification.

Conclusions

Coordinated expression of the identified proteins resulted in FHB resistance in Fhb1⁺NIL. The results provide insight into the pathway of Fhb1-mediated FHB resistance.     

小麦响应禾谷镰刀菌侵染的转录组学研究进展

由禾谷镰刀菌引起的小麦赤霉病直接为害作物穗部,不仅严重影响小麦产量,还可因为毒素污染问题威胁人畜健康。近年来对小麦与禾谷镰刀菌互作的转录组学研究带来了很多新见解,概述了小麦响应禾谷镰刀菌侵染的转录组学研究进展,主要比较了不同抗性品种、不同器官、不同籽粒发育时期的小麦穗部在禾谷镰刀菌侵染时的基因表达特征,总结了赤霉病感染时小麦的激素响应、信号传导、转录调控和防卫相关基因的表达规律,以期促进研究者对小麦响应禾谷镰刀菌侵染规律的理解。