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

A Putative Transcription Factor MYT1 Is Required for Female Fertility in the Ascomycete Gibberella zeae

Gibberella zeae is an important pathogen of major cereal crops. The fungus produces ascospores that forcibly discharge from mature fruiting bodies, which serve as the primary inocula for disease epidemics. In this study, we characterized an insertional mutant Z39P105 with a defect in sexual development and identified a gene encoding a putative transcription factor designated as MYT1. This gene contains a Myb DNA-binding domain and is conserved in the subphylum Pezizomycotina of Ascomycota. The MYT1 protein fused with green fluorescence protein localized in nuclei, which supports its role as a transcriptional regulator. The MYT1 deletion mutant showed similar phenotypes to the wild-type strain in vegetative growth, conidia production and germination, virulence, and mycotoxin production, but had defect in female fertility. A mutant overexpressing MYT1 showed earlier germination, faster mycelia growth, and reduced mycotoxin production compared to the wild-type strain, suggesting that improper MYT1 expression affects the expression of genes involved in the cell cycle and secondary metabolite production. This study is the first to characterize a transcription factor containing a Myb DNA-binding domain that is specific to sexual development in G. zeae

Taxonomic studies on Australian isolates of stemphylium spp. and associated teleomorphs

Taxonomic studies on monosporic pure cultures of Australian isolates of Stemphylium revealed the presence of three species, namely S. botryosum, S. globuliferum and S. vesicarium. A group intermediate between S. botryosum and S. vesicarium but more closely resembling S. vesicarium was recognised. The circumscription of S. vesicarium was broadened to accommodate this taxon which was found on Medicago sativa, M. rugosa and Simmondsia chinensis. Studies on herbarium specimens deposited as S. botryosum on M. sativa from a number of overseas locations indicated that in all cases the pathogen fitted our concept of S. vesicarium. Teleomorphs were induced in pure culture for each of the above-mentioned anamorphs, and in all instances the teleomorph was identified as Pleospora herbarum. The ascospore morphology was similar for all isolates, and the shape of the ends of the spore and the number of longitudinal septa were variable characters even within an isolate. However, the teleomorphs could be separated into two distinct groups on the basis of ascal length

A role for the mycotoxin deoxynivalenol in stem colonisation during crown rot disease of wheat caused by Fusarium graminearum and Fusarium pseudograminearum

Fusarium graminearum (Fg) can cause head blight and crown rot (CR) diseases of wheat but fungal colonisation and mycotoxin production by Fg during CR are little understood. Studies of an Australian strain of Fg demonstrated that expression of the Tri5 gene of Fg and deoxynivalenol (DON) production were induced during infection of the stem base and to levels equivalent to those observed in inoculated heads. To study fungal colonisation and DON production in CR disease, we inoculated stem bases, 14 days after sowing, with macroconidia of Australian and USA strains of Fg and of an Australian strain of Fusarium pseudograminearum, a related pathogen frequently associated with CR. At maturity, the fungal pathogen was subsequently detected by isolation on growth media in high percentages of plants at the stem base and the lowest node adjacent to the inoculation site (50–100%), in the non-inoculated flag-leaf node (FLN) (35–95%) and in asymptomatic non-inoculated mature heads (50–60%) and kernels (20%). Microscopic analysis suggested that colonisation of upper nodes occurred primarily via the pith parenchyma and lumen. Significant concentrations of DON (up to 35 ppm) were detected in the FLN and the head/rachis following inoculation of the stem base. To test the role of DON in CR a transgenic strain of Fg from the USA with the Tri5 gene deleted was compared with its original wild-type and these produced similar levels of CR lesion development and necrosis indicating that DON production was not necessary to cause CR disease symptoms. However, the DON-minus mutant was less frequently recovered from the FLN than the wild type suggesting that DON has a role in stem colonisation by the fungus