Fusarium resistance gene identification in wheat
SUPERVISOR: Hermann BÜRSTMAYR
PROJECT ASSIGNED TO: Kefas Luka BAIYI
Fusarium head blight (FHB) also known as wheat scab is an important economic disease affecting global production of wheat and other small cereals such as barley, oats etc. Fusarium graminearum and its related species have been identified as the causative organisms of this highly destructive disease. FHB affects wheat heads with a characteristic bleached spikelets and subsequent failed kernel development leading to significant yield losses in addition to its ability to produce mycotoxins which poses threats to feed and food quality. Among the most prevalent mycotoxins produced by F. graminearum, type-B trichothecene deoxynivalenol (DON) is the most severe largely because of its phytotoxic property acting as virulence factor for fungal spread in wheat heads. As a result, the control of FHB is of pivotal importance to wheat growers around the world.
Breeding for FHB is quantitative in nature and greatly influence by environmental factors such as high relative humidity, changing rainfall patterns among others. Many quantitative traits loci (QTL) have been identified scattered across the 21 chromosomes with only a few successfully deployed in breeding programs. A major QTL has been identified, mapped and shown to confer resistance to both fungal spread and DON via conjugation into the non-toxic DON-3-O-glucoside (D3G). However, the gene controlling the DON detoxification is completely unknown.
The aim of this project is to decipher the durable and highly effective resistance QTL against FHB and DON with a view to elucidate the causal factor(s). Three (3) susceptible mutant lines and the resistant wild-type line will be used for both transcriptomics and genome editing. Transcriptome analysis of the near-isogenic lines will enable us to identify differently expressed genes most likely involved in FHB spreading and DON resistance. Furthermore, transcriptomics will provide targets for CRISPR-Cas mediated mutagenesis and downstream targeted metabolomics analysis to validate functional results. CRISPR-Cas will be employed to produce a systemic series of deletions and targeted sequence changes within the candidate region and to analyse their effect on FHB spread, DON resistance and DON glycosylation.
Figure 1: Contrasting phenotypes for FHB spreading (A) and DON resistance (B) of lines differing in the FHB resistance QTL after treatment with Fusarium graminearum (A) or deoxynivalenol (B) (1mg/spike).
Figure 2: Graphical summary of the project’s strategy to elucidate a major FHB resistance QTL.
Figure 3: Expression analysis of genes located in the QTL region. (A) log2-transformed RNA-seq read counts for genes located in the region. Each subpanel comprises time-course-derived data (3–48 h) after inoculation with Fusarium graminearum or mock for either the resistance QTL-carrying NIL1 or the susceptible NIL2. Genes with no mapped reads are given in dark blue, highly expressed genes in red. (B) Differentially expressed genes in contrasts comparing F. graminearum-challenged to mock-treated samples in the resistant NIL1 and the susceptible NIL2 (left panels) and comparing mock-treated and F. graminearum-inoculated samples between the two NILs (right panels). Positive log2-transformed fold-change values indicate significant higher expression in response to the pathogen (left panels) or higher expression for the susceptible NIL2 when comparing similarly treated samples between NILs (right panels). White spaces represent samples with no significant (FDR >0.05) differences (yet differences in read counts as indicated in a might occur) (Schweiger et al. 2016, TAG 129:1607-1623).