Our SNB team is investigating the pathogenicity mechanism of Parastagonospora nodorum (the pathogen causing SNB on wheat). The team’s aim is to develop antifungal strategies that target weaknesses in the fungal metabolism and devise strategies to minimise the impact of SNB, a pathogen responsible for $108 million in yield loss of wheat per annum in Australia.
1. Necrotrophic effector biology
Parastagonospora nodorum uses necrotrophic proteinaceous effectors to disable the host plant during infection. These secreted fungal effectors cause tissue death on wheat varieties that possess a dominant sensitivity gene/receptor. Thus far, three proteinaceous necrotrophic effector genes were identified – ToxA, Tox1 and Tox3. In addition, the ToxA sensitivity gene Tsn1 was also recently identified in wheat. Experimental evidence suggests that P. nodorum possess many more novel necrotrophic effectors. Our research aim is to identify these novel effectors and genes that confer sensitivity in wheat.
Current projects are:
1.Biochemical purification of novel effectors from P. nodorum via fast protein liquid chromatography and mass spectrometry.
2.Identification of candidate effector genes via bioinformatics and heterologous expression in yeast and E. coli.
3.Identification of fungal signalling components that regulate effector gene expression.
4.Wheat genetic mapping to identify quantitative trait loci (QTL) that confer sensitivity to novel effectors and SNB.
5.Delivery of effector screening kits, QTL markers and enhanced germplams to wheat breeders.
2. Completing the Parastagonospora nodorum SN15 genome
Parastagonospora nodorum possess a sequenced genome that is comprised of 37.5 Mbp of nucleotides contained within 108 scaffolds. Gene prediction model and experimental evidence supports 12,380 genes with an additional 5,354 requires validation. Gaps, ambiguous nucleotides, indels and SNPs are still prevalent within the current assembly. Hence, we are currently completing the P. nodorum genome through:
1.Re-sequencing the P. nodorum SN15 genome using Illumina and PacBio technologies. Bioinformatic modelling and prediction of effector genes.
2.High-throughput proteogenomic validation of P. nodorum genes via subcellular proteomics.
3.Validating gene model via RNASeq.
3. Wheat metabolomics
We are currently profiling the metabolome of wheat in response to P. nodorum infection. A comprehensive metabolomics approach is being undertaken through the use of GC and LC-MS to identify phytoalexins that confer broad spectrum resistance to fungal diseases in wheat.
4. Development of novel metabolic components in P. nodorum that can be exploited as fungicide
Fungicides are being used more and more by Australian grain growers. Mounting fungicide resistance is observed and presents a significant problem in the cereal industry. Hence, the formulation of new broad spectrum antifungal strategies is required. We are currently using a forward genetics approach and RNAi to identify genes that can be exploited as new fungicide and/or in planta RNAi targets.
5. Identification of novel pathogenicity genes in P. nodorum
We have identified a group of P. nodorum genes that are strongly expressed during wheat infection using a genome-wide microarray. These genes are implicated in plant cell wall degradation, nutrient assimilation and signal transduction. We are currently assessing these genes for their role in pathogenicity through the generation of gene knockout mutants for infection and functional assays.