PS Seminar Series- PhD Exit Seminar - How does scald pathogen infect barley? Characterisation of the virulence factors of Rhynchosporium commune

Abstract - Rhynchosporium commune is a pathogenic fungus causing barley scald disease. Although scald disease has become a significant issue for commercial barley growers, the molecular mechanisms underpinning the disease are poorly understood.

To address this lack of resources in the R. commune field, I generated a long-read assembly of the genome of R. commune Australian isolate WAI453. The assembly contained 20 gapless nuclear contigs with size 57.76 Mbases. To complement this genome sequence, RNA-seq datasets were generated from in vitro and in planta samples and used to facilitate the genome annotation and also for differential gene expression (DGE) analysis. In the DGE dataset, the NIP2 effector genes, which are putatively involved in mediating disease, were highly expressed during in planta growth, with NIP2.1 had the highest expression level. Population genetics was performed to analyse the diversity of the NIP2 genes in the global population of R. commune and its sister species. Only a single haplotype of NIP2.3 was detected from 191 R. commune strains while NIP2.6 was found as a specific NIP2 genes of R. commune. In addition, functional studies of NIP2.1 protein was also performed by using the heterologous protein. This protein neither induces cell death nor suppresses the ROS burst in barley leaves.

Further analysis of the DGE dataset also revealed that some secondary metabolite gene clusters were also upregulated during disease. One of the clusters, PKS4, contained two predicted core enzymes and a specific transcription factor (TF). The expression of PKS4 cluster can be upregulated in the in vitro culture by generating the TF overexpression mutant. In addition, a novel PKS-terpene hybrid compound which has a phytotoxic activity was discovered as the product of the PKS4 cluster although only the partial structure of the compound has been elucidated so far. In addition, an independent mechanism of necrosis, which is not related with the PKS4 cluster product, was also demonstrated in barley leaves infiltrated with the culture filtrate of the TF overexpression mutant. A bottom-up proteomics was performed to identify the highly abundant protein in the TF overexpression mutant culture filtrate. This proteomics data will be useful for uncovering the new virulence factor of R. commune. Overall, these results advance our understanding about virulence factors of R. commune and provide a valuable community resource for further exploration of this important pathogen.

Biography – Rey is a PhD candidate in the Solomon Lab, Division of Plant Sciences, RSB, ANU. Prior to his PhD, he completed master’s degree in BioSciences at The University of Melbourne.