Dr. Peter S. Solomon

Research School of Biology

RN Robertson Building

The Australian National University

Canberra 0200

ACT

Australia

Ph: (02) 6125 3952
Fax: (02) 6125 4331

Email:peter.solomon@anu.edu.au

Information for prospective students

Current position:

Lab Leader, Functional Genomics of Plant-Pathogen Interactions

What is Stagonospora nodorum and why is it important?

Stagonospora nodorum is a fungus that causes leaf and glume blotch disease on wheat. This disease causes greater than $100 million dollars in yield losses per annum in Australia alone and has been recently ranked as the third most important disease of wheat in this country. Traditional breeding methods for disease controls have only been partially successful at best and new and innovative anti-fungal strategies are required to prevent disease and secure Australian and global wheat supplies in the future.

                                                                              (Source: http://www.grdc.com.au)

Not only is S. nodorum a critical pathogen, its also extremely interesting and a lot fun too! S. nodorum can be cultured in the lab and is amenable to many common genetic techniques such as targeted gene disruption and gene overexpression. The genome sequence has been completed and extensive proteomics and metabolomics resources have been developed making S. nodorum a perfect model pathogen to better understand plant-pathogen interactions.

Confocal images taken on leaves infected with S. nodorum transformed with green fluorescent protein (GFP)

Current projects

1. Host specific toxins (HSTs) in S. nodorum.

 

We have recently shown that S. nodorum produces proteinaceous HSTs that have a significant role in causing disease. These proteins appear to be secreted by the fungus during the very early stages of infection and internalised within the wheat host cells. Inside the host cells, the proteins then undergo a gene-for-gene interaction with corresponding host genes which results in disease. Our work to date has identified two host specific toxins, ToxA and Tox3.

 

Functional and genetic analysis of interaction between S. nodorum ToxA and the wheat gene Tsn1 (a) Bioassay of culture filtrates from ToxA dysfunctional mutants and controls on wheat line BG261 (ToxA-sensitive). a, SN15 wild type; b, SN15KO10; c, SN15KO18; d, SN15ECT2; e, Sn2000 wild-type; f, Sn2000KO6; g, Sn2000KO28; h, Sn2000ECT5. Fungal inoculation reactions with avirulent isolates Sn791087 (i) and Sn791087 transformed with P. tritici-repentis ToxA (j and k) and S. nodorum ToxA (l and m). (b) Interval regression map of chromosome 5BL indicating the association of Tsn1 with reaction to Sn2K and SN15 toxA mutants, including wild-type and ectopic transformants 7 d after inoculation. The dotted line represents the lod significance threshold of 3.0, and the R2 value for each significant QTL peak is given for each line. A centimorgan (cM) scale is shown at the top. (Friesen et al. 2006)

 

Our best understood candidate is ToxA, a protein that appears to be encoded by a gene that was subject to a horizontal gene transfer event from Pyrenophora tritici-repentis. We know that this protein is internalised by host cells and we also know it is targeted at the sub-cellular level. A second HST protein has been recently identified from S. nodorum, Tox3. Tox3 appears to be unique to S. nodorum and it interacts (either directly or indirectly) with the host protein Snn3 to cause disease. We have 2 projects currently ongoing in the lab working on HSTs from S. nodorum.

Project 1. Apart from ToxA and Tox3, we know S. nodorum also produces other proteinaceous HSTs that we have been able to identify by infiltrating the progeny of several different crosses. However the encoding genes remain elusive. Projects are currently ongoing to try and identify the genes encoding these HSTs, predominantly through purifying the proteins in a traditional manner. We are also approaching this problem through comparative genomics by comparing the genome sequence of our virulent strain that produces many of the toxins to the sequence of an avirulent strain (generated via Illumina) that we know does not produce HSTs. Once candidate genes have been identified, these can then be selectively deleted through homologous recombination to determine their true role.

 

Project 2. Projects are now also underway to determine the mode-of-action of both ToxA and Tox3. Both are known to interact with corresponding wheat dominant susceptibility genes however their modes-of-action are action are completely unknown. Projects are now underway to determine the wheat reponse at the proteome level to exposure to both ToxA and Tox3. A study will also begin shortly using metabolomics to characterise the primary and secondary metabolite response to HST exposure. Another project has also started to determine the localisation of Tox3 during infection. Previous studies by groups working on ToxA in P. tritici-repentis have shown that ToxA is taken up by the host cells. The localisation of Tox3 though is unknown and Tox3-GFP fusion proteins have now been developed to solve this problem.

 

These projects are in collaboration with Prof. Richard Oliver at the Australian Centre for Necrotrophic Fungal Pathogens (Murdoch University), Dr. Tim Friesen at the USDA (Fargo, ND, USA) and Dr. Richard Lipscombe (Proteomics International, Perth, Australia).

 

 

 2. Understanding the role and identifying targets of signal transduction in S. nodorum.

 

We have previously demonstrated the requirement for many of the signalling pathways in S. nodorum for infection. Our interest is not so much on elucidating the complexity of signal transduction, but rather the genes and proteins that are regulated by these pathways and are responsible for the mutant phenotypes. Our current approaches for identifying these candidate genes are using metabolomics and proteomics. For metabolomics, we predominantly use GC-MS for profiling low-molecular weight metabolites in a library of S. nodorum signal transduction mutants. These profiles are then compiled into metabolic pathways highlighting gene, protein and pathway signalling-dependent regulation. Candidate genes can then be selectively deleted via reverse genetic approaches to identify their role. We are also studying secondary metabolism using ESI-MS and LC-MS on various mutants of S. nodorum we have created lacking polyketide synthases and non-ribosomal peptide synthetases.

 

GC-MS metabolite profiling of signalling mutants identified the massive accumulation of a compound in the mutants.	Detailed analysis of the compound on the left identified it as alternariol, a mycotoxin never previously associated with S. nodorum. This discovery highlighted the power (and potential!) of dissecting signalling pathways using functional genomics.

3. Characterising the mechanism of asexual sporulation in S. nodorum.

Stagonospora nodorum is a polycyclic pathogen, and as such, is reliant on efficient asexual sporulation to cause disease and devastating yield losses. Studies to date by this lab and collaborators have identified several key genes and metabolic processes that are required for S. nodorum to undergo asexual sporulation, for example mannitol metabolism (see figure below).

Several projects are ongoing in the lab focused on understanding the mechanism of asexual sporulation;

Project 1. Previous studies have identified several mutants that are defective in different developmental stages of asexual sporulation. A project is currently ongoing using quantitative proteomics (iTRAQ) to identify changes in proteome associated with these developmental defects. Reverse genetics will then be used to selectively disrupt the genes encoding the identified proteins to determine their role in sporulation. This project is being funded through a collaborative ARC Linkage project with Dr. Richard Lipscombe (Proteomics International, Perth WA).

Project 2. Previous microarray data have identified a series of genes that are up-regulated during sporulation in planta but not expressed at the same developmental stage in vitro. Two genes significantly up-regulated during pathogenicity are being characterised by developing S. nodorum strains lacking these genes. The resulting strains will be phenotyped to determine if the highly expressed genes do play a role in asexual sporulation during infection.

PhD/Honours Projects

 

PhD and Honours projects are available in any of the above areas. This lab has expertise covering all areas gene expression, proteomics and metabolomics in plant-pathogen interactions. Other projects are also available to study another serious wheat pathogen, Mycosphaerella graminicola. Please contact Dr. Peter Solomon (peter.solomon@anu.edu.au) for further information on any of the above projects or other project ideas.

 

 

Group Members

Dr. Delphine Vincent Postdoctoral Fellow delphine.vincent@anu.edu.au	ToxA and Tox3 mode-of-action. Delphine is investigating the mode-of-action of the host specific toxins from S. nodorum, ToxA and Tox3. These studies are currently focused on dissecting the wheat proteome upon HST exposure using both gel-based (DiGE) and gel-free proteomics techniques.
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Dr. Corinna Paeper Postdoctoral Fellow corinna.paeper@anu.edu.au	Tox3 localisation. Corinna is using Tox3-GFP fusions and confocal microscopy to determine the localisation of Tox3 during infection. Several Tox3 variants (fused with GFP) are also being studied to determine amino acid sequences important for activity and localisation.
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Ms Rosemary Birch Technical Officer rosemary.birch@anu.edu.au	Rosemary is responsible for the smooth running of the lab. She also has an integral role in several on-going projects.
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Mr Liam Cassidy PhD student	Proteomic dissection of asexual sporulation. Liam's project is exploiting previously characterised S. nodorum mutants that are impaired in their ability  undergo asexual sporulation, albeit at different stages. These mutants are being analysed using iTRAQ proteomics to determine the protein changes associated with the developmental defect in sporulation.
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Mr Hulson Zhang Honours student	Reverse genetics to study asexual sporulation. Hulson is using reverse genetic approaches to characterise two unknown genes strongly up-regulated during sporulation of S. nodorum in planta. The localisation of the genes during infection is also being investigated using GFP fusions.

 

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Selected Publications

2009

Casey*, T., Solomon*, P.S., Bringans, S., Tan, K-C., Oliver, R.P. & Lipscombe, R. (2009) Quantitative proteomic analysis of G-protein signalling in Stagonospora nodorum using Isobaric Tags for Relative and Absolute Quantification (iTRAQ). Proteomics (in press).

Antoni, E., Rybak, K., Tucker, M., Hane, J.K., Solomon, P.S., Drenth, A., Shanker, M. & Oliver, R.P. (2009) Ubiquity of ToxA and absence of ToxB in Australian populations of Pyrenophora tritici-repentis. Australasian Plant Pathology. (in press)

Robinson, A.L., Ebeler, S.E., Heymann, H., Boss, P.K., Solomon, P.S. & Trengove, R.D. (2009) Interactions between wine volatile compounds and grape and wine matrix components influence aroma compound headspace partitioning. Journal of Agricultural and Food Chemistry (in press).

Bringans, S., Hane, J.K., Casey, T., Tan, K-C., Lipscombe, R., Solomon, P.S. & Oliver, R.P. (2009) Deep proteogenomics; high throughput gene validation by multidimensional liquid chromatography and mass spectrometry of proteins from the fungal wheat pathogen Stagonospora nodorum. BMC Bioinformatics 10: 301.

Liu, Z., Faris, J.D., Oliver, R.P., Tan, K-C., Solomon, P.S., McDonald, M.C., McDonald, B.A., Nunez, A., Lu, S., Rasmussen, J.B. & Friesen, T.L. (2009) SnTox3 acts in effector triggered susceptibility to induce disease on wheat carrying the Snn3 gene. PLoS Pathogens 5: e1000581.

Tan, K-C, IpCho, S.V.S., Trengove, R.D., Oliver, R.P. & Solomon, P.S. (2009) Assessing the impact of transcriptomics, proteomics and metabolomics on fungal phytopathology. Molecular Plant Pathology 10: 703-715. .

Tan, K-C., Trengove, R.D., Maker, G.L., Oliver, R.P. & Solomon, P.S. (2009) Metabolite profiling identifies the mycotoxin alternariol in the pathogen Stagonospora nodorum. Metabolomics 5: 330-335.

Lowe, R.G.T, Lord, M., Rybak, K., Trengove, R.D. & Solomon, P.S. (2009) Trehalose biosynthesis is involved in sporulation of Stagonospora nodorum. Fungal Genetics and Biology 46: 381-389.

Oliver, R.P., Rybak, K., Solomon, P.S. & Ferguson-Hunt, M. (2009) Prevalence of ToxA-sensitive alleles of the wheat gene Tsn1 in Australian and Chinese wheat cultivars. Crop and Pasture Science 60,:348-352.

Tan, K-C., Heazlewood, J.L., Millar, A.H., Oliver, R.P. & Solomon, P.S. (2009) Proteomic identification of extracellular proteins regulated by the Gna1 Ga subunit in Stagonospora nodorum. Mycological Research 113: 523-531.

 

2008

Lowe, R.G.T., Lord, M., Rybak, K., Trengove, R.D., Oliver, R.P., and Solomon, P.S. (2008) A metabolomic approach to dissecting osmotic stress in the wheat pathogen Stagonospora nodorum. Fungal Genetics and Biology 45: 1479-1486.

Tan, K.-C., Heazlewood, J.L., Millar, A.H., Thomson, G., Oliver, R.P., and Solomon, P.S. (2008) A signalling-regulated short-chain dehydrogenase of Stagonospora nodorum regulates asexual development. Eukaryotic Cell 7, 1916-1929.

Friesen, T.L., Faris, J.D., Solomon, P.S. & Oliver, R.P. (2008) Host specific toxins; effectors of necrotrophic pathogenicity. Cellular Microbiology 10: 1421-1428.

Li, W., Csukai, M., Corran, A. Crowley, P., Solomon, P.S. & Oliver, R.P. (2008) Malayamycin, a new streptomycete antifungal compound, specifically inhibits sporulation of Stagonospora nodorum, cause of wheat glume blotch disease. Pest Management Science 64: 1294-302.

Solomon, P.S., Ipcho, S.V.S., Hane, J.K., Tan, K-C & Oliver, R.P. (2008) A quantitative PCR approach to determine gene copy number. Fungal Genetics Reports 55: 5-8.

Oliver, R.P., Lord, M., Rybak, K., and Solomon, P.S. (2008) Can the recent emergence of Pyrenophora tritici-repentis in Australia be attributed to the introduction of ToxA-sensitive wheat cultivars? Phytopathology 98: 488-491.

Oliver, R.P., Rybak, K., Shankar, M., Loughman, R., Harry, N. & Solomon, P.S. (2008) Quantitative disease resistance assessment by real-time PCR. Plant Pathology 57: 527-532.

Oliver, R.P. and Solomon, P.S. (2008) Recent fungal diseases of crop plants; is lateral gene transfer a common theme? Molecular Plant-Microbe Interactions 21: 287-293.

Friesen, T.L., Zhang, Z., Solomon, P.S., Oliver, R.P., and Faris, J.D. (2008) Genetic characterization of a novel wheat-Stagonospora nodorum host-selective toxin interaction and its role in disease susceptibility. Plant Physiology 146: 682-693.

 

2007

Hane, J., Lowe, R.G.T., Solomon, P.S., Tan, K.-C., Schoch, C., Spatafora, J.W., Crous, P.W., Kodira, C., Birren, B., and Oliver, R.P. (2007) Dothideomycete-plant interactions illuminated by genome sequencing and EST analysis of the wheat pathogen Stagonospora nodorum. Plant Cell 19: 3347-3368.

Solomon, P.S., Waters, O.D.C., and Oliver, R.P. (2007) Decoding the enigmatic mannitol in filamentous fungi. Trends in Microbiology 15: 257-262.

Solomon, P.S., Waters, O.D.C., Joergens, C.I., Lowe, R.G.T., Rechberger, J., Trengove, R.D., and Oliver, R.P. (2006) Mannitol is required for asexual sporulation in the wheat pathogen Stagonospora nodorum (glume blotch). Biochemical Journal 399: 231-239.

 

2006

Solomon, P.S., Rybak, K., Trengove, R.D., and Oliver, R.P. (2006) Investigating the role of calcium/calmodulin-dependent protein signalling in Stagonospora nodorum. Molecular Microbiology 62: 367-381.

Solomon, P.S., Lowe, R.G.T., Trengove, R.D., Rechberger, J., and Oliver, R.P. (2006) Normalisation of metabolites in heterogenous systems using genomics. Analytical Biochemistry 350: 156-158.

Solomon, P.S., Joergens, C.I., and Oliver, R.P. (2006) delta-Aminolevulinic acid synthesis is required for virulence of the wheat pathogen Stagonospora nodorum. Microbiology 152: 1533-1538.

Solomon, P.S., Wilson, T.J.G., Rybak, K., Parker, K., Lowe, R.G.T., and Oliver, R.P. (2006) Structural characterisation of the interaction between Triticum aestivum and the dothideomycete pathogen Stagonospora nodorum. European Journal of Plant Pathology 114: 275-282.

Solomon, P.S., Lowe, R.G.T., Tan, K.-C., Waters, O.D.C. and Oliver, R.P. (2006) Stagonospora nodorum; cause of Septoria nodorum blotch of wheat. Molecular Plant Pathology 7: 147-156.

Friesen, T.L., Stukenbrock, E.H., Liu, Z., Meinhardt, S., Ling, H., Faris, J.D., Rasmussen, J.B., Solomon, P.S., McDonald, B.A., and Oliver, R.P. (2006) Horizontal transfer of a fungal virulence gene controlling host specificity. Nature Genetics 38: 953-956.

 

2005

Solomon, P.S., Waters, O.D.C., Simmonds, J., Cooper, R.M., and Oliver, R.P. (2005) The Mak2 MAP kinase signal transduction pathway is required for pathogenicity in Stagonospora nodorum. Current Genetics 48: 60-68.

Solomon, P.S., Tan, K.-C., and Oliver, R.P. (2005) Mannitol 1-phosphate metabolism is required for sporulation in planta of the wheat pathogen Stagonospora nodorum. Molecular Plant-Microbe Interactions 18: 110-115.

 

2004

Solomon, P.S., Tan, K.-C., Sanchez, P., Cooper, R.M., and Oliver, R.P. (2004) The disruption of a G-alpha subunit sheds new light on the pathogenicity of Stagonospora nodorum on wheat. Molecular Plant-Microbe Interactions 17: 456-466.

Solomon, P.S., Parker, K., Loughman, R., and Oliver, R.P. (2004) Both mating types of Phaeosphaeria (anamorph Stagonospora) nodorum are present in Western Australia. European Journal of Plant Pathology 110: 763-766.

Solomon, P.S., and Oliver, R.P. (2004) Functional characterisation of glyoxalase I from the fungal wheat pathogen Stagonospora nodorum. Current Genetics 46: 115-121.

Solomon, P.S., Lee, R.C., Wilson, T.J.G., and Oliver, R.P. (2004) Pathogenicity of Stagonospora nodorum requires malate synthase. Molecular Microbiology 53: 1065-1073.

Oliver, R.P., and Solomon, P.S. (2004) Does the oxidative stress used by plants for defence provide a source of nutrients for pathogenic fungi? Trends in Plant Science 9: 472-473.

Links:

 

 

http://www.metabolomics.net.au

 

 

 

http://www.bioplatforms.com

 

 

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