A specific fungal transcription factor controls effector gene expression and orchestrates the establishment of the necrotrophic pathogen lifestyle on wheat

The fungus Parastagonospora nodorum infects wheat through the use of necrotrophic efector (NE) proteins that cause host-specifc tissue necrosis. The Zn2Cys6 transcription factor PnPf2 positively regulates NE gene expression and is required for virulence on wheat. Little is known about other downstream targets of PnPf2. We compared the transcriptomes of the P. nodorum wildtype and a strain deleted in PnPf2 (pf2-69) during in vitro growth and host infection to further elucidate targets of PnPf2 signalling. Gene ontology enrichment analysis of the diferentially expressed (DE) genes revealed that genes associated with plant cell wall degradation and proteolysis were enriched in down-regulated DE gene sets in pf2-69 compared to SN15. In contrast, genes associated with redox control, nutrient and ion transport were up-regulated in the mutant. Further analysis of the DE gene set revealed that PnPf2 positively regulates twelve genes that encode efector-like proteins. Two of these genes encode proteins with homology to previously characterised efectors in other fungal phytopathogens. In addition to modulating efector gene expression, PnPf2 may play a broader role in the establishment of a necrotrophic lifestyle by orchestrating the expression of genes associated with plant cell wall degradation and nutrient assimilation.Tis study was supported by the Centre for Crop and Disease Management, a joint initiative of Curtin University and the Grains Research and Development Corporation [research grant CUR00023 (Programme 3)]. EJ was supported by the Australian Government Research Training Program Scholarshi

Low Amplitude Boom-and-Bust Cycles Define the Septoria Nodorum Blotch Interaction

Introduction: Septoria nodorum blotch (SNB) is a complex fungal disease of wheat caused by the Dothideomycete fungal pathogen Parastagonospora nodorum. The fungus infects through the use of necrotrophic effectors (NEs) that cause necrosis on hosts carrying matching dominant susceptibility genes. The Western Australia (WA) wheatbelt is a SNB “hot spot” and experiences significant under favorable conditions. Consequently, SNB has been a major target for breeders in WA for many years. Materials and Methods: In this study, we assembled a panel of 155 WA P. nodorum isolates collected over a 44-year period and compared them to 23 isolates from France and the USA using 28 SSR loci. Results: The WA P. nodorum population was clustered into five groups with contrasting properties. 80% of the studied isolates were assigned to two core groups found throughout the collection location and time. The other three non-core groups that encompassed transient and emergent populations were found in restricted locations and time. Changes in group genotypes occurred during periods that coincided with the mass adoption of a single or a small group of widely planted wheat cultivars. When introduced, these cultivars had high scores for SNB resistance. However, the field resistance of these new cultivars often declined over subsequent seasons prompting their replacement with new, more resistant varieties. Pathogenicity assays showed that newly emerged isolates non-core are more pathogenic than old isolates. It is likely that the non-core groups were repeatedly selected for increased virulence on the contemporary popular cultivars. Discussion: The low level of genetic diversity within the non-core groups, difference in virulence, low abundance, and restriction to limited locations suggest that these populations more vulnerable to a population crash when the cultivar was replaced by one that was genetically different and more resistant. We characterize the observed pattern as a low-amplitude boom-and-bust cycle in contrast with the classical high amplitude boom-and-bust cycles seen for biotrophic pathogens where the contrast between resistance and susceptibility is typically much greater. Implications of the results are discussed relating to breeding strategies for more sustainable SNB resistance and more generally for pathogens with NEs

Sensitivity to three Parastagonospora nodorum necrotrophic effectors in current Australian wheat cultivars and the presence of further fungal effectors

Parastagonospora nodorum is a major fungal pathogen of wheat in Australia causing septoria nodorum blotch (SNB). P. nodorum virulence is quantitative and depends to a large extent on multiple effector-host sensitivity gene interactions. The pathogen utilises a series of proteinaceous necrotrophic effectors to facilitate disease development on wheat cultivars that possess appropriate dominant sensitivity loci. Thus far, three necrotrophic effector genes have been cloned. Proteins derived from these genes were used to identify wheat cultivars that confer effector sensitivity. The goal of the study was to determine if effector sensitivity could be used to enhance breeding for SNB resistance. In this study, we have demonstrated that SnTox1 effector sensitivity is common in current commercial Western Australian wheat cultivars. Thirty-three of 46 cultivars showed evidence of sensitivity to SnTox1. Of these, 19 showed moderate or strong chlorotic/necrotic responses to SnTox1. Thirteen were completely insensitive to SnTox1. Disease susceptibility was most closely associated with SnTox3 sensitivity. In addition, we have identified biochemical evidence of a novel chlorosis-inducing protein or proteins in P. nodorum culture filtrates unmasked in strains that lack expression of ToxA, SnTox1 and SnTox3 activities

Pan-parastagonospora comparative genome analysis-effector prediction and genome evolution

We report a fungal pan-genome study involving Parastagonospora spp., including 21 isolates of the wheat (Triticum aestivum) pathogen Parastagonospora nodorum, 10 of the grass-infecting Parastagonospora avenae, and 2 of a closely related undefined sister species. We observed substantial variation in the distribution of polymorphisms across the pan-genome, including repeat-induced point mutations, diversifying selection and gene gains and losses.We also discovered chromosome-scale inter and intraspecific presence/absence variation of some sequences, suggesting the occurrence of one or more accessory chromosomes or regions that may play a role in host-pathogen interactions. The presence of known pathogenicity effector loci SnToxA, SnTox1, and SnTox3 varied substantially among isolates. Three P. nodorum isolates lacked functional versions for all three loci, whereas three P. avenae isolates carried one or both of the SnTox1 and SnTox3 genes, indicating previously unrecognized potential for discovering additional effectors in the P. nodorum-wheat pathosystem. We utilized the pangenomic comparative analysis to improve the prediction of pathogenicity effector candidates, recovering the three confirmed effectors among our top-ranked candidates. We propose applying this pan-genomic approach to identify the effector repertoire involved in other host-microbe interactions involving necrotrophic pathogens in the Pezizomycotina

Crop Updates 2009 - Cereals

This session covers twenty seven papers from different authors: PLENARY 1. Building soil carbon for productivity and implications for carbon accounting, Jeff Baldock, CSIRO Land and Water, Adelaide, SA 2. Fact or Fiction: Who is telling the truth and how to tell the difference, Doug Edmeades, agKnowledge Ltd, Hamilton 3. Four decades of crop sequence trials in Western Australia, Mark Seymour,Department of Agriculture and Food BREAK CROPS 4. 2008 Break Crops survey Report, Paul Carmody,Development Officer, Department of Agriculture and Food 5. Attitudes of Western Australian wheatbelt growers to ‘Break Crops’, Paul Carmody and Ian Pritchard, Development Officers, Department of Agriculture and Food 6. The value of organic nitrogen from lupins, Alan Meldrum, Pulse Australia 7.The area of break crops on farm: What farmers are doing compared to estimates based on maximising profit, Michael Robertson and Roger Lawes,CSIRO Floreat, Rob Sands,FARMANCO Farm Consultants, Peter White,Department of Agriculture and Food, Western Australia, Felicity Byrne and Andrew Bathgate,Farming Systems Analysis CROP SPECIFIC Breeding 8. Identification of WALAB2014 as a potential albus lupin variety for northern agricultural region of Western Australia, Kedar Adhikari, Department of Agriculture and Food 9. Enhancement of black spot resistance in field pea, Kedar Adhikari, Tanveer Khan, Stuart Morgan and Alan Harris, Department of Agriculture and Food 10. Desi chickpea breeding: Evaluation of advanced line, Khan, TN1, Harris, A1, Gaur, P2, Siddique, KHM3, Clarke, H4, Turner, NC4, MacLeod, W1, Morgan, S1 1Department of Agriculture and Food, Western Australia, 2International Crop Research Institute for the Semi Arid Tropics (ICRISAT), 3The University of Western Australia, 4Centre for Legumes in Mediterranean Agriculture 11. Pulse Breeding Australia-Australian Field Pea Improvement Program (AFPIP), Ian Pritchard1, Chris Veitch1, Stuart Morgan1, Alan Harris1 and Tony Leonforte 2 1 Department of Agriculture and Food, Western Australia, 2 Department off Primary Industries, Victoria Disease 12. Interaction between wheat varieties and fungicides to control stripe rust for grain and quality, Kith Jayasena, Geoff Thomas, Rob Loughman, Kazue Tanaka and Bill MacLeod, Department of Agriculture and Food 13. Findings of canola disease survey 2008 and its implications for better disease management in 2009, Ravjit Khangura, WJ MacLeod, P White, P Carmody and M Amjad, Department of Agriculture and Food 14. Combating wheat leaf diseases using genome sequencing and functional genomics, Richard Oliver, Australian Centre for Necrotrophic Fungal Pathogens, Murdoch University 15. Distribution and survival of wheat curl mite (Aceria tosichella), vector of Wheat Streak Mosaic Virus, in the WA grainbelt during 2008, Dusty Severtson, Peter Mangano, John Botha and Brenda Coutts, Department of Agriculture and Food 16. Partial resistance to Stagonspora (Septoria) Partial resistance to Stagonospora (Septoria) nodorum blotch and response to fungicide in a severe epidemic scenario, Manisha Shankar1, Richard Oliver2, Kasia Rybak2and Rob Loughman1 1Department of Agriculture and Food, Western Australia, 2Australian Centre for Necrotrophic Fungal Pathogens, Murdoch University, Western Australia 17. Black pod syndrome in lupins can be reduced by regular insecticide sprays, Peter White and Michael Baker,Department of Agriculture and Food Variety performance 18. Incorporating new herbicide tolerant juncea canola into low rainfall cropping systems in Western Australia, Mohammad Amjad, Department of Agriculture and Food 19. Varietal differences in germ end staining of barley, Andrea Hills,Department of Agriculture and Food 20. Wheat variety performance in the Central Agricultural Region in 2008, Shahajahan Miyan, Department of Agriculture and Food 21. Barley variety identification using DNA fingerprinting, Peter Portmann, Agriconnect, Perth WA Dr Nicole Rice, Southern Cross University, Lismore NSW Prof Robert Henry, Southern Cross University, Lismore NSW 22. Forecast disease resistance profile for the Western Australian barley crop over the next three years, Jeff J. Russell, Department of Agriculture and Food 23. Malting barley varieties differ in their flowering date and their response to changes in sowing date, BH Paynter and Jeff J. Russell,Department of Agriculture and Food 24. Market development for new barley varieties, Linda Price,Barley Australia 25. Response of wheat varieties to sowing time at Mt Barker, Katanning and Newdegate in 2008, Brenda Shackley and Vicki Scanlan,Department of Agriculture and Food 26. Flowering dates of wheat varieties in 2008 at three locations in Western Australia, Darshan Sharma, Brenda Shackley and Christine Zaicou-Kunesch, Department of Agriculture and Food 27. Agronomic responses of new wheat varieties in the norther agricultural region in 2008, Christine Zaicou-Kunesch, Department of Agriculture and Foo

Prevalence of ToxA-sensitive alleles of the wheat gene Tsn1 in Australian and Chinese wheat cultivars

A recent survey of worldwide isolates of Stagonospora nodorum showed that all Australian isolates expressed the host-specific toxin ToxA (Stukenbrock and McDonald 2007). In contrast, very few Chinese isolates did. All the Australian Pyrenophora tritici-repentis isolates that were tested expressed ToxA. We therefore postulated that the wheat gene that confers sensitivity to ToxA, Tsn1, would vary in prevalence in wheat cultivars in use in the two countries. Contrary to expectation, 10 out of 21 Chinese cultivars responded to ToxA as did 26 out of 46 Australian cultivars. The result suggests that ToxA has not had a determining effect on the survival of wheat cultivars in either country. They also suggest that despite the widespread use of Tsn1 markers in Australia, sensitive alleles are still commonplace. The removal of sensitive alleles from breeders' lines could be readily achieved and could significantly affect the resistance of wheat to both diseases

Ubiquity of ToxA and absence of ToxB in Australian populations of Pyrenophora tritici-repentis

Pyrenophora tritici-repentis, the causal organism of the necrotrophic foliar wheat disease tan spot [also known as yellow (leaf) spot in Australia] is an important disease in Australia and in many parts of the world. North American isolates of the pathogen have been shown to produce combinations of three host-specific toxins, ToxA, ToxB and ToxC. Each toxin interacts with a host sensitivity locus, respectively Tsn1, Tsc2 and Tsc1. The virulence of an isolate is partially correlated with the presence of these toxins and resistance in the host is associated with absence of the sensitivity loci. Breeding for resistance to tan spot can, therefore, be aided by knowledge of the prevalence of the toxin-encoding genes in local pathogen populations. Two of the toxins, A and B, are encoded by known genes and molecular tests for the genes have been developed. We screened a diverse collection of 119 tan spot isolates collected between 1984 and 2008 and from all affected regions of Australia (Queensland, New South Wales, Victoria and Western Australia). In all cases, the gene for ToxA was present and the gene for ToxB was absent. The implications for resistance breeding and epidemiology of the disease are discussed. We also define a diagnostic molecular marker for P. tritici-repentis

Ubiquity of ToxA and absence of ToxB in Australian populations of Pyrenophora tritici-repentis

Pyrenophora tritici-repentis, the causal organism of the necrotrophic foliar wheat disease tan spot [also known as yellow (leaf) spot in Australia] is an important disease in Australia and in many parts of the world. North American isolates of the pathogen have been shown to produce combinations of three host-specific toxins, ToxA, ToxB and ToxC. Each toxin interacts with a host sensitivity locus, respectively Tsn1, Tsc2 and Tsc1. The virulence of an isolate is partially correlated with the presence of these toxins and resistance in the host is associated with absence of the sensitivity loci. Breeding for resistance to tan spot can, therefore, be aided by knowledge of the prevalence of the toxin-encoding genes in local pathogen populations. Two of the toxins, A and B, are encoded by known genes and molecular tests for the genes have been developed. We screened a diverse collection of 119 tan spot isolates collected between 1984 and 2008 and from all affected regions of Australia (Queensland, New South Wales, Victoria and Western Australia). In all cases, the gene for ToxA was present and the gene for ToxB was absent. The implications for resistance breeding and epidemiology of the disease are discussed. We also de. ne a diagnostic molecular marker for P. tritici-repentis

Novel sources of resistance to Septoria nodorum blotch in the Vavilov wheat collection identified by genome-wide association studies

The fungus Parastagonospora nodorum is the causal agent of Septoria nodorum blotch (SNB) of wheat. The pathosystem is mediated by multiple fungal necrotrophic effector–host sensitivity gene interactions that include SnToxA–Tsn1, SnTox1–Snn1, and SnTox3–Snn3. A P. nodorum strain lacking SnToxA, SnTox1, and SnTox3 (toxa13) retained wild-type-like ability to infect some modern wheat cultivars, suggesting evidence of other effector-mediated susceptibility gene interactions or the lack of host resistance genes. To identify genomic regions harbouring such loci, we examined a panel of 295 historic wheat accessions from the N. I. Vavilov Institute of Plant Genetic Resources in Russia, which is comprised of genetically diverse landraces and breeding lines registered from 1920 to 1990. The wheat panel was subjected to effector bioassays, infection with P. nodorum wild type (SN15) and toxa13. In general, SN15 was more virulent than toxa13. Insensitivity to all three effectors contributed significantly to resistance against SN15, but not toxa13. Genome-wide association studies using phenotypes from SN15 infection detected quantitative trait loci (QTL) on chromosomes 1BS (Snn1), 2DS, 5AS, 5BS (Snn3), 3AL, 4AL, 4BS, and 7AS. For toxa13 infection, a QTL was detected on 5AS (similar to SN15), plus two additional QTL on 2DL and 7DL. Analysis of resistance phenotypes indicated that plant breeders may have inadvertently selected for effector insensitivity from 1940 onwards. We identify accessions that can be used to develop bi-parental mapping populations to characterise resistance-associated alleles for subsequent introgression into modern bread wheat to minimise the impact of SNB

A global metagenomic map of urban microbiomes and antimicrobial resistance

We present a global atlas of 4,728 metagenomic samples from mass-transit systems in 60 cities over 3 years, representing the first systematic, worldwide catalog of the urban microbial ecosystem. This atlas provides an annotated, geospatial profile of microbial strains, functional characteristics, antimicrobial resistance (AMR) markers, and genetic elements, including 10,928 viruses, 1,302 bacteria, 2 archaea, and 838,532 CRISPR arrays not found in reference databases. We identified 4,246 known species of urban microorganisms and a consistent set of 31 species found in 97% of samples that were distinct from human commensal organisms. Profiles of AMR genes varied widely in type and density across cities. Cities showed distinct microbial taxonomic signatures that were driven by climate and geographic differences. These results constitute a high-resolution global metagenomic atlas that enables discovery of organisms and genes, highlights potential public health and forensic applications, and provides a culture-independent view of AMR burden in cities.Funding: the Tri-I Program in Computational Biology and Medicine (CBM) funded by NIH grant 1T32GM083937; GitHub; Philip Blood and the Extreme Science and Engineering Discovery Environment (XSEDE), supported by NSF grant number ACI-1548562 and NSF award number ACI-1445606; NASA (NNX14AH50G, NNX17AB26G), the NIH (R01AI151059, R25EB020393, R21AI129851, R35GM138152, U01DA053941); STARR Foundation (I13- 0052); LLS (MCL7001-18, LLS 9238-16, LLS-MCL7001-18); the NSF (1840275); the Bill and Melinda Gates Foundation (OPP1151054); the Alfred P. Sloan Foundation (G-2015-13964); Swiss National Science Foundation grant number 407540_167331; NIH award number UL1TR000457; the US Department of Energy Joint Genome Institute under contract number DE-AC02-05CH11231; the National Energy Research Scientific Computing Center, supported by the Office of Science of the US Department of Energy; Stockholm Health Authority grant SLL 20160933; the Institut Pasteur Korea; an NRF Korea grant (NRF-2014K1A4A7A01074645, 2017M3A9G6068246); the CONICYT Fondecyt Iniciación grants 11140666 and 11160905; Keio University Funds for Individual Research; funds from the Yamagata prefectural government and the city of Tsuruoka; JSPS KAKENHI grant number 20K10436; the bilateral AT-UA collaboration fund (WTZ:UA 02/2019; Ministry of Education and Science of Ukraine, UA:M/84-2019, M/126-2020); Kyiv Academic Univeristy; Ministry of Education and Science of Ukraine project numbers 0118U100290 and 0120U101734; Centro de Excelencia Severo Ochoa 2013–2017; the CERCA Programme / Generalitat de Catalunya; the CRG-Novartis-Africa mobility program 2016; research funds from National Cheng Kung University and the Ministry of Science and Technology; Taiwan (MOST grant number 106-2321-B-006-016); we thank all the volunteers who made sampling NYC possible, Minciencias (project no. 639677758300), CNPq (EDN - 309973/2015-5), the Open Research Fund of Key Laboratory of Advanced Theory and Application in Statistics and Data Science – MOE, ECNU, the Research Grants Council of Hong Kong through project 11215017, National Key RD Project of China (2018YFE0201603), and Shanghai Municipal Science and Technology Major Project (2017SHZDZX01) (L.S.