Magnaporthe and Its Relatives

Abstract

The ascomycetous family Magnaporthaceae includes plant pathogenic fungi that cause diseases on members of the Poaceae worldwide, affecting the turfgrass industry and staple food crops such as rice, wheat, millet and maize. The economically significant turfgrass root pathogen Magnaporthe poae belongs to this family. Two of the most damaging fungal pathogens of wheat and rice also belong to this family: the intractable root‐infecting fungus and causal agent of take‐all disease, Gaeumannomyces graminis and the blast fungus Magnaporthe grisea. M. grisea has emerged as a paradigm for the understanding of fungal aerial attack. Interestingly, M. grisea can also infect roots and is far more amenable to transformation than G. graminis and M. poae. Consequently, M. grisea constitutes an excellent fungal model system for the dissection of genetic determinants required for infection on underground tissues, and for comparative analysis of the distinct tissue‐specific pathogenic mechanisms observed during leaf and root colonization.

Key concepts

  • Appressorium: Infection structure formed by fungal hypha that mediates attachment and penetration in aerial plant tissues. This term is also used for penetration structures produced by symbiotic fungi on roots.

  • Clade: Phylogenetic group which comprises a single common ancestor and all the descendants of that ancestor.

  • EST (expressed sequenced tags): Short cDNA (complementary deoxyribonucleic acid) sequences, generally obtained from cDNA libraries generated under different nutrient conditions and/or tissues.

  • Hyphopodium: Specialized structure produced at the tip of the hyphae that mediate fungal penetration into root tissue. G. graminis can produce simple or lobed hyphopodia.

  • QTL (quantitative trait locus): Region of DNA associated with a certain quantitative phenotypic trait. The molecular identification of QTLs usually enables the identification and sequencing of genes that are responsible for such a phenotypic trait.

Keywords: root infection; take‐all; rice blast; hyphopodium; fungal pathogenesis

Figure 1.

Take‐all symptoms produced by G. graminis var. tritici. (a–b) Blackened roots on three week old seedlings of barley (a) and wheat (b); (c) adult wheat plant with severe rot symptoms on the roots and the stem base; (d) circular patches of wheat plants in a field showing typical take‐all disease symptoms with visible white heads and stunted growth. Figures c and d are reproduced courtesy of Kansas State University.

Figure 2.

Summer patch disease on turfgrass. (a) Typical circular patches of yellow‐brown colour. (b) Necrotic root lesions caused by M. poae. Images are reproduced courtesy of Dr. Lane Tredway, North Carolina State University.

Figure 3.

The stem rot fungus (Magnaporthe salvinii) on rice. (a) Development of sigmoid conidia of M. salvinii on sympodial conidiophore. Denticle of each conidiogenous cell is clear. (b) Typical stem rot symptoms with black necrotic spots formed on outer leaf sheaths. (c) Formation of black small sclerotia into rice stem. Reproduced with permission of Dr. Mohammad Javan‐Nikkhah.

Figure 4.

Gray leaf spot on turfgrass. Disease symptoms caused by (a) M. grisea on tall fescue (Festuca arundinacea) and (b) St. Augustine grass (Stenotaphrum secundatum). Reproduced by courtesy of Dr. Lane Tredway, North Carolina State University.

Figure 5.

Blast disease on rice and M. grisea development on distinct plant tissues. (a) Panicle blast symptoms in a rice field; (b) noninfected (left) and infected (right) rice panicle with necrotic lesions on neck (a), leaf (b) and collar (c); (c) typical diamond‐shaped lesions with brown margins on 3‐weeks‐old rice leaves; (d) scanning electron micrograph showing a M. grisea conidium (CO) that has produced an appressorium (AP) on a rice leaf surface; (e) necrotic symptoms produced by 3‐weeks‐old seedlings; (f) confocal image of a M. grisea conidium producing an hyphopodium (HY) during rice root colonization. Images a and b Courtesy of Dr. Yulin Jia, USDA‐ARS, Dale Bumpers National Rice Research Center.

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Further Reading

Khang CH, Park SY, Lee YH, Valent B and Kang S (2008) Genome Organization and Evolution of the AVR‐Pita Avirulence Gene Family in the Magnaporthe grisea Species Complex. Molecular Plant Microbe Interactions 21: 658–670.

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Web Links

e‐fungi PFAM makes available protein family motifs, identified in predicted proteomes and secretomes from genomes of nine species of ascomycetes. http://obelix.ex.ac.uk/efungi/pfam.html

Magnaporthe grisea genome database (Broad Institute) http://www.broad.mit.edu/annotation/genome/magnaporthe_grisea/Home.html

MGOS, Magnaporthe grisea–Oryza sativa interaction database; a M. grisea‐community database. (Soderlund C et al. (2006). MGOS: A resource for studying Magnaporthe grisea and Oryza sativa interactions. Molecular Plant‐Microbe Interactions 19, 1055–1061.) http://www.mgosdb.org/

MPSS database (Massively Parallel Signature Sequencing): technique based on Solexa sequencing that estimates relative abundance of a gene present in a specific M. grisea cDNA library. http://mpss.udel.edu/mg/

OrygenesDB: an interactive tool for rice reverse genetics http://orygenesdb.cirad.fr/

Oryzabase: Integrated Rice Science Database http://www.shigen.nig.ac.jp/rice/oryzabase/top/top.jsp

PHI base (Pathogen–Host Interaction database) offers molecular and biological information on genes involved in host–pathogen interactions. http://www.phi‐base.org/

Phytopathogenic Fungi and Oomycete EST Database provides Expressed Sequence Tags obtained from eighteen species of plant pathogenic fungi, two species of phytopathogenic oomycetes and three species of saprophytic fungi. (Soanes DM and Talbot NJ (2005) A bioinformatic tool for analysis of EST transcript abundance during infection‐related development by Magnaporthe grisea. Molecular Plant Pathology 6, 503–512.) http://ri.imb.nrc.ca/cogeme/index.html

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Besi, Maria I, Tucker, Sara L, and Sesma, Ane(Mar 2009) Magnaporthe and Its Relatives. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021311]