The fungus Stagonospora nodorum is the causal agent of leaf and glume blotch
disease on wheat and is an emerging model for the study of the interaction between
plants and necrotrophic fungal pathogens. Signal transduction plays a critical role
during infection by allowing the pathogen to sense and appropriately respond to
environmental changes. The role of signal transduction in the pathogenicity of S.
nodorum was analysed by the targeted inactivation of genes encoding a Gá subunit
(Gna1) and a mitogen-activated protein kinase (Mak2). Strains carrying the inactivated
genes were impaired in virulence and demonstrated a host of phenotypic impairments
such as abolished sporulation. Therefore, it was hypothesised that Gna1 and Mak2
regulate downstream effector molecules that are critical for pathogenic development. A
2D gel-based proteomic approach was used to compare the extracellular and
intracellular proteomes of the wild-type fungus and signalling mutants for differences in
protein abundance. Tandem mass spectrometry (LC-MS/MS) analysis and patternmatching
against the S. nodorum genome sequence led to the identification of 26 genes
from 34 differentially abundant protein spots. These genes possess probable roles in
protein cycling, plant cell wall degradation, stress response, nucleotide metabolism,
proteolysis, quinate and secondary metabolism. A putative short-chain dehydrogenase
gene (Sch1) was identified and its expression was shown to be reduced in both
signalling mutants. The transcript level of Sch1 increased during the latter period of
infection coinciding with pycnidiation. Sch1 was inactivated by targeted gene deletion.
Mutants were able to effectively colonise the host but asexual sporulation was
dramatically reduced and pycnidial ontogeny was severely disrupted. Furthermore, the
sch1 mutants showed alterations in the metabolome. GC-MS analysis identified a
metabolite which accumulated in the sch1 mutants. Computational and database
analyses indicated that the compound possesses a cyclic carbon backbone. Based on
these findings, Sch1 may be a suitable target for fungicides that inhibit asexual
sporulation and the accumulated compound may be used to design novel antifungal
compounds. 2D SDS-PAGE analysis identified increased abundance of another
putative short-chain dehydrogenase (Sch2) and a nitroreductase in the sch1-deleted
background. It was also shown that Sch2 was regulated by Gna1.
| Identifer | oai:union.ndltd.org:ADTP/221918 |
| Date | January 2007 |
| Creators | Karchun.tan@yahoo.com.au, Kar-Chun Tan |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Kar-Chun Tan |
Page generated in 0.0025 seconds