Handbook Part 2 - International Mycological Association

ORAL ABSTRACTS THURSDAY AUGUST 23
0800-1000
SYMPOSIUM 42 - Genomes and Fitness
S42IS1 - 0774
Competition of heterozygous deletant Saccharomyces cerevisiae strains in a grape juice environment
G.W. Griffith1, E.J.M Cross1, H.M. Davey1, D. Delneri 2, D.C. Hoyle2, D.B. Kell 2, S.G. Oliver 2
1University of Wales Aberystwyth, Wales, United Kingdom, 2 University of Manchester, Manchester, United Kingdom
The existence of a complete set of 6000 single-gene deletant strains of the yeast Saccharomyces cerevisiae represents
an important tool for qualitative and quantitative analysis of gene function. The presence of unique barcodes and a
selective marker in each deletion cassette allows parallel analysis of strains by microarray hybridisation. Strain
abundance can thus be quantified as a means of assessing the contribution of individual genes to fitness under a
range of environmental conditions. Using a pool of diploid heterozygous deletants, it was possible to identify strains
which were either haploinsufficient or haploproficient (i.e. decreased or increased fitness respectively when one
rather than both gene copies were present) under different fermentation conditions.
‘Competition’ experiments were conducted for up to 30 generations, in either continuous or semi-batch fermentor
systems, using red /white juices and in the presence and absence of competitor organisms. Changes in fitness
identified in grape juice were compared to responses in synthetic nutrient limited media. Whilst fruit juices are
generally N-limited, there was incomplete overlap between the strains showing altered fitness in juice vs. N-limited
media. Comparison of continuous and semi batch fermentations suggested that growth rate in exponential phase
was not the only determinant of fitness.
S42IS2 - 0739
Functions determining yeast fitness during stress, derived from genome wide haploinsufficiency tests
S.V. Avery1, E. Lodwig1, S.L. Holland1, T. Sideri1, I. Clarke 2, K. Gkargkas2, D.C. Hoyle 2, D. Delneri 2, S.G. Oliver 2
1University of Nottingham, Nottingham, United Kingdom, 2 University of Manchester, Manchester, United Kingdom
We have performed microarray-based competitive growth assays of >6,000 heterozygous S. cerevisiae deletion strains
in the presence of different toxic metals and pro-oxidants. The heterozygous collection encompasses mutants in
essential gene functions which, combined with the sensitivity of the assay system, should help to give new insight to
the mechanism(s) of cellular metal or oxidant toxicity. Strains were grown together for >20 generations in C-limited
continuous culture and samples taken at intervals to determine relative strain growth rates, according to the
abundances of amplified strain-specific oligonucleotide tags. Media were supplemented with either Cu(NO3)2,
Cd(NO3)2, CrO3, H2O2 or diamide, supplied at concentrations that extended doubling time by ~10%. Strains were
identified that gave a significant haplo-insufficient or -proficient phenotype in the various treatments. The
corresponding genes of interest were distributed among a range of functional groupings, though certain functions
were significantly enriched in our data. For example, protein synthesis and protein degradation functions were found
to be important determinants of Cr resistance. We have confirmed phenotypes for individual strains and are using
independent approaches to test new hypotheses developing from this study.
S42IS3 - 0853
Functional genomics of pathogenicity in Magnaporthe grisea
N.J. Talbot, T.A. Richards, D.M. Soanes, M.J. Gilbert, R.A. Wilson, G.K. Bhambra, Z.Y. Wang, Z. Caracuel-Rios
University of Exeter, Devon, United Kingdom
The rice blast fungus Magnaporthe grisea causes one of the most serious diseases of cultivated rice. The availability
of a full genome sequence for M. grisea (Dean et al., 2005) has allowed the first opportunity to define the gene
inventory associated with a fungal phytopathogen. M. grisea has a more complex secreted proteome than closely
related non-pathogenic fungi and also contains a high number of putative G-protein coupled receptor-encoding
genes. This indicates that the fungus possesses an enhanced capacity to respond to distinct environmental signals
and the ability to secrete large numbers of distinct proteins during pathogenesis. Consistent with this idea, we recently
identified a mutant of M. grisea that is impaired in polarised exocytosis (Gilbert et al., 2006). This mutant, ?Mgapt2, is
non-pathogenic and also fails to induce a hypersensitive reaction in an incompatible response, suggesting that it is
unable to secrete fungal proteins during plant infection that may act as pathogenicity determinants or cultivarspecific
elicitors of plant defence responses (avirulence gene products). MgApt2 is a Golgi-associated P-type ATPase
that belongs to the aminophospholipid translocase family. We are using a multi-disciplinary approach, involving high
throughput gene functional analysis, proteomics, cell biology and analytical biochemistry, to investigate the biology
of plant infection by M. grisea and to exploit the genomic resources that are now available for its study. Comparative
genomic analysis of M. grisea with phytopathogenic and free-living fungal species is central to this process and allows
us to explore the evolutionary relatedness of the gene inventories of M. grisea with other pathogenic species.
References
Dean, R.A. et al. (2005) The genome sequence of the rice blast fungus Magnaporthe grisea. Nature 434 :980-86
Gilbert, M.J., Thornton, C.R., Wakley, G.E., Talbot, N.J. (2006) A P-type ATPase required for rice blast disease and
induction of host defence Nature 440: 535-539
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