Cereal killers - molecular interactions between necrotrophic leaf blotch
pathogens and their cereal hosts
Leaf blotch caused by Parastagonospora nodorum
is a severe disease on wheat in Norway
leading to grain shriveling and reduced yield,
and is a main cause of fungicide application.
Figure 1 Leaf blotch caused by P. nodorum
Figure 2 Barley net blotch symptoms
Net blotch is a major disease on barley in Norway
caused by the necrotrophic fungus Pyrenophora
teres. Yield losses due to the disease can be as high
as 40%. Progress in resistance breeding has been
slow, and the genetics of resistance in Norwegian
barley are poorly understood. Two forms of this
pathogen have been described, one of them
producing net form symptoms and the other one
producing spot form symptoms, but we don’t know
to what extent the two forms are present in
Norway.
There is emerging evidence that the pathogens secrete
necrotrophic effectors (NE), which, in the presence of
corresponding susceptibility factors (SF) in the host, act
as virulence factors in order to enable host colonization.
This is the opposite situation of what is described in the
“classical” gene-for-gene hypothesis, where the
effector recognition by the plant leads to a resistance
response which usually involves a controlled form of
plant cell death to limit pathogen growth. Thus, it is
believed that the necrotrophic pathogens P. nodorum
and P. teres take advantage of this defense response in
order to grow on the dead plant tissue.
Recent advances in genome sequencing and
bioinformatics make it possible to study host-pathogen
interactions at the molecular level and develop new
robust tools for resistance breeding.
SF
sf
NE
Susceptible
Resistant
ne
Resistant
Resistant
Figure
3
“Inverse”
gene-for-gene
interaction between dominant NE and
dominant SF will result in a susceptible
reaction.
Focus of the project:
We use a combination of classical inoculation and infiltration experiments in the field and in
the greenhouse and next-generation sequencing and bioinformatics such as QTL mapping to
explore the molecular mechanisms that are decisive for resistance or susceptibility:
-
QTL mapping of resistance/susceptibility loci in different mapping populations of
wheat and barley:
o Infection at seedling stage under greenhouse conditions and as adult plants in
the field. Assessment of disease severity for each genotype. If resistance of
adult plants can be already predicted at the seedling stage, this will be a useful
screening tool for breeders.
o Construction of genetic maps based on high-density SNP markers
o QTL mapping to find genetic regions that are associated with resistance or
susceptibility
-
Identification of necrotrophic effectors and corresponding host susceptibility factors
by infiltration bioassays of wheat and barley seedlings
-
ddRAD (double digest restriction associated DNA tags) genotyping-by-sequencing of
400 P. teres isolates in order to unravel the genetic diversity and structure of the
Norwegian P. teres population
Suggested master thesis topics:
-
Seedling inoculations with culture filtrates of selected isolates in order to screen for
differential disease reactions and to identify potential NEs.
o This method can be used to identify isolates which secrete potential NEs. By
growing the fungus in a liquid medium it is possible to collect the secreted
proteome. These so-called culture filtrates are then infiltrated into the host
and it is observed whether differential disease symptoms are developing. By
fractioning the filtrates according to protein size by LC-MS and infiltrating
these filtrate fractions into the plant, it is possible to get an idea of the size of
the potential NE. Additionally, we can use the phenotypic data from infiltration
experiments to identify effector sensitivity loci in the plant by QTL/association
mapping.
-
Sequencing and haplotype investigation of NE genes from a collection of Norwegian
P. nodorum isolates. This can tell us something about the variation and also population
structure of the pathogen.
-
Characterization and purification of potential NEs by chromatography and/or
ultrafiltration methods
-
Deep sequencing of selected isolates in search of candidate effector loci
-
QTL and association mapping for resistance/susceptibility loci in wheat/barley, based
on the genetic maps and phenotypic data from field and seedling trials
o Extensive seedling and adult plant phenotypic data is already available, but it
is possible to screen more isolates on seedlings as well as being involved in
data analysis and association mapping.
-
Association mapping of effector genes in P. teres
o A collection of 365 Norwegian and 40 international P. teres isolates is available
for resistance screenings on selected barley lines. These isolates are currently
being ddRAD genotyped in order to obtain SNP markers, enabling association
mapping for candidate effector loci in the pathogen.
-
Validation of molecular marker-assays on plant breeding materials.
Depending on the topic and on the field of interest of the student, the work will involve a
combination of greenhouse work, molecular lab work and bioinformatics.
The cereal leaf blotch group:
Morten Lillemo (researcher) morten.lillemo@nmbu.no
Andrea Ficke (researcher; NIBIO) andrea.ficke@nibio.no
Anja Ruud (PhD student) anja.ruud@nmbu.no
Ronja Wonneberger (PhD student) ronja.wonneberger@nmbu.no