SA Grain May 2017

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MUTANT
COLLECTION STRAIN HOST(S) TESTED ISOLATES
PHENOTYPICALLY
ALTERED ISOLATES
GENES RESPONDING
TO TREATMENT
A. tumefaciens -
mutagenesis
M. oryzae KJ201 Rice 21 070 2,6% 203
M. oryzae Guy11 Barley cv. Golden Promise
and rice cv. CO-39
5 248 0,1% 1
Bidirectional-
genetics
M. oryzae KJ201 Rice cv. Nakdongbyeo 1 139 11,2% 3
Targeted gene
deletion
M. oryzae Ina72 Barley cv. Nigrate and rice cv.
Shin No. 2
78 1,2% 1
F. graminearum
Z3643
Not tested on host plant 127 32% 40
Plasmid-mediated
integration
F. graminearum PH-1 Wheat cv. Bobwhite 1 170 0,6% 146
F. graminearum PH-1 Wheat cv. Bobwhite 650 1,2% 456
Transcription
factor
F. graminearum 3639 Not tested on host plant 657 25,8% 170
M. oryzae 70-15 Barley and rice cv. CO39 104 58,6% 61
M. oryzae 70-15 Barley and rice cv. CO39 47 97% 46
TABLE 1: MUTANT COLLECTIONS IN F. GRAMINEARUM AND M. ORYZAE.
mechanisms used by fungi to infect their host plants. As a result of
these large-scale genetic studies, numerous genes have been as-
signed roles in the biological processes of fungal pathogens.
Owing to the importance of these genetic resources, a scientific
literature study, focusing on papers looking at virulence gene dis-
covery, modes of pathogenicity and regulation, and host-pathogen
interactions was conducted. A more in-depth analysis involved
splitting of papers citing mutant collections into twelve different
scientific aspects (Figure 2).
The results produced ten relevant mutant screens, a striking
observation of which was that a large number of generated mu-
tant isolates represented only a portion of phenotypically altered
isolates; these phenotypically altered isolates are the very fungal
strains containing mutations in specific genes, while the remainder
of the genome is either uninterrupted or less important for fungal
functions.
However, given that a few mutant isolates were altered, a few
genes responding to different treatments were thus represented
(Table 1). This may be due to dependence on less sensitive pheno-
typic assays and lack of additional phenotypic or in planta screens.
Citations of fungal mutant collections were assessed, the relevance
of which is crucial to see if findings from these collections are
channelled to solve agricultural problems in the South African
context. Interestingly, none of the reports came from South Africa
when a total of 397 citing papers, 116 citing F. graminearum mutant
screens and 281 citing M. oryzae mutant screens (Figure 2), were
screened.
Therefore, there is a huge gap to generate and screen fungal mu-
tant collections in South Africa. Ultimately, performing such
mutant screens, more in particular for F. graminearum, will drive
the identification of virulence genes relevant to crops in this
country. Furthermore, increasing the number of genes and related
pathways involved in virulence will potentially complement the on-
going breeding efforts made for the South African producer.
To conclude, it is apparent that the application of fungal mutant
collections is still in infancy when it comes to effector search. Only
M. oryzae targeted gene disruption (TGD) collection provides
screening of effectors. Available transcription factor (TF) mutant
collections can potentially guide the development of alternative and
effective fungicides, which target conserved TF proteins.
Since TFs control multiple genes which influence multiple biologi-
cal processes, associated developmental costs of fungicides which
target these TFs will substantially drop. This is because such fun-
gicides will not be developed for countless downstream genes of
TFs. Disease control procedures should thus unify findings from
effector and TF mutant collections to advanced effector-assisted
breeding and biological control using TFs as potential targets. The
prospect of making collections of mutants for the South African
molecular pathologist is within reach, and will potentially involve
the inclusion to the list of mutant collections of fungi such as
wheat rusts.
Having these genetic resources in the country can greatly facili-
tate and accelerate disease combat efforts as well as significantly
improve crop production and profitability for producers.
For more information, contact Dr Thabiso Motaung at