Page 142 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

with resistance found, which only partially account for the observed resistance, to date. To investigate the
resistance mechanisms further, we have sequenced the genomes of 18 Clarireedia isolates (including C.
jacksonii and C. monteithiana) with a range of sensitivities to DMIs, including isolates obtained before
DMI registration in Canada. The genomes have been investigated for previously documented
mechanisms of DMI resistance and searched for any novel mutations associated with resistant isolates.
Multiple insertions and point mutations have been observed in the CYP51A promoter of two resistant
isolates as well as multiple point mutations in the coding sequence of the AtrB drug efflux transporter and
the MfsM2 transcription factor in six and seven resistant isolates (out of 10 resistant isolates),
respectively. We are currently conducting genome wide association studies to characterize identify
potential sources of resistance and select targets for gene expression analysis. Further characterization
of the DMI resistance mechanisms in these species may provide valuable insights into how DMI
resistance occurs in C. jacksonii, and potentially lead to the development of improved resistance
management and remediation strategies.

*[O82] FUNCTION OF THE CONCANAMYCIN PHYTOTOXINS IN THE POTATO COMMON SCAB
PATHOGEN STREPTOMYCES SCABIEI. Corrie V. Vincent and Dawn R. D. Bignell. Department of
Biology, Memorial University of Newfoundland, 45 Arctic Ave, St. John's, NL, Canada, A1C 5S7
Correspondence to: dbignell@mun.ca

Potato common scab (CS) is an economically important plant disease that occurs worldwide, including in
potato growing regions in Canada. The disease is characterized by the development of superficial, raised,
or pitted lesions on the potato tuber surface. The presence of CS lesions on potato tubers reduces the
quality and market value of the crop, leading to significant financial losses for growers. The soil-dwelling
bacterium Streptomyces scabiei (syn. S. scabies) is distributed worldwide and is the best-characterized
causative agent of CS. S. scabiei produces several phytotoxic specialized metabolites that are known or
predicted to contribute to CS disease development and severity. The principal pathogenicity factor
produced by S. scabiei is the diketopiperazine thaxtomin A, which functions as an inhibitor of cellulose
biosynthesis. S. scabiei also biosynthesizes polyketide compounds belonging to the concanamycin family,
which function as inhibitors of vacuolar-type ATPases. Concanamycins are known to have phytotoxic
activity, though their exact role in the pathogenicity of S. scabiei has not been established. It has been
suggested that concanamycins may influence the CS lesion type and severity, and may have synergistic
effects on toxicity with thaxtomin A. The purpose of this research is to investigate the function of the
concanamycins in CS disease development. Mutant strains of S. scabiei that are altered in the production
of concanamycins and/or thaxtomin A have been constructed, including gene deletion mutants that are
unable to biosynthesize concanamycins and/or thaxtomin A, and overexpression strains that produce
elevated levels of concanamycins along with normal or abolished thaxtomin A production. The mutants
along with wild-type S. scabiei have been used in radish seedling and potato tuber slice bioassays to
assess the virulence phenotypes of each. In the radish seedling assay, relative to the wild type, the
concanamycin mutant and concanamycin overexpression strains showed a slight decrease and increase
in virulence, respectively. The thaxtomin/concanamycin double mutant was significantly reduced in
virulence relative to the thaxtomin mutant, while the thaxtomin mutant overproducing concanamycins was
significantly increased in virulence. In the potato slice assay, the concanamycin mutant showed reduced
pitting relative to wild-type, while concanamycin overproduction along with normal or abolished thaxtomin
A production showed more severe pitting. Overall, these results demonstrate that production of
concanamycins enhances the virulence of S. scabiei and may contribute to the development of more
deep-pitted scab lesions on potato tubers.

*[O83] TRANSGENIC EXPRESSION OF PROTEIN-BASED INHIBITOR AGAINST TURNIP YELLOW
MOSAIC VIRUS IN ARABIDOPSIS THALIANA. J K Anuradha De Silva , Kihun Kim , Jacky Chung ,
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John Weiland , Jihyun Hwang , Melvin Bolton , Mohammed Mira , Claudio Stasolla , Sachdev Sidhu ,
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and Brian Mark . Department of Microbiology, Faculty of Science, University of Manitoba; Faculty of
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Pharmacy, University of Waterloo; Sugarbeet and Potato Research Unit, USDA Agricultural Research
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Services, ND, USA; and Department of Plant Science, Faculty of Agriculture, University of Manitoba
4
Correspondence to: anuradhadesilvajk@gmail.com
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