Page 225 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

consisting of two cultivars of soybean (susceptible; S and moderately resistant, MR) and two highly
aggressive F.graminearum isolates was used to assess the expression of ten defense-related genes in
soybean : Phenylalanine ammonia-lyase2 (PAL2), Isochorismate synthase1 (ICS1), Isochorismate
synthase 2( ICS2), Allene oxide synthase 2 ( AOS2), 12-Oxophytodienoate reductase 3 (OPR3),
Nonexpressor of PR1(NPR1), Jasmonic acids-amido synthetase 1 (JAR1), Pathogenesis-related proteins
2 (PR-2), 3 (PR-3), and 4 (PR-4). These genes were selected because they are usually associated with
either the salicylic acid (SA) or jasmonic acid (JA) defense signaling pathways. Expression of these
genes was assessed in soybean roots at 6-,12- and 24-hour post-inoculation (hpi). We recorded a
gradual increase in gene expression of PAL2, with significant induction at 24 hpi in both susceptible and
moderately resistant lines. In contrast, gene expression of ICS1 and ICS2 was significant only at 6 and 12
hpi, respectively. This suggests that both the PAL and ICS pathways contribute to pathogen-induced SA
response in soybean. Furthermore, gene expression of ICS1, ICS2, and PAL2 was more pronounced in
moderately resistant lines compared to the susceptible ones. Additionally, we measured gene expression
of AOS2, OPR3, and JAR1. AOS2 showed significant expression at 24 hpi, while JAR1 did at 6 hpi in
moderately resistant line, along with OPR3. Gene expression of PR-3 and PR-4 was significantly induced
at 24 hpi compared to the control. Additionally, the NPR1 gene exhibited significant expression at 6 hpi.
These results indicate that the SA and JA pathways are involved in soybean defense against F.
graminearum at different timings and add to the data gathered to elucidate the spatio-temporal signaling
mechanisms in this host-pathogen interaction. If property integrated with knowledge on soybean
responses to different Fusarium species, these data may contribute to reducing FRR effects on soybean
yield.

[P43] LOSS OF CENTRAL METABOLIC GENES IN PLASMODIOPHORA BRASSICAE: A
2
1
1
COMPARATIVE GENOMIC STUDY. A. Sedaghatkish , B. D. Gossen , and M. R. McDonald .
2
1 Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1, Canada; and Saskatoon
Research and Development Centre, Agriculture and Agri-Food Canada, Saskatoon, SK S7N 0X2,
Canada
Correspondence to: asedagha@uoguelph.ca

Plasmodiophora brassicae Wor. is an obligate soil-borne Chromist that causes clubroot disease in
brassica crops. Growing resistant cultivars is the best management strategy for producing canola in
clubroot infested fields. However, the resistance is not durable and has been rapidly overcome by the
pathogen. Obligate biotrophic pathogens such as P. brassicae strictly require living host cells to complete
their life cycle. Cultivating P. brassicae in the lab would simplify gene discovery for breeding and
contribute to other studies of the pathogen biology. It is not known what compounds must be supplied to
this and other obligate biotrophs to allow growth on an artificial medium. Comparative genomic studies
were conducted on the core genes responsible for central metabolites in P. brassicae to determine why it
cannot grow and reproduce outside a living cell. A total of 120 essential genes in core metabolisms of P.
brassicae were compared with 12 published plant pathogens including four fungi that can grow in culture
(Colletotrichum higginsianum, Magnaporthe grisea, Sclerotinia sclerotiorum, and Saccharomyces
cerevisiae) and eight obligate plant pathogens such as rusts and powdery mildews (Blumeria graminis,
Erysiphe necator, Erysiphe pisi, Erysiphe necator, Golovinomyces orontii, Puccinia graminis and Puccinia
triticiana) and the Oomycete , Hyaloperonospora arabidopsidis. Plasmodiophora brassicae lacks all 120
genes coding for essential core metabolites. These included important genes in nitrogen assimilation,
thiamin biosynthesis, glutamate, glutathione, uracil, methionine, alcohol, and amino acid metabolism as
well as channels and transporters and stress responses. The gene absence was similar to the powdery
mildew pathogens examined (B. graminis, E. necator, E. pisi, and G. orontii). However, the two Puccinia
species and Oomycete H. arabidopsidis posses some of these metabolic genes, which may explain why
some rust pathogens such as Puccinia spp. have been cultured artificially, albeit with slow and poor
growth. The lack of essential genes in P. brassicae demonstrates its inability to process inorganic
compounds like nitrogen (e.g., ammonia, nitrate) provided in culture media, necessitating the provision of
organic nitrogen compounds such as amino acids, amides, and vitamins. This deficiency in core
metabolic genes explains many failed attempts to grow P. brassicae in vitro. Understanding the
specialized nutritional requirements of P. brassicae will aid in developing a selective culture medium for
this pathogen. Successful in vitro culture will enable the cultivation of pure isolates and lead to improved
breeding for resistance and management strategies.

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