Page 201 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

bud development, with only minor changes observed in the dormant period. The expression of PtDOMT1
is coordinate with bud developmental and expansion. To our knowledge, this work represents the first
molecular analysis of leaf bud resin biosynthesis in plants.

[O194] REGIOSELECTIVE O-METHYLATION OF STILBENES IN SACCHARINAE GRASSES. Nan
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Lin , Andy CW Lui , Kah Chee Pow , Zhuming Fan , Chen Jing Khoo , Quan Hao , and Clive Lo . School
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of Biological Sciences and School of Biomedical Sciences, The University of Hong Kong, Pokfulam
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Road, Hong Kong, China
Correspondence to: clivelo@hku.hk

Stilbenes are plant specialized metabolites synthesized in response to abiotic or biotic challenges,
offering protection against reactive oxygen species or pathogen infection. They are also promising
candidates for nutraceutical and pharmacological applications due to a wide range of health beneficial
properties. Interestingly, stilbenes are only sporadically distributed in several phylogenetically distinct
lineages. In the grass family, sorghum (Sorghum bicolor) and sugarcane (Saccharum officinarum) were
reported to accumulate resveratrol and piceatannol, respectively, which are stress-induced hydroxylated
stilbenes. Sorghum and Saccharum are closely related genera belonging to subtribe Saccharinae.

In this study, we report the identification of O-methylated stilbenes, pinostilbene (3-O-methylated in A ring)
and pterostilbene (3,5-bis-O-methylated in A ring) in infected sorghum seedlings, and isorhapontigenin
(3’-O-methylated in B ring) in wounded wild sugarcane. Meanwhile, we have characterized a novel
stilbene O-methyltransferase (SbSOMT) which is essential for pathogen-inducible pterostilbene
biosynthesis in sorghum. SbSOMT and related homologs are restricted to Sorghum but not found in
Saccharum or other Saccharinae genera. Phylogenetic analysis suggested that the genus-specific SOMT
were recruited from canonical caffeic acid O-methyltransferases (COMTs) after divergence of Sorghum
genus from other genera in Saccharinae. COMTs are widespread in the plant kingdom catalyzing O-
methylation of a wide range of phenolic substrates.

Using piceatannol as a substrate in recombinant enzyme assays, SbSOMT catalyzed A-ring O-
methylation to produce 3’hydroxypinostilbene and 3’-hydroxypterostilbene successively. On the other
hand, SbCOMT catalyzed B-ring O-methylation of piceatannol to produce isorhapontigenin.
Subsequently, crystal structures of SbSOMT-stilbene complexes were solved and the enzyme was
depicted as a homodimer with an open conformation. SbSOMT shows strong global resemblance to
sorghum COMT (SbCOMT), but close examination of the substrate binding pockets revealed subtle
differences in their amino acid compositions. Molecular characterization demonstrated the requirement of
two hydrophobic residues (Ile144 and Phe337) for substrate binding that leads to stilbene A-ring O-
methylation. On the other hand, the equivalent residues (Asn128 and Asn323) in SbCOMT facilitate an
opposite binding orientation that favors stilbene B-ring O-methylation. In this regard, a highly conserved
COMT likely catalyzes the wounding-induced isorhapontigenin production in wild sugarcane. Overall, this
work rationalized the regioselectivities of stilbene O-methylations by SOMT and COMT, facilitating future
attempts for bioengineering of different O-methylated stilbenes.

*[O195] MODULATION OF CLOCK IN WHEAT VIA DIPLOID AND HAPLOID GENE EDITING. Sandhya
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Gautam , Fengying Jiang , Chelsi Harvey , Andre Laroche , Guanqun Chen , and John Laurie .
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1 Department of Agricultural, Food and Nutritional Science, University of Alberta, 2-06 Agriculture-Forestry
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Center, Edmonton, AB, Canada, T6G 1C9; and Lethbridge Research and Development Center,
Agriculture and Agri-Food Canada, 5403 1 Avenue South, Lethbridge, AB, Canada, T1J 4B1
Correspondence to: sgauta1@ualberta.ca

Wheat (Triticum aestivum) is one of the major field crops of Canada with significant nutritional and
economic value. Climate change has impacted Canada’s overall wheat production in recent years.
Therefore, the development of new wheat germplasm resilient to variable climatic conditions is essential.
Genetic changes play a crucial role in crop improvement. Genetic modification in wheat; a complex
polyploid crop (AABBDD), is challenging due to large genome and multiple gene copies. This study
focuses on modulating circadian clock genes in wheat to enhance various plant characteristics. Core
clock genes are a group of transcription factors that regulate a large number of downstream genes
involved in various important biological pathways and therefore, play a vital role in plant growth and
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