Page 242 - PC2019 Program & Proceedings

PLANT CANADA 2019

P57. Understanding the regulatory role of rbcL RNA S1-Binding domain (RLSB) protein in the
single-cell C4 species Bienertia sinuspersici
*
Yogadasan, N. ; S. Chuong
University of Waterloo

Compartmentalization of RuBisCO in C4 plants prevents its premature interaction with atmospheric O2
and allows for the C4 pathway enzymes to concentrate CO2 first, thereby reducing oxygenase activity.
rbcL RNA S1-Binding domain protein (RLSB), encoded by the nuclear RLSB gene, has been previously
implicated to play a role in the post-transcriptional regulation of the plastid encoded RuBisCO large
subunit (rbcL) in C3 and Kranz-type C4 plants. RLSB, after import into chloroplasts, has been suggested
to bind and stabilize rbcL transcripts in Arabidopsis (C3) and Zea mays (Kranz - C4), thus preventing
degradation and promoting translation. RLSB has also been shown to post-transcriptionally regulate other
plastid encoded genes via transcript stabilization and/or translational activation in the C3 and Kranz-type
C4 systems. The following work aims to characterize the role of the RLSB homolog (BsRLSB) found in
the model single-cell C4 species Bienertia sinuspersici. Subcellular localization studies using RLSB-GFP
fusions in protoplasts demonstrate chloroplast localization of the BsRLSB homolog and reveal that only
the first 65 amino acids of BsRLSB are necessary and sufficient for the observed chloroplast import.
Preliminary in-vitro binding assays reveal a BsRLSB interaction with the 5’UTR of the rbcL transcript
derived from the BIenertia sinuspersici rbcL gene. This work will further our understanding of the
mechanisms governing compartmentalization of RuBisCO and other plastid-encoded genes in single-cell
C4 species.

Nilanth Yogadasan (nilanth.yogadasan@gmail.com)

P58. Biochemical evidence for flavonol α-rhamnosidase activity in plants
*
Unterlander, N. ; H. Gordon; L. McGary; G. Bozzo
University of Guelph

Flavonols are plant antioxidants and photoprotectants that are bioactive in humans. In various plant
species, including Arabidopsis thaliana, flavonols accumulate as rhamnoside conjugates, such as
kaempferol 3-O-β-glucoside-7-O-⍺-rhamnoside, during abiotic stress. Recently, we determined that
flavonol 3-O-β-glucoside-7-O-⍺-rhamnosides are catabolized to flavonol 7-O-⍺-rhamnosides in
Arabidopsis leaves during the recovery from simultaneous nitrogen deficiency and low temperature
stresses. The transient accumulation of flavonol 7-O-⍺-rhamnosides during the recovery from abiotic
stress implies they are further catabolized in planta. We hypothesize that flavonol 7-O-⍺-rhamnoside
degradation in plants is dependent upon ⍺-rhamnosidase activity. High-performance liquid
chromatography analysis revealed cell-free Arabidopsis leaf extracts contained ⍺-rhamnosidase activity
against various 7-O-⍺-rhamnosylated flavonols. This activity was highest in leaves of 5 week-old plants,
and was inhibited in assays containing the monosaccharide rhamnose. Negligible activity was present in
roots and stems. Preliminary analysis points to a similar flavonol 7-O-⍺-rhamnoside ⍺-rhamnosidase
activity in radish leaves. Consumption of flavonol-rich foods reduces the risk of chronic illnesses; thus
the on-going biochemical and functional characterization of flavonol ⍺-rhamnosidase activity in plants
will facilitate biotechnological strategies aimed at boosting flavonol levels in genetically-related crucifer
crops. Moreover, as flavonols are known to inhibit auxin-mediated plant development, this research will
provide knowledge on the relationship between flavonol catabolism and renewed growth following
transient abiotic stresses. This information is crucial for maximizing agricultural productivity in regions
that are prone to climate change.

Nicole Unterlander (nunterla@uoguelph.ca)

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