Page 277 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

*[P146] SOMETHING SWEET: SUGAR MEDIATED CHANGES IN CELL PROLIFERATION VIA TOR-
BRASSINOSTEROID SIGNALLING REQUIRE THE MICROTUBULE ASSOCIATED PROTEIN CLASP.
Sean P.A. Ritter, Dr. Laryssa Halat, and Dr. Geoffrey Wasteneys. The University of British Columbia
Correspondence to: sean.ritter@botany.ubc.ca

To survive, organisms need to be able to coordinate energy-demanding processes, such as growth, with
prevailing environmental conditions. In plants, sugars are the major energy source utilized to power
cellular processes. Thus, plants must be able to perceive sugar levels, and enact appropriate cellular
responses. TARGET OF RAPAMYCIN (TOR) is a conserved protein kinase activated by growth factors
and inactivated by energy deprivation, thereby acting as a master regulator of metabolic pathways in all
eukaryotes. In plants, TOR has been shown to alter cell proliferation and growth in response to changing
light levels and sugar availability. While numerous targets of TOR kinase activity have been identified,
such as the brassinosteroid-responsive transcription factor BRASSINAZOLE RESISTANT 1 (BZR1), how
TOR kinase activity is translated into altered growth at the cellular level remains unclear. I propose that
the microtubule-associated protein CLIP-ASSOCIATED PROTEIN (CLASP) is a crucial component of the
TOR signaling pathway, providing a mechanism by which sugar affects root meristem activity and growth.
CLASP expression is altered by both BZR1 activity and light availability, resulting in microtubule-
dependent fine-tuning of cell proliferation in response to environmental conditions. In addition, CLASP
also modulates meristem activity through its direct interaction with SORTING NEXIN 1 (SNX1). This
interaction maintains the plasma membrane distribution of the auxin transporter PIN2, a known target of
TOR. My research shows that CLASP null mutant plants have greatly reduced sensitivity to
pharmacological inhibition of TOR at the organ, cellular and subcellular levels, and fail to increase cell
proliferation in response to sugar. Furthermore, in the absence of CLASP both PIN2 levels at the plasma
membrane, and auxin distribution patterns are unaltered by TOR inhibition. This effect is mediated by the
brassinosteroid signalling pathway, as both constitutively active BZR1 and mutation of the BZR1 binding
site within the CLASP promoter prevent TOR-dependent changes in CLASP expression, and root growth.
Together, these findings indicate that CLASP is required for TOR-mediated meristem activity. Through
characterization of the interaction between CLASP, TOR and plant hormones, this work provides insight
on how the sugar provision is translated into altered root development, thereby furthering our
understanding of how plants perceive and respond to their changing environment.

*[P147] TRACKING HOP LATENT VIROID (HLVD) IN HOP (HUMULUS LUPULUS (L).) TISSUE. Taylor
1
1,2 1
1
1
Atsaidis Royal , Abdurraouf Abaya , Rene Van Acker , and Melanie Kalischuk . Department of Plant
Agriculture, University of Guelph, Guelph, ON; and Department of Plant Agriculture, University of
2
Guelph, Simcoe, ON
Correspondence to: troyal@uoguelph.ca

Hop Latent Viroid (HLVd) is a mechanically transmitted pathogen of hop (Humulus lupulus) and cannabis
(Cannabis sativa) which impacts yield and secondary metabolites. Symptoms vary from severe, causing
‘dudding disease’ as in cannabis, to latent and symptomless as in reservoir species such as stinging
nettle (Urtica dioica). HLVd is a member of the genus Cocadviroid, family Posiviroidae, and forms a stable
self-complementary RNA structure 256-nt in length. Currently, a sound agricultural management strategy
for viroids would include beginning a hop yard with clean plant germplasm. To evaluate clean plant
material, a sensitive and specific diagnostic and sampling strategy is required. Mapping distribution of
HLVd in plant tissue will assist in developing a method to sample plants with a diagnostic, leading to
higher yields and better-quality products. In silico characterization of the HLVd genome discovered motifs
including the conserved region, pathogenicity region, and functional hairpins. A survey for viroid presence
and titer among tissue types was conduced on 20 randomly selected mature (3 year old) hop plants (10
‘Centennial’, 10 ‘Chinook’) at the Ontario Crop Research Center yard near Simcoe, Ontario. Field
samples were taken of leaf, cone and root tissue to compare viroid titer using RT qPCR, due to the latent
nature of HLVd in hop. Of the 20 hop plants randomly selected for the survey, HLVd was detected in
100% of sampled units with variable titer and tissue distribution. A two way ANOVA revealed statistically
significant differences in titer between hop tissue types but not cultivar (F(2, 33) = [5.368], p = 0.009)
where root tissue had significantly lower titre than leaf and cone tissue (p = 0.007, 95% C.I = [0.83, 4.24]).
Inconsistent spread of HLVd in tissues may have explanations founded in mode of transmission,
276