Page 134 - Plant Canada 2024 Proceeding

PLANT CANADA 2024

acid (NHP), which synergistically potentiate both basal immunity and systemic acquired resistance to
numerous pathogens. The SA and NHP pathways are particularly vulnerable to suppression by elevated
temperatures simulating heat waves above the normal growth range. However, the mechanistic basis for
heat-mediated suppression of SA and/or NHP has remained elusive, representing a significant concern
for crop protection amidst a warming climate. In our recent work, we identified a novel thermosensitive
mechanism governing the SA and NHP pathways via the CALMODULIN-BINDING PROTEIN 60-LIKE G
(CBP60g) and SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (SARD1) genes. CBP60g and
SARD1 encode master transcription factors regulating SA and NHP biosynthetic genes, as well as other
drivers of the plant immune system. While ambient temperature conditions led to immune-responsive
CBP60g and SARD1 gene transcription, elevated temperature largely suppressed this induced
expression. Further investigations led to the discovery that thermosensitive CBP60g/SARD1 transcription
is controlled by GUANYLATE-BINDING PROTEIN-LIKE 3 (GBPL3), an intrinsically disordered region-
containing GTPase protein that can form membraneless nuclear assemblies called GBPL defence-
activated condensates (GDACs). These GDACs concentrate essential transcriptional regulators (e.g.
Mediator complex) and enzymes (e.g. RNA polymerase II) during plant immune elicitation. We observed
that GDAC formation is dynamically regulated by temperature, with a notable decrease in condensate
formation in planta at higher temperatures. This resulted in reduced recruitment of the Mediator complex
and RNA polymerase II to the CBP60g and SARD1 promoter regions, which decreased downstream gene
transcription and worsened disease susceptibility of plants under warm conditions. Genetically
engineering this temperature-vulnerable CBP60g/SARD1 transcriptional node effectively restored
SA/NHP biosynthesis and strengthened plant immune resilience. Taken together, we successfully
identified the GBPL3-CBP60g/SARD1 regulatory network that governs the thermosensitivity of the plant
immune landscape. This promises a broadly applicable roadmap to safeguard plant disease resistance
for a warming climate.

*[O65] BACK TO THE ROOTS: EXPLORING PLANT-INSECT INTERACTIONS IN CULTIVATED AND
1,2 1
2
1,2
WILD TOMATOES. Andreea Bosorogan , Osmond Hui , and Eliana Gonzales-Vigil . Department of
Cell and Systems Biology, University of Toronto, Toronto, ON, Canada, M5S 3G5; and Department of
2
Biological Sciences, University of Toronto - Scarborough, Scarborough, ON, Canada, M1C A14
Correspondence to: e.gonzalesvigil@utoronto.ca

Conventional breeding has improved several agronomic traits in tomato (Solanum lycopersicum), yet
herbivore resistance remains a critical challenge in tomato production. Plants use a plethora of strategies
including specialized structures (e.g., cuticles containing epicuticular waxes) and a diversity of
metabolites (e.g., terpenes) to reduce insects’ feeding ability and development. However, cultivated
tomatoes lack the chemical diversity of wild relatives, like S. habrochaites. Despite S. habrochaites' rich
chemical variation, little is known about its contribution of the chemical diversity to herbivore resistance
traits. In this study, we examined the variation in epicuticular waxes and terpenes among 17 accessions
of S. habrochaites and S. lycopersicum, and evaluated their resistance to herbivory by exposing the
plants to Trichoplusia ni (Lepidoptera) larvae. Large differences in insect mortality and weight gain were
seen across the 17 accessions. Specifically, five S. habrochaites accessions were highly resistant,
causing over 80% mortality and reduced mass gain in T. ni. The significant differences in insect
performance among cultivated and wild tomatoes were followed up by chemical characterization. Terpene
diversity and abundance varied significantly across the accessions, yet the epicuticular wax profiles of S.
habrochaites were similar to those of cultivated tomatoes. Accessions with elevated levels of several
terpenes, including bergamotene, santalene, and elemene, showed high resistance to insect damage,
suggesting potential repellent or toxic effects on T. ni. Yet, it is still to be determined whether chemical
diversity or quantity has the largest effect on herbivory, as increased quantities of total terpenes and
epicuticular waxes were negatively correlated with insect performance. Overall, this study provides a
critical step in understanding insect interactions with complex specialized metabolites in S.
habrochaites, which will inform the development of resilient tomato cultivars with enhanced resistance to
Lepidopteran herbivores.

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