Climate change poses a significant threat to global food security and ecosystem stability by increasing the frequency and intensity of extreme weather events, such as heat waves. These events profoundly impact plant health, particularly their ability to defend against pathogens. Salicylic acid (SA) is a crucial plant hormone central to the plant immune system, mediating both pathogen-triggered immunity (PTI) and effector-triggered immunity (ETI). Previous research has demonstrated that elevated temperatures can suppress SA production, rendering plants more susceptible to diseases. However, the underlying mechanisms of this temperature-sensitive SA pathway remained unclear. This study aimed to unravel these mechanisms, focusing on the impact of high temperatures on SA biosynthesis and signaling, to develop strategies for improving plant resilience to climate change. The importance of this research lies in its potential to contribute to the development of climate-resilient crops that can maintain effective immune responses even under extreme weather conditions, safeguarding agricultural productivity and biodiversity. The study utilizes Arabidopsis thaliana as a model plant system, given its established role in plant immunity research, and its relevance as a model for understanding the complex interactions between environmental stress and plant immune responses.

Prior studies have established the critical role of SA in plant immunity and its temperature sensitivity. Research has shown that SA production is induced by a proton transmembrane relay, a process affected by higher temperatures within the optimal plant growth range. However, the mechanisms underlying the selective suppression of the SA pathway during heat waves exceeding the optimal temperature range remained largely unknown. This knowledge gap highlights the need to understand how climate change-induced extreme heat impacts the efficacy of plant immune systems. The existing literature points to the complex interplay between SA and other stress hormones like jasmonate and abscisic acid, which are upregulated at higher temperatures. However, the specific interactions and their roles in temperature-mediated SA suppression require further investigation. The current understanding of SA signaling involves the interaction of NPR receptors with TGA-containing bZIP transcription factors, which regulate the expression of key immune-related genes like CBP60g. This study built upon these previous findings to investigate the specific molecular mechanisms involved in temperature-mediated suppression of SA pathway and proposes possible strategies to increase the resilience of plants.

The study employed a combination of experimental approaches using *Arabidopsis thaliana* as a model organism. The researchers investigated the impact of elevated temperatures (28°C) on SA production and plant immunity compared to optimal growth temperatures (23°C). They used pathogen infection assays with *Pseudomonas syringae* pv. tomato (Pst) DC3000, both virulent and non-pathogenic strains, to assess plant susceptibility. Gene expression analysis, including RNA sequencing (RNA-seq) and quantitative PCR (qPCR), was conducted to measure the transcript levels of key genes in the SA pathway, including *ICS1* (a key SA biosynthetic gene) and *CBP60g* and *SARD1* (master immune transcription factors). SA levels were quantified to assess the impact of temperature on SA accumulation. The researchers examined the role of established thermosensors such as PHOTOTCHROME B8 (phyB) and EARLY FLOWERING 3D (ELF3) in temperature-mediated SA suppression using relevant mutant lines and transgenic plants with constitutively activated thermosensors. They investigated whether downregulation of *ICS1* is the rate-limiting step for SA suppression. Constitutive expression of *ICS1*, *NRP1*, and various genetic modifications were used to determine if they could restore SA accumulation under elevated temperatures. Chromatin immunoprecipitation (ChIP)-qPCR was used to analyze the recruitment of key signaling proteins, including NPR1, GBPL3, and Mediator subunits, to the promoters of *CBP60g* and *SARD1* at different temperatures. Confocal microscopy was employed to visualize the formation of GDACs. Finally, the researchers examined the effect of constitutive overexpression of *CBP60g* on SA production, plant immunity, and growth, comparing it to other SA pathway regulators. They also tested an optimized expression strategy using the oUFR5::SA system to minimize the growth-defense trade-off. The experiments were conducted with multiple biological replicates to ensure statistical robustness of the findings. Two-way ANOVA with Tukey's HSD post-hoc test was used for statistical analysis.

The study revealed that elevated temperatures (28°C) significantly suppressed SA production in *Arabidopsis*, leading to increased susceptibility to *P. syringae*. This suppression was not mediated by the known thermosensors phyB and ELF3. Instead, high temperatures reduced the formation of GBPL3 GDACs, impairing the recruitment of GBPL3 and SA-associated Mediator subunits to the promoters of *CBP60g* and *SARD1*. This impaired recruitment of these key factors directly hindered the expression of the *CBP60g* and *SARD1* genes. The downregulation of *ICS1*, a key SA biosynthesis gene, was not the primary cause of the temperature-mediated SA suppression, as constitutive expression of *ICS1* did not rescue SA levels at elevated temperatures. Similarly, manipulating SA receptors (NPR1, NRP3, and NRP4) did not restore SA-mediated immunity at 28°C. Importantly, optimized expression of *CBP60g*, particularly through the oUFR5::SA system, significantly restored pathogen-induced SA production and plant immunity at elevated temperatures without causing negative effects on plant growth and development. This restoration extended to both PTI and ETI responses. Overexpression of CBP60g significantly restored the expression of ICS1 and other SA pathway genes at elevated temperature in Arabidopsis, tobacco, and rice, demonstrating a broad applicability of this finding across plant species. The findings highlight the selective nature of temperature effects on the SA pathway, specifically targeting the *CBP60g* and *SARD1* promoters and their regulatory elements. This targeted approach has potential for the development of climate-resilient plants, minimizing the trade-off between growth and defense.

This study provides crucial insights into the mechanisms underlying the temperature sensitivity of the plant SA pathway. The identification of GBPL3 GDAC formation and the subsequent impaired recruitment of transcriptional machinery to the *CBP60g* and *SARD1* promoters as the key points of temperature-mediated suppression is a significant advancement. The finding that optimizing *CBP60g* expression is sufficient to restore SA-mediated immunity at elevated temperatures offers a promising avenue for engineering climate-resilient plants. The observed broad-spectrum effect of CBP60g overexpression, restoring pathogen-induced expression of SA pathway genes across diverse plant species, demonstrates the potential for this approach to enhance the disease resistance of various crops. The results also highlight the selective nature of temperature effects on the SA pathway, suggesting that not all components are equally sensitive to temperature changes. The study successfully disentangles the complex interplay between temperature, SA signaling, and plant immunity. The utilization of the oUFR5::SA system for optimized *CBP60g* expression successfully addressed the common growth-defense trade-off associated with enhancing plant immunity, paving the way for practical applications in agriculture.

This research demonstrates that high temperatures suppress plant immunity by targeting the formation of GBPL3-containing biomolecular condensates and consequently reducing the expression of the master immune regulators *CBP60g* and *SARD1*. Optimizing *CBP60g* expression is a promising strategy for enhancing climate resilience in plants. Future studies could focus on exploring the detailed molecular mechanisms governing GBPL3 GDAC formation and stability at various temperatures, which could lead to additional approaches for improving plant immunity and climate resilience. Further investigation into the potential of applying this strategy to a wider range of plant species, especially crops, is needed to translate these findings into practical solutions for improving agricultural production in the face of climate change. The study should also focus on exploring the wider ecological implications of these findings in various ecosystems.

The study primarily focuses on *Arabidopsis thaliana*, a model plant species. The extent to which these findings can be directly translated to other plant species, particularly economically important crops, requires further investigation. While the oUFR5::SA system addressed growth-defense trade-offs, the long-term effects and potential unintended consequences of constitutive *CBP60g* expression require further assessment. The study primarily investigates the response to *P. syringae*, and it would be beneficial to test the generalizability of these findings to a broader range of plant pathogens.