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Authors: Iftah Marash, Rupali Gupta, Gautam Anand, Meirav Leibman-Markus, Naomi Lindner, Alon Israeli, Dov Nir, Adi Avni and Maya Bar.
Plant, Cell & Environment (2024)
Abstract: "Plants constantly perceive and process environmental signals and balance between the energetic demands of growth and defense. Growth arrest upon pathogen attack was previously suggested to result from a redirection of the plants' metabolic resources towards the activation of plant defense. The energy sensor Target of Rapamycin (TOR) kinase is a conserved master coordinator of growth and development in all eukaryotes. Although TOR is positioned at the interface between development and defense, little is known about the mechanisms by which TOR may potentially regulate the relationship between these two modalities. The plant hormones cytokinin (CK) and gibberellin (GA) execute various aspects of plant development and defense. The ratio between CK and GA was reported to determine the outcome of developmental programmes. Here, investigating the interplay between TOR-mediated development and TOR-mediated defense in tomato, we found that TOR silencing resulted in rescue of several different aberrant developmental phenotypes, demonstrating that TOR is required for the execution of developmental cues. In parallel, TOR inhibition enhanced immunity in genotypes with a low CK/GA ratio but not in genotypes with a high CK/GA ratio. TOR-inhibition mediated disease resistance was found to depend on developmental status, and was abolished in strongly morphogenetic leaves, while being strongest in mature, differentiated leaves. CK repressed TOR activity, suggesting that CK-mediated immunity may rely on TOR downregulation. At the same time, TOR activity was promoted by GA, and TOR silencing reduced GA sensitivity, indicating that GA signalling requires normal TOR activity. Our results demonstrate that TOR likely acts in concert with CK and GA signalling, executing signalling cues in both defense and development. Thus, differential regulation of TOR or TOR-mediated processes could regulate the required outcome of development-defense prioritisation."
Authors: Shuyao Kong, Mingyuan Zhu, Maria Regina Scarpin, David Pan, Longfei Jia, Ryan E Martinez, Simon Alamos, Vijaya Lakshmi Vadde, Hernan G. Garcia, Shu-Bing Qian, Jacob O. Brunkard and Adrienne H. K. Roeder.
bioRxiv (2023)
Abstract: "Robustness is the invariant development of phenotype despite environmental changes and genetic perturbations. In the Arabidopsis flower bud, four sepals initiate at robust positions and times and grow to equal size to enclose and protect the inner floral organs. We previously characterized the mutant development related myb-like1 (drmy1), where 3-5 sepals initiate at irregular positions and variable times and grow to different sizes, compromising their protective function. The molecular mechanism underlying this loss of robustness was unclear. Here, we show that drmy1 has reduced TARGET OF RAPAMYCIN (TOR) activity, ribosomal content, and translation. Translation reduction decreases the protein level of ARABIDOPSIS RESPONSE REGULATOR7 (ARR7), a rapidly synthesized and degraded cytokinin signaling inhibitor. The resultant upregulation of cytokinin signaling disrupts the robust positioning of auxin signaling, causing variable sepal initiation. Our work shows that the homeostasis of translation, a ubiquitous cellular process, is crucial for the robust spatiotemporal patterning of organogenesis."
Authors: Denis Janocha, Anne Pfeiffer, Yihan Dong, Ondřej Novák, Miroslav Strnad, Lyuba A. Ryabova and Jan U. Lohmann.
bioRxiv (2021)
Abstract: "Plants continuously adjust the rate at which new organs are produced in accordance with endogenous and environmental signals. Therefore, a multitude of signaling pathways converge to modulate stem cell activity. We have shown previously, that the TOR kinase network integrates metabolic- and light signals to control expression of WUSCHEL, a transcriptional master regulator of stem cells in the shoot apical meristem (SAM). However, the link between TOR and WUS promoter activity remained unresolved. Here we demonstrate that TOR controls trans-Zeatin abundance, the cytokinin derivative that is the main driver of shoot development. Moreover, we identify TOR mediated translational control of cytokinin degrading CYTOKININ OXIDASES/DEHYDROGENASE (CKX) enzymes as the underlying mechanism, which allows the plant to adjust the stem cell signaling environment and growth pattern within minutes after changes in environmental parameters."
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Authors: Iftah Marash, Rupali Gupta, Gautam Anand, Meirav Leibman-Markus, Naomi Lindner, Alon Israeli, Dov Nir, Adi Avni and Maya Bar.
bioRxiv (2023)
Abstract: "Plants constantly perceive and process environmental signals and balance between the energetic demands of growth and defense. Growth arrest upon pathogen attack was previously suggested to result from a redirection of the plants' metabolic resources towards the activation of plant defense. The energy sensor Target of Rapamycin (TOR) kinase is a conserved master coordinator of growth and development in all eukaryotes. Although TOR is positioned at the interface between development and defense, little is known about the mechanisms in which TOR may potentially regulate the relationship between these two modalities. The plant hormones cytokinin (CK) and gibberellin (GA) execute various aspects of plant development and defense. The ratio between CK and GA was reported to determine the outcome of developmental programs. Here, investigating the interplay between TOR-mediated development and TOR-mediated defense in tomato, we found that TOR silencing resulted in rescue of several different aberrant developmental phenotypes, demonstrating that TOR is required for the execution of developmental cues. In parallel, TOR inhibition enhanced immunity in genotypes with a low CK/GA ratio but not in genotypes with a high CK/GA ratio. TOR-inhibition mediated disease resistance was found to depend on developmental status, and was abolished in strongly morphogenetic leaves, while being strongest in mature, differentiated leaves. CK repressed TOR activity, suggesting that CK-mediated immunity may rely on TOR downregulation. At the same time, TOR activity was promoted by GA , and TOR silencing reduced GA sensitivity, indicating that GA signaling requires normal TOR activity. Our results demonstrate that TOR likely acts in concert with CK and GA signaling, executing signaling cues in both defense and development. Thus, differential regulation of TOR or TOR-mediated processes could regulate the required outcome of development-defense prioritization."
Authors: Iftah Marash, Rupali Gupta, Meirav Leibman-Markus, Adi Avni and Maya Bar.
bioRxiv (2022)
Abstract: "Target of Rapamycin (TOR) kinase is a conserved energy sensor that regulates plant growth and development in response to nutritional and environmental inputs. TOR downregulation enhances plant immunity. Cytokinin (CK) also mediates both development and defense processes. Although TOR is positioned at the interface between development and defense, little is known about the mechanisms in which TOR may potentially regulate the switch between these two modalities. Here, we investigated this switch, by examining of the relationship between TOR and CK-driven cues. We show that TOR-silencing or inhibition enhanced immunity in WT or CK-deficient backgrounds, while it reduced immunity in a high-CK background. TOR-silencing resulted in "normalization" of developmental phenotypes associated with high or low CK levels, as well as of other classical developmental mutants, demonstrating that TOR is required for the execution of developmental cues. We found that CK represses TOR activity, suggesting the existence of a cross talk mechanism between the two pathways. Our results demonstrate that TOR likely acts downstream to CK signaling and hormonal signaling in general, executing signaling cues resulting from both high and low CK, in both defense and development. Thus, differential regulation of TOR or TOR-mediated processes could underlie a development-defense switch."
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