Search

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. Summary Statement: Target of Rapamycin (TOR) is positioned at the interface between development and defense, but little is known about the mechanisms by which TOR may regulate shifts between them. Here, we demonstrate that TOR likely acts in concert with cytokinin and gibberellin to execute signalling cues in both defense and development. [ABSTRACT FROM AUTHOR]

Nutrient elements play essential roles in plant growth, development, and reproduction. Balanced nutrition is critical for plant health and the ability to withstand biotic stress. Treatment with essential elements has been shown to induce disease resistance in certain cases. Understanding the functional mechanisms underlying plant immune responses to nutritional elements has the potential to provide new insights into crop improvement. In the present study, we investigated the effect of various elements--potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na)--in promoting resistance against the necrotrophic fungus Botiytis cinerea and the hemibiotrophic bacterium Xanthomonas euvesicatoria in tomato. We demonstrate that spray treatment of essential elements was sufficient to activate immune responses, inducing defense gene expression, cellular leakage, reactive oxygen species, and ethylene production. We report that different defense signaling pathways are required for induction of immunity in response to different elements. Our results suggest that genetic mechanisms that are modulated by nutrient elements can be exploited in agricultural practices to promote disease resistance. [ABSTRACT FROM AUTHOR]

All organisms need to sense and process information about the availability of nutrients, energy status, and environmental cues to determine the best time for growth and development. The conserved target of rapamycin (TOR) protein kinase has a central role in sensing and perceiving nutritional information. TOR connects environmental information about nutrient availability to developmental and metabolic processes to maintain cellular homeostasis. Under favourable energy conditions, TOR is activated and promotes anabolic processes such as cell division, while suppressing catabolic processes. Conversely, when nutrients are limited or environmental stresses are present, TOR is inactivated, and catabolic processes are promoted. Given the central role of TOR in regulating metabolism, several previous works have examined whether TOR is wired to plant defence. To date, the mechanisms by which TOR influences plant defence are not entirely clear. Here, we addressed this question by testing the effect of inhibiting TOR on immunity and pathogen resistance in tomato. Examining which hormonal defence pathways are influenced by TOR, we show that tomato immune responses and disease resistance to several pathogens increase on TOR inhibition, and that TOR inhibition‐mediated resistance probably requires a functional salicylic acid, but not jasmonic acid, pathway. Our results support the notion that TOR is a master regulator of the development–defence switch in plants. [ABSTRACT FROM AUTHOR]

Phytohormones are involved in the regulation of plant responses to biotic stress. How a limited number of hormones differentially regulate defence responses and influence the outcome of plant–biotic interactions is not fully understood. In recent years, cytokinin (CK) was shown to induce plant resistance against several pathogens. In the present study, we investigated the effect of CK in inducing tomato resistance against the hemibiotrophic pathogenic bacteria Xanthomonas campestris pv. vesicatoria (Xcv) and Pseudomonas syringae pv. tomato (Pst). We demonstrate that CK enhances tomato resistance to Xcv and Pst through a process that relies on salicylic acid and ethylene signalling. CK did not directly affect the growth or biofilm formation ability of these pathogens in vitro. Overall, our work provides insight into the underlying mechanisms of CK‐induced immune responses against bacterial pathogens in tomato. [ABSTRACT FROM AUTHOR]

Plant immunity is often defined by the immunity hormones: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). These hormones are well known for differentially regulating defence responses against pathogens. In recent years, the involvement of other plant growth hormones such as auxin, gibberellic acid, abscisic acid, and cytokinins (CKs) in biotic stresses has been recognized. Previous reports have indicated that endogenous and exogenous CK treatment can result in pathogen resistance. We show here that CK induces systemic immunity in tomato (Solanum lycopersicum), modulating cellular trafficking of the pattern recognition receptor (PRR) LeEIX2, which mediates immune responses to Xyn11 family xylanases, and promoting resistance to Botrytis cinerea and Oidium neolycopersici in an SA‐ and ET‐dependent mechanism. CK perception within the host underlies its protective effect. Our results support the notion that CK promotes pathogen resistance by inducing immunity in the host. [ABSTRACT FROM AUTHOR]

Auxin response factors (ARFs) are a family of transcription factors that regulate auxin-dependent developmental processes. Class A ARFs function as activators of auxin-responsive gene expression in the presence of auxin, while acting as transcriptional repressors in its absence. Despite extensive research on the functions of ARF transcription factors in plant growth and development, the extent, and mechanisms of their involvement in plant resistance, remain unknown. We have previously reported that mutations in the tomato AUXIN RESPONSE FACTOR8 (ARF8) genes SlARF8A and SlARF8B result in the decoupling of fruit development from pollination and fertilization, leading to partial or full parthenocarpy and increased yield under extreme temperatures. Here, we report that fine-tuning of SlARF8 activity results in increased resistance to fungal and bacterial pathogens. This resistance is mostly preserved under fluctuating temperatures. Thus, fine-tuning SlARF8 activity may be a potent strategy for increasing overall growth and yield. • In addition to its growth-regulation activities, auxin has reported roles in plant immunity and microbial pathogenesis. • Auxin response factors (ARFs) are a family of transcription factors that regulate auxin-dependent developmental processes. • We have previously reported that mutations in the tomato ARF8 genes led to increased yield under extreme temperatures. • Here, we report that reducing ARF8 activity results in increased resistance to fungal and bacterial pathogens. • This resistance is mostly preserved under fluctuating temperatures. • Thus, fine-tuning SlARF8 activity may be a potent strategy for increasing overall growth and yield. [ABSTRACT FROM AUTHOR]