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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]

Botrytis cinerea is the causative agent of gray mold disease, and infects more than 1400 plant species, including important crop plants. In tomato, B. cinerea causes severe damage in greenhouses and post-harvest storage and transport. Plant viruses of the Tobamovirus genus cause significant damage to various crop species. In recent years, the tobamovirus tomato brown rugose fruit virus (ToBRFV) has significantly affected the global tomato industry. Most studies of plant-microbe interactions focus on the interaction between the plant host and a single pathogen, however, in agricultural or natural environments, plants are routinely exposed to multiple pathogens. Here, we examined how preceding tobamovirus infection affects the response of tomato to subsequent infection by B. cinerea. We found that infection with the tobamoviruses tomato mosaic virus (ToMV) or ToBRFV resulted in increased susceptibility to B. cinerea. Analysis of the immune response of tobamovirus-infected plants revealed hyperaccumulation of endogenous salicylic acid (SA), upregulation of SA-responsive transcripts, and activation of SA-mediated immunity. Deficiency in SA biosynthesis decreased tobamovirus-mediated susceptibility to B. cinerea, while exogenous application of SA enhanced B. cinerea symptoms. These results suggest that tobamovirus-mediated accumulation of SA increases the plants' susceptibility to B. cinerea, and provide evidence for a new risk caused by tobamovirus infection in agriculture. [ABSTRACT FROM AUTHOR]

The mechanisms underlying the ability of plants to differentiate between pathogens and commensals in their environment are currently unresolved. It has been suggested that spatiotemporal regulation of pattern-recognition receptor (PRR) content could be one of the components providing plants with the ability to distinguish between pathogens and nonpathogenic microbes. The LeEIX PRRs recognize xylanases derived from beneficial or commensal plant colonizers of Trichoderma species, including the xylanase known as EIX. Here, we investigated possible general roles of PRRs from the LeEIX locus in immunity and pathogen resistance in tomato. Mutating the inhibitory PRR LeEIX1, or overexpressing the activating PRR LeEIX2, resulted in resistance to a wide range of pathogens and increased basal and elicited immunity. LeEIX1 knockout caused increases in the expression level of several tested PRRs, including FLS2, as well as bacterial pathogen resistance coupled with an increase in flg22-mediated immunity. The wild tomato relative Solanum pennellii contains inactive LeEIX PRR variants. S. pennellii does not respond to elicitation with the LeEIX PRR ligand EIX. Given that EIX is derived from a mostly nonpathogenic microbe, the connection of its PRRs to disease resistance has not previously been investigated directly. Here, we observed that compared with S. lycopersicum cultivar M82, S. pennellii was more sensitive to several fungal and bacterial pathogens. Our results suggest that the LeEIX locus might determine resistance to fungal necrotrophs, whereas the resistance to biotrophs is effected in combination with a gene/quantitative trait locus not within the LeEIX locus. [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]

Plants employ systemic‐induced resistance as part of their defence arsenal against pathogens. In recent years, the application of mild heating has been found to induce resistance against several pathogens. In the present study, we investigated the effect of root zone warming (RZW) in promoting tomato's resistance against the necrotrophic fungus Botrytis cinerea (Bc), the hemibiotrophic bacterium Xanthomonas campestris pv. vesicatoria (Xcv) and the biotrophic fungus Oidium neolycopersici (On). We demonstrate that RZW enhances tomato's resistance to Bc, On and Xcv through a process that is dependent on salicylic acid and ethylene. RZW induced tomato immunity, resulting in increased defence gene expression, reactive oxygen species (ROS) and ethylene output when plants were challenged, even in the absence of pathogens. Overall, the results provide novel insights into the underlying mechanisms of warming‐induced immune responses against phytopathogens with different lifestyles in tomato. Plants are often exposed to several stresses simultaneously, particularly in agricultural settings; here, we investigate the relationships between heat and pathogen stresses. We demonstrate that root zone warming induces systemic immunity and promotes resistance to several tomato pathogens, through a process that is dependent on salicylic acid and ethylene. [ABSTRACT FROM AUTHOR]

Plants rely on innate immunity to perceive and ward off microbes and pests, and are able to overcome the majority of invading microorganisms. Even so, specialized pathogens overcome plant defenses, posing a persistent threat to crop and food security worldwide, raising the need for agricultural products with broad, efficient resistance. Here we report a specific mutation in a tomato (S. lycopersicum) helper nucleotide-binding domain leucine-rich repeat H-NLR, SlNRC4a, which results in gain of function constitutive basal defense activation, in absence of PRR activation. Knockout of the entire NRC4 clade in tomato was reported to compromise Rpi-blb2 mediated immunity. The SlNRC4a mutant reported here possesses enhanced immunity and disease resistance to a broad-spectrum of pathogenic fungi, bacteria and pests, while lacking auto-activated HR or negative effects on plant growth and crop yield, providing promising prospects for agricultural adaptation in the war against plant pathogens that decrease productivity. Lorena Pizarro, Meirav Leibman-Markus et al. explore the genetic mechanisms for plant innate immunity. They functionally characterize a gain of function mutation in SlNRC4a in tomato. They characterize the structure of the mutant protein and functionally demonstrate that it confers broad-spectrum resistance without triggering a hypersensitive response or negatively impacting plant growth and crop yield. [ABSTRACT FROM AUTHOR]

Plants possess an efficient, two-tiered immune system to combat pathogens and pests. Several decades of research have characterized different features of these two well-known tiers, PTI and ETI (Pattern/ Effector-triggered Immunity). NLR (Nucleotide-binding domain Leucine-rich Repeat) receptors have been found to link PTI to ETI, and be required for full potentiation of plant immune responses in several systems. Intra-cellular helper-NLRs (h-NLRs) mediate ETI and have been focused on extensively in recent research. Previously, we investigated the roles of the h-NLR SlNRC4a in tomato immunity, finding that a specific mutation in this gene results in gain of function constitutive defense activation and broad disease resistance. Deletion of the entire NRC4 clade, which contains 3 genes, can compromise tomato immunity. Here, we decided to investigate the role of an additional clade member, SlNRC4b , in basal immunity. We generated a gain of function mutant in SlNRC4b using CRISPR-Cas9, as well as a double gain of function mutant in both genes. Similarly to the slnrc4a mutant, a slnrc4b mutant also possessed increased basal immunity and broad spectrum disease resistance. The double mutant displayed additive effects in some cases, with significant increases in resistance to fungal phytopathogens as compared with each of the single mutants. Our work confirms that the NRC4 family h-NLRs are important in the plant immune system, suggesting that this gene family has the potential to be promising in targeted agricultural adaptation in the Solanaceae family, promoting disease resistance and prevention of yield loss to pathogens. • h-NLR receptors mediate ETI and link ETI to PTI within the plant immune system. • A gain of function mutation in the h-NLR SlNRC4a activates defense constitutively. Here, we investigated the role of SlNRC4b in basal immunity. • A slnrc4b mutant possessed increased basal immunity and disease resistance. • The double slnrc4a/b mutant displayed additive effects. • The NRC4 family shows promise for targeted agricultural adaptation for disease resistance. [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]