Phytosulfokine (PSK), a plant peptide hormone with a wide range of biological functions, is recognized by its receptor PHYTOSULFOKINE RECEPTOR 1 (PSKR1). Previous studies have reported that PSK plays important roles in plant growth, development, and stress responses. However, the involvement of PSK in fruit development and quality formation remains largely unknown. Here, using tomato (Solanum lycopersicum) as a research model, we show that exogenous application of PSK promotes the initiation of fruit ripening and quality formation, while these processes are delayed in pskr1 mutant fruits. Transcriptomic profiling revealed that molecular events and metabolic pathways associated with fruit ripening and quality formation are affected in pskr1 mutant lines and transcription factors are involved in PSKR1-mediated ripening. Yeast screening further identified that DEHYDRATION-RESPONSIVE ELEMENT BINDING PROTEIN 2F (DREB2F) interacts with PSKR1. Silencing of DREB2F delayed the initiation of fruit ripening and inhibited the promoting effect of PSK on fruit ripening. Moreover, the interaction between PSKR1 and DREB2F led to phosphorylation of DREB2F. PSK improved the efficiency of DREB2F phosphorylation by PSKR1 at the tyrosine-30 site, and the phosphorylation of this site increased the transcription level of potential target genes related to the ripening process and functioned in promoting fruit ripening and quality formation. These findings shed light on the involvement of PSK and its downstream signaling molecule DREB2F in controlling climacteric fruit ripening, offering insights into the regulatory mechanisms governing ripening processes in fleshy fruits.

Summary Low light intensities affect the outbreak of plant diseases. However, the underlying molecular mechanisms remain poorly understood. High‐performance liquid chromatography analysis of tomato ( Solanum lycopersicum ) revealed that apoplastic glucose (Glc) levels decreased in response to low light. Conversely, low‐light‐induced susceptibility to Pseudomonas syringae pv tomato ( Pst ) DC3000 was significantly alleviated by exogenous Glc treatment. Using cell‐based biolayer interferometry assays, we found that Glc specifically binds to the tomato regulator of G protein signaling 1 (RGS1). Laser scanning confocal microscopy imaging revealed that Glc triggers RGS1 endocytosis, which influences the uncoupling of the RGS1‐Gα (GPA1) and GPA1‐Gβ (SlGB1) proteins, in a dose‑ and duration‐dependent manner. Analysis of G protein single and double mutants revealed that RGS1 negatively regulates disease resistance under low light and is required for Glc‐enhanced defense. Downstream of RGS1‐Glc binding, GPA1 negatively mediates the light‐intensity‐regulated defense, whereas SlGB1 positively regulates this process. These results reveal a novel light‐intensity‐responsive defense system that is mediated by a Glc–RGS1–G protein signaling pathway. This information will be critical for future investigations of how plant cells sense extracellular sugars and adjust defense under different environments, as well as for genetic engineering approaches to improve stress resilience.

[背景]在全球气候变化的背景下,大气CO2浓度的升高会影响植物病害的发生,进而影响农业生产.β型碳酸酐酶(β-carbonic anhydrase,βCA)是植物CO2感应和浓缩系统中的重要组成元件,参与拟南芥和烟草的植物免疫过程,但在番茄(Solanum lycopersicum)等园艺作物中的研究较少.[目的]通过探究番茄S1βCA3在抵御植物病害中的作用及机制,为番茄生产中的抗性调控提供科学依据.[方法]以拟南芥AtβCA氨基酸系列为参考序列,在番茄So1 genomics network数据库中鉴定到4个S1βCA.进一步以野生型(wild-type,WT)番茄'Ailsa Craig'(AC)为材料接种丁香假单胞菌番茄致病变种(Pseudomonas syringae pv.toma to DC3000,Pst DC3000),利用 qRT-PCR 技术测定叶片中S1βCA的表达量,筛选出受Pst DC3000诱导表达的基因S1βCA3.在此基础上,以AC为背景,利用农杆菌介导法进行番茄遗传转化,构建S1βCA3稳定过表达植株(OE-S1βCA3).通过观察OE-S1βCA3植株接种PstDC3000后的抗性表型,明确S1βCA3在番茄抵御Pst DC3000过程中的作用.为了研究S1βCA3调控植物抗病性的内在机制,比较WT和OE-S1βCA3植株接种PstDC3000与对照条件下转录组的变化,并利用KEGG数据库对差异基因进行功能分析,推测糖代谢与S1βCA3介导的免疫反应有关.最后,通过测定WT和OE-S1βCA3植株糖代谢及其信号途径相关基因表达量以及葡萄糖、果糖和蔗糖含量,对转录组结果进行验证及分析.[结果]OE-S1βCA3植株对PstDC3000的抗性增强,接种Pst DC3000后,叶片中的细菌生长量、病斑数以及死细胞积累量明显减少.转录组测序结果显示,正常条件下,OE-S1βCA3植株转录谱没有发生明显变化;接种PstDC3000后,在WT和OE-S1βCA3植株中检测到2 100个PstDC3000诱导基因,其中有63.3％的基因在OE-S1βCA3植株中表达量更高.KEGG分析结果显示,依赖于S1βCA3过表达的Pst DC3000诱导基因富集在糖代谢相关路径中,包括淀粉和蔗糖代谢,内质网中的蛋白质加工(糖基化),氨基糖和核苷酸糖代谢,真核生物中的核糖体生物合成以及光合作用等路径.糖代谢与糖信号密不可分,qRT-PCR及糖含量测定结果显示,接种PstDC3000后,OE-S1βCA3植株叶片中糖代谢及其信号传导途径相关基因表达量与葡萄糖、果糖和蔗糖的含量较WT更高.[结论]番茄S1βCA3的过表达增强了植株对Pst DC3000的抗性,该过程可能与糖代谢及其信号通路在植物免疫中的作用有关.

Leucine-rich repeat receptor-like kinases (LRR-RLKs) are ubiquitous in higher plants and act as receptors of extracellular signals to trigger multiple physiological processes. However, the functions of the majority of LRR-RLKs remain largely unknown, especially in tomato (Solanum lycopersicum L.). Here, we found that MRK1 (Multiple resistance-associated kinase 1), encoding a novel tomato LRR-RLK, was significantly induced by temperature stresses and bacterial pathogen attacks. Knocking out MRK1 impaired tolerance to both cold and heat stress, accompanied by decreased transcript levels of the master regulators C-repeat binding factor 1 (CBF1) and Heat shock transcription factor a-1a (HsfA1a), respectively. In addition, mrk1 mutants were hypersensitive to Pseudomonas syringae pv. tomato DC3000 and Ralstonia solanacearum and showed compromised pattern-triggered immunity (PTI) responses, as evidenced by decreased production of reactive oxygen species and reduced upregulation of PTI marker genes. Moreover, bimolecular fluorescence complementation, split-luciferase assays, and co-immunoprecipitation supported the formation of a complex of MRK1, FLS2, and Somatic embryogenesis receptor kinase (SERK3A/SERK3B) in a ligand-independent manner. This work demonstrates that tomato MRK1 is a novel positive regulator of multiple stress responses and may be a potential breeding target for improving crop stress resistance.

Atmospheric CO2 concentrations exert a strong influence on the susceptibility of plants to pathogens. However, the mechanisms involved in the CO2 -dependent regulation of pathogen resistance are largely unknown. Here we show that the expression of tomato (Solanum lycopersicum) β-CARBONIC ANHYDRASE 3 (βCA3) is induced by the virulent pathogen Pseudomonas syringae pv. tomato DC3000. The role of βCA3 in the high CO2 -mediated response in tomato and two other Solanaceae crops is distinct from that in Arabidopsis thaliana. Using βCA3 knock-out and over-expression plants, we demonstrate that βCA3 plays a positive role in the activation of basal immunity, particularly under high CO2 . βCA3 is transcriptionally activated by the transcription factor NAC43 and is also post-translationally regulated by the receptor-like kinase GRACE1. The βCA3 pathway of basal immunity is independent on stomatal- and salicylic-acid-dependent regulation. Global transcriptome analysis and cell wall metabolite measurement implicate cell wall metabolism/integrity in βCA3-mediated basal immunity under both CO2 conditions. These data not only highlight the importance of βCA3 in plant basal immunity under high CO2 in a well-studied susceptible crop-pathogen system, but they also point to new targets for disease management strategies in a changing climate.

Jasmonates (JAs) are phytohormones with crucial roles in plant defense. Plants accumulate JAs in response to wounding or herbivore attack, but how JA biosynthesis is triggered remains poorly understood. Here we show that herbivory by cotton bollworm (Helicoverpa armigera) induced both ethylene (ET) and JA production in tomato (Solanum lycopersicum) leaves. Using RNA-seq, ET mutants, and inhibitors of ET signaling, we identified ET-induced ETHYLENE RESPONSE FACTOR 15 (ERF15) and ERF16 as critical regulators of JA biosynthesis in tomato plants. Transcripts of ERF15 and ERF16 were markedly upregulated and peaked at 60 and 15 min, respectively, after simulated herbivore attack. While mutation in ERF16 resulted in the attenuated expression of JA biosynthetic genes and decreased JA accumulation 15 min after the simulated herbivory treatment, these changes were not observed in erf15 mutants until 60 min after treatment. Electrophoretic mobility shift assays and dual-luciferase assays demonstrated that both ERFs15 and 16 are transcriptional activators of LIPOXYGENASE D, ALLENE OXIDE CYCLASE, and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3, key genes in JA biosynthesis. Furthermore, JA-activated MYC2 and ERF16 also function as the transcriptional activators of ERF16, contributing to dramatic increases in ERF16 expression. Taken together, our results demonstrated that ET signaling is involved in the rapid induction of the JA burst. ET-induced ERF15 and ERF16 function as powerful transcriptional activators that trigger the JA burst in response to herbivore attack.

Plant glutamate-like receptor genes (GLRs) are homologous to mammalian ionotropic glutamate receptors genes (iGluRs). Although GLRs have been implicated in plant defenses to biotic stress, the relationship between GLR-mediated plant immunity against fungal pathogens and electrical signals remains poorly understood. Here, we found that pretreatment with a GLR inhibitor, 6,7-dinitriquinoxaline-2,3-dione (DNQX), increased the susceptibility of tomato plants to the necrotrophic fungal pathogen Botrytis cinerea. Assessment of the glr3.3, glr3.5 and glr3.3/glr3.5 double-mutants upon B. cinerea infection showed that tomato GLR3.3 and GLR3.5 are essential for plant immunity against B. cinerea, wherein GLR3.3 plays the main role. Analysis of the membrane potential changes induced by glutamate (Glu) or glycine (Gly) revealed that amplitude was significantly reduced by knocking out GLR3.3 in tomato. While treatment with Glu or Gly significantly increased immunity against B. cinerea in wild-type plants, this effect was significantly attenuated in glr3.3 mutants. Thus, our data demonstrate that GLR3.3- and GLR3.5-mediated plant immunity against B. cinerea is associated with electrical signals in tomato plants.

Plants intensely modulate respiration when pathogens attack, but the function of mitochondrial respiration-related genes in plant-bacteria interaction is largely unclear. Here, the functions of alpha-ketoglutarate dehydrogenase (alpha-kGDH) E2 subunit and alternative oxidase (AOX) were investigated in the interaction between tomato and the virulent bacterial pathogen Pseudomonas syringae pv. tomato DC3000 (Pst). Pst inoculation suppressed the transcript abundance of alpha-kGDH E2, but enhanced AOX expression and salicylic acid (SA) accumulation. Gene silencing and transient overexpression approaches revealed that plant susceptibility to Pst was significantly reduced by silencing alpha-kGDH E2 in tomato, but increased by overexpressing alpha-kGDH E2 in Nicotiana benthamiana, whereas silencing or overexpressing of AOX1a did not affect plant defense. Moreover, silencing octanoyltransferase (LIP2), engaged in the lipoylation of alpha-kGDH E2, significantly reduced disease susceptibility and hydrogen peroxide accumulation. Use of transgenic NahG tomato plants that cannot accumulate SA as well as the exogenous SA application experiment evidenced that alpha-kGDH E2 acts downstream of SA defense pathway. These results demonstrate tomato alpha-kGDH E2 plays a negative role in plant basal defense against Pst in an AOX-independent pathway but was associated with lipoylation and SA defense pathways. The findings help to elucidate the mechanisms of mitochondria-involved plant basal immunity.

Tropospheric CO2 concentrations were remarkably increasing, especially since the Industrial Revolution. The CO2 fertilization technology was increasingly used in greenhouse agriculture cultivation because of its benefit to crop quality and yield. But, as a consequence of elevated CO2, the plant-pathogen interactions in natural or agricultural ecosystems have large potential to be affected. So far, the effects of elevated CO2 on plant defense against pathogen are complicated and the underlying mechanism remained poorly understood. Here, using tomato plants, we found that elevated CO2 significantly suppressed the plant defense against necrotrophic pathogen Botrytis cinerea, which is accompanied by the disturbed homeostasis between defense-related salicylic acid- and jasmonic acid- (JA-) signaling. But, exogenous application of bacterial secreta N-decanoyl-homoserine lactone (DHL) drastically rescued B. cinerea disease susceptibility under elevated CO2 condition. Moreover, JA biosynthesis mutant spr2 and JA signaling gene-silenced plants blocked DHL-induced plant defense under elevated CO2 condition, which suggested JA signaling was indispensable to the alleviated effect of DHL on plant susceptibility to B. cinerea under elevated CO2 condition. Overall, this information will be benefit to manipulate DHL as an attractive disease management strategy in agriculture cultivation under changing CO2 conditions.

This article unveiled that ethylene biosynthesis and signaling play a critical role in heat stress response of tomato plants under elevated CO2. Plant responses to elevated CO2 and heat stress are tightly regulated by an intricate network of phytohormones. Plants accumulate ethylene (ET), the smallest hormone, in response to heat stress; however, the role of ET and its signaling in elevated CO2-induced heat stress response remains largely unknown. In this study, we found that transcript levels of multiple genes relating to ET synthesis, signaling, and heat shock proteins (HSPs) were induced by elevated CO2 (800 μmol mol−1) compared to ambient CO2 (400 μmol mol−1) in tomato leaves under controlled temperature conditions (25 °C). Elevated CO2-induced responses to heat stress (42 °C) were closely associated with increased ET production and HSP70 expression at both transcript and protein levels. Pretreatment with an antagonist of ET, 1-methylcyclopropene that inhibits ET-dependent responses, abolished elevated CO2-induced stress response without affecting the ET production rate. In addition, silencing of ethylene response factor 1 (ERF1) compromised elevated CO2-induced responses to heat stress, which was associated with the concomitant reduction in the transcript of heat shock factor A2, HSP70 and HSP90, indicating that ERF1 is required for elevated CO2-induced responses to heat. All these results provide convincing evidence on the importance of ET biosynthesis and signaling in elevated CO2-induced heat stress response in tomato plants. Thus, the study advances our understanding of the mechanisms of elevated CO2-induced stress response and may potentially be useful for breeding heat-tolerant tomatoes in the era of climate change.

Climate changes such as heat waves often affect plant growth and pose a growing threat to natural and agricultural ecosystems. Elevated atmospheric CO2 can mitigate the negative effects of heat stress, but the underlying mechanisms remain largely unclear. We examined the interactive effects of elevated CO2 (eCO2 ) and temperature on the generation of the hydrogen peroxide (H2 O2 ) and stomatal movement characteristics associated with heat tolerance in tomato seedlings grown under two CO2 concentrations (400 and 800 µmol mol-1 ) and two temperatures (25 and 42°C). eCO2 ameliorated the negative effects of heat stress, which was accompanied by greater amounts of RESPIRATORY BURST OXIDASE 1 (RBOH1) transcripts, apoplastic H2 O2 accumulation and decreased stomatal aperture. Silencing RBOH1 and SLOW-TYPE ANION CHANNEL, impeded eCO2 -induced stomatal closure and compromised the eCO2 -enhanced water use efficiency as well as the heat tolerance. Our findings suggest that RBOH1-dependent H2 O2 accumulation was involved in the eCO2 -induced stomatal closure, which participate in maintaining balance between water retention and heat loss under eCO2 concentrations. This phenomenon may be a contributor to eCO2 -induced heat tolerance in tomato, which will be critical for understanding how plants respond to both future climate extremes and changes in CO2 .