NPR1, a key immune regulator for plant survival under biotic and abiotic stresses

Hydrolase P1 in Bacillus velezensis HN-2 confers tobacco resistance by delaying TMV infection

BACKGROUND

Tobacco is a critical cash crop globally, contributing significantly to government revenues. However, its production is severely threatened by tobacco mosaic virus (TMV), which causes substantial yield and quality losses, leading to economic damage. Given the limited efficacy of chemical controls, biological control methods have gained prominence. Bacillus spp. are recognized as effective agents for plant disease management. In prior research, Bacillus velezensis HN-2 demonstrated promising traits for inducing plant resistance.

RESULTS

This study revealed that the total protein extract from B. velezensis HN-2 triggers the production of reactive oxygen species, upregulates antioxidant enzymes, activates immune-related protein genes, and induces systemic resistance in plants. Its effectiveness surpassed that of benzothiadiazole and Dufulin in delaying TMV invasion. Further analysis identified a specific hydrolase protein within the total protein extract that plays a key role in the observed antiviral activity. Exogenous expression and functional assays confirmed that this hydrolase, designated P1, is the primary active protein in B. velezensis HN-2 responsible for delaying TMV infection.

CONCLUSION

Hydrolase protein P1 acts as an elicitor to induce systemic resistance in the tobacco plant against TMV Infection. These findings provide an experimental foundation for the application of B. velezensis HN-2 in biological control strategies and offer theoretical insights into the use of Bacillus-derived proteins for TMV management. © 2025 Society of Chemical Industry.

Exploring the modulation of phosphorylation and SUMOylation-dependent NPR1 conformational switching on immune regulators TGA3 and WRKY70 through molecular simulation

NPR1 (Nonexpressor pathogenesis-related genes 1) is regulated by multisite phosphorylation and SUMOylation, serving as a master switch for effector-triggered plant immunity through a transcriptional activator (TGA3) and repressor (WRKY70) are experimentally well studied. However, the conformational relationship between the various phosphorylation, un-phosphorylation states, and SUMOylation's role in the functional switch remains unclear. Using deep learning-based molecular modeling, docking, and multi-nanosecond simulations (totaling 2 μs) with end-state free energy calculations, we unveil how different phosphorylation states impact the dynamic stability of NPR1's four phospho-serine residues (Ser11, Ser15, Ser55, & Ser59) and binding of the TGA3-WRKY70 over SUMOylation. Results from our simulations show that the salicylic-acid induced P-Ser11/15NPR1-SUMO3 stabilizes helices and the flexible activation loop (α22Lys423 - α1Arg50 & L35Asp467-Arg51α51, and Gly27L3), thereby switching association with TGA3. The inter-helix salt-bridge formed (L10Arg99-Glu323α9 and α14Glu280-Pro264L6) between the phosphorylated NPR1-SUMO3-TGA3 engage in tight control of conformational regulation were disengaged in the unphosphorylated system. The P-Ser55/59NPR1-SUMO3-WRKY70 reorients itself and forms an electrostatic and hydrogen bond with Lys145α7 - L2Asp26, L6Arg99 - Leu293L18 and Lys262L15 - Glu241L15, α13Val239 (α310), & L17Leu267 keeps complex stable and quiescent compare to unphosphorylated NPR1-WRKY70. Subsequently, the essential dynamic and secondary structural analysis reveals that the phosphorylation inhibits the α516 (long helix) formation and reduces the communication space between the 460α25-βturn3-α30-L42590 (NPR1) and 90L9-L10107 (SUMO3), making the binding more suitable for TGA3 (260βturn-L6270) and WRKY70 (230L15-L16265) via activation loop. These findings, which reveal the atomic and structural details of the NPR1's post-translational modification, will illuminate future investigations into enhancing plant immunity.

N-hydroxypipecolic acid and salicylic acid play key roles in autoimmunity induced by loss of the callose synthase PMR4

In Arabidopsis thaliana, the POWDERY MILDEW RESISTANT4 (PMR4)/GLUCAN SYNTHASE LIKE5 (GSL5) callose synthase is required for pathogen-induced callose deposition in cell wall defense. Paradoxically, pmr4/gsl5 mutants exhibit strong resistance to both powdery and downy mildew. The powdery mildew resistance of pmr4/gsl5 has been attributed to upregulated salicylic acid (SA) signaling based on its dependance on PHYTOALEXIN DEFICIENT4 (PAD4), which controls SA accumulation, and its abolishment by bacterial NahG salicylate hydroxylase. Our study revealed that disruption of PMR4/GSL5 also leads to early senescence. Suppressor analysis uncovered that PAD4 and N-hydroxypipecolic acid (NHP) biosynthetic genes ABERRANT GROWTH AND DEATH2-LIKE DEFENSE RESPONSE PROTEIN1 (ALD1) and FLAVIN-DEPENDENT MONOXYGENASE1 (FMO1) are required for early senescence of pmr4/gsl5 mutants. The critical role of NHP in the early senescence of pmr4/gsl5 was supported by greatly increased accumulation of pipecolic acid in pmr4/gsl5 mutants. In contrast, disruption of the SA biosynthetic gene ISOCHORISMATE SYNTHASE1/SA-INDUCTION DIFFICIENT 2 (ICS1/SID2), which greatly reduces SA accumulation, had little effect on impaired growth of pmr4/gsl5. Furthermore, while disruption of PAD4 completely abolished the powdery mildew resistance in pmr4/gsl5, mutations in ICS1/SID2, ALD1, or FMO1 had only a minor effect on the resistance of the mutant plants. However, disruption of both ICS1/SID2 and FMO1 abolished the enhanced immunity of the callose synthase mutants against the fungal pathogen. Therefore, while NHP plays a crucial role in the early senescence of pmr4/gsl5 mutants, both SA and NHP have important roles in the strong powdery mildew resistance induced by the loss of the callose synthase.

Bacteria suppress immune responses in Arabidopsis by inducing methylglyoxal accumulation and promoting H2O2 scavenging

Various reactive small molecules, naturally produced via cellular metabolism, function in plant immunity. However, how pathogens use plant metabolites to promote their infection is poorly understood. Here, we identified that infection with a virulent bacterial strain represses glyoxalase I (GLYI) activity, leading to elevated levels of methylglyoxal (MG) in Arabidopsis. Genetic analysis of GLYIs further supports that MG promotes bacterial infection. Mechanistically, MG modifies TRIPHOSPHATE TUNNEL METALLOENZYME2 (TTM2) at Arg-351, facilitating its interaction with CATALASE2 (CAT2), resulting in higher CAT2 activity and lower hydrogen peroxide (H2O2) accumulation. Taken together, we demonstrate that the bacterial pathogen harnesses the plant metabolite MG to promote its infection by scavenging H2O2.

Exogenous proline mediates OsNPR1 to regulate the innate pool of IAA in response to Cr exposure in rice plants

Indole acetic acid (IAA) orchestrates a myriad of physiological and biochemical responses in plants under stressful conditions, highlighting its indispensable role in plant resilience. The widespread contamination of chromium (Cr) poses a significant threat to rice cultivation, as its accumulation in plants disrupts various metabolic processes, consequently hindering growth. Of course, the utilization of exogenous growth regulators, including proline (Pro), has notably surged as a strategy to mitigate stress in plants. Pro can trigger the activation of other growth-regulating molecules, including IAA, to coordinate stress responses. To explore the complex interaction between exogenous Pro and the endogenous pool of IAA under Cr(VI) toxicity, a hydroponic system was established. The rice plants treated with exogenous Pro in coupled with Cr(VI) [Cr(VI)+Pro] showed significantly greater content of IAA than the plants not treated with exogenous Pro [Cr(VI)-Pro]. The expression analysis of genes involved in the speciation of IAA reactions reveals that the downregulation of OsNPR1 under "Cr(VI)+Pro" treatments might be the crucial player in increasing the IAA content in rice plants. The increase in IAA by Pro treatment under Cr toxicity might lead to an improvement in root activity and root architecture elements. Importantly, no significant difference was observed in the accumulation of Cr in [Cr(VI)-Pro]- and [Cr(VI)+Pro]-treated rice plants. These results reveal that exogenous Pro can improve plant growth by inducing IAA accumulation in plant tissues exposed to Cr(VI) toxicity, without increasing Cr toxicity in plants.

Efficient production of salicylic acid through CmeR-PcmeO biosensor-assisted multiplexing pathway optimization in Escherichia coli

To address the challenge of microbial tolerance in industrial biomanufacturing, we developed an adaptive evolution strategy for Escherichia coli W3110 to enhance its salicylic acid (SA) tolerance. Utilizing a CmeR-PcmeO biosensor-enabled high-throughput screening system, we isolated an SA-tolerant variant (W3110K-4) that exhibited a 2.3-fold increase in tolerance (from 0.9 to 2.1 g/L) and a 2.1-fold improvement in SA production (from 283 to 588.1 mg/L). Subsequently, the designed sensors were combined with multi-pathway sgRNA arrays to dynamically modulate the other three branched-chain acid derivatives, achieving a balance between biomass growth and rapid SA production in the adaptively evolved strain, resulting in a maximum SA yield of 1477.8 mg/L, which represents a 30% improvement over the non-evolved control strain W3110K-W2 (1138.2 mg/L) using the same metabolic strategy. Whole-genome sequencing revealed that adaptive mutations in genes such as ducA* and anti-drug resistance C2 mutation genes (ymdA*, ymdB*, clsC*, csgB*, csgA*, and csgC*) play a key role in enhancing SA tolerance and productivity. Notably, the evolved strain W3110K-4 exhibits significant resistance to bacteriophages, making it a promising candidate for large-scale SA fermentation. This work develops and expands the CmeR-PcmeO system, proposes new insights into improved strains through biosensor screening, guided multi-pathway metabolism, and adaptive evolution, and provides a paradigm for engineers to obtain engineered strains.

The kinase CPK5 phosphorylates MICRORCHIDIA1 to promote broad-spectrum disease resistance

In Arabidopsis (Arabidopsis thaliana), MICRORCHIDIA 1 (MORC1), a member of the MORC family of evolutionarily conserved GHKL-type ATPases, plays important roles in multiple layers of plant immunity. However, the molecular mechanism by which MORC1 regulates plant immunity remains obscure. Here, we report that the pathogen-responsive kinase CALCIUM-DEPENDENT PROTEIN KINASE 5 (CPK5) directly interacts with and phosphorylates MORC1, thereby promoting its stability and nuclear translocation. In the nucleus, MORC1 associates with the NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1)-TGACG-BINDING FACTOR (TGA) transcriptional complex to upregulate defense-responsive genes and promote plant resistance against several pathogens, such as the bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and fungal pathogen Botrytis cinerea. Therefore, this study uncovers a MORC1-mediated immune signaling pathway, in which the CPK5-MORC1-NPR1-TGA module transduces Ca2+ signals, leading to the upregulation of defense genes involved in plant immunity.

CmTGA8-CmAPX1/CmGSTU25 regulatory model involved in trehalose induced cold tolerance in oriental melon seedlings

Plants have developed complex regulatory networks to adapt to various stresses, including cold stress. Trehalose (Tre), known as the "sugar of life," plays a crucial role in enhancing cold tolerance by triggering antioxidation. However, the underlying regulatory mechanisms remain unclear. This study examines the transcription factor gene CmTGA8, which is induced by Tre under normal and cold conditions in melon seedlings (Cucumis melo L.), through transcriptome analysis and RT-qPCR. Reverse genetic analyses showed that silencing CmTGA8 reduced ascorbate peroxidase (APX) and glutathione S-transferase (GST) activities, suppressed CmAPX1 and CmGSTU25 expression, and increased cold susceptibility in melon seedlings. Our previous reports illustrated that Tre treatment significantly induced the expression of respiratory burst oxidase homologues (CmRBOHD) gene, encoding NADPH oxidases responsible for generating apoplastic H2O2. Silencing CmRBOHD markedly inhibited CmTGA8, CmAPX1, and CmGSTU25 expression and reduced cold tolerance. Moreover, H2O2 treatment upregulated CmTGA8 expression, while the NADPH oxidase inhibitor diphenyleneiodonium (DPI) treatment downregulated it. Additionally, CmTGA8 physically interacted with CmAPX1 and CmGSTU25 to promote their expression. Silencing CmGSTU25 decreased GST activity and ferric reducing ability of plasma (FRAP), further increasing cold sensitivity. These findings identify a novel regulatory hierarchy of the H2O2-CmTGA8-CmAPX1/CmGSTU25 cascade in the Tre-mediated cold response pathway in melon seedlings.

Interaction between pathogenesis-related (PR) proteins and phytohormone signaling pathways in conferring disease tolerance in plants

Pathogenesis-related (PR) proteins are critical defense signaling molecules induced by phytopathogens. They play a vital role in plant's defense signaling pathways and innate immunity, particularly in systemic acquired resistance (SAR) and serve as key molecular markers of plant defense. Overexpressing PR genes, such as chitinase, thaumatin, glucanase, thionin and defensin, either individually or in combination, have significantly boosted plants' defense responses against various pathogens. However, signaling pathways regulating the expression of these versatile proteins remain only partially understood. Plant hormones like salicylic acid (SA) and jasmonic acid (JA) are known for their well-established roles in regulating PR gene responses to pathogens and other stress conditions. PR genes interact with various components of hormonal signaling pathways, including receptors (e.g., NPR1 in SA signaling), transcription factors (e.g., MYC2 in JA signaling), and cis-regulating elements (e.g., W-box), to modulate plant defense responses. Recent studies have highlighted the contributions of different plant hormones to plant immunity and their interactions with PR proteins in a process known as hormonal crosstalk, which helps coordinate immunity activation. This review provides a comprehensive overview of the PR proteins, their complexity, and hormonal crosstalk in immunity, aiming to understand these interactions for improved pathogen resistance.

β-Aminobutyric acid-induced resistance in postharvest peach fruit involves interaction between the MAPK cascade and SNARE13 protein in the salicylic acid-dependent pathway

The inducer β-aminobutyric acid (BABA) participates in the immune response in various plants. However, the specific mitogen-activated protein kinase (MAPK) cascade involved in BABA-induced resistance (BABA-IR) has not yet been elucidated. Here, peach (Prunus persica) fruits treated with the BABA exhibited pattern-triggered immunity defense against Rhizopus stolonifer, accompanied by the generation of reactive oxygen species and activation of a MAPK cascade. Transcriptome sequencing suggested that a total of 15 MAPK kinase kinase (PpMAPKKK)/MAPK kinase (PpMAPKK)/PpMAPK genes were involved in BABA-IR in peach fruit. Further qRT-PCR analysis showed that the transcript profiles of PpMAPKKK3, PpMAPKK5, and PpMAPK1 were elevated. Subsequently, yeast two-hybrid, luciferase complementation imaging, pull-down, and in vitro phosphorylation assays were conducted to characterize the complete MAPK cascade (PpMAPKKK3-PpMAPKK5-PpMAPK1) involved in peach fruit. Moreover, the downstream events of MAPK1 include the involvement of SNARE13 and the corresponding NONEXPRESSOR OF PATHOGENESIS-RELATED GENES 1 (NPR1)-responsive defense. Single silencing of MAPKKK3, MAPKK5, or MAPK1 and double silencing of MAPKKK3 and MAPKK5 or MAPKK5 and MAPK1 resulted in enhanced susceptibility to the fungus R. stolonifer in mutants and attenuated salicylic acid (SA)-dependent defense gene expression. In contrast, the homologous or heterologous overexpression of PpSNARE13 in peach fruit or Arabidopsis led to an enhanced SA pool and elevated expression of pathogenesis related (PR) genes. Reciprocally, the ppsnare13cas9 mutants were generally compromised in the priming of SA-dependent resistance. Therefore, the MAPKKK3-MAPKK5-MAPK1 cascade contributed to pattern-triggered immunity signal transduction in BABA-elicited peach fruit, by combination with downstream events such as SNARE13, NPR1, and SA-dependent signaling.

Genome-wide characterization and expression profiling of the TGA gene family in sweet orange (Citrus sinensis) reveal CsTGA7 responses to multiple phytohormones and abiotic stresses

Citrus is widely recognized as one of the most economically important fruit crops worldwide. However, citrus growth is frequently hindered by external environmental stresses, which severely limit its development and yield. The TGA (TGACG motif-binding factor) transcription factors (TFs) are members of the bZIP family and play essential roles in plant defense responses and organ development. Nevertheless, the systematic identification and functional analysis of the TGA family in citrus remains unreported. In this study, genome-wide analysis identified a total of seven CsTGA TFs in Citrus sinensis, which were classified into five subgroups. Phylogenetic and syntenic analysis revealed that the CsTGA genes are highly conserved, with no tandem or segmental duplication events among family members. Promoter sequence analysis identified numerous cis-acting elements associated with transcriptional regulation, phytohormone response, and environmental adaptation in the promoters of CsTGA genes. The expression patterns under five phytohormones and three abiotic stresses demonstrated significant responses of multiple CsTGA genes under various forms of adversity. Among all tested treatments, CsTGA7 showed the most robust response to multiple stresses. Tissue-specific expression pattern analysis revealed potential functional biases among CsTGA genes. In-depth analysis showed that CsTGA7 localized in the nucleus and possessed transcriptional activation activity, consistent with the typical characteristic of transcriptional regulators. In summary, our research systematically investigated the genomic signature of the TGA family in C. sinensis and unearthed CsTGA7 with potential functions in phytohormone signaling transduction and abiotic stress responses. Our study establishes a basis for further exploration of the function of CsTGA genes under abiotic stress.

NPR1-like genes in Theobroma cacao: Evolutionary insights and potential in enhancing resistance to Phytophthora megakarya

Nonexpressor of pathogenesis-related 1 (NPR1) is crucial for activating the plant immune system through the signaling molecule salicylic acid (SA), which triggers systemic acquired resistance (SAR) in Arabidopsis. In this study, three putative genes associated with NPR1 from Arabidopsis have been identified in the genome of Theobroma cacao, namely, TcNPR1, TcNPR2, and TcNPR3, suggesting a functional diversification among the three gene entities. Phylogenetic analysis revealed that TcNPR1 and TcNPR2 branched alongside their Arabidopsis orthologs, NPR1 and NPR2, indicating that these genes maintain a conserved role in SA signaling pathways across different species. In contrast, TcNPR3 exists in a separate clade, suggesting unique functional roles and evolutionary divergence. A comparative analysis of the physiochemical properties of these TcNPRs showed a different subcellular localization, as TcNPR1 persists in the cytoplasm, while TcNPR3 is found in the nucleus, aligning with its proposed role in SA signaling and transcriptional regulation. Furthermore, we identified microRNAs that target TcNPR3, suggesting that P. megakarya may exploit the transcriptional regulatory network to bypass plant defense activation. Transient overexpression or suppression of TcNPR gene expression through RNA interference-mediated gene silencing could be sufficient to study the impact on the production of other molecules, such as SA, some PR protein expressions, and resistance against P. megakarya. The interactions between proteins encoded by TcNPRs and cellular proteins of P. megakarya will provide insight into whether the pathogen manipulates host defenses. Finally, the expression of TcNPR genes in response to infection by P. megakarya offers valuable information regarding the temporal and spatial activation during the defense response.

Transcriptome Analysis Reveals the Role of OsCBM1 in Rice Defense Against Xanthomonas oryzae pv.oryzae

Carbohydrate-binding malectin/malectin-like domain-containing proteins (CBMs) represent a newly discovered subclass of lectins that participate in various biological processes across the bacterial, animal, and plant kingdoms. The OsCBM1 gene in rice enhances reactive oxygen species (ROS) burst, contributing to drought-stress tolerance. Nonetheless, the functions of OsCBM1 in response to biotic stress remain poorly understood. In this research, we discovered that OsCBM1 was activated by Xoo infection, and overexpression of OsCBM1 increased rice resistance to bacterial blight, while suppression of its expression shows the opposite trend. OsCBM1 may influence resistance to bacterial blight by regulating ROS burst and the SA signaling pathway through RNA-seq analysis. Overexpression of OsCBM1 increased SA content and enhanced activities of SOD, POD, and CAT enzymes, whereas knockdown of OsCBM1 exhibited the opposite trend. The expression of genes associated with the SA and enzyme activity pathways was validated through quantitative real-time polymerase chain reaction (qRT-PCR). These results further clarify the function of OsCBM1 in biotic stress resistance, providing references for disease-resistant rice breeding.

TaANK-TPR1 enhances wheat resistance against stripe rust via controlling gene expression and protein activity of NLR protein TaRPP13L1

Nucleotide-binding site, leucine-rich repeat (NLR) proteins activate a robust immune response on recognition of pathogen invasion. However, the function and regulatory mechanisms of NLRs during Puccinia striiformis f. sp. tritici (Pst) infection in wheat remain elusive. Here, we identify an ankyrin (ANK) repeat and tetratricopeptide repeat (TPR)-containing protein, TaANK-TPR1, which plays a positive role in the regulation of wheat resistance against Pst and the immune response of NLR. TaANK-TPR1 targets the NLR protein TaRPP13L1 (Recognition of PeronosporaParasitica 13-like 1) to facilitate its homodimerization and cell death to enhance the resistance of wheat against Pst. Meanwhile, TaANK-TPR1 binds to the TGACGT motif (methyl jasmonate-responsive element) of the TaRPP13L1 promoter and activates TaRPP13L1 transcription. Both TaANK-TPR1 and TaRPP13L1 respond to jasmonic acid (JA) signaling via the TGACGT element. Importantly, overexpressing TaRPP13L1 confers robust rust resistance without impacting important agronomic traits in the field. These findings identify a regulatory mechanism of NLR protein and provide targets for improving crop disease resistance.

Genome-wide identification of wheat USP gene family and functional dissection of TaUSP85 involved in heat tolerance

A collection of conserved proteins known as universal stress protein (USP) is present in a wide range of species, including plants, fungi, bacteria, and animals. USPs are named for their ability to respond to a variety of stress conditions, such as heat stroke, osmotic stress, nutrient limitation, and exposure to toxins or antibiotics. While the USP response to different stress conditions in plants has been reported, little is known about the USP family in wheat (Triticum aestivum L.). In wheat, we identified 88 USP genes distributed across 21 chromosomes classified into four subfamilies. Phylogenetic tree and synteny analysis across multiple species revealed a highly conserved evolution of the USP family between monocots and dicots. Based on comparative analysis of protein domains, gene structure and conserved motifs, TaUSPs showed significant differences among the four subfamilies. Furthermore, expression pattern analysis of TaUSPs showed significant differences among various tissues and under different abiotic stress conditions. We further conducted transformation experiments with the TaUSP85 gene, which significantly enhanced yeast thermotolerance. Silencing of TaUSP85 through VIGS experiments in wheat resulted in significant wilting, decreased chlorophyll content, and increased MDA accumulation compared to control plants. The silenced plant lines had much more ROS accumulation than the control group, as determined by the findings of DAB and NBT staining. The interaction proteins TaUSP1 and TaUSP11 of TaUSP85 were screened by yeast two-hybrid and their interaction relationship was further verified by LCI. Overall, our findings enhance the comprehension of the USP gene family in wheat and provide a valuable resource for further investigation of these genes in wheat and related cereal crops.

Identification of new salicylic acid signaling regulators for root development and microbiota composition in plants

Besides playing a crucial role in plant immunity via the nonexpressor of pathogenesis-related (NPR) proteins, increasing evidence shows that salicylic acid (SA) can also regulate plant root growth. However, the transcriptional regulatory network controlling this SA response in plant roots is still unclear. Here, we found that NPR1 and WRKY45, the central regulators of SA response in rice leaves, control only a reduced sector of the root SA signaling network. We demonstrated that SA attenuates root growth via a novel NPR1/WRKY45-independent pathway. Furthermore, using regulatory network analysis and mutant characterization, we identified a set of new NPR1/WRKY45-independent regulators that conservedly modulate the root development and root-associated microbiota composition in both Oryza sativa (monocot) and Arabidopsis thaliana (dicot) in response to SA. Our results established the SA signaling as a central element regulating plant root functions under ecologically relevant conditions. These results provide new insights to understand how regulatory networks control plant responses to abiotic and biotic stresses.

Swords and shields: the war between Candidatus Liberibacter asiaticus and citrus

Citrus Huanglongbing (HLB) represents a significant threat to the citrus industry, mainly caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus (CLas). In this review, we summarize recent advances in understanding the relationship between citrus and CLas, particularly examining the functions of Sec-dependent effectors (SDEs) and non-classically secreted proteins (ncSPs) in virulence, as well as their targeted interactions with citrus. We further investigate the impact of SDEs on various physiological processes, including systemic acquired resistance (SAR), reactive oxygen species (ROS) accumulation, vesicle trafficking, callose deposition, cell death, autophagy, chlorosis and flowering. Additionally, we focus on the functional research on specific disease-resistant genes in citrus and the molecular mechanisms underlying disease resistance. Finally, we discuss the existing gaps and unresolved questions regarding citrus-CLas interactions, proposing potential solutions to facilitate the development of HLB-resistant citrus varieties.

NPR1 promotes blue light-induced plant photomorphogenesis by ubiquitinating and degrading PIF4

Light is a major determinant of plant growth and survival. NONEXPRESSER OF PATHOGENESIS-RELATED GENES 1 (NPR1) acts as a receptor for salicylic acid (SA) and serves as the key regulator of SA-mediated immune responses. However, the mechanisms by which plants integrate light and SA signals in response to environmental changes, as well as the role of NPR1 in regulating plant photomorphogenesis, remain poorly understood. This study shows that SA promotes plant photomorphogenesis by regulating PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Specifically, NPR1 promotes photomorphogenesis under blue light by facilitating the degradation of PIF4 through light-induced polyubiquitination. NPR1 acts as a substrate adaptor for the CULLIN3-based E3 ligase, which ubiquitinates PIF4 at Lys129, Lys252, and Lys428, and leading to PIF4 degradation via the 26S proteasome pathway. Genetically, PIF4 is epistatic to NPR1 in the regulation of blue light-induced photomorphogenesis, suggesting it acts downstream of NPR1. Furthermore, cryptochromes mediate the polyubiquitination of PIF4 by NPR1 in response to blue light by promoting the interaction and ubiquitination between NPR1 and PIF4. Transcriptome analysis revealed that under blue light, NPR1 and PIF4 coordinately regulate numerous downstream genes related to light and auxin signaling pathways. Overall, these findings unveil a role for NPR1 in photomorphogenesis, highlighting a mechanism for posttranslational regulation of PIF4 in response to blue light. This mechanism plays a pivotal role in the fine-tuning of plant development, enabling plants to adapt to complex environmental changes.

A Critical Review of Recent Advances in Maize Stress Molecular Biology

With the intensification of global climate change and environmental stress, research on abiotic and biotic stress resistance in maize is particularly important. High temperatures and drought, low temperatures, heavy metals, salinization, and diseases are widespread stress factors that can reduce maize yields and are a focus of maize-breeding research. Molecular biology provides new opportunities for the study of maize and other plants. This article reviews the physiological and biochemical responses of maize to high temperatures and drought, low temperatures, heavy metals, salinization, and diseases, as well as the molecular mechanisms associated with them. Special attention is given to key transcription factors in signal transduction pathways and their roles in regulating maize stress adaptability. In addition, the application of transcriptomics, genome-wide association studies (GWAS), and QTL technology provides new strategies for the identification of molecular markers and genes for maize-stress-resistance traits. Crop genetic improvements through gene editing technologies such as the CRISPR/Cas system provide a new avenue for the development of new stress-resistant varieties. These studies not only help to understand the molecular basis of maize stress responses but also provide important scientific evidence for improving crop tolerance through molecular biological methods.

Applications of CRISPR Technologies in Forestry and Molecular Wood Biotechnology

Forests worldwide are under increasing pressure from climate change and emerging diseases, threatening their vital ecological and economic roles. Traditional breeding approaches, while valuable, are inherently slow and limited by the long generation times and existing genetic variation of trees. CRISPR technologies offer a transformative solution, enabling precise and efficient genome editing to accelerate the development of climate-resilient and productive forests. This review provides a comprehensive overview of CRISPR applications in forestry, exploring its potential for enhancing disease resistance, improving abiotic stress tolerance, modifying wood properties, and accelerating growth. We discuss the mechanisms and applications of various CRISPR systems, including base editing, prime editing, and multiplexing strategies. Additionally, we highlight recent advances in overcoming key challenges such as reagent delivery and plant regeneration, which are crucial for successful implementation of CRISPR in trees. We also delve into the potential and ethical considerations of using CRISPR gene drive for population-level genetic alterations, as well as the importance of genetic containment strategies for mitigating risks. This review emphasizes the need for continued research, technological advancements, extensive long-term field trials, public engagement, and responsible innovation to fully harness the power of CRISPR for shaping a sustainable future for forests.

Translationally controlled tumor protein interacts with TaCIPK23 to positively regulate wheat resistance to Puccinia triticina

Hypersensitive response-programmed cell death (HR-PCD) regulated by Ca2+ signal is considered the major regulator of resistance against Puccinia triticina (Pt.) infection in wheat. In this study, the bread wheat variety Thatcher and its near-isogenic line with the leaf rust resistance locus Lr26 were infected with the Pt. race 260 to obtain the compatible and incompatible combinations, respectively. The expression of translationally controlled tumor protein (TaTCTP) was upregulated upon infection with Pt., through a Ca2+-dependent mechanism in the incompatible combination. The knockdown of TaTCTP markedly increased the area of dying cell and the number of Pt. haustorial mother cells (HMCs) at the infection sites, whereas plants overexpressing the gene exhibited enhanced resistance. The interaction between TaTCTP and calcineurin B-like protein-interacting protein kinase 23 (TaCIPK23) was also investigated, and the interaction was found occurred in the endoplasmic reticulum. TaCIPK23 phosphorylated TaTCTP in vitro. The expression of a phospho-mimic TaTCTP mutant in Nicotiana benthamiana promoted HR-like cell death. Silencing TaCIPK23 or TaCIPK23/TaTCTP co-silencing resulted in the same results as silencing TaTCTP. This suggested that TaTCTP is a novel phosphorylation target of TaCIPK23, and both participate in the resistance of wheat to Pt. in the same pathway.

Small size, big impact: Small molecules in plant systemic immune signaling

Plants produce diverse small molecules rapidly in response to localized pathogenic attack. Some of the molecules are able to migrate systemically as mobile signals, leading to the immune priming that protects the distal tissues against future infections by a broad-spectrum of invaders. Such form of defense is unique in plants and is known as systemic acquired resistance (SAR). There are many small molecules identified so far with important roles in the systemic immune signaling, some may have the potential to act as the mobile systemic signal in SAR establishment. Here, we summarize the recent advances in SAR research, with a focus on the role and mechanisms of different small molecules in systemic immune signaling.

Reactive Byproducts of Plant Redox Metabolism and Protein Functions

Living organisms exhibit an impressive ability to expand the basic information encoded in their genome, specifically regarding the structure and function of protein. Two basic strategies are employed to increase protein diversity and functionality: alternative mRNA splicing and post-translational protein modifications (PTMs). Enzymatic regulation is responsible for the majority of the chemical reactions occurring within living cells. However, plants redox metabolism perpetually generates reactive byproducts that spontaneously interact with and modify biomolecules, including proteins. Reactive carbonyls resulted from the oxidative metabolism of carbohydrates and lipids carbonylate proteins, leading to the latter inactivation and deposition in the form of glycation and lipoxidation end products. The protein nitrosylation caused by reactive nitrogen species plays a crucial role in plant morphogenesis and stress reactions. The redox state of protein thiol groups modified by reactive oxygen species is regulated through the interplay of thioredoxins and glutaredoxins, thereby influencing processes such as protein folding, enzyme activity, and calcium and hormone signaling. This review provides a summary of the PTMs caused by chemically active metabolites and explores their functional consequences in plant proteins.

Proxitome profiling reveals a conserved SGT1-NSL1 signaling module that activates NLR-mediated immunity

Suppressor of G2 allele of skp1 (SGT1) is a highly conserved eukaryotic protein that plays a vital role in growth, development, and immunity in both animals and plants. Although some SGT1 interactors have been identified, the molecular regulatory network of SGT1 remains unclear. SGT1 serves as a co-chaperone to stabilize protein complexes such as the nucleotide-binding leucine-rich repeat (NLR) class of immune receptors, thereby positively regulating plant immunity. SGT1 has also been found to be associated with the SKP1-Cullin-F-box (SCF) E3 ubiquitin ligase complex. However, whether SGT1 targets immune repressors to coordinate plant immune activation remains elusive. In this study, we constructed a toolbox for TurboID- and split-TurboID-based proximity labeling (PL) assays in Nicotiana benthamiana and used the PL toolbox to explore the SGT1 interactome during pre- and post-immune activation. The comprehensive SGT1 interactome network we identified highlights a dynamic shift from proteins associated with plant development to those linked with plant immune responses. We found that SGT1 interacts with Necrotic Spotted Lesion 1 (NSL1), which negatively regulates salicylic acid-mediated defense by interfering with the nucleocytoplasmic trafficking of non-expressor of pathogenesis-related genes 1 (NPR1) during N NLR-mediated response to tobacco mosaic virus. SGT1 promotes the SCF-dependent degradation of NSL1 to facilitate immune activation, while salicylate-induced protein kinase-mediated phosphorylation of SGT1 further potentiates this process. Besides N NLR, NSL1 also functions in several other NLR-mediated immunity. Collectively, our study unveils the regulatory landscape of SGT1 and reveals a novel SGT1-NSL1 signaling module that orchestrates plant innate immunity.

FaNPR3 Members of the NPR1-like Gene Family Negatively Modulate Strawberry Fruit Resistance against Colletotrichum acutatum

Strawberry fruit is highly appreciated worldwide for its organoleptic and healthy properties. However, this plant is attacked by many pathogenic fungi, which significantly affect fruit production and quality at pre- and post-harvest stages, making chemical applications the most effective but undesirable strategy to control diseases that has been found so far. Alternatively, genetic manipulation, employing plant key genes involved in defense, such as members of the NPR-like gene family, has been successful in many crops to improve resistance. The identification and use of the endogenous counterpart genes in the plant of interest (as it is the case of strawberry) is desirable as it would increase the favorable outcome and requires prior knowledge of their defense-related function. Using RNAi technology in strawberry, transient silencing of Fragaria ananassa NPR3 members in fruit significantly reduced tissue damage after Colletotrichum acutatum infection, whereas the ectopic expression of either FaNPR3.1 or FaNPR3.2 did not have an apparent effect. Furthermore, the ectopic expression of FaNPR3.2 in Arabidopsis thaliana double-mutant npr3npr4 reverted the disease resistance phenotype to Pseudomonas syringe to wild-type levels. Therefore, the results revealed that members of the strawberry FaNPR3 clade negatively regulate the defense response to pathogens, as do their Arabidopsis AtNPR3/AtNPR4 orthologs. Also, evidence was found showing that FaNPR3 members act in strawberry (F. ananassa) as positive regulators of WRKY genes, FaWRKY19 and FaWRKY24; additionally, in Arabidopsis, FaNPR3.2 negatively regulates its orthologous genes AtNPR3/AtNPR4. We report for the first time the functional characterization of FaNPR3 members in F. ananassa, which provides a relevant molecular basis for the improvement of resistance in this species through new breeding technologies.

Microneedle electrochemical sensor based on disposable stainless-steel wire for real-time analysis of indole-3-acetic acid and salicylic acid in tomato leaves infected by Pst DC3000 in situ

BACKGROUND

Indole-3-acetic acid (IAA) and salicylic acid (SA), pivotal regulators in plant growth, are integral to a variety of plant physiological activities. The ongoing and simultaneous monitoring of these hormones in vivo enhances our comprehension of their interactive and regulatory roles. Traditional detection methods, such as liquid chromatography-mass spectrometry, cannot obtain precise and immediate information on IAA and SA due to the complexity of sample processing. In contrast, the electrochemical detection method offers high sensitivity, rapid response times, and compactness, making it well-suited for in vivo or real-time detection applications.

RESULTS

A microneedle electrochemical sensor system crafted from disposable stainless steel (SS) wire was specifically designed for the real-time assessment of IAA and SA in plant in situ. This sensor system included a SS wire (100 μm diameter) coated with carbon cement and multi-walled carbon nanotubes, a plain platinum wire (100 μm diameter), and an Ag/AgCl wire (100 μm diameter). Differential pulse voltammetry and amperometry were adopted for detecting SA and IAA within the range of 0.1-20 μM, respectively. This sensor was applied to track IAA and SA fluctuations in tomato leaves during PstDC3000 infection, offering continuous data. Observations indicated an uptick in SA levels following infection, while IAA production was suppressed. The newly developed disposable SS wire-based microneedle electrochemical sensor system is economical, suitable for mass production, and inflicts minimal damage during the monitoring of SA and IAA in plant tissues.

SIGNIFICANCE

This disposable microneedle electrochemical sensor facilitates in vivo detection of IAA and SA in smaller plant tissues and allows for long-time monitoring of their concentrations, which not only propels research into the regulatory and interaction mechanisms of IAA and SA but also furnishes essential tools for advancing precision agriculture.

Adaptation of turnip mosaic virus to Arabidopsis thaliana involves rewiring of VPg-host proteome interactions

The outcome of a viral infection depends on a complex interplay between the host physiology and the virus, mediated through numerous protein-protein interactions. In a previous study, we used high-throughput yeast two-hybrid (HT-Y2H) to identify proteins in Arabidopsis thaliana that bind to the proteins encoded by the turnip mosaic virus (TuMV) genome. Furthermore, after experimental evolution of TuMV lineages in plants with mutations in defense-related or proviral genes, most mutations observed in the evolved viruses affected the VPg cistron. Among these mutations, D113G was a convergent mutation selected in many lineages across different plant genotypes, including cpr5-2 with constitutive expression of systemic acquired resistance. In contrast, mutation R118H specifically emerged in the jin1 mutant with affected jasmonate signaling. Using the HT-Y2H system, we analyzed the impact of these two mutations on VPg's interaction with plant proteins. Interestingly, both mutations severely compromised the interaction of VPg with the translation initiation factor eIF(iso)4E, a crucial interactor for potyvirus infection. Moreover, mutation D113G, but not R118H, adversely affected the interaction with RHD1, a zinc-finger homeodomain transcription factor involved in regulating DNA demethylation. Our results suggest that RHD1 enhances plant tolerance to TuMV infection. We also discuss our findings in a broad virus evolution context.

A salicylic acid-associated plant-microbe interaction attracts beneficial Flavobacterium sp. to the Arabidopsis thaliana phyllosphere

Both above- and below-ground parts of plants are constantly challenged with microbes and interact closely with them. Many plant-growth-promoting rhizobacteria, mostly interacting with the plant's root system, enhance the immunity of plants in a process described as induced systemic resistance (ISR). Here, we characterized local induced resistance (IR) triggered by the model PGPR Pseudomonas simiae WCS417r (WCS417) in Arabidopsis thaliana. Hydroponic application of WCS417 to Arabidopsis roots resulted in propagation of WCS417 in/on leaves and the establishment of local IR. WCS417-triggered local IR was dependent on salicylic acid (SA) biosynthesis and signalling and on functional biosynthesis of pipecolic acid and monoterpenes, which are classically associated with systemic acquired resistance (SAR). WCS417-triggered local IR was further associated with a priming of gene expression changes related to SA signalling and SAR. A metabarcoding approach applied to the leaf microbiome revealed a significant local IR-associated enrichment of Flavobacterium sp.. Co-inoculation experiments using WCS417 and At-LSPHERE Flavobacterium sp. Leaf82 suggest that the proliferation of these bacteria is influenced by both microbial and immunity-related, plant-derived factors. Furthermore, application of Flavobacterium Leaf82 to Arabidopsis leaves induced SAR in an NPR1-dependent manner, suggesting that recruitment of this bacterium to the phyllosphere resulted in propagation of IR. Together, the data highlight the importance of plant-microbe-microbe interactions in the phyllosphere and reveal Flavobacterium sp. Leaf82 as a new beneficial promoter of plant health.

The Mechanism of Exogenous Salicylic Acid and 6-Benzylaminopurine Regulating the Elongation of Maize Mesocotyl

The elongation of the mesocotyl plays an important role in the emergence of maize deep-sowing seeds. This study was designed to explore the function of exogenous salicylic acid (SA) and 6-benzylaminopurine (6-BA) in the growth of the maize mesocotyl and to examine its regulatory network. The results showed that the addition of 0.25 mmol/L exogenous SA promoted the elongation of maize mesocotyls under both 3 cm and 15 cm deep-sowing conditions. Conversely, the addition of 10 mg/L exogenous 6-BA inhibited the elongation of maize mesocotyls. Interestingly, the combined treatment of exogenous SA-6-BA also inhibited the elongation of maize mesocotyls. The longitudinal elongation of mesocotyl cells was the main reason affecting the elongation of maize mesocotyls. Transcriptome analysis showed that exogenous SA and 6-BA may interact in the hormone signaling regulatory network of mesocotyl elongation. The differential expression of genes related to auxin (IAA), jasmonic acid (JA), brassinosteroid (BR), cytokinin (CTK) and SA signaling pathways may be related to the regulation of exogenous SA and 6-BA on the growth of mesocotyls. In addition, five candidate genes that may regulate the length of mesocotyls were screened by Weighted Gene Co-Expression Network Analysis (WGCNA). These genes may be involved in the growth of maize mesocotyls through auxin-activated signaling pathways, transmembrane transport, methylation and redox processes. The results enhance our understanding of the plant hormone regulation of mesocotyl growth, which will help to further explore and identify the key genes affecting mesocotyl growth in plant hormone signaling regulatory networks.

The plant immune system: From discovery to deployment

Plant diseases cause famines, drive human migration, and present challenges to agricultural sustainability as pathogen ranges shift under climate change. Plant breeders discovered Mendelian genetic loci conferring disease resistance to specific pathogen isolates over 100 years ago. Subsequent breeding for disease resistance underpins modern agriculture and, along with the emergence and focus on model plants for genetics and genomics research, has provided rich resources for molecular biological exploration over the last 50 years. These studies led to the identification of extracellular and intracellular receptors that convert recognition of extracellular microbe-encoded molecular patterns or intracellular pathogen-delivered virulence effectors into defense activation. These receptor systems, and downstream responses, define plant immune systems that have evolved since the migration of plants to land ∼500 million years ago. Our current understanding of plant immune systems provides the platform for development of rational resistance enhancement to control the many diseases that continue to plague crop production.