Functional characterization of Ganoderma lucidum polysaccharide and the mechanism of inducing tomato resistance to Tomato yellow leaf curl virus

Using functional polysaccharides as elicitors to induce plant disease resistance has emerged as an effective plant protection strategy. In this study, we found that crude polysaccharides derived from by-products of Ganoderma lucidum can effectively prevent and control the Tomato Yellow Leaf Curl Virus (TYLCV). As a result, we isolated and purified a homogeneous polysaccharide known as glucan-like peptide (GLP1), from crude polysaccharide of G. lucidum and explored the mechanism behind GLP1's ability to induce resistance in tomatoes against TYLCV. Analysis of the monosaccharide composition and high-performance gel permeation chromatography (HPGPC) revealed that GLP1 is solely composed of glucose, with molecular weight (Mw), 7.367 KDa, a number-average molecular weight (Mn) of 6.876 KDa, and peak molecular weight (Mp) values 7.505 KDa. Fourier transform infrared spectroscopy indicated that GLP1 may have a pyranose structure with an α-glycosidic bond. Plant hormones play a crucial role in disease resistance, and we found that GLP1 affects hormone levels in tomato plants by increasing jasmonic acid (JA) and ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC). Additionally, GLP1promoting the expression of genes associated with the ethylene signaling pathway. When inhibitors of ethylene synthesis blocked ethylene signaling, the resistance of tomato to TYLCV was significantly reduced. These findings suggest that ethylene signaling is involved in GLP1-induced tomato resistance and likely interacts with other pathways to contribute to this resistance.

The glutathione S-transferase BnGSTU12 enhances the resistance of Brassica napus to Sclerotinia sclerotiorum through reactive oxygen species homeostasis and jasmonic acid signaling

Sclerotinia sclerotiorum is a severe disease that affects rapeseed (Brassica napus), resulting in significant yield losses. In previous study, we identified the candidate GLUTATHIONE S-TRANSFERASE (GST) gene, BnGSTU12, associated with sclerotiorum stem resistance and the expression levels of BnGSTU12 in resistant lines were higher than that in susceptible lines. We analyzed the function of the BnGSTU12 during S. sclerotiorum infection in this study. BnGSTU12 expression was induced by S. sclerotiorum, with a strong increase 24 h after onset of infection. Transgenic functional analysis indicated that overexpression of BnGSTU12 in Arabidopsis thaliana and B. napus enhanced resistance to S. sclerotiorum, whereas BnGSTU12 silencing decreased S. sclerotiorum resistance. The inoculated BnGSTU12-OE A. thaliana and B. napus plants showed higher antioxidant enzyme activity and lower H2O2 contents than the wild type. As BnGSTU12 was rapidly induced by the phytohormones salicylic acid (SA), ethylene, and methyl jasmonate (MeJA), we investigated the involvement of the JA and SA pathways in GSTU12-mediated S. sclerotiorum resistance. JA content was higher in infected BnGSTU12-OE plants than in the wild type, whereas their SA contents were comparable. In addition, the expression levels of JASMONATE RESISTANT (JAR) involved in JA-Ile biosynthesis and those of JA-responsive genes were higher, the expression of JAZ gene repressing JA signaling was less in OE plants than WT after 12 and 24 h inoculation with S. sclerotiorum. Our results show that BnGSTU12 enhances resistance to S. sclerotiorum through ROS homeostasis and JA signaling.

Ethylene response transcription factor 5 (ERF5) enhances defense against tobacco curly shoot virus and associated betasatellite (TbCSV/TbCSB) in Nicotiana benthamiana

Begomovirus/betasatellite disease complex significantly threatens global crop production. Identifying potential plant antiviral genes is crucial for disease control. Nicotiana benthamiana is susceptible to viruses and contains 266 ethylene response transcription factors (ERFs). This study identified 29 NbERFs that were differentially upregulated in tobacco curly shoot virus and its associated betasatellite (TbCSV/TbCSB) infection, with ERF5 being the most common. Nine NbERF5s cluster phylogenetically and Niben101Scf00163g22002 (NbERF5) responds significantly to exogenous ACC treatment. Further analysis confirms the nuclear localization and transcriptional activation activity of NbERF5. Protein interaction assays demonstrate that NbERF5 has no self-interaction and does not interact with the βC1 protein of TbCSB. Silencing NbERF5 enhances TbCSV/TbCSB infection, and overexpression of NbERF5 inhibits TbCSV/TbCSB infection. Importantly, NbERF5 positively regulates the expression of the pathogenesis-related (PR) genes, NbPR1a and NbNPR1. Our findings suggest that NbERF5 enhances TbCSV/TbCSB resistance by activating the PR genes, indicating that NbERF5 is a potential antiviral gene.

Decoding resilience: ecology, regulation, and evolution of biosynthetic gene clusters

Secondary metabolism is crucial for plant survival and can generate chemistry with nutritional, therapeutic, and industrial value. Biosynthetic genes of selected secondary metabolites cluster within localised chromosomal regions. The arrangement of these biosynthetic gene clusters (BGCs) challenges the long-held model of random gene order in eukaryotes, raising questions about their regulation, ecological significance, and evolution. In this review, we address these questions by exploring the contribution of BGCs to ecologically relevant plant-biotic interactions, while also evaluating the molecular-(epi)genetic mechanisms controlling their coordinated stress- and tissue-specific expression. Based on evidence that BGCs have distinct chromatin signatures and are enriched with transposable elements (TEs), we integrate emerging hypotheses into an updated evolutionary model emphasising how stress-induced epigenetic processes have shaped BGC formation.

SlABCG9 Functioning as a Jasmonic Acid Transporter Influences Tomato Resistance to Botrytis cinerea

Jasmonic acid (JA) is crucial for plant stress responses, which rely on intercellular jasmonate transport. However, JA transporters have not been fully identified, especially in tomato (Solanum lycopersicum L.). This study reveals that plasma-membrane-localized protein SlABCG9 in tomato regulates fruit resistance to Botrytis cinerea. Transcriptomic analysis indicated that the SlABCG9 expression was significantly upregulated after B. cinerea infection. Assays using Xenopus oocytes, yeast cell sensitivity, and JA-inhibited primary root growth confirmed that SlABCG9 functions as a JA influx transporter. The knockout mutant lines of SlABCG9 showed decreased JA contents, suppressed defense gene PDF1.2's expression, reduced antioxidant enzyme activity, and severe disease symptoms compared to wild-type controls. Our findings provide new knowledge for understanding how the JA transporter and signaling pathway are involved in the biotic stress responses and improve the resistant ability against pathogen infections.

Tomato B-cell lymphoma2 (Bcl2)-associated athanogene 5 (SlBAG5) contributes negatively to immunity against necrotrophic fungus Botrytis cinerea through interacting with SlBAP1 and modulating catalase activity

The evolutionarily conserved and multifunctional B-cell lymphoma2 (Bcl2)-associated athanogene proteins (BAGs), serving as co-chaperone regulators, play a pivotal role in orchestrating plant stress responses. In this study, the possible involvement of tomato SlBAG genes in resistance to Botrytis cinerea was examined. The SlBAG genes respond with different expression change patterns to B. cinerea and defense signaling hormones. SlBAG proteins are individually differentially localized to the nucleus, mitochondria, cytoplasm, endoplasmic reticulum (ER), or vacuole. Silencing of SlBAG5 enhanced immunity to B. cinerea, while overexpression weakened it, affecting Botrytis-induced JA/ET defense gene expression and JA levels. Chitin-induced ROS burst and expression of PTI marker genes SlPTI5 and SlLRR22 were strengthened in SlBAG5-silenced plants but were weakened in SlBAG5-overexpressing plants (SlBAG5-OE) plants. SlBAG5 interacts with BON1 ASSOCIATED PROTEIN 1 (SlBAP1) through its BAG domain, and the stability of SlBAP1 depends on the presence of SlBAG5. Silencing of SlBAP1 conferred increased resistance to B. cinerea through increased expression of JA/ET signaling and defense genes. SlBAP1 functions by recruiting and boosting SlCAT3 activity to remove H2O2. The findings suggest that SlBAG5 suppresses tomato immunity to B. cinerea by stabilizing SlBAP1, which modulates ROS scavenging and acts as a negative regulator of immunity.

Pseudomonas syringae lytic transglycosylase HrpH interacts with host ubiquitin ligase ATL2 to modulate plant immunity

Pseudomonas syringae deploys a type III secretion system (T3SS) to deliver effector proteins to facilitate infection of plant cells; however, little is known about the direct interactions between T3SS components and plants. Here, we show that the specialized lytic transglycosylase (SLT) domain of P. syringae pv. tomato (Pst) DC3000 T3SS component HrpH is necessary for effector translocation. HrpH and its SLT domain induce host cell death and suppress pattern-triggered immunity (PTI). Transgenic hrpH-Arabidopsis plants exhibit decreased PTI responses and enhanced susceptibility to Pst DC3000ΔhrcQ-U. HrpH suppresses salicylic acid (SA) signaling and interacts with the E3 ubiquitin ligase ATL2 via its SLT domain, independent of its catalytic glutamate. ATL2 silencing indicates that ATL2 is required for basal resistance to bacterial infection, HrpH-triggered cell death, and suppressing MAPK and SA signaling. Our findings highlight that beyond serving as a lytic transglycosylase for effector delivery, HrpH targets an E3 ligase to modulate plant immunity.

Strawberry plant growth enhancement: Effects of artificial light and methyl jasmonate-salicylic acid treatments on physiology and metabolism

Strawberries, known for their antioxidant properties, exhibit changes in physiology and metabolite profiles based on cultivation techniques. In Indonesia, strawberries are typically grown in highland regions, but climate change has necessitated adjustments in cultivation practices to enhance production and quality. This study investigates the adaptation of strawberry plants in lowland environments using light-emitting diodes (LEDs) and the exogenous application of methyl jasmonate (MeJA) and methyl salicylic acid (MeSA). A randomized block design was used with two factors: LED light types and MeJA-MeSA treatments. While the treatments did not significantly affect shoot growth (initially 1.5-2 cm, increasing 3-5 times by day 3), chlorophyll content, or fruit sugar levels, notable effects were observed in leaf glucose accumulation. The control group showed a fivefold increase (0.55 μg ml-1), while LED-hormone treatments resulted in a 27-64 % lower increase (0.20-0.40 μg ml-1). Fructose levels followed a similar pattern, and malic acid content was highest in the MeJA treatment (5.76 mg ml-1), with MeSA treatments also enhancing malic acid (5.91 mg ml-1). The secondary metabolite analysis, conducted using GC-MS and LC-MS, identified key defense-related compounds, including terpenoids, saturated fats, alkaloids, and amino acid derivatives, which play a role in the plant's defense mechanisms. These findings highlight the potential of LED lighting and hormone applications to modulate strawberry physiology and suggest further research into their role in plant stress responses.

Detection of Verticillium infection in cotton leaves using ATR-FTIR spectroscopy coupled with machine learning algorithms

Verticillium wilt (VW) is a soil-borne vascular disease that affects upland cotton and is caused by Verticillium dahliae Kleb. A rapid and user-friendly early diagnostic technique is essential for the preventing and controlling VW disease. In this study, Fourier transform infrared (FTIR) spectroscopy with attenuated total reflectance (ATR) technology was used to detect VW infection in cotton leaves. About 1800 FTIR spectra were obtained from 348 cotton leaves. The cotton leaves were collected from three categories: VW group, infected group and control group (non-infected). The vibrational peak of chitins at 1558 cm-1 was identified through mean and differential analysis of FTIR spectra as a criterion to differentiate the VW or infected group from the control group. Classification models were constructed using various machine learning algorithms. The support vector machines (SVM) model exhibited the highest predictive accuracy (>96 %) in each group and a total accuracy (>97 %) for the three groups. These results provide a new approach for detecting Verticillium infection in cotton leaves and shows a promising potential for the future applications of the method in plant science.

Plant Colonization by Biocontrol Bacteria and Improved Plant Health: A Review

The use of biological control agents is one of the best strategies available to combat the plant diseases in an ecofriendly manner. Biocontrol bacteria capable of providing beneficial effect in crop plant growth and health, have been developed for several decades. It highlights the need for a deeper understanding of the colonization mechanisms employed by biocontrol bacteria to enhance their efficacy in plant pathogen control. The present review deals with the in-depth understanding of steps involved in host colonization by biocontrol bacteria. The colonization process starts from the root zone, where biocontrol bacteria establish initial interactions with the plant's root system. Moving beyond the roots, biocontrol bacteria migrate and colonize other plant organs, including stems, leaves, and even flowers. Also, the present review attempts to explore the mechanisms facilitating bacterial movement within the plant such as migrating through interconnected spaces such as vessels or in the apoplast, and applying quorum sensing or extracellular enzymes during colonization and what is needed to establish a long-term association within a plant. The impacts on microbial community dynamics, nutrient cycling, and overall plant health are discussed, emphasizing the intricate relationships between biocontrol bacteria and the plant's microbiome and the benefits to the plant's above-ground parts, the biocontrol 40 bacteria confer. By unraveling these mechanisms, researchers can develop targeted strategies for enhancing the colonization efficiency and overall effectiveness of biocontrol bacteria, leading to more sustainability and resilience.

Functional Characterization of the PoWHY1 Gene from Platycladus orientalis and Its Role in Abiotic Stress Tolerance in Transgenic Arabidopsis thaliana

The frequent occurrence of extreme weather conditions in the world has brought many unfavorable factors to plant growth, causing the growth and development of plants to be hindered and even leading to plant death, with abiotic stress hindering the growth and metabolism of plants due to severe uncontrollability. The WHY1 transcription factor plays a critical role in regulating gene expression in plants, influencing chlorophyll biosynthesis, plant growth, and development, as well as responses to environmental stresses. The important role of the PoWHY1 gene in regulating plant growth and adaptation to environmental stress has become a hot research topic. However, the mechanism of the PoWHY1 gene in Platycladus orientalis under abiotic stress is still unclear. Here, the PoWHY1 gene was analyzed bioinformatically using P. orientalis as study material, and the role of the gene against abiotic stress conditions in Arabidopsis thaliana was verified using transgenic technology. It was found that overexpression of PoWHY1 increased seed germination, decreased malondialdehyde accumulation, increased proline content, and delayed the senescence process under salt stress. The expression levels of JAZ1, LOX1, ABI1, and ABI2 were decreased, while the expression levels of RAB18, APX1, GSTF6, and DREB2A were increased, indicating that overexpression of PoWHY1 enhanced the salt stress tolerance of A. thaliana. Furthermore, PoWHY1 overexpression also increased drought tolerance in A. thaliana. From the above results, it can be concluded that maintaining high PoWHY1 expression levels in the leaves of P. orientalis can improve their environmental adaptability. The results provide a scientific basis for understanding the gene function of the PoWHY1 gene of P. orientalis under stress conditions and lay the foundation for further research on the function of the PoWHY1 gene.

A dTALE approach demonstrates that induction of common bean OVATE Family Protein 7 promotes resistance to common bacterial blight

Common bacterial blight (CBB) is a devastating seed-transmitted disease of common bean (Phaseolus vulgaris L.), caused by Xanthomonas phaseoli pv. phaseoli and Xanthomonas citri pv. fuscans. The genes responsible for CBB resistance are largely unknown. Moreover, the lack of a reproducible and universal transformation protocol limits the study of genetic traits in common bean. We produced X. phaseoli pv. phaseoli strains expressing artificially designed transcription-activator like effectors (dTALEs) to target 14 candidate genes for resistance to CBB based on previous transcriptomic data. In planta assays in a susceptible common bean genotype showed that induction of PvOFP7, PvAP2-ERF71, or PvExpansinA17 expression by dTALEs resulted in CBB symptom reduction. After PvOFP7 induction, in planta bacterial growth was reduced at early colonization stages, and RNA-seq analysis revealed up-regulation of cell wall formation and primary metabolism, together with major down-regulation of heat shock proteins. Our results demonstrated that PvOFP7 contributes to CBB resistance, and underlined the usefulness of dTALEs for functional validation of genes whose induction impacts Xanthomonas-plant interactions.

NLR-mediated antiviral immunity in plants

Plant viruses cause substantial agricultural devastation and economic losses worldwide. Plant nucleotide-binding domain leucine-rich repeat receptors (NLRs) play a pivotal role in detecting viral infection and activating robust immune responses. Recent advances, including the elucidation of the interaction mechanisms between NLRs and pathogen effectors, the discovery of helper NLRs, and the resolution of the ZAR1 resistosome structure, have significantly deepened our understanding of NLR-mediated immune responses, marking a new era in NLR research. In this scenario, significant progress has been made in the study of NLR-mediated antiviral immunity. This review comprehensively summarizes the progress made in plant antiviral NLR research over the past decades, with a focus on NLR recognition of viral pathogen effectors, NLR activation and regulation, downstream immune signaling, and the engineering of NLRs.

Harnessing Genetic Resistance in Maize and Integrated Rust Management Strategies to Combat Southern Corn Rust

Southern corn rust (SCR) caused by Puccinia polysora Underw. has recently emerged as a focal point of study because of its extensive distribution, significant damage, and high prevalence in maize growing areas such as the United States, Canada, and China. P. polysora is an obligate biotrophic fungal pathogen that cannot be cultured in vitro or genetically modified, thus complicating the study of the molecular bases of its pathogenicity. High temperatures and humid environmental conditions favor SCR development. In severe cases, SCR may inhibit photosynthesis and cause early desiccation of maize, a decrease in kernel weight, and yield loss. Consequently, an expedited and accurate detection approach for SCR is essential for plant protection and disease management. Significant progress has been made in elucidating the pathogenic mechanisms of P. polysora, identifying resistance genes and developing SCR-resistant cultivars. A detailed understanding of the molecular interactions between maize and P. polysora will facilitate the development of novel and effective approaches for controlling SCR. This review gives a concise overview of the biological characteristics and symptoms of SCR, its life cycle, the molecular basis of interactions between maize and P. polysora, the genetic resistance of maize to SCR, the network of maize resistance to P. polysora infection, SCR management, and future perspectives.

Molecular characterization of an endophytic strain of Bacillus subtilis with plant growth-promoting properties from a wild relative of papaya

AIM

Bacillus subtilis is usually found in soil, and their biocontrol and plant growth-promoting capabilities are being explored more recently than ever. However, knowledge about metabolite production and genome composition of endophytic B. subtilis from seeds is limited. In the present study, B. subtilis EVCu15 strain isolated from the seeds of Vasconcellea cundinamarcensis (mountain papaya) was subjected to whole genome sequencing and detailed molecular and functional characterization.

METHODS AND RESULTS

Whole genome sequencing and sequence analysis of the endophytic bacterium from mountain papaya seed revealed that the bacterium was B. subtilis, strain EVCu15. The genomic sequence had more than 98% nucleotide similarity with two published whole genome sequences of B. subtilis strains. Some of the important secondary metabolite gene clusters involved in production of bioactive compounds such as surfactin, fengycin, plipastatin, bacillibactin, bacillaene, subtilomycin, subtilosin A, and bacilysin were identified from the whole genome sequence analysis. Genes encoding several plant growth-promoting metabolites, mostly involved in the nutrient metabolism, were identified in the bacterial genome. These included factors coding for nitrogen, phosphorus, iron, sulfur, potassium, and trehalose metabolism. Genes involved in auxin, riboflavin, acetoin biosynthesis, ACC deaminase activity, and xylan degradation were also identified. Proteomic analysis confirmed the biosynthesis and release of several bioactive secondary metabolites in the endophytic B. subtilis strain EVCu15. Liquid chromatography-mass spectrometry-based profiling for hormones and vitamins identified extracellular secretion of several important plant growth-promoting compounds such as IAA, salicylic acid, zeatin, vitamin D1, D2, E, K1, and pyridoxine. The in vitro and in vivo studies with the endophytic B. subtilis against various plant pathogenic fungi showed moderate to high levels of resistance. The B. subtilis EVCu15 compared to B. amyloliquefaciens showed better control over the root-knot nematode Meloidogyne incognita, in terms of egg hatching inhibition and the mortality of J2 juveniles.

CONCLUSION

Overall, this study underscores the biocontrol and plant growth-promoting potential of B. subtilis EVCu15, an endophyte isolated from mountain papaya seeds. Genomic analysis revealed a significant proportion of genes linked to biocontrol and plant growth promotion, corroborating its efficacy against M. incognita and various plant pathogens in vitro and in greenhouse studies. Furthermore, the bacterium's ability to produce diverse bioactive compounds, including proteins, hormones, and vitamins, was confirmed, highlighting its complex interactions within the plant system.

Characterization and metabolomic profiling of endophytic bacteria isolated from Moringa oleifera and Piper betel leaves

Endophytes are microorganisms residing in plant tissues without causing harm and their relevance in medicinal plants has grown due to their biomolecules used in pharmaceuticals. This study isolated two endophytic bacterial strains from the leaves of M. oleifera and P. betel collected from Junagadh Agricultural University. The isolates were characterized morphologically and physio-biochemically, confirming them as gram-positive or gram-negative rods and cocci. Identification using 16S rRNA gene sequencing identified isolates belonging to various genera, including Priestia aryabhattai and Kocuria rhizophila The SEM characterization of the five selected isolates revealed diverse morphological structures, including coccus and rod shapes, organized in various formations. Isolates varied in size, with N3 (Kocuria rhizophila) cocci and S5 (Priestia aryabhattai) rods. Metabolomic analysis using GC/MS and LC-MS revealed diverse metabolic profiles with key compounds like n-Hexadecanoic acid, Pyrrolo[1,2-a]pyrazine-1,4-dione, Dihydrocapsaicin, and β-Homoproline, highlighting the potential of these endophytic bacteria in agricultural applications due to their roles in membrane integrity, antioxidant properties, stress response, and antibacterial activity.

Machine learning-based identification of general transcriptional predictors for plant disease

This study investigated the generalizability of Arabidopsis thaliana immune responses across diverse pathogens, including Botrytis cinerea, Sclerotinia sclerotiorum, and Pseudomonas syringae, using a data-driven, machine learning approach. Machine learning models were trained to predict disease development from early transcriptional responses. Feature selection techniques based on network science and topology were used to train models employing only a fraction of the transcriptome. Machine learning models trained on one pathosystem where then validated by predicting disease development in new pathosystems. The identified feature selection gene sets were enriched for pathways related to biotic, abiotic, and stress responses, though the specific genes involved differed between feature sets. This suggests common immune responses to diverse pathogens that operate via different gene sets. The study demonstrates that machine learning can uncover both established and novel components of the plant's immune response, offering insights into disease resistance mechanisms. These predictive models highlight the potential to advance our understanding of multigenic outcomes in plant immunity and can be further refined for applications in disease prediction.

Structure-function relation of cytokinins determines their differential efficiency in mediating tobacco resistance against Pseudomonas syringae

The classic plant growth-promoting phytohormone cytokinin has been identified and established as a mediator of pathogen resistance in different plant species. However, the resistance effect of structurally different cytokinins appears to vary and may regulate diverse mechanisms to establish resistance. Hence, we comparatively analysed the impact of six different adenine- and phenylurea-type cytokinins on the well-established pathosystem Nicotiana tabacum-Pseudomonas syringae. The efficiency of resistance effects was evaluated based on impacts on the host plant defence response by scoring infection symptoms and the direct impact on the pathogen by assessment of proliferation in planta. To identify common and cytokinin-specific components involved in resistance effects, transcriptome profiling and targeted metabolomics were conducted in leaves treated with the different cytokinins. We observed clearly different potentials of the tested cytokinins in either suppressing infection symptoms or pathogen proliferation. Gene regulation and metabolite analyses revealed cytokinin-type specific impacts on defence components, such as salicylic acid and related signalling, expression of PR proteins, and regulation of specialised metabolism. Cytokinins also strongly affected plant cell physiological parameters, such as a remarkable decrease in amino acid pools. Hence, this study provides comparative information on the efficiency of diverse cytokinins in mediating resistance in one well-studied pathosystem and insights into the specific regulation of resistance effects mediated by different cytokinin molecules. This is particularly relevant for studies on the function of cytokinins or other phytohormones and compounds interacting with cytokinin activities in the context of pathogen infections and other stress scenarios, considering the diverse cytokinins present in plants.

Plant immune resilience to a changing climate: molecular insights and biotechnological roadmaps

Successful resistance to disease-causing pathogens is underpinned by properly regulated immune signalling and defence responses in plants. The plant immune system is controlled at multiple levels of gene and protein regulation-from chromatin-associated epigenetic processes to protein post-translational modifications. Optimal fine-tuning of plant immune signalling and responses is important to prevent plant disease development, which is being exacerbated by a globally changing climate. In this review, we focus on how changing climatic factors mechanistically intercept plant immunity at different levels of regulation (chromatin, transcriptional, post-transcriptional, translational, and post-translational). We specifically highlight recent studies that have provided molecular insights into critically important climate-sensitive nodes and mechanisms of the plant immune system. We then propose several potential future directions to build climate-resilient plant disease resistance using cutting-edge biotechnology. Overall, this conceptual understanding and promising biotechnological advances provide a foundational platform towards novel approaches to engineer plant immune resilience.

Methyl jasmonate induced tolerance effect of Pinus koraiensis to Bursaphelenchus xylophilus

BACKGROUND

Methyl jasmonate (MeJA) can affect the balance of hormones and regulate the disease resistance of plants. Exploring the application and mechanism of MeJA in inducing the tolerance of Pinus koraiensis to pine wood nematode (PWN) infection is of great significance for developing new strategies for pine wilt disease control.

RESULTS

Different concentrations (0.1, 1, 5 and 10 mm) of MeJA treatment groups showed differences in relative tolerance index and relative anti-nematode index of P. koraiensis seedlings to PWN infection. The treatment of 5 mm MeJA solution induced the best tolerance effect, followed by the 1 mm MeJA solution. Transcriptome analysis indicated that many plant defense-related genes upregulated after treatment with 1, 5 and 10 mm MeJA solutions. Among them, genes such as jasmonate ZIM domain-containing protein, phenylalanine ammonia-lyase and peroxidase also continuously upregulated after PWN infection. Metabolome analysis indicated that jasmonic acid (JA) was significantly increased at 7 days postinoculation with PWN, and after treatment with both 1 and 5 mm MeJA solutions. Integrated analysis of transcriptome and metabolome indicated that differences in JA accumulation might lead to ubiquitin-mediated proteolysis, and expression changes in trans-caffeic acid and trans-cinnamic acid-related genes, leading to the abundance differences of these two metabolisms and the formation of multiple lignin and glucosides.

CONCLUSIONS

MeJA treatment could activate the expression of defense-related genes that correlated with JA, regulate the abundance of defense-related secondary metabolites, and improve the tolerance of P. koraiensis seedlings to PWN infection. © 2024 Society of Chemical Industry.

Identifying the role of cellulase gene CsCEL20 upon the infection of Xanthomonas citri subsp. citri in citrus

Citrus canker is a devastating disease caused by Xanthomonas citri subsp. citri (Xcc), which secretes the effector PthA4 into host plants to trigger transcription of the susceptibility gene CsLOB1, resulting in pustule formation. However, the molecular mechanism underlying CsLOB1-mediated susceptibility to Xcc remains elusive. This study identified CsCEL20 as a target gene positively regulated by CsLOB1. Cell expansion and cell wall degradation were observed in sweet orange leaves after Xcc infection. A total of 69 cellulase genes were retrieved within the Citrus sinensis genome, comprising 40 endoglucanase genes and 29 glucosidase genes. Transcriptomic analysis revealed that expression levels of CsCEL8, CsCEL9, CsCEL20, and CsCEL26 were induced by Xcc invasion in sweet orange leaves, but not in the resistant genotype Citron C-05. Among them, CsCEL20 exhibited the highest expression level, with an over 430-fold increase following Xcc infection. Additionally, RT-qPCR analysis confirmed that CsCEL20 expression was induced in susceptible genotypes (Sweet orange, Danna citron, Lemon) upon Xcc invasion, but not in resistant genotypes (Citron C-05, Aiguo citron, American citron). A Single-Nucleotide Polymorphism (SNP) at -423 bp was identified in the CEL20 promoters and exhibits a difference between eight susceptible citrus genotypes and three resistant ones. Moreover, CsCEL20 expression was upregulated in CsLOB1-overexpression transgenic lines compared to the wild type. Dual-luciferase reporter assays indicated that CsLOB1 can target the -505 bp to -168 bp region of CsCEL20 promoter to trans-activate its expression. These findings suggest that CsCEL20 may function as a candidate gene for citrus canker development and may be a promising target for biotechnological breeding of Xcc-resistant citrus genotypes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01531-3.

Advances in understanding the interaction between Solanaceae NLR resistance proteins and the viral effector Avr

The rising prevalence of viral-induced diseases, particularly those caused by certain strains, poses a substantial risk to the genetic diversity of Solanaceae crops and the overall safety of horticultural produce. According to the "gene-for-gene" hypothesis, resistance proteins are capable of selectively identifying nontoxic effectors produced by pathogens, as they are under purview of the host's immune defenses. The sensitivity and responsiveness of Solanaceae plants to viral attacks play a crucial role in shaping the outcomes of their interactions with viruses. Pathogenic organisms, devise an array of infection tactics aimed at circumventing or neutralizing the host's immune defenses to facilitate effective invasion. The invasion often accomplishes by suppressing or disrupting the host's defensive mechanisms or immune signals, which are integral to the infection strategies of such invading pathogens. This comprehensive review delves into the myriad approaches that pathogenic viruses employ to infiltrate and overcome the sophisticated immune system of tomatoes. Furthermore, the review explores the possibility of utilizing these viral strategies to bolster the resilience of horticultural crops, presenting a hopeful direction for forthcoming progress in plant health and agricultural stability.

Potato β-aminobutyric acid receptor IBI1 manipulates VOZ1 and VOZ2 transcription factor activity to promote disease resistance

Upon infection with nonpathogenic microorganisms or treatment with natural or synthetic compounds, plants exhibit a more rapid and potent response to both biotic and abiotic stresses. However, the molecular mechanisms behind this phenomenon, known as defense priming, are poorly understood. β-minobutyric acid (BABA) is an endogenous stress metabolite that enhances plant tolerance to various abiotic stresses and primes plant defense responses, providing the ability to resist a variety of pathogens (broad-spectrum resistance). In this study, we identified an aspartyl-tRNA synthetase (AspRS), StIBI1 (named after Arabidopsis IMPAIRED IN BABA-INDUCED IMMUNITY 1 [IBI1]), as a BABA receptor in Solanum tuberosum. We elucidated the regulatory mechanisms by which StIBI1 interacts with two NAC (NAM, ATAF1, 2, and CUC2) transcription factors (TFs), StVOZ1 and StVOZ2 (VASCULAR PLANT ONE ZINC FINGER [VOZ]), to activate BABA-induced resistance (BABA-IR). StVOZ1 represses, whereas StVOZ2 promotes, immunity to the late blight pathogen Phytophthora infestans. Interestingly, BABA and StIBI1 influence StVOZ1- and StVOZ2-mediated immunity. StIBI1 interacts with StVOZ1 and StVOZ2 in the cytoplasm, reducing the nuclear accumulation of StVOZ1 and promoting the nuclear accumulation of StVOZ2. Our findings indicate that StVOZ1 and StVOZ2 finely regulate potato resistance to late blight through distinct signaling pathways. In summary, our study provides insights into the interaction between the potato BABA receptor StIBI1 and the TFs StVOZ1 and StVOZ2, which affects StVOZ1 and StVOZ2 stability and nuclear accumulation to regulate late blight resistance during BABA-IR. This research advances our understanding of the primary mechanisms of BABA-IR in potato and contributes to a theoretical basis for the prevention and control of potato late blight using BABA-IR.

Transcriptomic profiling reveals distinct responses to beet curly top virus (BCTV) infection in resistant and susceptible sugar beet genotypes

BACKGROUND

Sugar beets (Beta vulgaris L.) are grown worldwide and suffer economic loss annually due to curly top disease caused by the beet curly top virus (BCTV). The virus is spread by the beet leafhopper (BLH), Circulifer tenellus Baker. Current management strategies rely on chemical control and planting BCTV-resistant sugar beet genotypes. However, the genetic mechanism underlying BCTV resistance in sugar beet is unknown. This study aimed to determine these mechanisms by comparing a resistant (EL10) and susceptible (FC709-2) sugar beet genotype using host plant suitability (no-choice), host preference (choice) assays, and transcriptomic analysis.

RESULTS

Host plant suitability assays revealed no significant differences in adult survival or nymph production between viruliferous and non-viruliferous BLH on either genotype, suggesting that BCTV resistance is not directly associated with reduced beet leafhopper fitness. However, host preference assays showed that viruliferous BLH preferred settling on the susceptible genotype, FC709-2, compared to the resistant genotype, EL10 whereas the non-viruliferous BLH showed no preference. RNA-sequencing analysis of BCTV-inoculated (viruliferous BLH-fed) and mock-inoculated (non-viruliferous BLH-fed) plants at day 1, 7, or 14 post-inoculations highlighted dynamic and contrasting responses between the two genotypes. The resistant genotype had differentially expressed transcripts (DETs) associated with jasmonic acid and abscisic acid biosynthesis and signaling. DETs associated with stress mitigation mechanisms and reduction in plant primary metabolic processes were also observed. In contrast, the susceptible genotype had DETs associated with opposing phytohormones like salicylic acid and auxin. Moreover, this genotype exhibited an upregulation in DETs involved in volatile organic compounds (VOCs) production and increased primary plant metabolic processes.

CONCLUSIONS

These results provide novel insight into the opposing transcriptional responses underlying BCTV resistance and susceptibility in sugar beet. Understanding and classifying the mechanisms of resistance or susceptibility to BCTV infection in sugar beet is beneficial to researchers and plant breeders as it provides a basis for further exploration of the host plant-virus-vector interactions.

Transcriptome analysis reveals role of transcription factor WRKY70 in early N-hydroxy-pipecolic acid signaling

N-Hydroxy-pipecolic acid (NHP) is a mobile metabolite essential for inducing and amplifying systemic acquired resistance (SAR) following a pathogen attack. Early phases of NHP signaling leading to immunity have remained elusive. Here, we report the early transcriptional changes mediated by NHP and the role salicylic acid (SA) plays during this response in Arabidopsis (Arabidopsis thaliana). We show that distinct waves of expression within minutes to hours of NHP treatment include increased expression of WRKY transcription factor genes as the primary transcriptional response, followed by the induction of WRKY-regulated defense genes as the secondary response. Most genes induced by NHP within minutes were SA dependent, whereas those induced within hours were SA independent. These data suggest that NHP induces the primary transcriptional response under basal levels of SA and that new SA biosynthesis via ISOCHORISMATE SYNTHASE 1/SA-INDUCTION DEFICIENT 2 is dispensable for inducing the secondary transcriptional response. We demonstrate that WRKY70 is required for the induced expression of a set of genes defining some of the secondary transcriptional response, SAR protection, and NHP-dependent enhancement of reactive oxygen species production in response to flagellin treatment. Our study highlights the key genes and pathways defining early NHP responses and the role of WRKY70 in regulating NHP-dependent transcription.

"Ca. Nitrosocosmicus" members are the dominant archaea associated with plant rhizospheres

Archaea catalyzing the first step of nitrification in the rhizosphere possibly have an influence on plant growth and development. In this study, we found a distinct archaeal community, dominated by ammonia-oxidizing archaea (AOA), associated with the root system of pepper (Capsicum anuum L.) and ginseng plants (Panax ginseng C.A. Mey.) compared to bulk soil not penetrated by roots. While the abundance of total AOA decreased in the rhizosphere soils, AOA related to "Candidatus Nitrosocosmicus," which harbor gene encoding manganese catalase (MnKat) in contrast to most other AOA, dominated the AOA community in the rhizosphere soils. For both plant species, the ratio of copy numbers of the AOA MnKat gene to the amoA gene (encoding the ammonia monooxygenase subunit A) was significantly higher in the rhizospheres than in bulk soils. In contrast to MnKat-negative strains from other AOA clades, the catalase activity of a representative isolate of "Ca. Nitrosocosmicus" was demonstrated. Members of this clade were enriched in H2O2-amended bulk soils, and constitutive expression of their MnKat gene was observed in both bulk and rhizosphere soils. Due to their abundance, "Ca. Nitrosocosmicus" members can be considered important players mediating the nitrification process in rhizospheres. The dominance of this MnKat-containing AOA in rhizospheres of agriculturally important plants hints at a previously overlooked AOA-plant interaction.

IMPORTANCE

Ammonia-oxidizing archaea (AOA) are widespread in terrestrial environments and outnumber other ammonia oxidizers in the rhizosphere, possibly exerting an influence on plant growth and development. However, little is known about the selection forces that shape their composition, functions, survival, and proliferation strategies in the rhizosphere. Here, we observed a distinct AOA community on root systems of two different plant species compared to bulk soil. Our results show that the "Ca. Nitrosocosmicus" clade, which possesses functional MnKat genes unlike most other AOA, dominated the rhizosphere soils. Moreover, members of this clade were enriched in H2O2-amended bulk soil, which mimics the ROS stress in root systems. While research on AOA-plant interactions in the rhizosphere is still in its infancy, these findings suggest that "Ca. Nitrosocosmicus" may be an important clade of AOA with potential AOA-plant interaction.

WRKY1-Mediated Interconversion of MeSA and SA in Neighbouring Apple Plants Enhances Defence Against Powdery Mildew

Powdery mildew (PM), caused by the biotrophic fungus Podospharea leucotricha, is a major threat to apple production. Plant-plant communication (PPC) is a crucial strategy for plant communities to enhance their defence against pathogens. The interconversion of methyl salicylate (MeSA) and salicylic acid (SA) is critical for PPC regulation, but the mechanism of MeSA-mediated PPC is not fully understood. This study reveals a significant increase in SA and MeSA levels in neighbouring plants (receivers) following PM attack on emitter plants, activating defence responses in receivers. Notably, the expression of WRKY1, a previously characterized transcription factor, was upregulated in receivers, implicating its role in defence response modulation. WRKY1 was found to promote SA accumulation and enhance PM resistance in receivers. Importantly, WRKY1 positively regulates the expression of SABP2a, which catalysers MeSA to SA conversion, and negatively regulates SAMT1a, which functions in the reverse reaction. Consequently, WRKY1 facilitates the conversion of MeSA to SA in receivers, preventing its reversion and sustaining elevated SA levels. Collectively, our findings clarify the role of WRKY1 in enhancing the defence response to PM in receivers.

Disrupted oxylipin biosynthesis mitigates pathogen infections and pest infestations in cotton (Gossypium hirsutum)

Cotton (Gossypium hirsutum) is the world's most important fiber crop, critical to global textile industries and agricultural economies. However, cotton yield and harvest quality are undermined by the challenges introduced from invading pathogens and pests. Plant-synthesized oxylipins, specifically 9-hydroxy fatty acids resulting from 9-lipoxygenase activity (9-LOX), enhance the growth and development of many microbes and pests. We hypothesized that targeted disruption of 9-LOX-encoding genes in cotton could bolster crop resilience against prominent agronomic threats. Fusarium oxysporum f. sp. vasinfectum (FOV), Aphis gossypii (cotton aphid), and tobacco rattle virus induced the expression of 9-oxylipin biosynthesis genes, suggesting that the 9-LOX gene products were susceptibility factors to these stressors. Transiently disrupting the expression of the 9-LOX-encoding genes by virus-induced gene silencing significantly reduced target transcript accumulation, and this correlated with impaired progression of FOV infections and a significant decrease in the fecundity of cotton aphids. These findings emphasize that the cotton 9-LOX-derived oxylipins are leveraged by multiple pathogens and pests to enhance their virulence in cotton, and reducing the expression of 9-LOX-encoding genes can benefit cotton crop vitality.

Imaging the spatial distribution of structurally diverse plant hormones

Plant hormones are essential and structurally diverse molecules that regulate various aspects of plant growth, development, and stress responses. However, the precise analysis of plant hormones in complex biological samples poses a challenge due to their low concentrations, dynamic levels, and intricate spatial distribution. Moreover, the complexity and interconnectedness of hormone signaling networks make it difficult to simultaneously trace multiple hormone spatial distributions. In this review, we provide an overview of currently recognized small-molecule plant hormones, signal peptide hormones, and plant growth regulators, along with the analytical methods employed for their analysis. We delve into the latest advancements in mass spectrometry imaging and in situ fluorescence techniques, which enable the examination of the spatial distribution of plant hormones. The advantages and disadvantages of these imaging techniques are further discussed. Finally, we propose potential avenues in imaging techniques to further enhance our understanding of plant hormone biology.

Induction of antiherbivore defense responses in poplars using a methyl jasmonate and mesoporous silica nanoparticle complex

BACKGROUND

Poplar in China has long been plagued by the fall webworm Hyphantria cunea. Enhancing plant immunity using chemical elicitors is an environmentally friendly approach to pest control. The phytohormone methyl jasmonate (MeJA) can stimulate the chemical defenses of poplars against herbivores but has been shown to have limited efficacy in practice. Here, we studied the effects of a MeJA and mesoporous silica nanoparticle (MSN) complex (MeJA@MSN) regarding the induction of poplar resistance to H. cunea, which may provide strategies for the effective use of MeJA.

RESULTS

The silicon-based phytohormone complex (MeJA@MSNs) exhibited excellent biological and physiochemical properties, such as excellent biocompatibility and plant tissue transportability. The changes in metabolites in poplar leaves induced by MeJA, MSNs, and MeJA@MSNs were investigated by metabolic analysis. MeJA@MSNs led to highly potent induced resistance along with elevated salicylaldehyde content, which increased with the dose administered. The salicylaldehyde metabolite showed a strong antifeedant effect on H. cunea larvae at a dosage of 1 μg, with the 50% lethal dose being 20.4 μg/mg. Furthermore, transcriptional analysis showed that MeJA@MSNs upregulated key genes in biosynthetic pathways more than MeJA and MSNs.

CONCLUSION

Our results show that MeJA and MSNs interact positively in poplar, leading to salicylaldehyde accumulation and increased induced resistance to H. cunea, providing new insights into the underlying resistance mechanisms induced by MeJA@MSNs. © 2024 Society of Chemical Industry.

Enhancing crop disease management through integrating biocontrol bacteria and silicon fertilizers: Challenges and opportunities

To achieve sustainable disease management in agriculture, there's a growing interest in using beneficial microorganisms as alternatives to chemical pesticides. Bacteria, in particular, have been extensively studied as biological control agents, but their inconsistent performance and limited availability hinder broader adoption. Research continues to explore innovative biocontrol technologies, which can be enhanced by combining silicon (Si) with biocontrol plant growth-promoting rhizobacteria (PGPR). Both biocontrol PGPR and Si demonstrate effectiveness in reducing plant disease under stress conditions, potentially leading to synergistic effects when used together. This review examines the individual mechanisms by which biocontrol PGPR and Si fertilizers manage plant diseases, emphasizing their roles in enhancing plant defense and decreasing disease incidence. Various Si fertilizer sources allow for flexible application methods, suitable for different target diseases and plant species. However, challenges exist, such as inconsistent soil Si data, lack of standardized soil tests, and limited availability of Si fertilizers. Addressing these issues necessitates collaborative efforts to develop improved Si fertilizers and tailored application strategies for specific cropping systems. Additionally, exploring silicate-solubilizing biocontrol bacteria to enhance Si availability in soils introduces intriguing research avenues. Investigating these bacteria's diversity and mechanisms can optimize Si access for plants and bolster disease resistance. Overall, combining biocontrol PGPR and Si fertilizers or silicate-solubilizing biocontrol bacteria shows promise for sustainable agriculture, enhancing crop productivity while reducing reliance on chemical inputs and promoting environmental sustainability.

Genetic Warfare: The Plant Genome's Role in Fending Off Insect Invaders

The plant defense against insects is multiple layers of interactions. They defend through direct defense and indirect defense. Direct defenses include both physical and chemical barriers that hinder insect growth, development, and reproduction. In contrast, indirect defenses do not affect insects directly but instead suppress them by releasing volatile compounds that attract the natural enemies of herbivores. Insects overcome plant defenses by deactivating biochemical defenses, suppressing defense signaling through effectors, and altering their behavior through chemical regulation. There is always a genetic war between plants and insects. In this genetic war, plant-insect co-evolution act as both weapons and messengers. Because plants always look for new strategies to avoid insects by developing adaptation. There are molecular processes that regulate the interaction between plants and insect. Here, we examine the genes and proteins involved in plant-insect interactions and explore how their discovery has shaped the current model of the plant genome's role. Plants detect damage-associated and herbivore-associated molecular patterns through receptors, which trigger early signaling pathways involving Ca2+, reactive oxygen species, and MAP kinases. The specific defense mechanisms are activated through gene signaling pathways, including phytohormones, secondary metabolites, and transcription factors. Expanding plant genome approaches to unexplored dimensions in fending off insects should be a future priority in order to develop management strategies.

Spatiotemporal expression analysis of jasmonic acid and saponin-related genes uncovers a potential biosynthetic regulation in Panax notoginseng

BACKGROUND

Sanqi, the root of Panax notoginseng, has long been recognized for its therapeutic effects on cardiovascular diseases. Saponins, including ginsenosides and notoginsenosides, are the main bioactive components of P. notoginseng. The biosynthesis of saponins is closely related to the defense responses orchestrated by endogenous hormones.

RESULTS

To provide new insights into the underlying role of phytohormone jasmonic acid (JA) in the synthesis and regulation of saponins, we performed an ultra-performance liquid chromatography analysis of different tissues of P. notoginseng aged 2-4 years. Moreover, by combined evaluation of saponin content and transcriptome profiling of each tissue, the spatial and temporal distribution of saponins was analyzed. N notoginsenoside R1, ginsenoside Rb1 and ginsenoside Rd accumulated in the underground tissues, including the root, tuqi, fibril and rhizome. In agreement with this data, the corresponding genes of the endogenous hormone JAs, especially coronatine insensitive 1 (COI1) and myelocytomatosis proteins 2 (MYC2), were predominantly expressed in the underground tissues. The tissue- and age-specific distribution of saponins was consistent with the expression of genes involved in JA biosynthetic, metabolic and signaling pathways.

CONCLUSION

The present study has revealed the temporal and spatial effects of endogenous phtohormones in the synthesis and regulation of notoginsenosides, which will provide a significant impact on improving the ecological planting technology, cultivating new high-quality varieties and protecting the rare resources of medicinal P. notoginseng. © 2024 Society of Chemical Industry.

RNA-seq and Ribosome Profiling Reveal the Translational Landscape of Rice in Response to Rice Stripe Virus Infection

Rice is a crucial staple food for over half the global population, and viral infections pose significant threats to rice yields. This study focuses on the Rice Stripe Virus (RSV), which is known to drastically reduce rice productivity. We employed RNA-seq and ribosome profiling to analyze the transcriptional and translational responses of RSV-infected rice seedlings. Our results reveal that translational reprogramming is a critical aspect of the plant's defense mechanism, operating independently of transcriptional changes. Notably, less than half of the differentially expressed genes showed concordance between transcription and translation. Furthermore, RSV infection led to significant alterations in translational efficiency for numerous genes, suggesting that the virus selectively manipulates translation to enhance its pathogenicity. Our findings underscore the necessity of examining both transcriptional and translational landscapes to fully understand plant responses to viral infections.

The Characteristics and Expression Analysis of the Tomato KWL Gene Family Under Biotic Stress

BACKGROUND

Tomatoes are renowned for their popularity and nutritional value across the globe, yet their production and quality face significant challenges from various biotic stresses in their growing environments. Kiwellin (KWL) has been implicated in plant disease resistance. However, our comprehension of this gene family in plants is still remarkably insufficient.

METHODS

We conducted a comprehensive genomic analysis of the KWL gene family in tomatoes. The tertiary structures of SlKWLs were predicted by AlphaFold2. EMBOSS was used for codon analysis. RNA-seq and RT-qPCR analysis were performed to explore the expression profile of SlKWLs.

RESULTS

Our findings identified 12 distinct SlKWL members distributed across four chromosomes within the tomato genome. By examining their gene structure, conserved motifs, functional domains, and phylogenetic relationships, we elucidated the complex evolutionary relationships and potential functions of these genes. Notably, we identified numerous cis-regulatory elements within the promoter regions of the SlKWL genes which are associated with responses to both abiotic and biotic stresses, as well as hormone signaling pathways. This finding strongly implies that SlKWLs are integral to plant growth and adaptation to diverse stress conditions. Furthermore, RNA-seq and RT-qPCR analysis revealed an upregulation of five SlKWLs expressed subsequent to Phytophthora infestans infection. Particularly, SlKWL2 and SlKWL3 exhibited substantially elevated expression levels, underscoring their active involvement in biotic stress responses.

CONCLUSIONS

Collectively, these findings advance our comprehension of the SlKWL gene family and provide a robust foundation for future investigations into the roles of SlKWL genes in tomato stress responses.

Bibliometric and meta-analysis on the publication status, research trends and impact inducing factors of JA-SA interactions in plants

Interactions between jasmonic acid (JA) and salicylic acid (SA) pathways in plants are important for regulating metabolite production and resistance functions against environmental stresses. These interactions in plants have mostly been reported to be antagonistic, but also to be synergistic under specific external inducing conditions. At present, publications on plant JA-SA interactions lack a bibliometric analysis. External inducing factors that elicit synergism of JA-SA interactions need to be explored. Here, we use bibliometrics to analyze publications on plant JA-SA interactions over the past three decades, and analyze external inducing factors that influence the quality of JA-SA interactions in plants by meta-analysis. More contributions have been made by authors in China, Netherlands, the United States of America, and Germany than elsewhere. Considerable research has been performed on variation in plant defense mediated by two pathways, the transduction mechanisms of JA-SA signaling crosstalk, and plant hormone signaling networks. Meta-analysis showed that the excitation sequence of the two pathways, and the concentrations of pathway excitors are key factors that affect pathways interactions. The JA and SA pathways tend to be reciprocally antagonistic when elicited simultaneously, whereas JA-SA interactions tend to be synergistic when the two pathways are elicited at different times and the pre-treated inducer is at a lower concentration. The SA pathway is more susceptible to being synergized by the JA pathway. Key molecular nodes identified in the JA-SA signaling interaction in model plants, and prospects for future research are discussed.

Biosynthesis of Phenolic Compounds of Medicago truncatula After Inoculation with Selected PGPR Strains

The phenylpropanoid biosynthesis pathway is involved in the response of plants to stress factors, including microorganisms. This paper presents how free-living strains of rhizobacteria Pseudomonas brassicacearum KK5, P. corrugata KK7, Paenibacillus borealis KK4, and the symbiotic strain Sinorhizobium meliloti KK13 affect the expression of genes encoding phenylalanine ammonia-lyase (PAL), the activity of this enzyme, and the production of phenolic compounds in Medicago truncatula. Seedlings were inoculated with rhizobacteria, then at T0, T24, T72, and T168 after inoculation, the leaves and roots were analyzed for gene expression, enzyme activity, and the content of phenolic compounds. All bacteria affected PAL gene expression, in particular, MtPAL2, MtPAL3, and MtPAL4. Pseudomonas strains had the greatest impact on gene expression. The inoculation affected PAL activity causing it to increase or decrease. The most stimulating effect on enzyme activity was observed 168 h after inoculation. A varied effect was also observed in the case of the content of phenolic compounds. The greatest changes were observed 24 h after inoculation, especially with the KK7 strain. The influence of the studied rhizobacteria on the biosynthesis of phenolic compounds at the molecular level (expression of MtPAL genes) and biochemical level (PAL activity and content of phenolic compounds) was confirmed. The MtPAL3 gene underwent the most significant changes after inoculation and can be used as a marker to assess the interaction between M. truncatula and rhizobacteria. The Pseudomonas strains had the greatest influence on the biosynthesis pathway of phenolic compounds.

Antagonistic systemin receptors integrate the activation and attenuation of systemic wound signaling in tomato

Pattern recognition receptor (PRR)-mediated perception of damage-associated molecular patterns (DAMPs) triggers the first line of inducible defenses in both plants and animals. Compared with animals, plants are sessile and regularly encounter physical damage by biotic and abiotic factors. A longstanding problem concerns how plants achieve a balance between wound defense response and normal growth, avoiding overcommitment to catastrophic defense. Here, we report that two antagonistic systemin receptors, SYR1 and SYR2, of the wound peptide hormone systemin in tomato act in a ligand-concentration-dependent manner to regulate immune homeostasis. Whereas SYR1 acts as a high-affinity receptor to initiate systemin signaling, SYR2 functions as a low-affinity receptor to attenuate systemin signaling. The expression of systemin and SYR2, but not SYR1, is upregulated upon SYR1 activation. Our findings provide a mechanistic explanation for how plants appropriately respond to tissue damage based on PRR-mediated perception of DAMP concentrations and have implications for uncoupling defense-growth trade-offs.

Transcript profiling of plastid ferrochelatase two mutants reveals that chloroplast singlet oxygen signals lead to global changes in RNA profiles and are mediated by Plant U-Box 4

Background

In response to environmental stresses, chloroplasts generate reactive oxygen species, including singlet oxygen (1O2), an excited state of oxygen that regulates chloroplast-to-nucleus (retrograde) signaling, chloroplast turnover, and programmed cell death (PCD). Yet, the central signaling mechanisms and downstream responses remain poorly understood. The Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant conditionally accumulates 1O2 and Plant U-Box 4 (PUB4), a cytoplasmic E3 ubiquitin ligase, is involved in propagating 1O2 signals for chloroplast turnover and cellular degradation. Thus, the fc2 and fc2 pub4 mutants are useful genetic tools to elucidate these signaling pathways. Previous studies have focused on the role of 1O2 in promoting cellular degradation in fc2 mutants, but its impact on retrograde signaling from mature chloroplasts (the major site of 1O2 production) is poorly understood.

Results

To gain mechanistic insights into 1O2 signaling pathways, we compared transcriptomes of adult wt, fc2, and fc2 pub4 plants. The accumulation of 1O2 in fc2 plants broadly repressed genes involved in chloroplast function and photosynthesis, while inducing genes and transcription factors involved in abiotic and biotic stress, the biosynthesis of jasmonic acid (JA) and salicylic acid (SA), microautophagy, and senescence. Elevated JA and SA levels were observed in 1O2-stressed fc2 plants. pub4 reversed most of this 1O2-induced gene expression and reduced the JA content in fc2 plants. The pub4 mutation also blocked JA-induced senescence pathways in the dark. However, fc2 pub4 plants maintained constitutively elevated levels of SA even in the absence of bulk 1O2 accumulation.

Conclusions

Together, this work demonstrates that in fc2 plants, 1O2 leads to a robust retrograde signal that may protect cells by downregulating photosynthesis and ROS production while simultaneously mounting a stress response involving SA and JA. The induction of microautophagy and senescence pathways indicate that 1O2-induced cellular degradation is a genetic response to this stress, and the bulk of this transcriptional response is modulated by the PUB4 protein. However, the effect of pub4 on hormone synthesis and signaling is complex and indicates that an intricate interplay of SA and JA are involved in promoting stress responses and programmed cell death during photo-oxidative damage.

Paraburkholderia tropica Primes a Multilayered Transcriptional Defense Response to the Nematode Meloidogyne spp. in Tomato

Meloidogyne causes a devastating disease known as root-knot that affects tomatoes and other cash crops worldwide. Conversely, Paraburkholderia tropica has proven beneficial in mitigating the effects of various pathogens in plants. We aimed to unravel the molecular events that underlie the beneficial effects of the bacterium and the detrimental impacts of the nematode when inoculated separately or together in tomato plants. The transcriptional responses induced by P. tropica (TB group (tomato-bacteria group)), Meloidogyne spp. (TN group (tomato-nematode group)) or by the two agents (TBN group (tomato-bacteria-nematode group)) in tomato were assessed by RNA-seq. We implemented a transcript discovery pipeline which allowed the identification of 2283 putative novel transcripts. Differential expression analysis revealed that upregulated transcripts were much more numerous than downregulated ones. At the gene ontology level, the most activated term was 'hydrolase activity acting on ester bonds' in all groups. In addition, when both microbes were inoculated together, 'hydrolase activity acting on O-glycosyl compounds' was activated. This finding suggests defense responses related to lipid and carbohydrate metabolism, membrane remodeling and signal transduction. Notably, defense genes, transcription factors and protein kinases stood out. Differentially expressed transcripts suggest the activation of a multifaceted plant defense response against the nematode occurred, which was exacerbated by pre-inoculation of P. tropica.

Expression analysis of defense signaling marker genes in Capsicum annuum in response to phytohormones elicitation

BACKGROUND

To tolerate biotic stress, plants employ phytohormones such as jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) to regulate the immune response against different pathogens. Phytohormone-responsive genes, known as "Defense signaling marker genes," are used to evaluate plant disease resistance during pathogen infection. Most information on these marker genes derives from studies on the model plant Arabidopsis thaliana. The present study was aimed analyze the effect of hormonal elicitation at different concentrations at 24 h pos-treatment in the transcript level of 8 traditional genes selected for molecular studies plant-pathogen interactions in Capsicum.

METHODS AND RESULTS

Chemical treatment was achieved by spraying leaves of in vitro seedlings C. annuum L. with 0.1 mM, 1 mM or 2.5 mM ET; 1 mM, 2.5 mM, or 5 mM SA; 2.5 mM BABA; or 0.150 mM MeJA. Twenty-four hours after treatments were applied molecular analyses were carried out using qPCR to investigate the expression. Results revealed that 1 mM of ET or 0.15 mM of MeJA activated the expression CaPR1 (18--11.64-fold change), CaLOX2 (13.80-fold), CaAP2/ERF06 (22- 5.3- fold change), and CaPDF1.2 (2.3-1.5- fold). While, 5 mM of SA present effect of negative regulation on the expression in most of these genes.

CONCLUSIONS

Our results show that the expression profile induced by phytohormones in CaPR1 are particular in C. annuum, because were significantly induced for ET/MeJA, and dow-regulation with SA Contrary to Arabidopsis. Although, on both plants it is observed the cross talk between JA/ET and SA mediated signal pathways for the regulation of this gene.

Integrated Transcriptome and sRNAome Analysis Reveals the Molecular Mechanisms of Piriformospora indica-Mediated Resistance to Fusarium Wilt in Banana

Bananas (Musa spp.) are among the most important fruit and staple food crops globally, holding a significant strategic position in food security in tropical and subtropical regions. However, the industry is grappling with a significant threat from Fusarium wilt, a disease incited by Fusarium oxysporum f. sp. cubense (Foc). In this study, we explored the potential of Piriformospora indica (Pi), a mycorrhizal fungus renowned for bolstering plant resilience and nutrient assimilation, to fortify bananas against this devastating disease. Through a meticulous comparative analysis of mRNA and miRNA expression in control, Foc-inoculated, Pi-colonized, and Pi-colonized followed by Foc-inoculated plants via transcriptome and sRNAome, we uncovered a significant enrichment of differentially expressed genes (DEGs) and DE miRNAs in pathways associated with plant growth and development, glutathione metabolism, and stress response. Our findings suggest that P. indica plays a pivotal role in bolstering banana resistance to Foc. We propose that P. indica modulates the expression of key genes, such as glutathione S-transferase (GST), and transcription factors (TFs), including TCP, through miRNAs, thus augmenting the plant's defensive capabilities. This study offers novel perspectives on harnessing P. indica for the management of banana wilt disease.

Biotic interactions, evolutionary forces and the pan-plant specialized metabolism

Plant specialized metabolism has a complex evolutionary history. Some aspects are conserved across the green lineage, but many metabolites are unique to certain lineages. The network of specialized metabolism continuously diversified, simplified or reshaped during the evolution of streptophytes. Many routes of pan-plant specialized metabolism are involved in plant defence. Biotic interactions are recalled as major drivers of lineage-specific metabolomic diversification. However, the consequences of this diversity of specialized metabolism in the context of plant terrestrialization and land plant diversification into the major lineages of bryophytes, lycophytes, ferns, gymnosperms and angiosperms remain only little explored. Overall, this hampers conclusions on the evolutionary scenarios that shaped specialized metabolism. Recent efforts have brought forth new streptophyte model systems, an increase in genetically accessible species from distinct major plant lineages, and new functional data from a diversity of land plants on specialized metabolic pathways. In this review, we will integrate the recent data on the evolution of the plant immune system with the molecular data of specialized metabolism and its recognition. Based on this we will provide a contextual framework of the pan-plant specialized metabolism, the evolutionary aspects that shape it and the impact on adaptation to the terrestrial environment.This article is part of the theme issue 'The evolution of plant metabolism'.

Arabidopsis GLYI4 Reveals Intriguing Insights into the JA Signaling Pathway and Plant Defense

Plant hormones play a central role in various physiological functions and mediate defense responses against (a)biotic stresses. Jasmonic acid (JA) has emerged as one of the key phytohormones involved in the response to necrotrophic pathogens. Under stressful conditions, plants can also produce small molecules, such as methylglyoxal (MG), a cytotoxic aldehyde. The enzymes glyoxalase I (GLYI) and glyoxalase II primarily detoxify MG. In Arabidopsis thaliana, GLYI4 has been recently characterized as having a crucial role in MG detoxification and emerging involvement in the JA pathway. Here, we investigated the impact of a GLYI4 loss-of-function on the Arabidopsis JA pathway and how MG affects it. The results showed that the glyI4 mutant plant had stunted growth, a smaller rosette diameter, reduced leaf size, and an altered pigment concentration. A gene expression analysis of the JA marker genes showed significant changes in the JA biosynthetic and signaling pathway genes in the glyI4 mutant. Disease resistance bioassays against the necrotroph Botrytis cinerea revealed altered patterns in the glyI4 mutant, likely due to increased oxidative stress. The MG effect has a further negative impact on plant performance. Collectively, these results contribute to clarifying the intricate interconnections between the GLYI4, MG, and JA pathways, opening up new avenues for further explorations of the intricate molecular mechanisms controlling plant stress responses.

Viral proteins resolve the virus-vector conundrum during hemipteran-mediated transmission by subverting salicylic acid signaling pathway

Hemipteran insects transmit viruses when infesting plants, during which vectors activate salicylic acid (SA)-regulated antiviral defenses. How vector-borne plant viruses circumvent these antiviral defenses is largely unexplored. During co-infections of begomoviruses and betasatellites in plants, betasatellite-encoded βC1 proteins interfere with SA signaling and reduce the activation of antiviral resistance. βC1 inhibits SA-induced degradation of NbNPR3 (Nicotiana benthamiana nonexpressor of pathogenesis-related genes 3), a negative regulator of SA signaling. βC1 does not bind directly to NbNPR3, but regulates NbNPR3 degradation via heat shock protein 90s (NbHSP90s). NbHSP90s bind to both NbNPR3 and βC1 and suppress SA signaling. This viral success strategy appears to be conserved as it is also documented for viral proteins encoded by two aphid-borne viruses. Our findings reveal an exquisite mechanism that facilitates the persistence of vector-borne plant viruses and provide important insights into the intricacies of the virus life cycle.

Fermentation broth of a novel endophytic fungus enhanced maize salt tolerance by regulating sugar metabolism and phytohormone biosynthesis or signaling

Soil salinization is a major environmental factor that severely affects global agriculture. Root endophytes can enter root cells, and offer various ecological benefits, such as promoting plant growth, improving soil conditions, and enhancing plant resistance. Su100 is a novel strain of endophytic fungus that was characterized from blueberry roots. In this study, we focused on evaluating the effects of Su100 secretion on maize growth. The results demonstrated that maize treated with Su100 fermentation broth (SFB) exhibited significantly stronger salt tolerance than the control. It is worth mentioning that the treated root system not only had an advantage in terms of biomass but also a change in root structure with a significant increase in lateral roots (LRs) compared to the control. Transcriptome analysis combined with hormone content measurements indicated that SFB upregulated the auxin signaling pathway, and also caused alterations in brassinosteroids (BR) and jasmonic acid (JA) biosynthesis and signaling pathways. Transcriptome analyses also indicated that SFB caused significant changes in the sugar metabolism of maize roots. The major changes included: enhancing the conversion and utilization of sucrose in roots; increasing carbon flow to uridine diphosphate glucose (UDPG), which acted as a precursor for producing more cell wall polysaccharides, mainly pectin and lignin; accelerating the tricarboxylic acid cycle, which were further supported by sugar content determinations. Taken together, our results indicated that the enhanced salt tolerance of maize treated with SFB was due to the modulation of sugar metabolism and phytohormone biosynthesis or signaling pathways. This study provided new insights into the mechanisms of action of endophytic fungi and highlighted the potential application of fungal preparations in agriculture.

The Spotted Lanternfly Contains High Concentrations of Plant Hormones in its Salivary Glands: Implications in Host Plant Interactions

The spotted lanternfly (SLF), Lycorma delicatula is an invasive species in the United States that has emerged as a significant pest in vineyards. This polyphagous insect causes significant damage to grapevines and tree of heaven (TOH). SLF feeds voraciously on plant tissues using its piercing and sucking mouthparts through which it injects saliva and uptakes plant sap. Despite its impact, research on fundamental mechanisms mediating SLF interactions with their predominant hosts is limited. This study documents the morphology of salivary glands and quantifies plant hormones in salivary glands of SLF adults fed on grapevines and TOH using Liquid Chromatography-Mass Spectrometry (LC/MS). SLF adults have one pair of large salivary glands, ranging from 10 to 15 mm in length that extend from the insect's head to the last sections of the abdomen. The salivary glands of SLF contain salicylic acid (89 ng/g), abscisic acid (6.5 ng/g), 12-oxo-phytodienoic acid (5.7 ng/g), indole-3-acetic acid (2 ng/g), jasmonic acid (0.6 ng/g), jasmonic acid isoleucine (0.037 ng/g), and the cytokinin ribosides trans-zeatin (0.6 ng/g) and cis-zeatin (0.1 ng/g). While the concentrations of these hormones were similar in insects fed on grapevines and TOH, abscisic acid was more abundant in insects fed on grapevines, and jasmonic acid isoleucine was only detected in insects fed on grape. These results are discussed in the context of the possible implications that these hormones may have on the regulation of plant defenses. This study contributes to our understanding of the composition of SLF saliva and its potential role in plant immunity.

Comparative transcriptome analysis highlights resistance regulatory networks of maize in response to Exserohilum turcicum infection at the early stage

Northern corn leaf blight, caused by Exserohilum turcicum (E. turcicum), is one of the most destructive diseases in maize, leading to serious yield losses. However, the underlying molecular mechanisms of E. turcicum infection response in maize remain unclear. In this study, we performed comparative transcriptome analysis in resistant maize inbred line J9D207 (R) and susceptible maize inbred line PH4CV (S) after infecting with E. turcicum at 0 h, 24 h and 72 h, respectively. Compared with 0 h, 9656 (24 h) and 8748 (72 h) differentially expressed genes (DEGs) were identified in J9D207, and 7915 (24 h) and 7865 (72 h) DEGs were identified in PH4CV. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that alpha-linolenic acid metabolism, benzoxazinoid biosynthesis, flavonoid biosynthesis and phenylpropanoid biosynthesis might be involved in maize defense reactions. Some DEGs coded for transcription factors, such as MYB-related, ERF, NAC, bZIP, bHLH and WRKY families, which indicated that they may participate in resistance against E. turcicum. In addition, DEGs involved in SA, JA, ABA and ET signaling pathways were revealed. Moreover, 75 SOD activity-related genes and 421 POD activity-related genes were identified through weighted gene co-expression network analysis (WGCNA), respectively. These results provide a novel insight into the resistance mechanism of maize in response to E. turcicum inoculation.

Microbe-Friendly Plants Enable Beneficial Interactions with Soil Rhizosphere Bacteria by Lowering Their Defense Responses

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant-microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into "microbe-friendly" cultivars (with little or no defense responses against beneficial microbes) and "microbe-hostile" cultivars (with strong defense responses). These results validate the notion that "microbe-friendly" (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields.

Citrus Fruits Produce Direct Defense Responses against Oviposition by Bactrocera minax (Diptera: Tephritidae)

Plants perceive and orchestrate defense responses when herbivorous insects are ovipositing. Fruits, as a crucial reproductive organ in plants, have rarely been researched on the responses to insect eggs. Here, we found that oviposition by the specialist insect Bactrocera minax in navel oranges activated the lignin synthesis pathway and cell division, causing mechanical pressure that crushed the eggs. Transcriptome and metabolome analyses revealed an enrichment of oviposition-induced genes and metabolites within the lignin synthesis pathway, which was confirmed by histochemical staining. Furthermore, hydrogen peroxide (H2O2) accumulation was observed at the oviposition sites. Plant defense-related hormones jasmonic acid (JA) and salicylic acid (SA) exhibited rapid induction after oviposition, while indole-3-acetic acid (IAA) activation occurred in the later stages of oviposition. Additionally, secondary metabolites induced by prior egg deposition were found to influence larval performance. Our studies provide molecular evidence that host fruits have evolved defense mechanisms against insect eggs and pave the way for future development of insect-resistant citrus varieties.