Dynamics of 'Candidatus Liberibacter asiaticus' Growth, Concentrations of Reactive Oxygen Species, and Ion Leakage in Huanglongbing-Positive Sweet Orange.

Citrus Huanglongbing (HLB) caused by 'Candidatus Liberibacter asiaticus' (CLas) is the most devastating citrus disease worldwide. CLas induces systemic and chronic reactive oxygen species (ROS) production, which has been suggested to be a primary cause of cell death in phloem tissues and subsequent HLB symptoms. Mitigating oxidative stress caused by CLas using horticultural approaches has been suggested as a useful strategy to reduce HLB damages. To provide information regarding the application timing to mitigate ROS, we investigated monthly dynamics of CLas concentration, CLas-triggered ROS, and phloem cell death in the bark tissues of asymptomatic and symptomatic branches of HLB-positive Hamlin and Valencia sweet orange trees in the field. Healthy branches in the screenhouse were used as controls. CLas concentration exhibited significant variations over the course of the year, with two distinct peaks observed in Florida citrus groves-late spring/early summer and late fall. Within both Hamlin and Valencia asymptomatic tissues, CLas concentration demonstrated a negative correlation with the deviation between the monthly average mean temperature and the optimal temperature for CLas colonization in plants (25.7°C). However, such a correlation was not evident in symptomatic tissues of Hamlin or Valencia sweet oranges. ROS levels were consistently higher in symptomatic or asymptomatic branches than in healthy branches in most months. ROS concentrations were higher in symptomatic branches than in asymptomatic branches in most months. CLas triggered significant increases in ion leakage in most months for asymptomatic and symptomatic branches compared with healthy controls. In asymptomatic branches of Hamlin, a positive correlation was observed between CLas concentration and ROS concentrations, CLas concentration and ion leakage levels, as well as ROS and ion leakage. Intriguingly, such a relationship was not observed in Valencia asymptomatic branches or in the symptomatic branches of Hamlin and Valencia. This study sheds light on the pathogenicity of CLas by providing useful information on the temporal dynamics of ROS production, phloem cell death, and CLas growth, as well as provides useful information in determining the timing for application of antioxidants and antimicrobial agents to control HLB.

Toxic effects of triclosan on hepatic and intestinal lipid accumulation in zebrafish via regulation of m6A-RNA methylation.

Triclosan (TCS), recognized as an endocrine disruptor, has raised significant concerns due to its widespread use and potential health risks. To explore the impact of TCS on lipid metabolism, both larval and adult zebrafish were subjected to acute and chronic exposure to TCS. Through analyzes of biochemical and physiological markers, as well as Oil Red O (ORO) and hematoxylin and eosin (H&E) staining, our investigation revealed that TCS exposure induced hepatic and intestinal lipid accumulation in larval and adult zebrafish, leading to structural damage and inflammatory responses in these tissues. The strong affinity of TCS with PPARγ and subsequent pathway activation indicate that PPARγ pathway plays a crucial role in TCS-induced lipid buildup. Furthermore, we observed a decrease in m6A-RNA methylation levels in the TCS-treated group, which attributed to the increased activity of the demethylase FTO and concurrent suppression of the methyltransferase METTL3 gene expression by TCS. The alteration in methylation dynamics is identified as a potential underlying mechanism behind TCS-induced lipid accumulation. To address this concern, we explored the impact of folic acid-a methyl donor for m6A-RNA methylation-on lipid accumulation in zebrafish. Remarkably, folic acid administration partially alleviated lipid accumulation by restoring m6A-RNA methylation. This restoration, in turn, contributed to a reduction in inflammatory damage observed in both the liver and intestines. Additionally, folic acid partially mitigates the up-regulation of PPARγ and related genes induced by TCS. These findings carry substantial implications for understanding the adverse effects of environmental pollutants such as TCS. They also emphasize the promising potential of folic acid as a therapeutic intervention to alleviate disturbances in lipid metabolism induced by environmental pollutants.

Neurotoxic effects of 2-ethylhexyl diphenyl phosphate exposure on zebrafish larvae: Insight into inflammation-driven changes in early motor behavior.

The extensive utilization and potential adverse impacts of the replacement flame-retardant 2-Ethylhexyl Diphenyl Phosphate (EHDPP) have raised concerns. Currently, there is limited knowledge regarding the developmental, neurological, and immunotoxic consequences of EHDPP exposure, as well as its potential behavioral outcomes. In this study, we undertook a comprehensive examination and characterization of the toxic effects over the EHDPP concentration range of 14-1400 nM. Our findings unveiled that EHDPP, even at an environmentally relevant concentration of 14 nM, exhibited excitatory neurotoxicity, eliciting a 13.5 % increase in the swimming speed of zebrafish larvae. This effect might be attributed to the potential influence of EHDPP on the release of neurotransmitters like serotonin and dopamine, which, in turn, mediated anxiety-like behavior in the zebrafish larvae. Conversely, sublethal dose EHDPP (1400 nM) exposure significantly suppressed the swimming vigor of zebrafish larvae, accompanied by morphological changes, abnormal behaviors, and alterations in intracerebral molecules. Transcriptomics revealed the underlying mechanism. The utilization of pathway inhibitors reshaped the inflammatory homeostasis and alleviated the toxicity induced by EHDPP exposure, anchoring the pivotal role played by the TLR4/NF-κB signaling pathway in EHDPP-induced adverse changes in zebrafish behavior and neurophysiology. This study observed the detrimental effects of EHDPP on fish sustainability at environmentally relevant concentrations, highlighting the practical significance for EHDPP risk management. Elucidating the toxic mechanisms of EHDPP will contribute to a deeper comprehension of how environmental pollutants can intricately influence human health.

Deciphering the molecular mediators of triclosan-induced lipid accumulation: Intervention via short-chain fatty acids and miR-101a.

As a potential environmental obesogen, triclosan (TCS) carries inherent risks of inducing obesity and metabolic disorders. However, the underlying molecular mechanisms behind the lipid metabolism disorder induced by TCS have remained elusive. Through a fusion of transcriptomics and microRNA target prediction, we hypothesize that miR-101a as a responsive miRNA to TCS exposure in zebrafish, playing a central role in disturbing lipid homeostasis. As an evidence, TCS exposure triggers a reduction in miR-10a expression that accompanied by elevation of genes linked to regulation of lipid homeostasis. Through precision-controlled interventions involving miRNA expression modulation, we discovered that inhibition of miR-101a enhanced expression of its target genes implicated in lipid homeostasis, subsequently triggering excessive fat accumulation. Meanwhile, the overexpression of miR-101a acts as a protective mechanism, counteracting the lipid metabolism disorder induced by TCS in the larvae. Notably, the combination of short-chain fatty acids (SCFAs) emerged as a potential remedy to alleviate TCS-induced lipid accumulation partially by counteracting the decline in miR-101a expression induced by TCS. These revelations provide insight into a prospective molecular framework underlying TCS-triggered lipid metabolism disorders, thereby paving the way for pre-emptive strategies in combating the ramifications of TCS pollution.

Phylogenomic analysis of 343 Xanthomonas citri pv. citri strains unravels introduction history and dispersal paths.

Xanthomonas citri pv. citri (Xcc) causes the devastating citrus canker disease. Xcc is known to have been introduced into Florida, USA in at least three different events in 1915, 1986 and 1995 with the first two claimed to be eradicated. It was questioned whether the Xcc introduction in 1986 has been successfully eradicated. Furthermore, it is unknown how Xcc has spread throughout the citrus groves in Florida. In this study, we investigated the population structure of Xcc to address these questions. We sequenced the whole genome of 343 Xcc strains collected from Florida groves between 1997 and 2016. Our analysis revealed two distinct clusters of Xcc. Our data strongly indicate that the claimed eradication of the 1986 Xcc introduction was not successful and Xcc strains from 1986 introduction were present in samples from at least 8 counties collected after 1994. Importantly, our data revealed that the Cluster 2 strains, which are present in all 20 citrus-producing counties sampled in Florida, originated from the Xcc introduction event in the Miami area in 1995. Our data suggest that Polk County is the epicenter of the dispersal of Cluster 2 Xcc strains, which is consistent with the fact that three major hurricanes passed through Polk County in 2004. As copper-based products have been extensively used to control citrus canker, we also investigated whether Xcc strains have developed resistance to copper. Notably, none of the 343 strains contained known copper resistance genes. Twenty randomly selected Xcc strains displayed sensitivity to copper. Overall, this study provides valuable insights into the introduction, eradication, spread, and copper resistance of Xcc in Florida.

Endometrial cancer (EC) derived G3BP1 overexpression and mutant promote EC tumorigenesis and metastasis via SPOP/ERα axis.

BACKGROUND: Ras-GTPase-activating protein binding protein 1 (G3BP1) is an oncogenic factor, which highly expressed in a variety of cancers. In recent years, G3BP1 has been reported to promote the development of prostate cancer by inhibiting the degradation of AR through inhibiting SPOP. However, whether G3BP1 contributes in a similar manner to the abnormal accumulation of ERα, which is also an important target for hormone therapy, remains unknown. This article addresses this issue and explores potential mechanisms. METHODS: Bioinformatics tools were used for G3BP1 expression analysis, survival analysis, and clinical association analysis. Immunohistochemical staining was used to examine the correlation between G3BP1 and ERα in EC patients. In addition, western blot and co-immunoprecipitation were used to detect the half-life of G3BP1 and mutant, and the effect of G3BP1 and mutant on the ubiquitination and degradation of ERα mediated by SPOP. Then, the oncogenic functions of G3BP1 dependent on the SPOP/ERα axis were determined by CCK8 cell proliferation assay, colony formation assay and cell migration assay. Finally, we established the EC cells treated or untreated with fulvestrant, exploring the possibility of fulvestrant combined with the reduction of G3BP1 to improve the efficacy of fulvestrant. RESULTS: G3BP1 is abnormally high expressed and characterized by high-frequency mutation in EC. In addition, there is a positive correlation between G3BP1 protein and ERα protein. Mechanistically, both G3BP1 and mutant, the latter is displaying the longer half-life, competitively bind SPOP with ERα, thereby inhibiting SPOP-mediated ubiquitination and degradation of ERα. Functionally, G3BP1 and mutant promote the proliferation and migration of EC cells by regulating the G3BP1/SPOP/ERα axis. However, fulvestrant can reverse the cancer-promoting effects of G3BP1 and mutant. CONCLUSIONS: G3BP1 and its mutant positively regulate ERα signaling pathway by inhibiting SPOP-mediated ubiquitination and degradation of ERα, indicating the promising effect of fulvestrant on the suppression the occurrence and development of EC with high expressed G3BP1 and G3BP1 mutants. Video Abstract.

Metabolic reprogramming and epigenetic modifications in cancer: from the impacts and mechanisms to the treatment potential.

Metabolic reprogramming and epigenetic modifications are hallmarks of cancer cells. In cancer cells, metabolic pathway activity varies during tumorigenesis and cancer progression, indicating regulated metabolic plasticity. Metabolic changes are often closely related to epigenetic changes, such as alterations in the expression or activity of epigenetically modified enzymes, which may exert a direct or an indirect influence on cellular metabolism. Therefore, exploring the mechanisms underlying epigenetic modifications regulating the reprogramming of tumor cell metabolism is important for further understanding tumor pathogenesis. Here, we mainly focus on the latest studies on epigenetic modifications related to cancer cell metabolism regulations, including changes in glucose, lipid and amino acid metabolism in the cancer context, and then emphasize the mechanisms related to tumor cell epigenetic modifications. Specifically, we discuss the role played by DNA methylation, chromatin remodeling, noncoding RNAs and histone lactylation in tumor growth and progression. Finally, we summarize the prospects of potential cancer therapeutic strategies based on metabolic reprogramming and epigenetic changes in tumor cells.

Faraday cage-type ECL biosensor for the detection of circulating tumor cell MCF-7.

Herein, a Faraday cage-type electrochemiluminescence biosensor was designed for the detection of human breast cancer cell MCF-7. Two kinds of nanomaterials, Fe3O4-APTs and GO@PTCA-APTs, were synthesized as capture unit and signal unit, respectively. In presence of the target MCF-7, the Faraday cage-type electrochemiluminescence biosensor was constructed by forming a complex "capture unit-MCF-7-signal unit". In this case, lots of electrochemiluminescence signal probes were assembled and could participate in the electrode reaction, achieving a significant increase in sensitivity. In addition, the double aptamer recognition strategy was adopted to improve the capture, enrichment efficiency and detection reliability. Under optimal experimental conditions, the limit of detection was 3 cells/mL. And, the sensor could afford the detection of actual human blood samples, which is the first report on the detection of intact circulating tumor cells by the Faraday cage-type electrochemiluminescence biosensor.

FBXO7, a tumor suppressor in endometrial carcinoma, suppresses INF2-associated mitochondrial division.

Endometrial carcinoma (ECa) is the most common malignant gynecological cancer, with an increased incidence and fatality rate worldwide, while the pathogenesis is still largely unknown. In this study, we confirmed that FBXO7, a gene coding FBXO7 E3 ubiquitin ligase, is significantly downregulated and mutated (5.87%; 31/528) in ECa specimens, and the abnormal low expression and mutations of FBXO7 are associated with the occurrence of ECa. We also identify the excessive expression of INF2 protein, a key factor that triggers mitochondrial division by recruiting the DRP1 protein, and the elevated INF2 protein is significantly negatively correlated with the low FBXO7 protein in ECa specimens. Mechanistically, FBXO7 restrains ECa through inhibiting INF2-associated mitochondrial division via FBXO7-mediated ubiquitination and degradation of INF2. Moreover, we found that ECa-associated FBXO7 mutants are defective in the ubiquitination and degradation of INF2, promoting ECa cells proliferation, migration and apoptosis inhibition via inducing mitochondrial hyper-division. In addition, we found that it could reverse FBXO7 deletion or ECa-associated FBXO7 mutants-induced proliferation, migration, apoptosis inhibition and mitochondrial hyper-division of ECa cells by INF2 or DNM1L knockdown, or DRP1 inhibitor Mdivi-1. In summary, our study shows that FBXO7 acts as a novel tumor suppressor in ECa by inhibiting INF2-DRP1 axis-associated mitochondrial division through the ubiquitination and degradation of INF2 while the effect is destroyed by ECa-associated FBXO7 and INF2 mutants, highlights the key role of FBXO7-INF2-DRP1 axis in ECa tumorigenesis and provides a new viewpoint to treat ECa patients with FBXO7 deletion or mutations by targeting INF2-DRP1 axis-associated mitochondrial division.

LPLUNC1 reduces glycolysis in nasopharyngeal carcinoma cells through the PHB1-p53/c-Myc axis.

Cancer cells prefer glycolysis to support their proliferation. Our previous studies have shown that the long palate, lung, and nasal epithelial cell clone 1 (LPLUNC1) can upregulate prohibitin 1 (PHB1) expression to inhibit the proliferation of nasopharyngeal carcinoma (NPC) cells. Given that PHB1 is an important regulator of cell energy metabolism, we explored whether and how LPLUNC1 regulated glucose glycolysis in NPC cells. LPLUNC1 or PHB1 overexpression decreased glycolysis and increased oxidative phosphorylation (OXPHOS)-related protein expression in NPC cells, promoting phosphorylated PHB1 nuclear translocation through 14-3-3σ. LPLUNC1 overexpression also increased p53 but decreased c-Myc expression in NPC cells, which were crucial for the decrease in glycolysis and increase in OXPHOS-related protein expression induced by LPLUNC1 overexpression. Finally, we found that treatment with all-trans retinoic acid (ATRA) reduced the viability and clonogenicity of NPC cells, decreased glycolysis, and increased OXPHOS-related protein expression by enhancing LPLUNC1 expression in NPC cells. Therefore, the LPLUNC1-PHB1-p53/c-Myc axis decreased glycolysis in NPC cells, and ATRA upregulated LPLUNC1 expression, ATRA maybe a promising drug for the treatment of NPC.

The characteristics of FBXO7 and its role in human diseases.

E3 ligases are involved in various cellular biological processes, and their loss of function or improper targeting can induce multiple types of human diseases. F-box protein 7(FBXO7) is a unit in the SKP1-Cullin1-F-box (SCF) SCFFBXO7 E3 ligase composite, playing the role of recognizing some substrates. Additionally, FBXO7 is involved in the regulation of the proteasome complex, mitophagy, the cell cycle, cell proliferation, and germ cell differentiation. Although many articles have reviewed the pathogenesis of FBXO7, which is associated with Parkinson disease-15 (PARKIN15), a summary of the role of FBXO7 as an E3 ligase and its SCF-independent function is incomplete, as well as an overview of FBXO7 in cancer. Therefore, we summarized FBXO7-related substrates and the roles of FBXO7 in human cancers. In addition, based on previous studies, we supplemented the newly discovered FBXO7 mutations in PARKIN15 patients and some potential pathogenic mechanisms that may lead to PARKIN15. A profound exploration of the general pathophysiological mechanisms of this protein could provide potential evidence for the targeted treatment of PARKIN15 and malignant tumors.

Microscopic and Transcriptomic Analyses of Early Events Triggered by 'Candidatus Liberibacter asiaticus' in Young Flushes of Huanglongbing-Positive Citrus Trees.

'Candidatus Liberibacter asiaticus' (CLas) is associated with the devastating citrus disease Huanglongbing (HLB). Young flushes are the center of the HLB pathosystem due to their roles in the psyllid life cycle and in the acquisition and transmission of CLas. However, the early events of CLas infection and how CLas modulates young flush physiology remain poorly understood. Here, transmission electron microscopy analysis showed that the mean diameter of the sieve pores decreased in young leaves of HLB-positive trees after CLas infection, consistent with CLas-triggered callose deposition. RNA-seq-based global expression analysis of young leaves of HLB-positive sweet orange with (CLas-Pos) and without (CLas-Neg) detectable CLas demonstrated a significant impact on gene expression in young leaves, including on the expression of genes involved in host immunity, stress response, and plant hormone biosynthesis and signaling. CLas-Pos and CLas-Neg expression data displayed distinct patterns. The number of upregulated genes was higher than that of the downregulated genes in CLas-Pos for plant-pathogen interactions, glutathione metabolism, peroxisome, and calcium signaling, which are commonly associated with pathogen infections, compared with the healthy control. On the contrary, the number of upregulated genes was lower than that of the downregulated genes in CLas-Neg for genes involved in plant-pathogen interactions and peroxisome biogenesis/metabolism. Additionally, a time-course quantitative reverse transcription-PCR-based expression analysis visualized the induced expression of companion cell-specific genes, phloem protein 2 genes, and sucrose transport genes in young flushes triggered by CLas. This study advances our understanding of early events during CLas infection of citrus young flushes.

Construction of a cuproptosis-related lncRNA signature for predicting prognosis and immune landscape in osteosarcoma patients.

BACKGROUND: Long noncoding RNAs (lncRNAs) influence the onset of osteosarcoma. Cuproptosis is a novel cell death mechanism. We attempted to identify a cuproptosis-related lncRNA signature to predict the prognosis and immune landscape in osteosarcoma patients. METHODS: Transcriptional and clinical data of 85 osteosarcoma patients were derived from the TARGET database and randomly categorized into the training and validation cohorts. We implemented the univariate and multivariate Cox regression, along with LASSO regression analyses for developing a cuproptosis-related lncRNA risk model. Kaplan-Meier curves, C-index, ROC curves, univariate and multivariate Cox regression, and nomogram were used to assess the capacity of this risk model to predict the osteosarcoma prognosis. Gene ontology, KEGG, and Gene Set Enrichment (GSEA) analyses were conducted for determining the potential functional differences existing between the high-risk and low-risk patients. We further conducted the ESTIMATE, single-smaple GSEA, and CIBERSORT analyses for identifying the different immune microenvironments and immune cells infiltrating both the risk groups. RESULTS: We screened out four cuproptosis-related lncRNAs (AL033384.2, AL031775.1, AC110995.1, and LINC00565) to construct the risk model in the training cohort. This risk model displayed a good performance to predict the overall survival of osteosarcoma patients, which was confirmed by using the validation and the entire cohort. Further analyses showed that the low-risk patients have more immune activation and immune cells infiltrating as well as a good response to immunotherapy. CONCLUSIONS: We developed a novel cuproptosis-related lncRNA signature with high reliability and accuracy for predicting outcome and immunotherapy response in osteosarcoma patients, which provides new insights into the personalized treatment of osteosarcoma.

The roles of KLHL family members in human cancers.

The Kelch-like (KLHL) family members consist of three domains: bric-a-brac, tramtrack, broad complex/poxvirus and zinc finger domain, BACK domain and Kelch domain, which combine and interact with Cullin3 to form an E3 ubiquitin ligase. Research has indicated that KLHL family members ubiquitinate target substrates to regulate physiological and pathological processes, including tumorigenesis and progression. KLHL19, a member of the KLHL family, is associated with tumorigenesis and drug resistance. However, the regulation and cross talks of other KLHL family members, which also play roles in cancer, are still unclear. Our review mainly explores studies concerning the roles of other KLHL family members in tumor-related regulation to provide novel insights into KLHL family members.

The function of prohibitins in mitochondria and the clinical potentials.

Prohibitins (PHBs) are a class of highly evolutionarily conserved proteins that widely distribute in prokaryotes and eukaryotes. PHBs function in cell growth and proliferation or differentiation, regulating metabolism and signaling pathways. PHBs have different subcellular localization in eukaryotes, but they are mainly located in mitochondria. In the mitochondria, PHBs stabilize the structure of the mitochondrial membrane and regulate mitochondrial autophagy, mitochondrial dynamics, mitochondrial biogenesis and quality control, and mitochondrial unfolded protein response. PHBs has shown to be associated with many diseases, such as mitochondria diseases, cancers, infectious diseases, and so on. Some molecule targets of PHBs can interfere with the occurrence and development of diseases. Therefore, this review clarifies the functions of PHBs in mitochondria, and provides a summary of the potential values in clinics.

Functional roles of E3 ubiquitin ligases in prostate cancer.

Prostate cancer (PCa) is a malignant epithelial tumor of the prostate gland with a high male cancer incidence. Numerous studies indicate that abnormal function of ubiquitin-proteasome system (UPS) is associated with the progression and metastasis of PCa. E3 ubiquitin ligases, key components of UPS, determine the specificity of substrates, and substantial advances of E3 ubiquitin ligases have been reached recently. Herein, we introduce the structures and functions of E3 ubiquitin ligases and summarize the mechanisms of E3 ubiquitin ligases-related PCa signaling pathways. In addition, some progresses in the development of inhibitors targeting E3 ubiquitin ligases are also included.

The roles of G3BP1 in human diseases (review).

Ras-GTPase-activating protein binding protein 1 (G3BP1) is a multifunctional binding protein involved in a variety of biological functions, including cell proliferation, metastasis, apoptosis, differentiation and RNA metabolism. It has been revealed that G3BP1, as an antiviral factor, can interact with viral proteins and regulate the assembly of stress granules (SGs), which can inhibit viral replication. Furthermore, several viruses have the ability to hijack G3BP1 as a cofactor, recruiting translation initiation factors to promote viral proliferation. However, many functions of G3BP1 are associated with other diseases. In various cancers, G3BP1 is a cancer-promoting factor, which can promote the proliferation, invasion and metastasis of cancer cells. Moreover, compared with normal tissues, G3BP1 expression is higher in tumor tissues, indicating that it can be used as an indicator for cancer diagnosis. In this review, the structure of G3BP1 and the regulation of G3BP1 in multiple dimensions are described. In addition, the effects and potential mechanisms of G3BP1 on various carcinomas, viral infections, nervous system diseases and cardiovascular diseases are elucidated, which may provide a direction for clinical applications of G3BP1 in the future.

Whole-exome sequencing identified a novel pathogenic mutation of the CYP4F22 gene in a Chinese patient with autosomal recessive congenital ichthyosis and in vitro study of the mutant CYP4F22 protein.

Autosomal recessive congenital ichthyosis (ARCI) is a heterogeneous group of rare cornification disorders. Of the 14 genes already known to cause ARCI, CYP4F22 is a relatively new genetic etiology, the mutation spectrum of which has yet to be profiled. Using whole-exome sequencing in family trios, we identified the compound heterozygous mutations, c.844C>T (p.R282W) and c.1189C>T (p.R397C), of the CYP4F22 gene (NM_173483.4) in a Chinese neonatal boy with a congenital ichthyosis phenotype. In combination with multiple in silico analyses and the following in vitro functional studies, we provided evidence to classify these two variations as pathogenic mutations and demonstrated that both variants significantly reduced the CYP4F22 protein amount. Interestingly, the reduction of both mutant CYP4F22 protein could be recovered by trichostatin A (TSA) treatment, suggesting some deacetylation factors involved in regulating the mutant CYP4F22 protein and implying TSA might be a potential candidate compound for congenital ichthyosis caused by CYP4F22 variations.

Citrus Huanglongbing is a pathogen-triggered immune disease that can be mitigated with antioxidants and gibberellin.

Huanglongbing (HLB) is a devastating disease of citrus, caused by the phloem-colonizing bacterium Candidatus Liberibacter asiaticus (CLas). Here, we present evidence that HLB is an immune-mediated disease. We show that CLas infection of Citrus sinensis stimulates systemic and chronic immune responses in phloem tissue, including callose deposition, production of reactive oxygen species (ROS) such as H2O2, and induction of immunity-related genes. The infection also upregulates genes encoding ROS-producing NADPH oxidases, and downregulates antioxidant enzyme genes, supporting that CLas causes oxidative stress. CLas-triggered ROS production localizes in phloem-enriched bark tissue and is followed by systemic cell death of companion and sieve element cells. Inhibition of ROS levels in CLas-positive stems by NADPH oxidase inhibitor diphenyleneiodonium (DPI) indicates that NADPH oxidases contribute to CLas-triggered ROS production. To investigate potential treatments, we show that addition of the growth hormone gibberellin (known to have immunoregulatory activities) upregulates genes encoding H2O2-scavenging enzymes and downregulates NADPH oxidases. Furthermore, foliar spray of HLB-affected citrus with gibberellin or antioxidants (uric acid, rutin) reduces H2O2 concentrations and cell death in phloem tissues and reduces HLB symptoms. Thus, our results indicate that HLB is an immune-mediated disease that can be mitigated with antioxidants and gibberellin.