Abscisic Acid Promotes Jasmonic Acid Accumulation and Plays a Key Role in Citrus Canker Development

Qin, Long; Xie, Yingxin; He, Yongrui; Li, Qiang; Zou, Xin; Chen, Shanchun

doi:10.3389/fpls.2019.01634

Cited by 35 publications

(20 citation statements)

References 62 publications

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“…To evaluate canker resistance in the CsWRKY22 transgenic plants, leaves of transgenic and WT plants were inoculated with an Xcc suspension by the infiltration method 23 . Ten days after inoculation (dai), CsWRKY22 -overexpressing plants showed much more serious symptoms than WT plants, whereas the opposite trend was observed in RNAi plants (Fig.…”

Section: Resultsmentioning

confidence: 99%

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Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

Qin

Long

et al. 2021

Hortic Res

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Pathological hypertrophy (cell enlargement) plays an important role in the development of citrus canker, but its regulators are largely unknown. Although WRKY22 is known to be involved in pathogen-triggered immunity and positively regulates resistance to bacterial pathogens in Arabidopsis, rice and pepper, the CRISPR/Cas9-mediated partial knockout of CsWRKY22 improves resistance to Xanthomonas citri subsp. citri (Xcc) in Wanjincheng orange (Citrus sinensis Osbeck). Here, we demonstrate that CsWRKY22 is a nucleus-localized transcriptional activator. CsWRKY22-overexpressing plants exhibited dwarf phenotypes that had wrinkled and thickened leaves and were more sensitive to Xcc, whereas CsWRKY22-silenced plants showed no visible phenotype changes and were more resistant to Xcc. Microscopic observations revealed that the overexpression of CsWRKY22 increased cell size in the spongy mesophyll. Transcriptome analysis showed that cell growth-related pathways, such as the auxin and brassinosteroid hormonal signaling and cell wall organization and biogenesis pathways, were significantly upregulated upon CsWRKY22 overexpression. Interestingly, CsWRKY22 activated the expression of CsLOB1, which is a key gene regulating susceptibility to citrus canker. We further confirmed that CsWRKY22 bound directly to the W-boxes just upstream of the transcription start site of CsLOB1 in vivo and in vitro. We conclude that CsWRKY22 enhances susceptibility to citrus canker by promoting host hypertrophy and CsLOB1 expression. Thus, our study provides new insights into the mechanism regulating pathological hypertrophy and the function of WRKY22 in citrus.

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Section: Resultsmentioning

confidence: 99%

“…Healthy 6-month-old leaves from transgenic and WT plants were used to perform in vitro inoculation with our previously described methods 23 . The pathogen Xcc was isolated from naturally infected leaves of sweet orange in an orchard in Yunnan Province, China 11 .…”

Section: Methodsmentioning

confidence: 99%

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

Qin

Long

et al. 2021

Hortic Res

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“…JA regulates plant development in many aspects, including inhibition of seed germination, promoting lateral root formation and inducing root regeneration (Huang et al ., 2017). Interestingly, our group previously showed that ABA cooperated with JA and SA signaling to affect Xcc‐induced pustule formation and the susceptibility to citrus canker in sweet orange (Long et al ., 2019). Together, these data above strongly indicate that CsLOB1 regulates cell division and growth via mediation of hormone signaling.…”

Section: Discussionmentioning

confidence: 99%

“…The plant hormone treatments were performed as described previously (Long et al ., 2019). Fully mature leaves were inoculated with sterile cotton pre‐soaked with 5 ml solution of 10 µ m NAA, 1 µ m ZT, 1 µ m BL, 400 µ m GA or 100 µ m ABA (Sigma, USA), or water.…”

Section: Methodsmentioning

confidence: 99%

CsLOB1 regulates susceptibility to citrus canker through promoting cell proliferation in citrus

Zou

Liu

et al. 2021

The Plant Journal

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Citrus sinensis lateral organ boundary 1 (CsLOB1) was previously identified as a critical disease susceptibility gene for citrus bacterial canker, which is caused by Xanthomonas citri subsp. citri (Xcc). However, the molecular mechanisms of CsLOB1 in citrus response to Xcc are still elusive. Here, we constructed transgenic plants overexpressing and RNAi-silencing of CsLOB1 using the canker-disease susceptible 'wanjincheng' orange (C. sinensis Osbeck) as explants. CsLOB1-overexpressing plants exhibited dwarf phenotypes with smaller and thicker leaf, increased branches and adventitious buds clustered on stems. These phenotypes were followed by a process of pustule-and canker-like development that exhibited enhanced cell proliferation. Pectin depolymerization and expansin accumulation were enhanced by CsLOB1 overexpression, while cellulose and hemicellulose synthesis were increased by CsLOB1 silence. Whilst overexpression of CsLOB1 increased susceptibility, RNAi-silencing of CsLOB1 enhanced resistance to canker disease without impairing pathogen entry. Transcriptome analysis revealed that CsLOB1 positively regulated cell wall degradation and modification processes, cytokinin metabolism, and cell division. Additionally, 565 CsLOB1-targeted genes were identified in chromatin immunoprecipitation-sequencing (ChIP-seq) experiments. Motif discovery analysis revealed that the most highly overrepresented binding sites had a conserved 6-bp 'GCGGCG' consensus DNA motif. RNA-seq and ChIP-seq data suggested that CsLOB1 directly activates the expression of four genes involved in cell wall remodeling, and three genes that participate in cytokinin and brassinosteroid hormone pathways. Our findings indicate that CsLOB1 promotes cell proliferation by mechanisms depending on cell wall remodeling and phytohormone signaling, which may be critical to citrus canker development and bacterial growth in citrus.

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“…The pathogen of citrus canker appeared to promote JA accumulation through hijacking host ABA production, which could suppress SA-mediated defenses and benefit pathogen development (Long et al, 2019 ). Consistently, DEGs involved in JA, ET, and ABA signaling were nearly all upregulated in the C Las-infected leaves and barks ( Figure 6 ), and so were those participating in JA biosynthesis, such as allene oxide cyclase 4 ( AOC4 ), lipoxygenase 3 ( LOX3 ), 12-oxophytodienoate reductase 2 ( OPR2 ), and peroxisomal acyl-coenzyme A oxidase 1 ( ACX1 , Supplementary Tables 2 , 3 ).…”

Section: Discussionmentioning

confidence: 99%

Integrated Transcriptomics and Metabolomics Analyses Provide Insights Into the Response of Chongyi Wild Mandarin to Candidatus Liberibacter Asiaticus Infection

et al. 2021

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Candidatus Liberibacter asiaticus (CLas) is the causative agent of Huanglongbing (HLB), which has caused great economic losses to the citrus industry. The molecular mechanism of the host response to CLas in wild citrus germplasm has been reported less. Eighteen weeks after inoculation via grafting, all the CLas-inoculated Chongyi wild mandarin (Citrus reticulata) were positive and showed severe anatomical aberrations, suggesting its susceptibility to HLB. Transcriptomics and metabolomics analyses of leaves, barks, and roots from mock-inoculated (control) and CLas-inoculated seedlings were performed. Comparative transcriptomics identified 3,628, 3,770, and 1,716 differentially expressed genes (DEGs) between CLas-infected and healthy tissues in the leaves, barks, and roots, respectively. The CLas-infected tissues had higher transcripts per kilobase per million values and more genes that reached their maximal expression, suggesting that HLB might cause an overall increase in transcript accumulation. However, HLB-triggered transcriptional alteration showed tissue specificity. In the CLas-infected leaves, many DEGs encoding immune receptors were downregulated. In the CLas-infected barks, nearly all the DEGs involved in signaling and plant-pathogen interaction were upregulated. In the CLas-infected roots, DEGs encoding enzymes or transporters involved in carotenoid biosynthesis and nitrogen metabolism were downregulated. Metabolomics identified 71, 62, and 50 differentially accumulated metabolites (DAMs) in the CLas-infected leaves, barks and roots, respectively. By associating DEGs with DAMs, nitrogen metabolism was the only pathway shared by the three infected tissues and was depressed in the CLas-infected roots. In addition, 26 genes were determined as putative markers of CLas infection, and a hypothesized model for the HLB susceptibility mechanism in Chongyi was proposed. Our study may shed light on investigating the molecular mechanism of the host response to CLas infection in wild citrus germplasm.

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Abscisic Acid Promotes Jasmonic Acid Accumulation and Plays a Key Role in Citrus Canker Development

Cited by 35 publications

References 62 publications

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

CsLOB1 regulates susceptibility to citrus canker through promoting cell proliferation in citrus

Integrated Transcriptomics and Metabolomics Analyses Provide Insights Into the Response of Chongyi Wild Mandarin to Candidatus Liberibacter Asiaticus Infection

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