Functional characterization of the citrus canker susceptibility gene CsLOB1 (original) (raw)
Related papers
BMC Genomics, 2014
Background: Transcriptional activator-like (TAL) effectors, formerly known as the AvrBs3/PthA protein family, are DNA-binding effectors broadly found in Xanthomonas spp. that transactivate host genes upon injection via the bacterial type three-secretion system. Biologically relevant targets of TAL effectors, i.e. host genes whose induction is vital to establish a compatible interaction, have been reported for xanthomonads that colonize rice and pepper; however, citrus genes modulated by the TAL effectors PthA"s" and PthC"s" of the citrus canker bacteria Xanthomonas citri (Xc) and Xanthomonas aurantifolii pathotype C (XaC), respectively, are poorly characterized. Of particular interest, XaC causes canker disease in its host lemon (Citrus aurantifolia), but triggers a defense response in sweet orange.
Over-expression of the citrus gene CtNH1 confers resistance to bacterial canker disease
Physiological and Molecular Plant Pathology, 2013
Citrus canker is a devastating disease, caused by Xanthomonas axonopodis pv. citri (Xac). It is well established that the NPR1 gene plays a pivotal role in systemic acquired resistance (SAR) in Arabidopsis. In this study, we report the isolation and characterization of an NPR1 homolog from citrus, namely Citrus NPR1 homolog 1 (CtNH1). Sequence alignment and phylogenetic analysis indicate that CtNH1 is closelyrelated to the Arabidopsis NPR1 gene and its orthologs from rice, grapevine, and cacao. When overexpressed in citrus, CtNH1 confers resistance to Xac and leads to constitutive expression of the pathogenesis-related (PR) gene chitinase 1 (Chi1), suggesting that CtNH1 is orthologous to NPR1.
Over-expression of the Arabidopsis NPR1 gene in citrus increases resistance to citrus canker
European Journal of Plant Pathology, 2010
Citrus canker, caused by the bacterial pathogen Xanthomonas citri subsp. citri (Xcc), is a serious leaf and fruit spotting disease affecting many important citrus cultivars including grapefruit and certain sweet oranges. Currently, efficacious and economical disease control measures for highly susceptible citrus cultivars are lacking. Development of commercial cultivars with greater field resistance to citrus canker is the optimum strategy for effective disease management. In this study, we generated transgenic 'Duncan' grapefruit (DG) and 'Hamlin' sweet orange (Ham) expressing the Arabidopsis NPR1 gene (AtNPR1), which is a key positive regulator of the long-lasting broad-spectrum resistance known as systemic acquired resistance (SAR). Our results indicate that over-expression of AtNPR1 in citrus increases resistance to citrus canker and that the resistance is related with the expression levels of AtNPR1 in the transgenic plants. The line (DG 42-2) with the highest expression level of AtNPR1 was also the most resistant, which developed significant fewer lesions accompanied by a ten-fold reduction in Xcc population. The lesions developed on DG 42-2 were smaller and darker than those on the control and lacked callus formation. These lesion phenotypes resemble those on canker resistant kumquats and canker susceptible citrus trees treated with SAR-inducing compounds. Therefore, over-expression of AtNPR1 in citrus is a promising approach for development of more resistant cultivars to citrus canker.
Background:Enormous work has shown that polyamines are involved in a variety of physiological processes, but information is scarce on the potential of modifying disease response through genetic transformation of a polyamine biosynthetic gene. Results:In the present work, an apple spermidine synthasegene (MdSPDS1) was introduced into sweet orange (Citrus sinensisOsbeck‘Anliucheng’) via Agrobacterium-mediated transformation of embryogenic calluses. Two transgenic lines (TG4 and TG9) varied in the transgene expression and cellular endogenous polyamine contents. Pinprick inoculation demonstrated that the transgenic lines were less susceptible toXanthomonas axonopodispv. citri(Xac), the causal agent of citrus canker, than the wild type plants (WT). In addition, our data showed that upon Xac attack TG9 had significantly higher free spermine (Spm) and polyamine oxidase (PAO) activity when compared with the WT, concurrent with an apparent hypersensitive response and the accumulation of more H2O2 . Pretreatment of TG9 leaves with guazatine acetate, an inhibitor of PAO, repressed PAO activity and reduced H2O2 accumulation, leading to more conspicuous disease symptoms than the controls when both were challenged with Xac. Moreover, mRNA levels of most of the defense-related genes involved in synthesis of pathogenesis-related protein and jasmonic acid were upregulated in TG9 than in the WT regardless of Xac infection. Conclusion:Our results demonstrated that overexpression of theMdSPDS1gene prominently lowered the sensitivity of the transgenic plants to canker. This may be, at least partially, correlated with the generation of more H2O2due to increased production of polyamines and enhanced PAO-mediated catabolism, triggering hypersensitive response or activation of defense-related genes.
Molecular plant …, 2008
Xanthomonas axonopodis pv. citri (Xac) and Xanthomonas axonopodis pv. aurantifolii pathotype C (Xaa) are responsible for citrus canker disease; however, while Xac causes canker on all citrus varieties, Xaa is restricted to Mexican lime, and in sweet oranges it triggers a defence response. To gain insights into the differential pathogenicity exhibited by Xac and Xaa and to survey the early molecular events leading to canker development, a detailed transcriptional analysis of sweet orange plants infected with the pathogens was performed. Using differential display, suppressed subtractive hybridization and microarrays, we identified changes in transcript levels in approximately 2.0% of thẽ 32 000 citrus genes examined. Genes with altered expression in response to Xac/Xaa surveyed at 6 and 48 h post-infection (hpi) were associated with cell-wall modifications, cell division and expansion, vesicle trafficking, disease resistance, carbon and nitrogen metabolism, and responses to hormones auxin, gibberellin and ethylene. Most of the genes that were commonly modulated by Xac and Xaa were associated with basal defences triggered by pathogen-associated molecular patterns, including those involved in reactive oxygen species production and lignification. Significantly, we detected clear changes in the transcriptional profiles of defence, cell-wall, vesicle trafficking and cell growth-related genes in Xac-infected leaves between 6 and 48 hpi. This is consistent with the notion that Xac suppresses host defences early during infection and simultaneously changes the physiological status of the host cells, reprogramming them for division and growth. Notably, brefeldin A, an inhibitor of vesicle trafficking, retarded canker development. In contrast, Xaa triggered a mitogen-activated protein kinase signalling pathway involving WRKY and ethylene-responsive transcriptional factors known to activate downstream defence genes.
Xanthomonas axonopodis pv. citri (Xac) and Xanthomonas axonopodis pv. aurantifolii pathotype C (Xaa) are responsible for citrus canker disease; however, while Xac causes canker on all citrus varieties, Xaa is restricted to Mexican lime, and in sweet oranges it triggers a defence response. To gain insights into the differential pathogenicity exhibited by Xac and Xaa and to survey the early molecular events leading to canker development, a detailed transcriptional analysis of sweet orange plants infected with the pathogens was performed. Using differential display, suppressed subtractive hybridization and microarrays, we identified changes in transcript levels in approximately 2.0% of thẽ 32 000 citrus genes examined. Genes with altered expression in response to Xac/Xaa surveyed at 6 and 48 h post-infection (hpi) were associated with cell-wall modifications, cell division and expansion, vesicle trafficking, disease resistance, carbon and nitrogen metabolism, and responses to hormones auxin, gibberellin and ethylene. Most of the genes that were commonly modulated by Xac and Xaa were associated with basal defences triggered by pathogen-associated molecular patterns, including those involved in reactive oxygen species production and lignification. Significantly, we detected clear changes in the transcriptional profiles of defence, cell-wall, vesicle trafficking and cell growth-related genes in Xac-infected leaves between 6 and 48 hpi. This is consistent with the notion that Xac suppresses host defences early during infection and simultaneously changes the physiological status of the host cells, reprogramming them for division and growth. Notably, brefeldin A, an inhibitor of vesicle trafficking, retarded canker development. In contrast, Xaa triggered a mitogen-activated protein kinase signalling pathway involving WRKY and ethylene-responsive transcriptional factors known to activate downstream defence genes.
Horticultural Plant Journal, 2016
To study the functions of the early auxin-responsive genes CsGH3.1 and CsGH3.6 in citrus resistance against canker disease, we cloned CsGH3.1 and CsGH3.6 in 'Newhall' Navel Orange (Citrus sinensis Osbeck). They are 1 797 bp and 1 887 bp and encode 598 and 629 amino acids, respectively. In vitro mature leaves from susceptible 'Newhall' and resistant Calamondin (C. madurensis) were inoculated by a Xanthomonas axonopodis pv. citri (Xac) bacterial suspension, and expression of CsGH3.1 and CsGH3.6 in the two varieties were analyzed using quantitative real-time PCR (qRT-PCR). 'Newhall' leaves were treated with different hormones for 3 days, inoculated by Xac bacterial suspension, and then the symptoms in these leaves were investigated. We used qRT-PCR to analyze the effect of different hormones on CsGH3.1 and CsGH3.6 expression in 'Newhall' leaves. The expression levels of both CsGH3.1 and CsGH3.6 were significantly induced by Xac in 'Newhall' leaves, compared with levels in Calamondin leaves. 1-naphthy acetic acid (NAA) increased the hypertrophy of infection sites in 'Newhall' leaves, while naphthyl-phthalamic acid (NPA) had no visible effect on lesion development. NAA hormone greatly improved expression of CsGH3.1 in 'Newhall', but not CsGH3.6. These results indicate that the auxin primary-response gene CsGH3.1 plays an important role in citrus susceptibility to Xac.
Phytopathology, 2016
Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a devastating disease of most commercial citrus varieties. In our previous study, we analyzed the transcriptional response of Valencia sweet orange to Xcc wild type and pthA4 mutant infection at 48 hours post inoculation (hpi). Using microarray analysis, two PthA4 targets, CsLOB1 and CsSWEET1, were identified. We have shown that PthA4 binds to the EBE (Effector Binding Element) of CsLOB1 and activates gene expression of this susceptibility gene. However, how PthA4 modulates host genes at different stages of infection remains to be determined. In this study, we compared the transcriptional profiles between citrus leaf tissue inoculated with Xcc306 and those inoculated with a pthA4-deletion mutant strain Xcc306∆pthA4 at 6, 48 and 120 hpi. At both 48 and 120 hpi, the PthA4-mediated infection significantly up-regulated expression of a variety of genes involved in cell wall degradation and modification, DNA packaging, G-pr...
Role of the Citrus sinensis RNA deadenylase CsCAF1 in citrus canker resistance
Molecular Plant Pathology, 2019
Poly(A) tail shortening is a critical step in messenger RNA (mRNA) decay and control of gene expression. The carbon catabolite repressor 4 (CCR4)-associated factor 1 (CAF1) component of the CCR4-NOT deadenylase complex plays an essential role in mRNA deadenylation in most eukaryotes. However, while CAF1 has been extensively investigated in yeast and animals, its role in plants remains largely unknown. Here, we show that the Citrus sinensis CAF1 (CsCAF1) is a magnesium-dependent deadenylase implicated in resistance against the citrus canker bacteria Xanthomonas citri. CsCAF1 interacted with proteins of the CCR4-NOT complex, including CsVIP2, a NOT2 homologue, translin-associated factor X (CsTRAX) and the poly(A)-binding proteins CsPABPN and CsPABPC. CsCAF1 also interacted with PthA4, the main X. citri effector required for citrus canker elicitation. We also present evidence suggesting that PthA4 inhibits CsCAF1 deadenylase activity in vitro and stabilizes the mRNA encoded by the citrus canker susceptibility gene CsLOB1, which is transcriptionally activated by PthA4 during canker formation. Moreover, we show that an inhibitor of CsCAF1 deadenylase activity significantly enhanced canker development, despite causing a reduction in PthA4-dependent CsLOB1 transcription. These results thus link CsCAF1 with canker development and PthA4dependent transcription in citrus plants.