-
[show abstract]
[hide abstract]
ABSTRACT: TRANSPARENT TESTA GLABRA (TTG) proteins that contain the WD40 protein interaction domain are implicated in multiple signalling pathways in plants. The salicylic acid (SA) signalling pathway regulates the resistance of plants to pathogens through defence responses via pathogenesis-related (PR) gene transcription activated by the NPR1 (nonexpresser of PR genes 1) protein, which contains WD40-binding domains. In this study, we report that tobacco (Nicotiana tabacum) NtTTG2 quells the resistance to viral and bacterial pathogens by repressing the nuclear localisation of NPR1 and SA/NPR1-regulated defence in plants. Nullification of the NtTTG2 protein production by silencing of the NtTTG2 gene resulted in the enhancement of resistance and PR gene expression, but NtTTG2 overexpression or NtTTG2 protein overproduction caused the opposite effects. Concurrent NtTTG2 and NPR1 gene silencing or NtTTG2 silencing in the absence of SA accumulation compensated for the compromised defence as a result of the NPR1 single-gene silencing or due to the absence of SA. To our surprise, NtTTG2 did not interact with NPR1 but was able to modulate the subcellular localisation of the NPR1 protein. When the production of NtTTG2 was nullified, NPR1 was found predominantly in the nucleus and the PR genes were expressed. On the contrary, when NtTTG2 accumulated in transgenic plants, a large proportion of NPR1 was retained in the cytoplasm and the PR genes were not expressed. These results suggest that NtTTG2 represses SA/NPR1-regulated defence by sequestering NPR1 from nuclear localisation and the transcriptional activation of the defence-response genes.
Journal of Cell Science 07/2012; · 6.11 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Waterlogging usually results from overuse or poor management of irrigation water and is a serious constraint due to its damaging effects. RAP2.6L (At5g13330) overexpression enhances plant resistance to jasmonic acid, salicylic acid, abscisic acid (ABA) and ethylene in Arabidopsis thaliana. However, it is not known whether RAP2.6L overexpression in vivo improves plant tolerance to waterlogging stress. In this study, the RAP2.6L transcript was induced by waterlogging or an ABA treatment, which was reduced after pretreatment with an ABA biosynthesis inhibitor tungstate. Water loss and membrane leakage were reduced in RAP2.6L overexpression plants under waterlogging stress. Time course analyses of ABA content and production of hydrogen peroxide (H(2)O(2)) showed that increased ABA precedes the increase of H(2)O(2). It is also followed by a marked increase in the antioxidant enzyme activities. Increased ABA promoted stomatal closure and made leaves exhibit a delayed waterlogging induced premature senescence. Furthermore, RAP2.6L overexpression caused significant increases in the transcripts of antioxidant enzyme genes APX1 (ascorbate peroxidase 1) and FSD1 (Fe-superoxide dismutase 1), the ABA biosynthesis gene ABA1 (ABA deficient 1) and signaling gene ABH1 (ABA-hypersensitive 1) and the waterlogging responsive gene ADH1 (alcohol dehydrogenase 1), while the transcript of ABI1 (ABA insensitive 1) was decreased. ABA inhibits seed germination and seedling growth and phenotype analysis showed that the integration of abi1-1 mutation into the RAP2.6L overexpression lines reduces ABA sensitivity. These suggest that RAP2.6L overexpression delays waterlogging induced premature senescence and might function through ABI1-mediated ABA signaling pathway.
Plant Molecular Biology 06/2012; 79(6):609-22. · 4.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Harpin proteins secreted by phytopathogenic bacteria have been shown to activate the plant defense pathway, which involves transduction of a hydrogen peroxide (H(2)O(2)) signal generated in the apoplast. However, the way in which harpins are recognized in the pathway and what role the apoplastic H(2)O(2) plays in plant defenses are unclear. Here, we examine whether the cellular localization of Hpa1(Xoo), a harpin protein produced by the rice bacterial leaf blight pathogen, impacts H(2)O(2) production and pathogen resistance in Arabidopsis thaliana. Transformation with the hpa1 (Xoo) gene and hpa1 (Xoo) fused to an apoplastic localization signal (shpa1 (Xoo)) generated h pa1 (Xoo)- and sh pa1 (Xoo)-expressing transgenic A . t haliana (HETAt and SHETAt) plants, respectively. Hpa1(Xoo) was associated with the apoplast in SHETAt plants but localized inside the cell in HETAt plants. In addition, Hpa1(Xoo) localization accompanied H(2)O(2) accumulation in both the apoplast and cytoplasm of SHETAt plants but only in the cytoplasm of HETAt plants. Apoplastic H(2)O(2) production via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) located in the plasma membrane is a common feature of plant defenses. In SHETAt plants, H(2)O(2) was generated in apoplasts in a NOX-dependent manner but accumulated to a greater extent in the cytoplasm than in the apoplast. After being applied to the wild-type plant, Hpa1(Xoo) localized to apoplasts and stimulated H(2)O(2) production as in SHETAt plants. In both plants, inhibiting apoplastic H(2)O(2) generation abrogated both cytoplasmic H(2)O(2) accumulation and plant resistance to bacterial pathogens. These results suggest the possibility that the apoplastic H(2)O(2) is subject to a cytoplasmic translocation for participation in the pathogen defense.
Plant Molecular Biology 05/2012; 79(4-5):375-91. · 4.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: HrpNEa is a harpin protein from Erwinia amylovora, a bacterial pathogen that causes fire blight in rosaceous plants. Treating plants with HrpNEa stimulates ethylene and abscisic acid (ABA) to induce plant growth and drought tolerance, respectively. Herein, we report
that both growth hormones cooperate to mediate the role of HrpNEa in promoting root growth of Arabidopsis thaliana seedlings. Root growth is promoted coordinately with elevation in levels of ABA and ethylene subsequent to soaking of germinating
seeds of wild-type (WT) Arabidopsis in a solution of HrpNEa. However, these responses are arrested by inhibiting WT roots from synthesizing ethylene as well as sensing of ABA and ethylene.
The effects of HrpNEa on roots are also nullified in ethylene-insensitive etr1-1 and ein5-1 mutants and in the ABA-insensitive mutant abi2-1 of Arabidopsis. These results provide evidence for presence of a relationship between root growth enhancement and signaling by ABA and ethylene
in response to HrpNEa. Nevertheless, when HrpNEa is applied to leaves, ethylene signaling is active in the absence of ABA signaling to promote plant growth. This suggests
the presence of a different signaling mechanism in leaves from that in roots.
Plant Molecular Biology Reporter 04/2012; 26(3):225-240. · 2.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Harpin proteins from plant pathogenic bacteria can activate distinct signaling pathways and cause multiple effects in plants.
When Arabidopsis thaliana (Arabidopsis) plants are treated with the HrpNEa harpin produced by Erwinia amylovora, a bacterial pathogen that causes fire blight in rosaceous plants, abscisic acid (ABA) is stimulated to mediate drought tolerance,
and ethylene signaling is activated to regulate plant growth enhancement and insect resistance. It is unclear if ABA and ethylene
signaling interacts in response to harpin proteins. Here we report that ethylene signaling is dispensable to the induction
of ABA-mediated drought tolerance in Arabidopsis. In wild-type (WT) plants growing under drought stress conditions, ABA, but not ethylene, was required for HrpNEa to promote cellular adaptive responses and decrease drought severity of plants. During the induction of drought tolerance
in HrpNEa-treated WT plants, expression of the ABA signaling gene ABI2 was induced coincidently with decreases in transcripts of ETR1, which encodes an ethylene receptor, and several other genes that are also involved in ABA and ethylene signal transduction
pathways. In response to HrpNEa, the Arabidopsis etr1-1 mutant developed drought tolerance similarly as did WT, but the abi2-1 mutant did not, suggesting that sensing of ABA is essential, but sensing of ethylene is not. Consistently, the induction
of drought tolerance was abolished by inhibiting WT to synthesize ABA, instead of ethylene. Our results suggest that HrpNEa treatment enables plants to prioritize the ABA signal transduction pathway over ethylene signaling in accordance with the
real-time requirement to survive under drought stress conditions.
Plant Molecular Biology Reporter 04/2012; 25(3):98-114. · 2.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Expression of HpaGxoo, a bacterial type-III effector protein, in transgenic plants induces disease resistance. Resistance also can be elicited
by biocontrol bacteria. We studied effects of the biocontrolBacillus subtilis strain B-916 on the rice variety R109 and the thehpaG
xoo
-expressing rice line HER1. Colonisation of roots by B-916 caused 12.5±1.3% and 0.5±0.05% increases, in contrast to controls,
in root growth of R109 and HER1. Growth of R109 leaves and stems was increased by 0.5±0.05% but that of HER1 was inhibited.
When B-916 colonisation was subsequent to plant inoculation withRhizoctonia solani, a pathogen that causes sheath blight, the disease was less severe than controls in both R109 and HER1; HER1, nevertheless,
was more resistant, suggesting that B-916 and HpaGxoo cooperate in inducing disease resistance. In R109 roots, theOsARF1 gene, which regulates plant growth, was expressed in consistence with growth promotion by B-916. Inversely, the depression
ofOsARF1 expression was coincident with inhibition in growth of HER1 leaves and stems. In both plants, the expression ofOsEXP1, which encodes an expansin protein involved in plant growth, was concomitant with growth promotion in leaves and roots responding
to B-916. We also studiedOsMAPK5b encoding a mitogen-activated protein kinase involved in multiple defence responses in rice. In response to B-916, early expression
ofOsMAPK5b was coincident with R109 resistance to the disease, while HER1 expressed the gene similarly whether B-916 was present or
not. Evidently, B916 and HER1 interact differently in rice growth and resistance. The combinative efffects should stimulate
agricultural use and furthestudies on mechanisms that underlie the interaction.
Annals of Microbiology 04/2012; 56(4):281-287. · 0.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Expression of HpaGXoo, a bacterial type-III effector, in transgenic plants induces disease resistance. Resistance also can be elicited by biocontrol
bacteria. In both cases, plant growth is often promoted. Here we address whether biocontrol bacteria and HpaGXoo can act together to provide better results in crop improvement. We studied effects ofPseudomonas cepacia on the rice variety R109 and the hpaGXoo-expressing rice line HER1. Compared to R109, HER1 showed increased growth, grain yield, and defense responses toward diseases
and salinity stress. Colonization of roots byP. cepacia caused 20% and 13% increase, in contrast to controls, in root growth of R109 and HER1. Growth of leaves and stems also increased
in R109 but that of HER 1 was inhibited. WhenP. cepacia colonization was subsequent to plant inoculation withRhizoctonia solani, a pathogen that causes sheath blight, the disease was less severe than controls in both R109 and HER1; HER1, nevertheless,
was more resistant, suggesting thatP.cepacia and HpaGXoo cooperate in inducing disease resistance. Several genes that critically regulate growth and defense behaved differentially
in HER1 and R109 while responding toP. cepacia. In R109 leaves, theOsARF1 gene, which regulates plant growth, was expressed in consistence with growth promotion byP. cepacia. Inversely,OsARF1 expression was coincident with inhibition in growth of HER1 leaves. In both plants, the expression ofOsEXP1, which encodes an expansin protein involved in plant growth, was concomitant with growth promotion in leaves instead of roots,
in response toP. cepacia. We also studiedOsMAPK, a gene that encodes a mitogen-activated protein kinase and controls defense responses toward salinity and infection by pathogens
in rice. In response toP. cepacia, an early expression ofOsMAPK was coincident with R109 resistance to the disease, while HER1 expressed the gene similarly whetherP. cepacia was present or not. Evidently,P. cepacia and GXoo-gene mediated resistance may act differently in rice growth and resistance. Whereas combinative effectsof P. cepacia and HpaGXoo in disease resistance have a great potential in agricultural use, it is interesting to study mechanisms that underlie interactions
involving biocontrol bacteria, type-III effectors and pathogens.
Journal of Biosciences 04/2012; 31(5):617-627. · 1.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The MYB proteins constitute one of the largest transcription factor families in plants. Much research has been performed to determine their structures, functions, and evolution, especially in the model plants, Arabidopsis, and rice. However, this transcription factor family has been much less studied in wheat (Triticum aestivum), for which no genome sequence is yet available. Despite this, expressed sequence tags are an important resource that permits opportunities for large scale gene identification. In this study, a total of 218 sequences from wheat were identified and confirmed to be putative MYB proteins, including 1RMYB, R2R3-type MYB, 3RMYB, and 4RMYB types. A total of 36 R2R3-type MYB genes with complete open reading frames were obtained. The putative orthologs were assigned in rice and Arabidopsis based on the phylogenetic tree. Tissue-specific expression pattern analyses confirmed the predicted orthologs, and this meant that gene information could be inferred from the Arabidopsis genes. Moreover, the motifs flanking the MYB domain were analyzed using the MEME web server. The distribution of motifs among wheat MYB proteins was investigated and this facilitated subfamily classification.
Molecular Biotechnology 12/2011; 52(2):184-92. · 2.17 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Riboflavin mediates many bioprocesses associated with the generation of hydrogen peroxide (H₂O₂), a cellular signal that regulates defense responses in plants. Although plants can synthesize riboflavin, the levels vary widely in different organs and during different stages of development, indicating that changes in riboflavin levels may have physiological effects. Here, we show that changing riboflavin content affects H₂O₂ accumulation and a pathogen defense in Arabidopsis thaliana. Leaf content of free riboflavin was modulated by ectopic expression of the turtle gene encoding riboflavin-binding protein (RfBP). The RfBP-expressing Arabidopsis thaliana (REAT) plants produced the RfBP protein that possessed riboflavin-binding activity. Compared with the wild-type plant, several tested REAT lines had >70% less flavins of free form. This change accompanied an elevation in the level of H₂O₂ and an enhancement of plant resistance to a bacterial pathogen. All the observed REAT characters were eliminated due to RfBP silencing (RfBPi) under REAT background. When an H₂O₂ scavenger was applied, H₂O₂ level declined in all the plants, and REAT no longer exhibited the phenotype of resistance enhancement. However, treatment with an NADPH oxidase inhibitor diminished H₂O₂ content and pathogen defense in wild-type and RfBPi but not in REAT. Our results suggest that the intrinsic down-regulation of free flavins is responsible for NADPH oxidase-independent H₂O₂ accumulation and the pathogen defense.
Plant Molecular Biology 07/2011; 77(1-2):185-201. · 4.15 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Abiotic stress seriously affects crop growth and productivity. To better understand the mechanisms plant uses to cope with drought, cold and salt stress, it is necessary to isolate and characterize important regulators response to these stresses. In this study, we cloned a MYB gene from wheat (Triticum aestivum L.) and designated it as TaMYB3R1 based on its conserved three repeats in MYB domain. The sequence of TaMYB3R1 protein shares high identity to other plant MYB3R proteins. Subcellular localization experiment in onion epidermal cells proved that TaMYB3R1 localized in the nucleus. Trans-activation essays in yeast cells confirmed that TaMYB3R1 was a transcriptional activator, and only C-terminal region was able to activate the expression of β-galactosidase. DNA-binding test showed the MSA cis element-binding activity of TaMYB3R1. After exogenous application of phytohormone ABA, the expression of TaMYB3R1 was induced, and its transcripts accumulated up to 24h; this is also the case for MeJA treatment, but after it peaked at 4h, it decreased to low levels. However, either SA or ET had no obvious effect on the expression of TaMYB3R1. Furthermore, the TaMYB3R1 was initially expressed at low levels and was gradually induced following treatment with salt, and continued to increase up to 72 h. This was similar for the cold treatment. In contrast, the peak appeared at 6h of the PEG treatment, and then gradually decreased to low levels. Our results suggest that TaMYB3R1 is potentially involved in wheat response to drought, salt and cold stress.
Gene 06/2011; 485(2):146-52. · 2.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: In Arabidopsis thaliana (Arabidopsis) treated with the harpin protein HrpN Ea, resistance to the green peach aphid Myzus persicae, a generalist phloem-feeding insect, develops with induced expression of the AtMYB44 gene. Special GLUCAN SYNTHESIS-LIKE (GSL) genes and beta-1,3-glucan callose play an important role in plant defence responses to attacks by phloem-feeding insects. Here we report that AtGLS5 and AtMYB44 are both required for Hrp Ea-induced repression of M. persicae feeding from the phloem of Arabidopsis leaves. In 24 h successive surveys on large-scale aphid populations, the proportion of feeding aphids was much smaller in HrpN Ea-treated plants than in control plants, and aphids preferred to feed from the 37 tested atgsl mutants rather than the wild-type plant. The atgsl mutants were generated previously by mutagenesis in 12 identified AtGSL genes (AtGSL1 through AtGSL12); in the 24 h survey, both atgsl5 and atgsl6 tolerated aphid feeding, and atgsl5 was the most tolerant. Consistently, atgsl5 was also most inhibitive to the deterrent effect of HrpN Ea on the phloem-feeding activity of aphids as monitored by the electrical penetration graph technique. These results suggested an important role of the AtGSL5 gene in the effect of HrpN Ea. In response to HrpN Ea, AtGSL5 expression and callose deposition were induced in the wild-type plant but not in atgsl5. In response to HrpN Ea, moreover, the AtMYB44 gene known to be required for repression of aphid reproduction on the plant was also required for repression of the phloem-feeding activity. Small amounts of the AtGSL5 transcript and callose deposition were detected in the atmyb44 mutant, as in atgsl5. Both mutants performed similarly in tolerating the phloem-feeding activity and impairing the deterrent effect of HrpN Ea, suggesting that AtGSL5 and AtMYB44 both contributed to the effect.
Journal of Biosciences 03/2011; 36(1):123-37. · 1.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: AtMYB44 is a transcription factor that functions in association with the ethylene-signaling pathway in Arabidopsis thaliana. The pathway depends on ETHYLENE INSENSITIVE2 (EIN2), an essential component of ethylene signaling, to regulate defense responses in the plant following treatment with HrpN(Ea), a harpin protein from a bacterial plant pathogen. Here, we show that AtMYB44 regulates induced expression of the EIN2 gene in HrpN(Ea)-treated Arabidopsis plants. A HrpN(Ea) and ethylene-responsive fragment of the AtMYB44 promoter is sufficient to support coordinate expression of AtMYB44 and EIN2 in specific transgenic Arabidopsis. In the plant, the AtMYB44 protein localizes to nuclei and binds the EIN2 promoter; the HrpN(Ea) treatment promotes AtMYB44 production, binding activity, and transcription of AtMYB44 and EIN2. AtMYB44 overexpression results in increased production of the AtMYB44 protein and the occurrence of AtMYB44-EIN2 interaction under all genetic backgrounds of wild-type Arabidopsis and the etr1-1, ein2-1, ein3-1, and ein5-1 mutants, which have defects in the ethylene receptor ETR1 and the signal regulators EIN2, EIN3, and EIN5. However, AtMYB44 overexpression leads to enhanced EIN2 expression only under backgrounds of wild type, ein3-1, and ein5-1 but not etr1-1 and ein2-1, suggesting that ethylene perception is necessary to the regulation of EIN2 transcription by AtMYB44.
Molecular Plant-Microbe Interactions 03/2011; 24(3):377-89. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Riboflavin mediates many bioprocesses associated with the generation of hydrogen peroxide (H2O2), a cellular signal that regulates defense responses in plants. Although plants can synthesize riboflavin, the levels vary widely in different organs and during different stages of development, indicating that changes in riboflavin levels may have physiological effects. Here, we show that changing riboflavin content affects H2O2 accumulation and a pathogen defense in Arabidopsis thaliana. Leaf content of free riboflavin was modulated by ectopic expression of the turtle gene encoding riboflavin-binding protein (RfBP). The RfBP-expressing Arabidopsis thaliana (REAT) plants produced the RfBP protein that possessed riboflavin-binding activity. Compared with the wild-type plant, several tested REAT lines had >70% less flavins of free form. This change accompanied an elevation in the level of H2O2 and an enhancement of plant resistance to a bacterial pathogen. All the observed REAT characters were eliminated due to RfBP silencing (RfBPi) under REAT background. When an H2O2 scavenger was applied, H2O2 level declined in all the plants, and REAT no longer exhibited the phenotype of resistance enhancement. However, treatment with an NADPH oxidase inhibitor diminished H2O2 content and pathogen defense in wild-type and RfBPi but not in REAT. Our results suggest that the intrinsic down-regulation of free flavins is responsible for NADPH oxidase-independent H2O2 accumulation and the pathogen defense.
Plant Molecular Biology. Doi: 10.1007/s11103-011-9802-0. 01/2011;
-
Chunling Zhang,
Haojie Shi,
Lei Chen,
Xiaomeng Wang,
Beibei Lü,
Shuping Zhang,
Yuan Liang,
Ruoxue Liu,
Jun Qian,
Weiwei Sun,
Zhenzhen You, Hansong Dong
[show abstract]
[hide abstract]
ABSTRACT: Treatment of plants with HrpNEa, a protein of harpin group produced by Gram-negative plant pathogenic bacteria, induces plant resistance to insect herbivores, including the green peach aphid Myzus persicae, a generalist phloem-feeding insect. Under attacks by phloem-feeding insects, plants defend themselves using the phloem-based defense mechanism, which is supposed to involve the phloem protein 2 (PP2), one of the most abundant proteins in the phloem sap. The purpose of this study was to obtain genetic evidence for the function of the Arabidopsis thaliana (Arabidopsis) PP2-encoding gene AtPP2-A1 in resistance to M. persicae when the plant was treated with HrpNEa and after the plant was transformed with AtPP2-A1.
The electrical penetration graph technique was used to visualize the phloem-feeding activities of apterous agamic M. persicae females on leaves of Arabidopsis plants treated with HrpNEa and an inactive protein control, respectively. A repression of phloem feeding was induced by HrpNEa in wild-type (WT) Arabidopsis but not in atpp2-a1/E/142, the plant mutant that had a defect in the AtPP2-A1 gene, the most HrpNEa-responsive of 30 AtPP2 genes. In WT rather than atpp2-a1/E/142, the deterrent effect of HrpNEa treatment on the phloem-feeding activity accompanied an enhancement of AtPP2-A1 expression. In PP2OETAt (AtPP2-A1-overexpression transgenic Arabidopsis thaliana) plants, abundant amounts of the AtPP2-A1 gene transcript were detected in different organs, including leaves, stems, calyces, and petals. All these organs had a deterrent effect on the phloem-feeding activity compared with the same organs of the transgenic control plant. When a large-scale aphid population was monitored for 24 hours, there was a significant decrease in the number of aphids that colonized leaves of HrpNEa-treated WT and PP2OETAt plants, respectively, compared with control plants.
The repression in phloem-feeding activities of M. persicae as a result of AtPP2-A1 overexpression, and as a deterrent effect of HrpNEa treatment in WT Arabidopsis rather than the atpp2-a1/E/142 mutant suggest that AtPP2-A1 plays a role in plant resistance to the insect, particularly at the phloem-feeding stage. The accompanied change of aphid population in leaf colonies suggests that the function of AtPP2-A1 is related to colonization of the plant.
BMC Plant Biology 01/2011; 11:11. · 3.45 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Various thioredoxin (Trx) proteins have been identified in plants. However, many of the physiological roles played by these proteins remain to be elucidated. We cloned a TRXh-like gene predicted to encode an h-type Trx in tobacco (Nicotiana tabacum) and designated it NtTRXh3, based on the biochemical activity of the NtTRXh3 protein. Overexpression of NtTRXh3 conferred resistance to Tobacco mosaic virus and Cucumber mosaic virus, both of which showed reduced multiplication and pathogenicity in NtTRXh3-overexpressing plants compared with controls. NtTRXh3 overexpression also enhanced tobacco resistance to oxidative stress induced by paraquat, an herbicide that inhibits the production of reducing equivalents by chloroplasts. The NtTRXh3 protein localized exclusively to chloroplasts in coordination with the maintenance of cellular reducing conditions, which accompanied an elevation in the glutathione/glutathione disulfide couple ratio. NtTRXh3 gene expression and NtTRXh3 protein production were necessary for these defensive responses, because they were all arrested when NtTRXh3 was silenced and the production of NtTRXh3 protein was abrogated. These results suggest that NtTRXh3 is involved in the resistance of tobacco to virus infection and abiotic oxidative stress.
Molecular Plant-Microbe Interactions 11/2010; 23(11):1470-85. · 4.43 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Reactive oxygen species (ROS) are important signalling molecules in living cells. It is believed that ROS molecules are the main triggers of the hypersensitive response (HR) in plants. In the present study of the effect of riboflavin, which is excited to generate ROS in light, on the development of the HR induced by the elicitin protein ParA1 in tobacco (Nicotiana tabacum), we found that the extent of the ParA1-induced HR was diminished by hydroxyl radical (OH•), a type of ROS. As compared with the zones treated with ParA1 only, the HR symptom in the zones that were infiltrated with ParA1 plus riboflavin was significantly diminished when the treated plants were placed in the light. However, this did not occur when the plants were maintained in the dark. Trypan blue staining and the ion leakage measurements confirmed HR suppression in the light. Further experiments proved that HR suppression is attributed to the involvement of the photoexcited riboflavin, and that the suppression can be eliminated with the addition of hydrogen peroxide scavengers or OH• scavengers. Fenton reagent treatment and EPR measurements demonstrated that it is OH• rather than hydrogen peroxide that contributes to HR suppression. Accompanying the endogenous OH• formation, suppression of the ParA1-induced HR occurred in the tobacco leaves that had been treated with high-level abscisic acid, and that suppression was also removed by OH• scavengers. These results offer evidence that OH•, an understudied and little appreciated ROS, participates in and modulates biologically relevant signalling in plant cells.
FEBS Journal 10/2010; 277(24):5097-111. · 3.79 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The harpin protein HrpN Ea induces Arabidopsis resistance to the green peach aphid by activating the ethylene signalling pathway and by recruiting EIN2, an essential regulator of ethylene signalling, for a defence response in the plant. We investigated 37 ethylene-inducible Arabidopsis transcription factor genes for their effects on the activation of ethylene signalling and insect defence. Twenty-eight of the 37 genes responded to both ethylene and HrpN Ea, and showed either increased or inhibited transcription, while 18 genes showed increased transcription not only by ethylene but also by HrpN Ea. In response to HrpN Ea, transcription levels of 22 genes increased, with AtMYB44 being the most inducible, six genes had decreased transcript levels, and nine remained unchanged. When Arabidopsis mutants previously generated by mutagenicity at the 37 genes were surveyed, 24 mutants were similar to the wild type plant while four mutants were more resistant and nine mutants were more susceptible than wild type to aphid infestation. Aphid-susceptible mutants showed a greater susceptibility for atmyb15, atmyb38 and atmyb44, which were generated previously by T-DNA insertion into the exon region of AtMYB15 and the promoter regions of AtMYB38 and AtMYB44. The atmyb44 mutant was the most susceptible to aphid infestation and most compromised in induced resistance. Resistance accompanied the expression of PDF1.2, an ethylene signalling marker gene that requires EIN2 for transcription in wild type but not in atmyb15, atmyb38, and atmyb44, suggesting a disruption of ethylene signalling in the mutants. However, only atmyb44 incurred an abrogation in induced EIN2 expression, suggesting a close relationship between AtMYB44 and EIN2.
Journal of Biosciences 09/2010; 35(3):435-50. · 1.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Lumazine synthase (LS) catalyzes the penultimate reaction in the multistep riboflavin biosynthesis pathway, which is involved in plant defenses. Plant defenses are often subject to synergistic effects of jasmonic acid and ethylene whereas LS is a regulator of jasmonic acid signal transduction. However, little is known about whether the enzyme contributes to defense responses. To study the role of LS in plant pathogen defenses, we generated transgenic tobacco expressing the rice (Oryza sativa) LS gene, OsLS. OsLS was cloned and found to have strong identity with its homologues in higher plants and less homology to microbial orthologues. The OsLS protein localized to chloroplasts in three OsLS-expressing transgenic tobacco (LSETT) lines characterized as enhanced in growth and defense. Compared with control plants, LSETT had higher content of both riboflavin and the cofactors flavin mononucleotide and flavin adenine dinucleotide. In LSETT, jasmonic acid and ethylene were elevated, the expression of defense-related genes was induced, levels of resistance to pathogens were enhanced, and resistance was effective to viral, bacterial, and oomycete pathogens. Extents of OsLS expression correlated with increases in flavin, jasmonic acid, and ethylene content, and correlated with increases in resistance levels, suggesting a role for OsLS in defense responses.
Phytopathology 06/2010; 100(6):573-81. · 2.80 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Quercetin is a potent antioxidant and has been extensively used as a therapy intervention to prevent age-associated diseases. However, emerging studies showed it can also act as a prooxidant and induce H(2)O(2) under certain conditions. In the current study, our results showed that quercetin contributed to the pathogen resistance in Arabidopsis thaliana (Arabidopsis) in response to the infection of virulent strain Pseudomonas syringae pv. Tomato DC3000 (Pst). Various defense responses, such as H(2)O(2) burst, callose deposition, cell death, PR1 (pathogenesis-related 1) and PAL1 (Phe ammonia-lyase 1) gene expression, have been investigated in quercetin-pretreated Pst-inoculated Arabidopsis Col-0 and there was a strong defensive response in quercetin-pretreated Arabidopsis against virulent Pst. However, with the presence of catalase, the protective effects of quercetin on pathogen resistance to virulent Pst disappeared in Arabidopsis, suggesting that H(2)O(2) may play a key role in plant defense responses. In addition, we confirmed that quercetin did not show any beneficial effect on pathogen-free leaves in Arabidopsis, indicating that pathogen challenge is also required to induce the defense responses in quercetin-pretreated Arabidopsis. Furthermore, strong defense responses have been observed in quercetin-pretreated Arabidopsis mutant jar1, ein2, and abi1-2 under Pst challenge, whereas no protective effect has been observed in quercetin-pretreated Arabidopsis mutant NahG and npr1. These findings indicate that quercetin induces the resistance to Pst in Arabidopsis via H(2)O(2) burst and involvement of SA and NPR1.
Biochemical and Biophysical Research Communications 05/2010; 396(2):522-7. · 2.48 Impact Factor
-
Yunpeng Wang,
Ruoxue Liu,
Lei Chen,
Yuancong Wang,
Yuancun Liang,
Xiaojing Wu,
Baoyan Li,
Jiandong Wu,
Yuan Liang,
Xiaomeng Wang,
Chunling Zhang,
Qiuxia Wang,
Xiaoyue Hong, Hansong Dong
[show abstract]
[hide abstract]
ABSTRACT: Leaf trichomes serve as a physical barrier and can also secrete antimicrobial compounds to protect plants from attacks by insects and pathogens. Besides the use of the physical and chemical mechanisms, leaf trichomes might also support plant responses by communicating the extrinsic cues to plant intrinsic signalling pathways. Here we report a role of leaf trichomes in tobacco (Nicotiana tabacum) hypersensitive cell death (HCD) induced by ParA1, an elicitin protein from a plant-pathogenic oomycete. After localized treatment with ParA1, reactive oxygen species were produced first in the leaf trichomes and then in mesophylls. Reactive oxygen species are a group of intracellular signals that are crucial for HCD to develop and for cells to undergo cell death subsequent to chromatin condensation, a hallmark of HCD. These events were impaired when the production of hydrogen peroxide (H(2)O(2)) was inhibited by catalase or a NADPH-oxidase inhibitor applied to trichomes, suggesting the importance of H(2)O(2) in the pathway of HCD signal transduction from the trichomes to mesophylls. This pathway was no longer activated when leaf trichomes were treated with C51S, a ParA1 mutant protein defective in its interaction with N. tabacum TTG1 (NtTTG1), which is a trichome protein that binds ParA1, rather than C51S, in vitro and in trichome cells. The ParA1-NtTTG1 interaction and the HCD pathway were also abrogated when NtTTG1 was silenced in the trichomes. These observations suggest that NtTTG1 plays an essential role in HCD signal transduction from leaf trichomes to mesophylls.
Journal of Cell Science 09/2009; 122(Pt 15):2673-85. · 6.11 Impact Factor
