PLDα1介导ABA调控的拟南芥主根伸长并参与根毛生长

探讨了磷脂酶Dα1（PLDα1）在ABA抑制拟南芥主根伸长过程中的作用。PLOα1基因突变体pldα1主根伸长受ABA抑制小于野生型（WT）;根系PLDα1活性在ABA处理下升高;拟南芥根细胞原生质体中活性氧（ROS）含量在ABA处理下升高,但是pldα1升高小于WT;根系NADPH氧化酶活性在ABA处理下升高,pldα1升高小于WT,外源加入10μmol/L^-1 PA（磷脂酸,PLD水解产物）后,前者活性显著升高;外源加入H2O2可诱导WT和pldα1主根伸长都受到抑制,且二者差异不明显。结果表明,PLDα1产生的PA通过激活NADPH氧化酶产生ROS介导ABA调控的拟南芥主根伸长过程。此外,初步探讨了PLDα1在拟南芥根毛尖端生长中的作用：pldα1突变体根毛长度小于WT,根毛尖端ROS和Ca^2＋浓度低于WT。     

甘蓝型油菜根系突变体lrn1、prl1和野生型根系显微结构的差异

油菜外源细胞分裂素不敏感突变体lrn1和prl1表现为磷高效。营养液培养0.2μmol/L细胞分裂素(6-BA)处理,与甘蓝型油菜野生型‘宁油7号’(WT)相比,突变体lrn1侧根较多,prl1主根较长。本研究利用体式显微技术、非切片压片法以及石蜡切片等技术,对3个基因型在ddH2O和0.2μmol/L 6-BA处理下的根毛、根表皮细胞分化及根尖解剖结构的差异进行了观察,结果表明:ddH2O处理,种子发芽后第1、3、6、9 d,lrn1、prl1和WT根尖成熟区根毛较少。0.2μmol/L 6-BA处理,种子发芽后第3 d,lrn1、prl1和WT根尖形成大量根毛,其中WT根毛最多、密度最大;prl1根毛最少,密度也最小;lrn1处于两者之间。种子发芽后第6 d,lrn1、prl1和WT分生区和伸长区明显缩短,lrn1和prl1分生区面积无显著差异,但两者均显著大于WT;lrn1和prl1根冠细胞结构较正常,而WT根冠细胞结构畸形;lrn1皮层原细胞之间排列较WT和prl1紧密。种子发芽后第9 d,lrn1已有4条侧根,但prl1与WT无侧根形成。6-BA处理,prl1主根较长,与其根尖分生区面积较大密切相关;lrn1侧根较多,可能与中柱原细胞排列密度较高密切相关。     

异三聚体G蛋白在NAA诱导的拟南芥根生长发育中的作用

以拟南芥的野生型(ws)、异三聚体G蛋白α亚基基因GPA1缺失突变体(gpa1-1,gpa1-2)和超表达突变体(wGα,cGα)为材料,通过施加不同浓度(0~0.2 mg/L)的NAA处理,对拟南芥根生长发育的一些形态指标进行了观测比较.结果表明:(1)随着培养基中NAA浓度的不断升高,5种基因型主根的伸长生长均受到抑制,且抑制作用随浓度升高而增强;4种突变体和野生型主根的生长在相同浓度NAA处理下,无明显差异;(2)NAA在一定浓度范围内,对拟南芥侧根的生长发育起促进作用;在NAA诱导的侧根生长中,G蛋白超表达突变体比野生型更敏感,缺失突变体则不敏感.初步证明G蛋白不参与主根生长发育的调节,而在侧根生长发育中可能起正调节作用.     

低氮下拟南芥叶酰聚谷氨酸合成酶突变体atdfb根发育研究

利用叶酰聚谷氨酸合成酶功能缺失突变体atdfb解析叶酸在拟南芥根发育过程中的生物学功能。纯合T-DNA插入功能缺失突变体atdfb 在土壤培养条件下生长3周,与野生型表型无明显差异。在氮源充足的1/2MS培养基上,atdfb的主根显著短于野生型,互补植株的主根长度恢复到野生型水平,说明主根缩短的表型是由AtDFB基因功能缺失造成的。在1/2MS培养基生长11 d的突变体主根长度只有野生型的23%。在低氮条件下,突变体的生长发育几乎停滞,培养11 d的突变体主根长度只有野生型的4%;5-甲酰四氢叶酸(5-F-THF)可以恢复低氮条件下atdfb-3的表型,其主根长度、根毛长度及静止中心的细胞排列均得到恢复。进一步分析发现,低氮条件下培养少于3 d的atdfb-3补充充足的5-F-THF,3 d后能像野生型一样适应低氮环境。由此说明叶酸对拟南芥根部发育及对低氮环境的适应是必需的。     

生长素和乙烯互作调控硝酸铵诱导的根毛分叉

以野生型拟南芥(WT)及其生长素和乙烯不敏感型突变体(aux1-7、axr1-3、etr1-1和etr1-3)为实验材料,采用固体培养法研究了高浓度硝酸铵对根毛发育的影响,以揭示其调控根毛发育的机制。结果表明:(1)随着外源硝酸铵浓度的逐渐增加,拟南芥根毛伸长受阻,产生大量的分叉根毛。(2)高浓度硝酸铵条件下,外源活性氧或活性氧产生抑制剂二苯基氯化碘(DPI)的添加能抑制高浓度硝酸铵诱导的分叉根毛产生。(3)高浓度硝酸铵条件下,外源生长素或乙烯合成前体物质1-氨基-环丙烷-1-羧酸(ACC)处理能恢复根毛的正常生长,解除高浓度硝酸铵诱导根毛分叉现象。(4)高浓度硝酸铵条件下,外源生长素处理乙烯不敏感型突变体或ACC处理生长素不敏感型突变体均能抑制突变体分叉根毛的形成。研究表明,活性氧、生长素和乙烯都参与了高浓度硝酸铵对根毛发育的过程调控;在硝酸铵诱导的根毛分叉中生长素和乙烯存在相互作用,在缺乏生长素信号通路时,乙烯能够发挥补充作用抑制分叉根毛的产生;在缺乏乙烯信号通路时,生长素也可以弥补缺失乙烯的作用抑制根毛的分叉,但是需要更高浓度的生长素才能充分抑制分叉根毛的产生。     

甾类激素炔雌醇、炔诺酮和左炔诺孕酮对拟南芥根生长的影响

采用不同浓度的人工合成甾类激素炔雌醇、炔诺酮和左炔诺孕酮处理拟南芥幼苗,研究3种激素对其根生长和根中内源激素含量的影响.结果表明:(1)30μg?L-1炔雌醇处理显著促进主根的伸长、侧根数及侧根总长的增加,促进主根根毛数和地下部鲜重的增加,增大内源IAA和iPAs含量,以及IAA/iPAs比值;3 000μg?L-1炔雌醇处理则增加主根的弯曲度;(2)炔诺酮活性相对较弱,浓度为300μg?L-1时对主根长、侧根数、侧根总长的促进效果最大,IAA含量增加而iPAs含量降低,IAA/iPAs比值最大;3 000μg?L-1炔诺酮则引起主根弯曲,抑制根毛的生长,但促进侧根数和的地下部鲜重的增加;(3)左炔诺孕酮的活性较高,3μg?L-1时对拟南芥主根长、主根根毛数增加最为显著;300μg?L-1时对侧根数、根毛密度的增幅最大,IAA含量增加,IAA/iPAs比值最大;3 000μg?L-1时显著抑制主根的生长和侧根的生成.     

拟南芥GLP13基因在植物抗氧化胁迫响应中的作用

类萌发素蛋白（germin-like protein, GLPs）是一类与小麦萌发素序列相似性较高、位于胞外基质的可溶性糖蛋白, 在植物的生长发育阶段以及对生物和非生物胁迫的应答中起着重要的作用。为了研究GLP13基因的生理功能, 我们分离并鉴定了GLP13的敲减突变体glp13, 同时构建了其超表达植株35S：：GLP13。用甲基紫精（methyl viologen, MV）处理2种不同基因型和野生型（WT）植株, 结果发现, 与野生型相比, 突变体glp13子叶变绿率较低, 主根生长受抑制较明显; 而超表达植株35S：：GLP13子叶变绿率较高, 主根生长的受抑制程度较WT轻。用MV处理2周的35S：：GLP13植株, 其叶绿素荧光参数Fv/Fm 的下降较野生型对照缓慢。半定量RT-PCR分析结果表明, 与野生型相比, 经MV处理4小时后的35S：：GLP13中抗氧化酶系基因FSD1的表达上调, 而CAT1、CSD1和UGT71C1的表达水平在35S：：GLP13、glp13和野生型植株三者之间没有明显差异。以上结果表明GLP13基因在拟南芥抗氧化胁迫响应中起重要作用。     

Leukamenin E调节拟南芥幼苗生长发育的模式及其机制

研究对映-贝壳杉烷型二萜化合物Leukamenin E对拟南芥种子萌发、下胚轴伸长以及根生长发育的作用模式,并探讨植物激素生长素和乙烯可能介导Leukamenin E影响拟南芥主根生长、侧根和根毛发育的初步机制。结果表明:Leukamenin E浓度在10~160μmol·L~(-1)范围对拟南芥种子的萌发率无显著影响,但高浓度Leukamenin E(80~160μmol·L-1)显著抑制种子的萌发速率。Leukamenin E对拟南芥幼苗根生长的抑制作用明显高于对下胚轴的抑制效应。进一步研究表明,Leukamenin E通过阻滞根尖细胞有丝分裂和细胞伸长进而抑制主根的生长,并能促进侧根提前发生并影响其形成数量,同时减少根毛密度及降低根毛长度。Leukamenin E联合乙烯利(乙烯释放剂)处理可阻止乙烯利单独使用对拟南芥幼苗根毛生长的促进作用,与Ag+(乙烯竞争抑制剂)联合乙烯利的作用效果相一致,表明Leukamenin E可能通过干扰根细胞乙烯途径而抑制根毛发育。流动注射化学发光分析和酶联免疫检测的结果发现,Leukamenin E显著上调拟南芥幼苗根组织中生长素(IAA)水平,表明生长素可能作为主要因子介导了Leukamenin E对拟南芥幼苗根生长发育的调节作用。     

病原菌Pst DC3000侵染拟南芥导致自噬和光合作用的抑制

在病原菌侵染下,植物体是如何通过超敏反应限制病原菌扩增的,到目前为止还不清楚。最近的研究显示自噬起了必要的作用,可见,研究自噬和超敏反应的机制非常重要。本研究通过观察在非寄主病原菌突变体丁香假单胞菌番茄致病变种(Pseudomonas syringae pv.tomatoDC3000,Pst DC3000)的侵染下,拟南芥光合功能的变化及自噬现象出现的情况,以为进一步研究植物抗病机理提供实验基础。以野生型拟南芥为材料,采用光谱分析和叶绿素荧光成像分析手段,研究不同浓度的Pst DC3000侵染对拟南芥离体叶片光合功能的影响;以转基因野生型拟南芥(绿色荧光蛋白标记的自噬基因8a)幼根为材料,应用共聚焦显微镜,研究不同浓度的Pst DC3000诱导拟南芥自噬的情况。实验发现,OD600=0.2的Pst DC3000侵染,可显著诱导拟南芥叶片活性氧的积累和迸发,并会引起拟南芥叶片光合作用效率的下降。同时发现,该病原菌处理2 h,可导致拟南芥根中自噬小体的产生。用2',7'-二氯二氢荧光素二乙酯(2',7'-dichlorodihydrofluorescein diacetate,H2DCFDA)标记活性氧,检测了P...     

磷脂酶Dα1与H2S参与冬凌草甲素对拟南芥的化感作用

以拟南芥哥伦比亚野生型(WT)、磷脂酶Dα1(PLDα1)缺失型突变体pldα1、D-/L-半胱氨酸脱巯基酶(D-/L-CDes)缺失型突变体d-cdes和l-cdes幼苗为试验材料,60 μmol·L^-1冬凌草甲素为处理浓度,研究了拟南芥响应二萜类化合物冬凌草甲素的化感作用中磷脂酶Dα1(PLDα1)与气体信号分子硫化氢(H₂S)的信号关系。结果表明: 冬凌草甲素显著提高了野生型拟南芥幼苗H₂S含量、PLD和D-/L-CDes酶的活性及其基因表达;冬凌草甲素处理下,pldα1突变体幼苗的D-CDes和L-CDes活性明显低于WT,外源添加磷脂酸(PA)后D-CDes和L-CDes活性显著提高,并高于WT;冬凌草甲素显著抑制4种株系根的生长,其中d-cdes和l-cdes对冬凌草甲素更加敏感,外施NaHS可以促进冬凌草甲素处理下4种株系根的生长及内源H₂S产生,外施PA只对冬凌草甲素处理下的WT、pldα1和l-cdes株系根的生长及内源H₂S产生有促进作用,而对d-cdes株系没有明显作用。说明PLDα1和H₂S在拟南芥响应冬凌草甲素过程中发挥作用,且PLDα1/PA位于D-CDes上游,参与调控拟南芥幼苗H₂S的产生及根生长的信号过程。     

Differential volatile emissions and salicylic acid levels from tobacco plants in response to different strains of<Emphasis Type="Italic"> Pseudomonas syringae</Emphasis>

Pathogen-induced plant responses include changes in both volatile and non-volatile secondary metabolites. To characterize the role of bacterial pathogenesis in plant volatile emissions, tobacco plants, Nicotiana tabacum L. K326, were inoculated with virulent, avirulent, and mutant strains of Pseudomonas syringae. Volatile compounds released by pathogen-inoculated tobacco plants were collected, identified, and quantified. Tobacco plants infected with the avirulent strains P. syringae pv. maculicola ES4326 (Psm ES4326) or pv. tomato DC3000 (Pst DC3000), emitted quantitatively different, but qualitatively similar volatile blends of (E)-beta-ocimene, linalool, methyl salicylate (MeSA), indole, caryophyllene, beta-elemene, alpha-farnesene, and two unidentified sesquiterpenes. Plants treated with the hrcC mutant of Pst DC3000 (hrcC, deficient in the type-III secretion system) released low levels of many of the same volatile compounds as in Psm ES4326- or Pst DC3000-infected plants, with the exception of MeSA, which occurred only in trace amounts. Interaction of the virulent pathogen P. syringae pv. tabaci (Pstb), with tobacco plants resulted in a different volatile blend, consisting of MeSA and two unidentified sesquiterpenes. Overall, maximum volatile emissions occurred within 36 h post-inoculation in all the treatments except for the Pstb infection that produced peak volatile emissions about 60 h post-inoculation. (E)-beta-Ocimene was released in a diurnal pattern with the greatest emissions during the day and reduced emissions at night. Both avirulent strains, Psm ES4326 and Pst DC3000, induced accumulation of free salicylic acid (SA) within 6 h after inoculation and conjugated SA within 60 h and 36 h respectively. In contrast, SA inductions by the virulent strain Pstb occurred much later and conjugated SA increased slowly for a longer period of time, while the hrcC mutant strain did not trigger free and conjugated SA accumulations in amounts significantly different from control plants. Jasmonic acid, known to induce plant volatile emissions, was not produced in significantly higher levels in inoculated plants compared to the control plants in any treatments, indicating that induced volatile emissions from tobacco plants in response to P. syringae are not linked to changes in jasmonic acid.     

Priming for enhanced defence responses by specific inhibition of the Arabidopsis response to coronatine

The priming agent β-aminobutyric acid (BABA) is known to enhance Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 by potentiating salicylic acid (SA) defence signalling, notably PR1 expression. The molecular mechanisms underlying this phenomenon remain unknown. A genome-wide microarray analysis of BABA priming during Pst DC3000 infection revealed direct and primed up-regulation of genes that are responsive to SA, the SA analogue benzothiadiazole and pathogens. In addition, BABA was found to inhibit the Arabidopsis response to the bacterial effector coronatine (COR). COR is known to promote bacterial virulence by inducing the jasmonic acid (JA) response to antagonize SA signalling activation. BABA specifically repressed the JA response induced by COR without affecting other plant JA responses. This repression was largely SA-independent, suggesting that it is not caused by negative cross-talk between SA and JA signalling cascades. Treatment with relatively high concentrations of purified COR counteracted BABA inhibition. Under these conditions, BABA failed to protect Arabidopsis against Pst DC3000. BABA did not induce priming and resistance in plants inoculated with a COR-deficient strain of Pst DC3000 or in the COR-insensitive mutant coi1-16. In addition, BABA blocked the COR-dependent re-opening of stomata during Pst DC3000 infection. Our data suggest that BABA primes for enhanced resistance to Pst DC3000 by interfering with the bacterial suppression of Arabidopsis SA-dependent defences. This study also suggests the existence of a signalling node that distinguishes COR from other JA responses.     

Virulence systems of Pseudomonas syringae pv. tomato promote bacterial speck disease in tomato by targeting the jasmonate signaling pathway

Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) causes bacterial speck disease on tomato. The pathogenicity of Pst DC3000 depends on both the type III secretion system that delivers virulence effector proteins into host cells and the phytotoxin coronatine (COR), which is thought to mimic the action of the plant hormone jasmonic acid (JA). We found that a JA-insensitive mutant (jai1) of tomato was unresponsive to COR and highly resistant to Pst DC3000, whereas host genotypes that are defective in JA biosynthesis were as susceptible to Pst DC3000 as wild-type (WT) plants. Treatment of WT plants with exogenous methyl-JA (MeJA) complemented the virulence defect of a bacterial mutant deficient in COR production, but not a mutant defective in the type III secretion system. Analysis of host gene expression using cDNA microarrays revealed that COR works through Jai1 to induce the massive expression of JA and wound response genes that have been implicated in defense against herbivores. Concomitant with the induction of JA and wound response genes, the type III secretion system and COR repressed the expression of pathogenesis-related (PR) genes in Pst DC3000-infected WT plants. Resistance of jai1 plants to Pst DC3000 was correlated with a high level of PR gene expression and reduced expression of JA/wound response genes. These results indicate that COR promotes bacterial virulence by activating the host's JA signaling pathway, and further suggest that the type III secretion system might also modify host defense by targeting the JA signaling pathway in susceptible tomato plants.     

Interplay between MAMP-triggered and SA-mediated defense responses

Plants respond to pathogen infection using an innate immune system with at least two distinct recognition mechanisms. One mechanism recognizes microbe-associated molecular patterns (MAMPs). The other is based on resistance (R) genes and specifically recognizes certain pathogen virulence factors, including those delivered through the type III secretion system (TTSS) of bacteria. Salicylic acid (SA)-mediated responses are an important part of the R gene-mediated defense. Substantial overlaps between MAMP-triggered and SA-mediated responses have been reported. However, interactions between MAMP-triggered and SA-mediated signaling mechanisms have not been well documented. Here we report intimate interactions between MAMP-triggered and SA-mediated signaling. We found that SA accumulated at a higher level 6 h after treatment with a MAMP, flg22 or inoculation with Pseudomonas syringae pv. tomato DC3000 ( Pst DC3000) hrcC mutant, which is deficient in TTSS function. Disruptions of SA signaling components, such as SID2 and PAD4 , strongly affected MAMP-triggered responses monitored by expression profiling. We found two groups of genes that were induced by Pst DC3000 hrcC in an SA-dependent manner. One group was SID2 -dependent at all time points, whereas the other was SID2 -independent at early time points and SID2 -dependent at later time points. Thus, the expression of the latter genes responds to MAMPs through both SA-independent and SA-dependent signaling mechanisms. Strong resistance to Pst DC3000 hrcC was dependent on SA signaling. These results indicate that the SA increase triggered by MAMPs is a major component of the MAMP-triggered signaling mechanism, explaining the overlapping spectra of MAMP-triggered and SA-mediated responses.     

Two homologous putative protein tyrosine phosphatases, OsPFA-DSP2 and AtPFA-DSP4, negatively regulate the pathogen response in transgenic plants

Protein phosphatases, together with protein kinases, regulate protein phosphorylation and dephosphorylation, and play critical roles in plant growth and biotic stress responses. However, little is known about the biological functions of plant protein tyrosine dual-specificity phosphatase (PFA-DSP) in biotic stresses. Here, we found that OsPFA-DSP2 was mainly expressed in calli, seedlings, roots, and young panicles, and localized in cytoplasm and nucleus. Ectopic overexpression of OsPFA-DSP2 in rice increased sensitivity to Magnaporthe grisea (M. grisea Z1 strain), inhibited the accumulation of hydrogen peroxide (H(2)O(2)) and suppressed the expression of pathogenesis-related (PR) genes after fungal infection. Interestingly, transgenic Arabidopsis plants overexpressing AtPFA-DSP4, which is homologous to OsPFA-DSP2, also exhibited sensitivity to Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), reduced accumulation of H(2)O(2) and decreased photosynthesic capacity after infection compared with Col-0. These results indicate that OsPFA-DSP2 and AtPFA-DSP4 act as negative regulators of the pathogen response in transgenic plants.     

The phytotoxin coronatine from Pseudomonas syringae pv. tomato DC3000 functions as a virulence factor and influences defence pathways in edible brassicas

The phytotoxin coronatine (COR) contributes to the virulence of Pseudomonas syringae pv. tomato ( Pst ) strain DC3000 on Arabidopsis thaliana and tomato. However, little is known regarding the role of COR in the virulence of DC3000 on cultivated Brassica spp. In this study, the role of COR and its precursors, coronafacic acid (CFA) and coronamic acid (CMA), were examined in the virulence of Pst DC3000 on collard and turnip, two important edible brassicas. Pst DC3000 and three well-defined COR⁻ biosynthetic mutants of DC3000 exhibited substantial differences in the timing and phenotype of disease lesions on collard and turnip. When examined 3 days post-inoculation (dpi), collard inoculated with DC3000 exhibited visible anthocyanin production and lesions were chlorotic and water-soaked. On turnip, chlorotic and necrotic lesions were evident on DC3000-inoculated leaves 5 dpi. The bacterial population dynamics on plants inoculated with DC3000 and the COR⁻ mutants indicated that COR was essential for DC3000 to maintain high populations in turnip, but not collard. Real-time quantitative PCR revealed that the jasmonic acid pathway responsive genes, LOX2 and CORI1 , were expressed in both hosts inoculated with Pst DC3000. PR1 , a marker associated with the salicylic acid pathway, was expressed in collard and turnip inoculated with the CFA⁻ CMA⁻ mutant DB29, but not DC3000. Further comparison of PR1 and LOX2 expression indicated that CFA plays a subtle role in modulating defence in turnip. This is the first study to investigate the role of COR in the interaction of Pst DC3000 and cultivated brassicas using genetically and biochemically defined COR⁻ mutants.     

褪黑素调节烟草丁香假单胞菌抗性的功能研究

为分析褪黑素(N-乙酰-5-甲氧基色胺)在植物先天免疫中的功能及调控机理,研究以病原菌丁香假单胞杆菌(Pseudomonas syringae pv.tomato DC3000,Pst DC3000)—烟草互作系统为模型,检测了病原菌侵染对烟草褪黑素相关基因表达的影响,并探讨了褪黑素对植物叶片病原菌生长以及气孔开度和活性氧自由基(reactive oxygen species,ROS)含量的影响以及调控机理。结果表明:(1)Pst DC3000处理提高了烟草褪黑素合成(NtSNAT1)和受体(NtPMTR1)基因表达,且外源褪黑素处理降低了叶片中的病原菌含量。(2)与野生型植物相比,过表达大豆GmSNAT1基因显著提高了转基因烟草中内源褪黑素含量和NtPMTR1的表达,且转基因烟草叶片中的Pst DC3000菌落数显著下降。(3)外源褪黑素和细菌鞭毛蛋白多肽flg22处理诱导了野生型和转基因烟草保卫细胞中ROS产生和气孔关闭,且转基因植物对褪黑素和flg22诱导的气孔关闭和ROS产生比野生型烟草更加敏感。综上所述,研究表明褪黑素可能通过受体NtPMTR1介导的信号途径促进保卫细胞ROS产生,诱导气孔关闭,从而降低病原菌Pst DC3000的入侵。     

Tomato SlSAP3, a member of the stress-associated protein family,is a positive regulator of immunity against Pseudomonas syringae pv. tomato DC3000

Tomato stress-associated proteins (SAPs) belong to A20/AN1 zinc finger protein family, some of which have been shown to play important roles in plant stress responses. However, little is known about the functions and underlying molecular mechanisms of SAPs in plant immune responses. In the present study, we reported the function of tomato SlSAP3 in immunity to Pseudomonas syringae pv. tomato (Pst) DC3000. Silencing of SlSAP3 attenuated while overexpression of SlSAP3 in transgenic tomato increased immunity to Pst DC3000, accompanied with reduced and increased Pst DC3000-induced expression of SA signalling and defence genes, respectively. Flg22-induced reactive oxygen species (ROS) burst and expression of PAMP-triggered immunity (PTI) marker genes SlPTI5 and SlLRR22 were strengthened in SlSAP3-OE plants but were weakened in SlSAP3-silenced plants. SlSAP3 interacted with two SlBOBs and the A20 domain in SlSAP3 is critical for the SlSAP3-SlBOB1 interaction. Silencing of SlBOB1 and co-silencing of all three SlBOB genes conferred increased resistance to Pst DC3000, accompanied with increased Pst DC3000-induced expression of SA signalling and defence genes. These data demonstrate that SlSAP3 acts as a positive regulator of immunity against Pst DC3000 in tomato through the SA signalling and that SlSAP3 may exert its function in immunity by interacting with other proteins such as SlBOBs, which act as negative regulators of immunity against Pst DC3000 in tomato.     

Salicylic acid-mediated innate immunity in Arabidopsis is regulated by SIZ1 SUMO E3 ligase

Reversible modifications of target proteins by small ubiquitin-like modifier (SUMO) proteins are involved in many cellular processes in yeast and animals. Yet little is known about the function of sumoylation in plants. Here, we show that the SIZ1 gene, which encodes an Arabidopsis SUMO E3 ligase, regulates innate immunity. Mutant siz1 plants exhibit constitutive systemic-acquired resistance (SAR) characterized by elevated accumulation of salicylic acid (SA), increased expression of pathogenesis-related (PR) genes, and increased resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000. Transfer of the NahG gene to siz1 plants results in reversal of these phenotypes back to wild-type. Analyses of the double mutants, npr1 siz1, pad4 siz1 and ndr1 siz1 revealed that SIZ1 controls SA signalling. SIZ1 interacts epistatically with PAD4 to regulate PR expression and disease resistance. Consistent with these observations, siz1 plants exhibited enhanced resistance to Pst DC3000 expressing avrRps4, a bacterial avirulence determinant that responds to the EDS1/PAD4-dependent TIR-NBS-type R gene. In contrast, siz1 plants were not resistant to Pst DC3000 expressing avrRpm1, a bacterial avirulence determinant that responds to the NDR1-dependent CC-NBS-type R gene. Jasmonic acid (JA)-induced PDF1.2 expression and susceptibility to Botrytis cinerea were unaltered in siz1 plants. Taken together, these results demonstrate that SIZ1 is required for SA and PAD4-mediated R gene signalling, which in turn confers innate immunity in Arabidopsis.