Heat Shock Transcription Factor HsfA2 Research Articles

Novel Pathway of Heat Shock- Induced Resistance in Tomato

High-temperature treatment induces disease resistance in various plants (heat shock-induced resistance; HSIR). The role of heat shock transcriptional factors (Hsfs) was investigated in this paper. Heat shock treatment induced disease resistance and up-regulate gene expression of pathogenesis related protein; PR1a2 at 12 and 24 h after treatment. PR1a2 has putative Hsfs binding site in the upstream area. On the other hand, a heat shock transcription factor HsfA2 up-regulated at 6 h after treatment, which was 6 h earlier than salicylic acid accumulation. This time lag suggested the direct contribution of Hsfs, additionally to salicylic acid pathway in the regulation of HSIR in tomato.

二氧化硫增强拟南芥植株对干旱的适应性

PDF HTML阅读 XML下载 导出引用 引用提醒 二氧化硫增强拟南芥植株对干旱的适应性 DOI: 10.5846/stxb201701110090 作者: 作者单位: 山西大学,山西大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（30870454，30470318，31371868）；高等学校博士学科点专项科研基金项目（20070108007，20121401110007） Sulfur dioxide improves drought adaptation in Arabidopsis plants Author: Affiliation: Shanxi University,Shanxi University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以模式植物拟南芥为材料，研究SO2对植物干旱适应性的影响。采用分光光度法检测植物干旱生理指标的变化，并用半定量RT-PCR技术分析了拟南芥热激基因和干旱响应基因的转录水平。研究发现：4周龄拟南芥植株暴露于30mg/m3的SO2后，6-72h间叶面气孔开度显著低于对照并逐渐减小，在暴露48h和72h时，热激转录因子HsfA2和热激基因Hsp17.7、Hsp17.6B、Hsp17.6C转录上调，干旱响应基因DREB2A、DREB2B和RD29A表达增强；在SO2熏气72h后进行干旱胁迫，干旱期间SO2预暴露植株的叶片相对含水量高于非熏气干旱处理组，植株萎蔫程度比后者明显减轻，且SO2预暴露植株的地上组织中可溶性糖和脯氨酸含量升高，超氧化物歧化酶活性提高，丙二醛含量降低。结果表明：SO2能降低气孔开度、提高抗氧化能力、上调热激基因和干旱响应基因转录，并能促进干旱期间植物细胞内渗透调节物质的合成和积累，促使抗氧化酶活性提高，从而降低干旱胁迫对植株造成的氧化损伤，增强拟南芥对干旱的适应性。植物通过基因转录应答、酶活性改变、渗透调节物质积累等，在适应环境高浓度SO2的同时，提高了对干旱的适应性。 Abstract:Plants have evolved some important mechanisms of adaptation to environmental stress. Plants might respond to multiple environmental factors simultaneously. The cross adaptation of plants provides mechanisms for plant survival under multiple stress conditions. Plant cross adaptation has been observed to occur under low/high temperature and drought stress as well as under saline and drought stress. Sulfur dioxide (SO2) is a common air pollutant with harmful effects on plants. However, it is not clear how plants respond to simultaneous changes in air SO2 concentration and availability of soil water. In this study, effects of SO2 exposure on the adaptation of plants to drought stress were investigated using Arabidopsis. The results showed that exposure to 30mg/m3 SO2 for 6 to 72 h significantly decreased stomatal aperture in Arabidopsis leaves. The transcriptional levels of heat shock transcription factor HsfA2 and its target genes encoding heat shock proteins Hsp17.7, Hsp17.6B and Hsp17.6C were increased after 48h and 72h of exposure to SO2. The expression of three tested drought-responsive genes DREB2A, DREB2B and RD29A in Arabidopsis were also up-regulated in SO2-fumigated Arabidopsis shoots after 48h and 72h of exposure. Moreover, pretreatment with SO2 caused higher relative water content and low degrees of wilting in Arabidopsis plants under drought stress, indicating improved drought adaptation in SO2-fumigated plants. The contents of soluble sugar and proline were increased in SO2-fumigated Arabidopsis plants, and these increases were accompanied by increases in antioxidant enzyme activity and low malondialdehyde content. The results indicate that SO2 exposure improves plant adaptation to drought stress through regulating stomatal closure, gene transcription and metabolic pathways. The improved antioxidant capacity and increased synthesis and accumulation of osmolytes in SO2-fumigated Arabidopsis plants help to prevent negative effects of drought stress and to enhance plant adaptation to drought stress. 参考文献 相似文献 引证文献

Interference with plastome gene expression and Clp protease activity in Arabidopsis triggers a chloroplast unfolded protein response to restore protein homeostasis.

Disruption of protein homeostasis in chloroplasts impairs the correct functioning of essential metabolic pathways, including the methylerythritol 4-phosphate (MEP) pathway for the production of plastidial isoprenoids involved in photosynthesis and growth. We previously found that misfolded and aggregated forms of the first enzyme of the MEP pathway are degraded by the Clp protease with the involvement of Hsp70 and Hsp100/ClpC1 chaperones in Arabidopsis thaliana. By contrast, the combined unfolding and disaggregating actions of Hsp70 and Hsp100/ClpB3 chaperones allow solubilization and hence reactivation of the enzyme. The repair pathway is promoted when the levels of ClpB3 proteins increase upon reduction of Clp protease activity in mutants or wild-type plants treated with the chloroplast protein synthesis inhibitor lincomycin (LIN). Here we show that LIN treatment rapidly increases the levels of aggregated proteins in the chloroplast, unleashing a specific retrograde signaling pathway that up-regulates expression of ClpB3 and other nuclear genes encoding plastidial chaperones. As a consequence, folding capacity is increased to restore protein homeostasis. This sort of chloroplast unfolded protein response (cpUPR) mechanism appears to be mediated by the heat shock transcription factor HsfA2. Expression of HsfA2 and cpUPR-related target genes is independent of GUN1, a central integrator of retrograde signaling pathways. However, double mutants defective in both GUN1 and plastome gene expression (or Clp protease activity) are seedling lethal, confirming that the GUN1 protein is essential for protein homeostasis in chloroplasts.

RRM domain of Arabidopsis splicing factor SF1 is important for pre-mRNA splicing of a specific set of genes.

The RNA recognition motif of Arabidopsis splicing factor SF1 affects the alternative splicing of FLOWERING LOCUS M pre-mRNA and a heat shock transcription factor HsfA2 pre-mRNA. Splicing factor 1 (SF1) plays a crucial role in 3' splice site recognition by binding directly to the intron branch point. Although plant SF1 proteins possess an RNA recognition motif (RRM) domain that is absent in its fungal and metazoan counterparts, the role of the RRM domain in SF1 function has not been characterized. Here, we show that the RRM domain differentially affects the full function of the Arabidopsis thaliana AtSF1 protein under different experimental conditions. For example, the deletion of RRM domain influences AtSF1-mediated control of flowering time, but not the abscisic acid sensitivity response during seed germination. The alternative splicing of FLOWERING LOCUS M (FLM) pre-mRNA is involved in flowering time control. We found that the RRM domain of AtSF1 protein alters the production of alternatively spliced FLM-β transcripts. We also found that the RRM domain affects the alternative splicing of a heat shock transcription factor HsfA2 pre-mRNA, thereby mediating the heat stress response. Taken together, our results suggest the importance of RRM domain for AtSF1-mediated alternative splicing of a subset of genes involved in the regulation of flowering and adaptation to heat stress.

The six Tomato yellow leaf curl virus genes expressed individually in tomato induce different levels of plant stress response attenuation.

Tomato yellow leaf curl virus (TYLCV) is a begomovirus infecting tomato plants worldwide. TYLCV needs a healthy host environment to ensure a successful infection cycle for long periods. Hence, TYLCV restrains its destructive effect and induces neither a hypersensitive response nor cell death in infected tomatoes. On the contrary, TYLCV counteracts cell death induced by other factors, such as inactivation of HSP90 functionality. Suppression of plant death is associated with the inhibition of the ubiquitin 26S proteasome degradation and with a deactivation of the heat shock transcription factor HSFA2 pathways (including decreased HSP17 levels). The goal of the current study was to find if the individual TYLCV genes were capable of suppressing HSP90-dependent death and HSFA2 deactivation. The expression of C2 (C3 and CP to a lesser extent) caused a decrease in the severity of death phenotypes, while the expression of V2 (C1 and C4 to a lesser extent) strengthened cell death. However, C2 or V2 markedly affected stress response under conditions of viral infection. The downregulation of HSFA2 signaling, initiated by the expression of C1 and V2, was detected in the absence of virus infection, but was enhanced in infected plants, while CP and C4 mitigated HSFA2 levels only in the infected tomatoes. The dependence of analyzed plant stress response suppression on the interaction of the expressed genes with the environment created by the whole virus infection was more pronounced than on the expression of individual TYLCV genes.

Identification of core subunits of photosystemII as action sites of HSP21, which is activated by the GUN5-mediated retrograde pathway in Arabidopsis.

PhotosystemII (PSII) is the most thermolabile photosynthetic complex. Physiological evidence suggests that the small chloroplast heat-shock protein21 (HSP21) is involved in plant thermotolerance, but the molecular mechanism of its action remains largely unknown. Here, we have provided genetic and biochemical evidence that HSP21 is activated by the GUN5-dependent retrograde signaling pathway, and stabilizes PSII by directly binding to its core subunits such as D1 and D2 proteins under heat stress. We further demonstrate that the constitutive expression of HSP21 sufficiently rescues the thermosensitive stability of PSII and survival defects of the gun5 mutant with dramatically improving granal stacking under heat stress, indicating that HSP21 is a key chaperone protein in maintaining the integrity of the thylakoid membrane system under heat stress. In line with our interpretation based on several lines of invitro and invivo protein-interaction evidence that HSP21 interacts with core subunits of PSII, the kinetics of HSP21 binding to the D1 and D2 proteins was determined by performing an analysis of microscale thermophoresis. Considering the major role of HSP21 in protecting the core subunits of PSII from thermal damage, its heat-responsive activation via the heat-shock transcription factor HsfA2 is critical for the survival of plants under heat stress. Our findings reveal an auto-adaptation loop pathway that plant cells optimize particular needs of chloroplasts in stabilizing photosynthetic complexes by relaying the GUN5-dependent plastid signal(s) to activate the heat-responsive expression of HSP21 in the nucleus during adaptation to heat stress in plants.

A homolog of splicing factor SF1 is essential for development and is involved in the alternative splicing of pre‐mRNA in Arabidopsis thaliana

During initial spliceosome assembly, SF1 binds to intron branch points and interacts with U2 snRNP auxiliary factor 65 (U2AF65). Here, we present evidence indicating that AtSF1, the Arabidopsis SF1 homolog, interacts with AtU2AF65a and AtU2AF65b, the Arabidopsis U2AF65 homologs. A mutant allele of AtSF1 (At5g51300) that contains a T-DNA insertion conferred pleiotropic developmental defects, including early flowering and abnormal sensitivity to abscisic acid. An AtSF1 promoter-driven GUS reporter assay showed that AtSF1 promoter activity was temporally and spatially altered, and that full AtSF1 promoter activity required a significant proportion of the coding region. DNA chip analyses showed that only a small proportion of the transcriptome was altered by more than twofold in either direction in the AtSF1 mutant. Expression of the mRNAs of many heat shock proteins was more than fourfold higher in the mutant strain; these mRNAs were among those whose expression was increased most in the mutant strain. An RT-PCR assay revealed an altered alternative splicing pattern for heat shock transcription factor HsfA2 (At2g26150) in the mutant; this altered splicing is probably responsible for the increased expression of the target genes induced by HsfA2. Altered alternative splicing patterns were also detected for the transcripts of other genes in the mutant strain. These results suggest that AtSF1 has functional similarities to its yeast and metazoan counterparts.

Involvement of Arabidopsis ROF2 (FKBP65) in thermotolerance

The ROF2 (FKBP65) is a heat stress protein which belongs to the FK506 Binding Protein (FKBP) family. It is homologous to ROF1 (FKBP62) which was recently shown to be involved in long term acquired thermotolerance by its interaction with HSP90.1 and modulation of the heat shock transcription factor HsfA2. In this study, we have demonstrated that ROF2 participates in long term acquired thermolerance, its mode of action being different from ROF1. In the absence of ROF2, the small heat shock proteins were highly expressed and the plants were resistant to heat stress, opposite to the effect observed in the absence of ROF1. It was further demonstrated that ROF2 transcription is modulated by HsfA2 which is also essential for keeping high levels of ROF2 during recovery from heat stress. ROF2 localization to the nucleus was observed several hours after heat stress exposure and its translocation to the nucleus was independent from the presence of HSP90.1 or HsfA2. ROF2 has been shown to interact with ROF1, to form heterodimers and it is suggested that via this interaction it can join the complex ROF1-HSP90.1- HsfA2. Transient expression of ROF2 together with ROF1 repressed transcription of small HSPs. A model describing the mode of action of ROF2 as a heat stress modulator which functions in negative feedback regulation of HsfA2 is proposed.

A Heat-Inducible Transcription Factor, HsfA2, Is Required for Extension of Acquired Thermotolerance in Arabidopsis

The expression of heat shock proteins (Hsps) induced by nonlethal heat treatment confers acquired thermotolerance (AT) to organisms against subsequent challenges of otherwise lethal temperature. After the stress signal is removed, AT gradually decays, with decreased Hsps during recovery. AT of sufficient duration is critical for sessile organisms such as plants to survive repeated heat stress in their environment, but little is known regarding its regulation. To identify potential regulatory components, we took a reverse genetics approach by screening for Arabidopsis (Arabidopsis thaliana) T-DNA insertion mutants that show decreased thermotolerance after a long recovery (2 d) under nonstress conditions following an acclimation heat treatment. Among the tested mutants corresponding to 48 heat-induced genes, only the heat shock transcription factor HsfA2 knockout mutant showed an obvious phenotype. Following pretreatment at 37 degrees C, the mutant line was more sensitive to severe heat stress than the wild type after long but not short recovery periods, and this could be complemented by the introduction of a wild-type copy of the HsfA2 gene. Quantitative hypocotyl elongation assay also revealed that AT decayed faster in the absence of HsfA2. Significant reduction in the transcript levels of several highly heat-inducible genes was observed in HsfA2 knockout plants after 4 h recovery or 2 h prolonged heat stress. Immunoblot analysis showed that Hsa32 and class I small Hsp were less abundant in the mutant than in the wild type after long recovery. Our results suggest that HsfA2 as a heat-inducible transactivator sustains the expression of Hsp genes and extends the duration of AT in Arabidopsis.