Histone Deacetylase Complex1 Expression Level Titrates Plant Growth and Abscisic Acid Sensitivity in Arabidopsis

Histone deacetylation regulates gene expression during plant stress responses and is therefore an interesting target for epigenetic manipulation of stress sensitivity in plants. Unfortunately, overexpression of the core enzymes (histone deacetylases [HDACs]) has either been ineffective or has caused pleiotropic morphological abnormalities. In yeast and mammals, HDACs operate within multiprotein complexes. Searching for putative components of plant HDAC complexes, we identified a gene with partial homology to a functionally uncharacterized member of the yeast complex, which we called Histone Deacetylation Complex1 (HDC1). HDC1 is encoded by a single-copy gene in the genomes of model plants and crops and therefore presents an attractive target for biotechnology. Here, we present a functional characterization of HDC1 in Arabidopsis thaliana. We show that HDC1 is a ubiquitously expressed nuclear protein that interacts with at least two deacetylases (HDA6 and HDA19), promotes histone deacetylation, and attenuates derepression of genes under water stress. The fast-growing HDC1-overexpressing plants outperformed wild-type plants not only on well-watered soil but also when water supply was reduced. Our findings identify HDC1 as a rate-limiting component of the histone deacetylation machinery and as an attractive tool for increasing germination rate and biomass production of plants.     

Abscisic Acid Suppresses the Highly Occurred Somatic Homologous Recombination in Arabidopsis rfc1 Mutant

The phytohormone abscisic acid (ABA) regulates many aspects of plant growth, including seed germination, root growth and cell division. Previous study indicates that ABA treatment increases DNA damage and somatic homologous recombination (HR) in Arabidopsis abo4/pol ? (aba overly-sensitive 4 /DNA polymerase ?) mutants. DNA replication factor C (RFC) complex is required for loading PCNA (Proliferating Cell Nuclear Antigen) during DNA replication. The defect in RFC1, the largest subunit of RFC, causes the high HR and DNA damage sensitivity in Arabidopsis. Here we found that like pol ε/abo4, rfc1 is sensitive to ABA in both ABA-inhibiting seed germination and root growth. However, ABA treatment greatly reduces HR and also reduces the expression of the DNA-damaged marker genes in rfc1. These results suggest that RFC1 plays critical roles in ABA-mediated HR in Arabidopsis.     

Gas Exchange, Stomatal Behavior, and deltaC Values of the flacca Tomato Mutant in Relation to Abscisic Acid

The relationship between stomatal conductance and capacity for assimilation was investigated in flacca, a mutant of tomato (Lycopersicon esculentum Mill.) that has abnormal stomatal behavior and low abscisic acid (ABA) content. The assimilation capacity, determined by measuring assimilation rate as a function of intercellular CO₂ pressure, did not differ in leaves of flacca and its parent variety, Rheinlands Ruhm (RR). On the other hand, stomatal conductance of flacca leaves was greater than that of RR, and could be phenotypically reverted by spraying with 30 micromolar ABA. Stomatal conductance of flacca leaves was also reduced by increasing CO₂ pressure, increasing leaf to air vapor pressure difference, and decreasing quantum flux, irrespective of ABA treatment.

The high conductance of flacca leaves resulted in a high intercellular CO₂ pressure. This allowed greater discrimination against ¹³CO₂, as evidenced by more negative δ ¹³C values for flacca as compared to RR. The δ ¹³C values of both flacca and RR plants as influenced by ABA treatment were consistent with predictions based on gas exchange measurements, using a recent model of discrimination.

     

Growth, Gas Exchange, Abscisic Acid, and Calmodulin Response to Salt Stress in Three Poplars

In the present study, we Investigated the effects of Increaslng sallnlty on growth, gas exchange, absclslc acld （ABA）, calmodulln （CAM）, and the relevance to salt tolerance In seedllngs of Populus euphratlca Ollv. and cutUngs of P. ＂pupularls 35-44＂ （P. popularls） and P. x euramerlcana cv. 1-214 （P. cv. Itallca）. The relatlve growth rates of shoot helght （RGR,） for P. cv. Itallca and P. popularls were severely reduced by Increaslng salt stress, whereas the growth reductlon was relatlvely less in P. euphratica. Slmllarly, P. euphratlca malntalned hlgher net photosynthetlc rates （Pn） and unlt transplration rotes （TRN） than P. cv. Itallca and P. popularls under condltlons of hlgher sallnlty. Sallnity caused a slgnlficant increase In leaf ABA and CaM In the three genotypes after the onset of stress, but NaCl-induced ABA and CaM accumulatlon was more pronounced In P. euphratlca, suggeeUng that P. euphratlca plants are more sensitlve in sensing soil salinlty than the other two poplars. Furthermore, P. euphratica maintained relatively higher ABA and CaM concentrations under conditions of high salinity. The higher capacity to synthesize stress signals, namely ABA and CaM, In P. euphratica and the contrlbuUon of this to the salt resistance of P. euphratica are discussed.     

Interaction of Osmotic Stress, Temperature, and Abscisic Acid in the Regulation of Gene Expression in Arabidopsis

The impact of simultaneous environmental stresses on plants and how they respond to combined stresses compared with single stresses is largely unclear. By using a transgene (RD29A-LUC) consisting of the firefly luciferase coding sequence (LUC) driven by the stress-responsive RD29A promoter, we investigated the interactive effects of temperature, osmotic stress, and the phytohormone abscisic acid (ABA) in the regulation of gene expression in Arabidopsis seedlings. Results indicated that both positive and negative interactions exist among the studied stress factors in regulating gene expression. At a normal growth temperature (22°C), osmotic stress and ABA act synergistically to induce the transgene expression. Low temperature inhibits the response to osmotic stress or to combined treatment of osmotic stress and ABA, whereas low temperature and ABA treatments are additive in inducing transgene expression. Although high temperature alone does not activate the transgene, it significantly amplifies the effects of ABA and osmotic stress. The effect of multiple stresses in the regulation of RD29A-LUC expression in signal transduction mutants was also studied. The results are discussed in the context of cold and osmotic stress signal transduction pathways.     

Bacterial Quorum-Sensing Signaling-Related drr1 Mutant Influences Abscisic Acid Responsiveness in Arabidopsis thaliana L.

Journal of Plant Growth Regulation - N-acyl-L-homoserine lactones (AHLs) are involved in cell-to-cell communication in Gram-negative bacteria through a process termed quorum-sensing (QS). In this...     

脱落酸与Em基因的表达调控

Em基因的表达受ABA诱导,干旱和盐胁通过增加ABA含量或改变植物细胞对ABA的敏感性而诱导Em基因的表达。植物Em基因启动子存在3个功能区:5′远端AT富集区通过影响转录调节表达量,作用类似于非专一性增强子;ABA应答元件ABRE在ABA存在的情况下与转录因子EmBP1相互作用能显著增强Em基因的表达;5′UTR可能通过转录后调控而影响最终表达水平 。     

Alterations in Water Status,Endogenous Abscisic Acid Content,and Expression of rab18 Gene during the Development of Freezing Tolerance in Arabidopsis thaliana

Treatments as diverse as exposure to low temperature (LT), exogenous abscisic acid (ABA), or drought resulted in a 4 to 5[deg]C increase in freezing tolerance of the annual herbaceous plant Arabidopsis thaliana. To correlate the increase in freezing tolerance with the physiological changes that occur in response to these treatments, we studied the alterations in water status, endogenous ABA levels, and accumulation of rab18 (V. Lang and E.T. Palva [1992] Plant Mol Biol 20: 951-962) mRNA. Exposure to LT and exogenous ABA caused only a minor decline in total water potential ([psi]w), in contrast to a dramatic decrease in [psi]w during drought stress. Similarly, the endogenous ABA levels were only slightly and transiently increased in LT-treated plants in contrast to a massive increase in ABA levels in drought-stressed plants. The expression of the ABA-responsive rab18 gene was low during the LT treatment but could be induced to high levels by exogenous ABA and drought stress. Taken together, these results suggest that the moderate increases in freezing tolerance of A. thaliana might be achieved by different mechanisms. However, ABA-deficient and ABA-insensitive mutants of A. thaliana have impaired freezing tolerance, suggesting that ABA is, at least indirectly, required for the development of full freezing tolerance.     

Studies of the Inhibition of Stomatal Opening by Naphth-1-ylacetic Acid and Abscisic Acid

Evidence is presented which confirms the inhibitory action ofthe synthetic auxin, NAA, on stomatal opening. In contrast tothe natural auxin IAA, NAA exerts effects which, in some respects,resemble those of ABA. The mode of action of NAA on the guardcells is, however, thought to be different from that of ABA.When NAA and ABA are applied together, their combined actionresults in a greater reduction in stomatal aperture than wouldbe predicted from their separate effects. Key words: NAA, ABA, IAA Stomata, Commelina     

拟南芥abi5基因的分子克隆及其在原核细胞中的表达和纯化

拟南芥abi5基因编码了一个碱性亮氨酸拉链类转录因子,它在ABA信号转导过程中发挥着关键调控作用。本文以拟南芥为材料,通过RT-PCR扩增、克隆了包含abi5基因编码区的片段。核苷酸序列分析表明,所克隆的基因与NCBI数据库收录的abi5基因（GenBank登录号NM129185.3）有99.0%的一致性;氨基酸序列存在4个残基差异。所克隆的abi5基因被进一步亚克隆至pET-32a表达载体。序列测定核实构建正确的重组质粒（pET32a-ABI5）转化入大肠杆菌BL21 Star（DE3）中诱导表达。表达产物经Ni-NTA亲和层析柱分离纯化、SDS-PAGE分析和质谱鉴定。结果表明,重组abi5基因在大肠杆菌表达的较适宜条件为：异丙基-β-D-硫代半乳糖苷（IPTG）终浓度为0.3 mmol L-1、30℃下诱导4 h,可达到细菌裂解液上清蛋白的29.1%。经Ni-NTA亲和层析柱纯化后的ABI5融合蛋白在SDS-PAGE电泳分析时呈现一条蛋白带。该条带经串联质谱分析证明为重组ABI5融合蛋白。     

Water Relations and Growth of the flacca Tomato Mutant in Relation to Abscisic Acid

The flacca mutant in tomato (Lycopersicon esculentum Mill. cv Rheinlands Ruhm) was employed to examine the effects of a relatively constant diurnal water stress on leaf growth and water relations. As the mutant is deficient in abscisic acid (ABA) and can be phenotypically reverted to the wild type by applications of the growth substance, inferences can be made concerning the involvement of ABA in responses to water stress. Water potential and turgor were lower in leaves of flacca than of Rheinlands Ruhm, and were increased by ABA treatment. ABA decreased transpiration rates by causing stomatal closure and also increased the hydraulic conductance of the sprayed plants. Osmotic adjustment did not occur in flacca plants despite the daily leaf water deficits. Stem elongation was inhibited by ABA, but leaf growth was promoted. It is concluded that, in some cases, ABA may promote leaf growth via its effect on leaf water balance.     

Water Relations of Cotton Plants under Nitrogen Deficiency: V. Environmental Control of Abscisic Acid Accumulation and Stomatal Sensitivity to Abscisic Acid

Suboptimal N nutrition increased the water potential for stomatal closure in water stressed cotton (Gossypium hirsutum L.) leaves. This increased sensitivity to water stress had two components, increased accumulation of abscisic acid (ABA) and increased apparent stomatal sensitivity to ABA. Low N increased the threshold water potentials for stomatal closure and ABA accumulation by about 4 bars and 2 bars, respectively. Low N also greatly increased stomatal response to low concentrations of exogenous ABA applied to excised leaves through the transpiration stream. In low N leaves, kinetin decreased stomatal response to ABA to the level observed with high N leaves. Kinetin by itself had little effect on stomata, nor did it alter stomatal response to ABA in high N leaves. The results suggest a cytokinin-ABA balance which is altered by suboptimal N nutrition to favor stomatal closure during stress.

Ambient temperature and N nutrition interacted to alter stomatal response to water stress. Stress-induced ABA accumulation and apparent stomatal sensitivity to ABA were independently affected. The effects of each treatment, and their interaction, could be explained as the net result of changes in both accumulation and apparent sensitivity. Although the results document environmental control of stomatal response to ABA, either altered partitioning of ABA between active and inactive pools, or altered sensitivity of the guard cells, could account for the data.

     

Modulation of Root Signals in Relation to Stomatal Sensitivity to Root-sourced Abscisic Acid in Drought-affected Plants

Stomatal sensitivity to root signals induced by soil drying may vary between environments and plant species. This is likely to be a result of the interactions and modulations ámong root signals. As a stress signal, abscisic acid （ABA） plays a central role in root to shoot signaling, pH and hydraulic signals may interact with ABA signals and thus, jointly regulate stomatal responses to changed soil water status, pH itself can be modified by several factors, among which the chemical compositions in the xylem stream and the live cells surrounding the vessels play crucial roles. In addition to the xylem pH, more attention should be paid to the direct modulation of leaf apoplastic pH, because many chemical compositions might strongly modify the leaf apoplastic pH while having no significant effect on the xylem pH. The direct modulation of the ABA signal intensity may be more important for the regulation of stomatal responses to soil drying than the ABA signal per se. The ABA signal is also regulated by the ABA catabolism and the supply of precursors to the roots if a sustained root to shoot communication of soil drying operates at the whole plant level. More importantly, ABA catabolism could play crucial roles in the determination of the fate of the ABA signal and thereby control the stomatal behavior of the root-sourced ABA signal.     

Modulation of Root Signals in Relation to Stomatal Sensitivity to Root-sourced Abscisic Acid in Drought-affected Plants

Stomatal sensitivity to root signals induced by soil drying may vary between environments and plant species. This is likely central role in root to shoot signaling. pH and hydraulic signals may interact with ABA signals and thus, jointly regulate stomatal responses to changed soil water status. pH itself can be modified by several factors, among which the chemical compositions In the xylem stream and the live cells surrounding the vessels play crucial roles. In addition to the xylem pH,more attention should be paid to the direct modulation of leaf apoplastic pH, because many chemical compositions might strongly modify the leaf apoplastlc pH while having no significant effect on the xylem pH. The direct modulation of the ABA signal intensity may be more important for the regulation of stomatal responses to soil drying than the ABA signal per se.The ABA signal is also regulated by the ABA catabolism and the supply of precursors to the roots If a sustained root to shoot communication of soil drying operates at the whole plant level. More importantly, ABA catabolism could play crucial roles In the determination of the fate of the ABA signal and thereby control the stomatal behavior of the root-sourced ABA signal.     

Mutations in Arabidopsis Fatty Acid Amide Hydrolase Reveal That Catalytic Activity Influences Growth but Not Sensitivity to Abscisic Acid or Pathogens

Fatty acid amide hydrolase (FAAH) terminates the endocannabinoid signaling pathway that regulates numerous neurobehavioral processes in animals by hydrolyzing N-acylethanolamines (NAEs). Recently, an Arabidopsis FAAH homologue (AtFAAH) was identified, and several studies, especially those using AtFAAH overexpressing and knock-out lines, have suggested an in vivo role for FAAH in the catabolism of NAEs in plants. We previously reported that overexpression of AtFAAH in Arabidopsis resulted in accelerated seedling growth, and in seedlings that were insensitive to exogenous NAEs but hypersensitive to abscisic acid (ABA) and hypersusceptible to nonhost pathogens. Here we show that whereas the enhanced growth and NAE tolerance of the AtFAAH overexpressing seedlings depend on the catalytic activity of AtFAAH, hypersensitivity to ABA and hypersusceptibility to nonhost pathogens are independent of its enzymatic activity. Five amino acids known to be critical for rat FAAH activity are also conserved in AtFAAH (Lys-205, Ser-281, Ser-282, Ser-305, and Arg-307). Site-directed mutation of each of these conserved residues in AtFAAH abolished its hydrolytic activity when expressed in Escherichia coli, supporting a common catalytic mechanism in animal and plant FAAH enzymes. Overexpression of these inactive AtFAAH mutants in Arabidopsis showed no growth enhancement and no NAE tolerance, but still rendered the seedlings hypersensitive to ABA and hypersusceptible to nonhost pathogens to a degree similar to the overexpression of the native AtFAAH. Taken together, our findings suggest that the AtFAAH influences plant growth and interacts with ABA signaling and plant defense through distinctly different mechanisms.