AtAPOSTART1, an Arabidopsis thaliana PH-START domain protein involved in seed germination

The seed in the mature and dry state is metabolically inactive (quiescent) and is thus able to withstand extreme environmental conditions, such as drought and cold. Germination commences when the dry seed, shed from its parent plant, takes up water (imbibition) and ends when the root emerges through the seed coat. During seedling establishment, the reserves stored in the seed are metabolized, whereas the subsequent vegetative and reproductive growth is supported by photosynthesis. Here, we describe the functional characterization of the PH-START protein AtAPO1 (Arabidopsis thaliana APOSTART1), the putative homologue of PpAPO1 (Poa pratensis APOSTART1) in Arabidopsis thaliana. By using translational fusion of the AtAPO1 promoter to the uiaD gene and in situ hybridization analyses, we show that AtAPO1 is expressed in mature embryo sacs and developing embryos. The functional analysis of two at-apostart mutant alleles suggests that AtAPO1 is involved in the control of seed germination.     

cDNA clones encoding Arabidopsis thaliana and Zea mays mitochondrial chaperonin HSP60 and gene expression during seed germination and heat shock

Mitochondria contain a nuclear-encoded heat shock protein, HSP60, which functions as a chaperonin in the post-translational assembly of multimeric proteins encoded by both nuclear and mitochondrial genes. We have isolated and sequenced full-length complementary DNAs coding for this mitochondrial chaperonin in Arabidopsis thaliana and Zea mays. Southern-blot analysis indicates the presence of a single hsp60 gene in the genome of A. thaliana. There is a high degree of homology at the predicted amino acid levels (43 to 60%) between plant HSP60s and their homologues in prokaryotes and other eukaryotes which indicates that these proteins must have similar evolutionarily conserved functions in all organisms. Northern- and western-blot analyses indicate that the expression of the hsp60 gene is developmentally regulated during seed germination. It is also heat-inducible. Developmental regulation of the (-subunit) of F₁-ATPase, an enzyme complex that is involved in the cyanide-sensitive mitochondrial electron transport system, indicates that imbibed embryos undergo rapid mitochondrial biogenesis through the early stages of germination. Based on the functional role of HSP60 in macromolecular assembly, these data collectively suggest that the presence of higher levels of HSP60 is necessary during active mitochondrial biogenesis, when the need for this protein is greatest in assisting the rapid assembly of the oligomeric protein structures.     

Arabidopsis thaliana seed germination and early seedling growth are inhibited by monoethanolamine salts of para-halogenated benzoic acids

Abstract

In spite of the simplicity of its molecules, the complex effects of benzoic acids on the regulation of plant growth are an increasingly attractive field of research to chemists and biologists. Halide substituted benzoic acids offer an excellent opportunity to explore the effect of electron withdrawing substituents (fluoro-, chloro-, bromo- and iodo-) on the response of plant growth stage. Under normal physiological conditions, benzoic acids are ionized molecules that exhibit low solubility in water. Monoethanolamine, a natural alkanolamine, was used to generate salts of monoethanolamine of halogenated para-substituted benzoic acids, new compounds with biological activity. This study reports on the biological effects of these substances at different concentrations on Arabidopsis thaliana seed germination and early seedling growth. Seed germination at 22°C, in a vertical position, under a photoperiod of 16 h light and 8 h darkness, was variable depending on the concentration of the compounds applied. Final germination percentages were similar for all treatments and control at 0.05 mM and 0.1 mM (exception p-Br BA and p-I MEASPBA). No germination occurred when seeds were treated with more than 0.5 mM. The results also revealed that the primary root length and the number of secondary roots are reduced in a concentration-dependent manner and also in relation to increasing atomic size of the substituents (F < Cl < Br < I). It is concluded that uptake rates of benzoic acid anions by roots decrease with a decrease in hydrophilic character of the anion and with an increase in molecular size.     

Comprehensive expression profiling of the pectin methylesterase gene family during silique development in Arabidopsis thaliana

Pectin methylesterases (PME, EC. 3.1.1.11) are enzymes that demethylesterify plant cell wall pectins in muro. In Arabidopsis thaliana, putative PME proteins are thought to be encoded by a 66-member gene family. This study used real-time RT-PCR to gain an overview of the expression of the entire family at eight silique developmental stages, in flower buds and in vegetative tissue in the Arabidopsis. Only 15% of the PMEs were not expressed at any of the developmental stages studied. Among expressed PMEs, expression data could be clustered into five distinct groups: 19 PMEs highly or uniquely expressed in floral buds, 4 PMEs uniquely expressed at mid-silique developmental stages, 16 PMEs highly or uniquely expressed in silique at late developmental stages, 16 PMEs mostly ubiquitously expressed, and 1 PME with a specific expression pattern, i.e. not expressed during early silique development. Comparison of expression and phylogenetic profiles showed that, within phylogenetic group 2, all but one PME belong to the floral bud expression group. Similar results were shown for a subset of one of the phylogenetic group, which differed from others by containing most of the PMEs that do not possess any PRO part next to their catalytic part. Expression data were confirmed by two promoter:GUS transgenic plant analysis revealing a PME expressed in pollen and one in young seeds. Our results highlight the high diversity of PME expression profiles. They are discussed with regard to the role of PMEs in fruit development and cell growth.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Sulfurtransferases 1 and 2 play essential roles in embryo and seed development in Arabidopsis thaliana

Sulfurtransferases (STRs) catalyze the transfer of a sulfur atom from a donor to a suitable acceptor molecule. The Arabidopsis thaliana genome encodes 20 putative STR proteins. The biological functions of most are unclear. We found that STR1 and STR2 play important roles in embryo/seed development. Mutation of STR1 alone resulted in a shrunken seed phenotype, although growth and development of vegetative and reproductive organs were not affected. The shrunken seed phenotype was associated with the delayed/arrested embryo development, in most cases, at the heart stage. The embryo defect of str1 mutant is not fully penetrant. Approximately 12.5% of embryos developed further and formed normal looking seeds. In severely shrunken seeds, no embryo could be identified after seed collection. Partially shrunken seeds that contained viable embryos could still germinate. However, cotyledons of the seedlings from such seeds were abnormal. An STR1-GUS fusion reporter revealed that the STR1 gene was universally expressed, with high levels of expression in specific tissues/organs including embryos. The incomplete penetrance of str1 embryo/seed phenotype is a result of functional STR2. Single str2 mutant had no phenotype. However, no str1(-/-)/str2(-/-) double mutant embryos were able to develop past the heart stage. Furthermore, STR2 is haplo-insufficient in str1 mutant background, and str1(-/-)/str2(+/-) embryos were 100% lethal. These data provide new insights into the biological functions of the ubiquitous sulfurtransferase in Arabidopsis embryogenesis and seed development.     

Structure and regulation of the Arabidopsis thaliana allene oxide synthase gene

Allene oxide synthase (AOS) is encoded by a single intronless gene in Arabidopsis thaliana (L.) Heynh. The promoter region of the AOS gene exhibits, in addition to the elements of a minimal promoter and the presence of general enhancers, cis-elements that, in other promoters, are responsible for stress- and ethylene-responsiveness. Arabidopsis thaliana and Nicotiana tabacum L. were transformed with a chimaeric gene consisting of a 1.9-kb 5′-upstream sequence and the first 95 nucleotides of the AOS coding sequence translationally fused to uid A encoding β-glucuronidase (GUS). Using histochemistry, GUS activity was seen in older leaves, in the bases of petioles and in stipules, during the early stages of carpel development, in maturing pollen grains and at the base of elongated filaments, as well as in abscission-zone scars. A role for jasmonates in floral organ abscission is suggested by these findings. Furthermore, the AOS promoter was activated both locally as well as systemically upon wounding. Jasmonic acid, 12-oxophytodienoic acid and coronatine strongly induced GUS activity. This induction remained confined to the treated leaf when agonists were applied locally to a leaf, suggesting that neither jasmonic acid nor 12-oxophytodienoic acid are physiologically relevant components of the systemic wound signal complex. Rather, the data show that jasmonates behave as local response regulators produced at or around the sites of action in response to appropriate triggers of their synthesis. Received: 21 September 1998 / Accepted: 30 December 1998     

Effects of gene expression on molecular evolution in Arabidopsis thaliana and Arabidopsis lyrata

We analyzed the complete genome sequence of Arabidopsis thaliana and sequence data from 83 genes in the outcrossing A. lyrata, to better understand the role of gene expression on the strength of natural selection on synonymous and replacement sites in Arabidopsis. From data on tRNA gene abundance, we find a good concordance between codon preferences and the relative abundance of isoaccepting tRNAs in the complete A. thaliana genome, consistent with models of translational selection. Both EST-based and new quantitative measures of gene expression (MPSS) suggest that codon preferences derived from information on tRNA abundance are more strongly associated with gene expression than those obtained from multivariate analysis, which provides further support for the hypothesis that codon bias in Arabidopsis is under selection mediated by tRNA abundance. Consistent with previous results, analysis of protein evolution reveals a significant correlation between gene expression level and amino acid substitution rate. Analysis by MPSS estimates of gene expression suggests that this effect is primarily the result of a correlation between the number of tissues in which a gene is expressed and the rate of amino acid substitution, which indicates that the degree of tissue specialization may be an important determinant of the rate of protein evolution in Arabidopsis.     

Regulation of proline accumulation in Arabidopsis thaliana (L.) Heynh during development and in response to desiccation

Significant differences were observed in the amount and proportion of free amino acids in different organs of Arabidopsis thaliana (L.) Heynh, ecotype Columbia. The most notable were found for proline, which formed 17–26% of the total free amino acid concentration in reproductive tissues (floret and seed), but only 1–3% of the total free amino acid concentration in vegetative tissues (rosette leaf and root). Proline accumulation was associated with tissues that had relatively low water contents. Tissues which displayed high water contents, such as rosette leaves, contained low levels of proline. A significant increase in the levels of proline accumulation occurred in plants subjected to experimentally induced low water potentials as compared to unstressed plants. For instance, an 8–10-fold increase in proline was observed in the presence of 120 mmol kg^?1 NaCl or KCl, and a 20-fold increase was stimulated by 60 mmol kg^?1 PEG. However, in addition to the accumulation of proline, massive accumulation of Na⁺, K⁺ and Cl^? ions occurred in tissues of plants stressed with salt. No significant differences were observed in mineral ions in plants stressed with PEG. Isotope tracer experiments with ¹⁴C compounds established that glutamate, ornithine and arginine are precursors of the proline biosynthesis induced by PEG in response to low water potentials in Arabidopsis thaliana. We conclude that the accumulation of proline in response to PEG occurs through increased biosynthesis.     

Classification of Genes Differentially Expressed during Water-deficit Stress in Arabidopsis thaliana: an Analysis using Microarray and Differential Expression Data

Many changes in gene expression occur in response to water-deficitstress. A challenge is to determine which changes support plantadaptation to conditions of reduced soil water content and whichoccur in response to lesions in metabolic and cellular functions.Microarray methods are being employed to catalogue all of thechanges in gene expression that occur in response to specificwater-deficit conditions. Although these methods do not measurethe amount or activities of specific proteins that functionin the water-deficit response, they do target specific biochemicaland cellular events that should be detailed in further work.Potential functions of approx. 130 genes of Arabidopsis thalianathat have been shown to be up-regulated are tabulated here.These point to signalling events, detoxification and other functionsinvolved in the cellular response to water-deficit stress. Asmicroarray techniques are refined, plant stress biologists willbe able to characterize changes in gene expression within thewhole genome in specific organs and tissues subjected to differentlevels of water-deficit stress.     

USP22在转录调控及肿瘤发生中的作用

泛素特异性蛋白酶22（ubiquitin specific protease 22,USP22）是一种组蛋白去泛素化酶,在核受体介导的基因转录调控中起增强转录活性的作用。USP22在肿瘤发生、发展中发挥着重要作用,影响癌基因c-Myc介导的基因转录,从而促进肿瘤的增殖和生长;另一方面,USP22可改变远上游识别序列结合蛋白1（far upstream element—binding protein1,FBP1）的泛素化水平,从而影响FBP1下游的抑癌基因p21的表达。USP22与胃癌、大肠癌、乳腺癌及膀胱癌等肿瘤的病理进程相关。此外,USP22在端粒稳态的维持中起作用。本文主要综述USP22参与核受体介导的基因转录调控的表观遗传学机制及其在肿瘤发生中的作用。     

The prohibitin genes in Arabidopsis thaliana: expression in seeds, hormonal regulation and possible role in cell cycle control during seed germination

A fragment encoding a partial sequence of a prohibitin (Phb) gene was isolated. The expression of Phb mRNA and protein in seeds of wild type and mutant Arabidopsis thaliana is presented. Phb mRNA is abundant in wild-type seeds; thus, it may have sequence or structural characteristics responsible for this stability. The 3' untranslated region sequence of a Phb gene has interesting features. We found that Arabidopsis Phb does not interact with a retinoblastoma-related protein or E2F in a yeast two-hybrid system, thus suggesting that the plant protein may have not conserved such interaction, described for mammalian Phb. The possible role of Phb in cell cycle regulation during germination is discussed.     

The role of COP1 in light control of Arabidopsis seedling development

The Arabidopsis seedling can follow two contrasting developmental programmes, photomorphogenesis in light and skotomorphogenesis in darkness. CONSTITUTIVE PHOTOMORPHOGENIC I (COP1) is an essential regulatory gene required for repression of seedling photomorphogenic development in darkness. Recent mutational and overexpression analyses of the COP1 gene suggest a central role for COP1 in light control of seedling development and point to functional implications of its structural domains. Cell biological studies of COP1 have provided a clue to how light regulates the repressive activity of COP1 and thus seedling development.