RESUMEN
Transposons are mobile elements that are commonly silenced to protect eukaryotic genome integrity. In plants, transposable element (TE)-derived inverted repeats (IRs) are commonly found near genes, where they affect host gene expression. However, the molecular mechanisms of such regulation are unclear in most cases. Expression of these IRs is associated with production of 24-nt small RNAs, methylation of the IRs, and drastic changes in local 3D chromatin organization. Notably, many of these IRs differ between Arabidopsis thaliana accessions, causing variation in short-range chromatin interactions and gene expression. CRISPR-Cas9-mediated disruption of two IRs leads to a switch in genome topology and gene expression with phenotypic consequences. Our data show that insertion of an IR near a gene provides an anchor point for chromatin interactions that profoundly impact the activity of neighboring loci. This turns IRs into powerful evolutionary agents that can contribute to rapid adaptation.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Cromatina/genética , ARN , Proteínas de Arabidopsis/genética , Metilación , Elementos Transponibles de ADN/genética , Metilación de ADN/genética , Regulación de la Expresión Génica de las PlantasRESUMEN
Euglena gracilis is a eukaryotic single-celled and photosynthetic organism grouped under the kingdom Protista. This phytoflagellate can accumulate the carbon photoassimilate as a linear ß-1,3-glucan chain called paramylon. This storage polysaccharide can undergo degradation to provide glucose units to obtain ATP and reducing power both in aerobic and anaerobic growth conditions. Our group has recently characterized an essential enzyme for accumulating the polysaccharide, the UDP-glucose pyrophosphorylase (Biochimie vol 154, 2018, 176-186), which catalyzes the synthesis of UDP-glucose (the substrate for paramylon synthase). Additionally, the identification of nucleotide sequences coding for putative UDP-sugar pyrophosphorylases suggests the occurrence of an alternative source of UDP-glucose. In this study, we demonstrate the active involvement of both pyrophosphorylases in paramylon accumulation. Using techniques of single and combined knockdown of transcripts coding for these proteins, we evidenced a substantial decrease in the polysaccharide synthesis from 39 ± 7 µg/106 cells determined in the control at day 21st of growth. Thus, the paramylon accumulation in Euglena gracilis cells decreased by 60% and 30% after a single knockdown of the expression of genes coding for UDP-glucose pyrophosphorylase and UDP-sugar pyrophosphorylase, respectively. Besides, the combined knockdown of both genes resulted in a ca. 65% reduction in the level of the storage polysaccharide. Our findings indicate the existence of a physiological dependence between paramylon accumulation and the partitioning of sugar nucleotides into other metabolic routes, including the Leloir pathway's functionality in Euglena gracilis.
Asunto(s)
Metabolismo de los Hidratos de Carbono , Euglena gracilis , Genética Inversa , Euglena gracilis/genética , Euglena gracilis/metabolismo , Glucanos/biosíntesis , Glucanos/genéticaRESUMEN
MicroRNAs are small regulatory RNAs involved in several processes in plants ranging from development and stress responses to defense against pathogens. In order to accomplish their molecular functions, miRNAs are methylated and loaded into one ARGONAUTE (AGO) protein, commonly known as AGO1, to stabilize and protect the molecule and to assemble a functional RNA-induced silencing complex (RISC). A specific machinery controls miRNA turnover to ensure the silencing release of targeted-genes in given circumstances. The trimming and tailing of miRNAs are fundamental modifications related to their turnover and, hence, to their action. In order to gain a better understanding of these modifications, we analyzed Arabidopsis thaliana small RNA sequencing data from a diversity of mutants, related to miRNA biogenesis, action, and turnover, and from different cellular fractions and immunoprecipitations. Besides confirming the effects of known players in these pathways, we found increased trimming and tailing in miRNA biogenesis mutants. More importantly, our analysis allowed us to reveal the importance of ARGONAUTE 1 (AGO1) loading, slicing activity, and cellular localization in trimming and tailing of miRNAs.
RESUMEN
Post-transcriptional gene silencing mediated by microRNAs (miRNAs) modulates numerous developmental and stress response pathways. For the last two decades, HASTY (HST), the ortholog of human EXPORTIN 5, was considered to be a candidate protein that exports plant miRNAs from the nucleus to the cytoplasm. Here, we report that HST functions in the miRNA pathway independent of its cargo-exporting activity in Arabidopsis. We found that Arabidopsis mutants with impaired HST shuttling exhibit normal subcellular distribution of miRNAs. Interestingly, protein-protein interaction and microscopy assays showed that HST directly interacts with the microprocessor core component DCL1 through its N-terminal domain. Moreover, mass spectrometry analysis revealed that HST also interacts independently of its N-terminal domain with the mediator complex subunit MED37. Further experiments revealed that HST could act as a scaffold to facilitate the recruitment of DCL1 to genomic MIRNA loci by stabilizing the DCL1-MED37 complex, which in turn promotes the transcription and proper processing of primary miRNA transcripts (pri-miRNAs). Taken together, these results suggest that HST is likely associated with the formation of the miRNA biogenesis complex at MIRNA genes, promoting the transcription and processing of pri-miRNAs rather than the direct export of processed miRNAs from the nucleus.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Núcleo Celular/metabolismo , Carioferinas/metabolismo , MicroARNs/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Silenciador del Gen/fisiología , Carioferinas/genética , Espectrometría de Masas , MicroARNs/genética , Procesamiento Postranscripcional del ARNRESUMEN
In plants, small RNAs are loaded into ARGONAUTE (AGO) proteins to fulfill their regulatory functions. MicroRNAs (miRNAs), one of the most abundant classes of endogenous small RNAs, are preferentially loaded into AGO1. Such loading, long believed to happen exclusively in the cytoplasm, was recently proposed to also occur in the nucleus. Here, we identified CONSTITUTIVE ALTERATIONS IN THE SMALL RNAS PATHWAYS9 (CARP9), a nuclear-localized, intrinsically disordered protein, as a factor promoting miRNA activity in Arabidopsis (Arabidopsis thaliana). Mutations in the CARP9-encoding gene led to a mild reduction of miRNAs levels, impaired gene silencing, and characteristic morphological defects, including young leaf serration and altered flowering time. Intriguingly, we found that CARP9 was able to interact with HYPONASTIC LEAVES1 (HYL1), but not with other proteins of the miRNA biogenesis machinery. In the same way, CARP9 appeared to interact with mature miRNA, but not with primary miRNA, positioning it after miRNA processing in the miRNA pathway. CARP9 was also able to interact with AGO1, promoting its interaction with HYL1 to facilitate miRNA loading in AGO1. Plants deficient in CARP9 displayed reduced levels of AGO1-loaded miRNAs, partial retention of miRNA in the nucleus, and reduced levels of AGO1. Collectively, our data suggest that CARP9 might modulate HYL1-AGO1 cross talk, acting as a scaffold for the formation of a nuclear post-primary miRNA-processing complex that includes at least HYL1, AGO1, and HEAT SHOCK PROTEIN 90. In such a complex, CARP9 stabilizes AGO1 and mature miRNAs, allowing the proper loading of miRNAs in the effector complex.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas Argonautas/metabolismo , Proteínas Intrínsecamente Desordenadas/metabolismo , Proteínas de Unión al ARN/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas Argonautas/genética , Núcleo Celular/metabolismo , Regulación de la Expresión Génica de las Plantas , Proteínas Intrínsecamente Desordenadas/genética , Proteínas de Unión al ARN/genéticaRESUMEN
Trichomes and the cuticle are two specialized structures of the aerial epidermis that are important for plant organ development and interaction with the environment. In this study, we report that Arabidopsis thaliana plants affected in the function of the class I TEOSINTE BRANCHED 1, CYCLOIDEA, PCF (TCP) transcription factors TCP14 and TCP15 show overbranched trichomes in leaves and stems and increased cuticle permeability. We found that TCP15 regulates the expression of MYB106, a MIXTA-like transcription factor involved in epidermal cell and cuticle development, and overexpression of MYB106 in a tcp14 tcp15 mutant reduces trichome branch number. TCP14 and TCP15 are also required for the expression of the cuticle biosynthesis genes CYP86A4, GPAT6, and CUS2, and of SHN1 and SHN2, two AP2/EREBP transcription factors required for cutin and wax biosynthesis. SHN1 and CUS2 are also targets of TCP15, indicating that class I TCPs influence cuticle formation acting at different levels, through the regulation of MIXTA-like and SHN transcription factors and of cuticle biosynthesis genes. Our study indicates that class I TCPs are coordinators of the regulatory network involved in trichome and cuticle development.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Tricomas/metabolismoRESUMEN
CURLY LEAF (CLF) encodes the methyltransferase subunit of the Polycomb Repressor Complex 2 (PRC2), which regulates the expression of target genes through H3K27 trimethylation. We isolated a new CLF mutant allele (clf-78) using a genetic screen designed to identify microRNA (miRNA) deficient mutants. CLF mutant plants showed impaired miRNA activity caused by increased ubiquitination and enhanced degradation of ARGONAUTE 1 (AGO1) in specific tissues. Such CLF-mediated AGO1 regulation was evident when plants were exposed to UV radiation, which caused increased susceptibility of clf mutants to some UV-induced responses. Furthermore, we showed that CLF directly regulates FBW2, which in turn triggers AGO1 degradation in the clf mutants. Interestingly, AGO1 bound to a target appeared particularly prone to degradation in the mutant plants, a process that was exacerbated when the complex bound a non-cleavable target. Thus, prolonged AGO1-target interaction seems to favor AGO1 degradation, suggesting that non-cleavable miRNA targets may overcome translation inhibition by modulating AGO1 stability in plants.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/genética , Proteínas Argonautas/metabolismo , Proteínas de Homeodominio/metabolismo , MicroARNs/genética , Alelos , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas Argonautas/genética , Regulación del Desarrollo de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Histonas/metabolismo , Proteínas de Homeodominio/genética , Mutación , Fenotipo , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Proteínas del Grupo Polycomb/metabolismoRESUMEN
Transposable elements (TEs) are extremely abundant in complex plant genomes. siRNAs of 24 nucleotides in length control transposon activity in a process that involves de novo methylation of targeted loci. Usually, these epigenetic modifications trigger nucleosome condensation and a permanent silencing of the affected loci. Here, we show that a TE-derived inverted repeat (IR) element, inserted near the sunflower HaWRKY6 locus, dynamically regulates the expression of the gene by altering chromatin topology. The transcripts of this IR element are processed into 24-nt siRNAs, triggering DNA methylation on its locus. These epigenetic marks stabilize the formation of tissue-specific loops in the chromatin. In leaves, an intragenic loop is formed, blocking HaWRKY6 transcription. While in cotyledons (Cots), formation of an alternative loop, encompassing the whole HaWRKY6 gene, enhances transcription of the gene. The formation of this loop changes the promoter directionality, reducing IR transcription, and ultimately releasing the loop. Our results provide evidence that TEs can act as active and dynamic regulatory elements within coding loci in a mechanism that combines RNA silencing, epigenetic modification, and chromatin remodeling machineries.
Asunto(s)
Ensamble y Desensamble de Cromatina/genética , Cromatina/genética , Regulación de la Expresión Génica de las Plantas , Helianthus/genética , Secuencias Invertidas Repetidas , ARN de Planta/genética , ARN Interferente Pequeño/genética , Transcripción Genética , Conformación de Ácido Nucleico , ARN no Traducido/genética , Secuencias Reguladoras de Ácidos NucleicosRESUMEN
Plants use molecular mechanisms to sense temperatures, trigger quick adaptive responses and thereby cope with environmental changes. MicroRNAs (miRNAs) are key regulators of plant development under such conditions. The catalytic action of DICER LIKE 1 (DCL1), in conjunction with HYPONASTIC LEAVES 1 (HYL1) and SERRATE (SE), produces miRNAs from double-stranded RNAs. As plants lack a stable internal temperature to which enzymatic reactions could be optimized during evolution, reactions such as miRNA processing have to be adjusted to fluctuating environmental temperatures. Here, we report that with decreasing ambient temperature, the plant miRNA biogenesis machinery becomes more robust, producing miRNAs even in the absence of the key DCL1 co-factors HYL1 and SE. This reduces the morphological and reproductive defects of se and hyl1 mutants, restoring seed production. Using small RNA-sequencing and bioinformatics analyses, we have identified specific miRNAs that become HYL1/SE independent for their production in response to temperature decrease. We found that the secondary structure of primary miRNAs is key for this temperature recovery. This finding may have evolutionary implications as a potential adaptation-driving mechanism to a changing climate.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Proteínas de Ciclo Celular/metabolismo , Regulación de la Expresión Génica de las Plantas , MicroARNs/metabolismo , Proteínas de Unión al ARN/metabolismo , Ribonucleasa III/metabolismo , Frío , Biología Computacional , Genes de Plantas , Mutación , Fenotipo , Polen/metabolismo , Estructura Secundaria de Proteína , Análisis de Secuencia de ARNRESUMEN
Light is the most influential environmental stimulus for plant growth. In response to deficient light, plants reprogram their development to adjust their growth in search for a light source. A fine reprogramming of gene expression orchestrates this adaptive trait. Here we show that plants alter microRNA (miRNA) biogenesis in response to light transition. When plants suffer an unusual extended period of light deprivation, the miRNA biogenesis factor HYPONASTIC LEAVES 1 (HYL1) is degraded but an inactive pool of phosphorylated protein remains stable inside the nucleus. Degradation of HYL1 leads to the release of gene silencing, triggering a proper response to dark and shade. Upon light restoration, a quick dephosphorylation of HYL1 leads to the reactivation of miRNA biogenesis and a switch toward a developmental program that maximizes the light uptake. Our findings define a unique and fast regulatory mechanism controlling the plant silencing machinery during plant light response.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas/genética , MicroARNs/metabolismo , Proteínas de Unión al ARN/metabolismo , Arabidopsis/metabolismo , Núcleo Celular/metabolismo , Silenciador del Gen , Luz , MicroARNs/genética , Mutación , Fosforilación , Hojas de la Planta/metabolismo , Procesamiento Postranscripcional del ARN/fisiologíaRESUMEN
Background and Aims: The symmetry of venation patterning in leaves is highly conserved within a plant species. Auxins are involved in this process and also in xylem vasculature development. Studying transgenic Arabidopsis plants ectopically expressing the sunflower transcription factor HaHB4, it was observed that there was a significant lateral-vein asymmetry in leaves and in xylem formation compared to wild type plants. To unravel the molecular mechanisms behind this phenotype, genes differentially expressed in these plants and related to auxin influx were investigated. Methods: Candidate genes responsible for the observed phenotypes were selected using a co-expression analysis. Single and multiple mutants in auxin influx carriers were characterized by morphological, physiological and molecular techniques. The analysis was further complemented by restoring the wild type (WT) phenotype by mutant complementation studies and using transgenic soybean plants ectopically expressing HaHB4 . Key Results: LAX2 , down-regulated in HaHB4 transgenic plants, was bioinformatically chosen as a candidate gene. The quadruple mutant aux1 lax1 lax2 lax3 and the single mutants, except lax1, presented an enhanced asymmetry in venation patterning. Additionally, the xylem vasculature of the lax2 mutant and the HaHB4 -expressing plants differed from the WT vasculature, including increased xylem length and number of xylem cell rows. Complementation of the lax2 mutant with the LAX2 gene restored both lateral-vein symmetry and xylem/stem area ratio in the stem, showing that auxin homeostasis is required to achieve normal vascular development. Interestingly, soybean plants ectopically expressing HaHB4 also showed an increased asymmetry in the venation patterning, accompanied by the repression of several GmLAX genes. Conclusions: Auxin influx carriers have a significant role in leaf venation pattering in leaves and, in particular, LAX2 is required for normal xylem development, probablt controlling auxin homeostasis.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Proteínas de Transporte de Membrana/fisiología , Hojas de la Planta/crecimiento & desarrollo , Xilema/crecimiento & desarrollo , Arabidopsis/anatomía & histología , Arabidopsis/crecimiento & desarrollo , Ácidos Indolacéticos/metabolismo , Análisis de Secuencia por Matrices de Oligonucleótidos , Fenotipo , Reguladores del Crecimiento de las Plantas/metabolismo , Reguladores del Crecimiento de las Plantas/fisiología , Hojas de la Planta/anatomía & histología , Plantas Modificadas Genéticamente , Reacción en Cadena en Tiempo Real de la Polimerasa , Glycine max/anatomía & histología , Glycine max/crecimiento & desarrolloRESUMEN
AtHB1 is an Arabidopsis (Arabidopsis thaliana) homeodomain-leucine zipper transcription factor that participates in hypocotyl elongation under short-day conditions. Here, we show that its expression is posttranscriptionally regulated by an upstream open reading frame (uORF) located in its 5' untranslated region. This uORF encodes a highly conserved peptide (CPuORF) that is present in varied monocot and dicot species. The Arabidopsis uORF and its maize (Zea mays) homolog repressed the translation of the main open reading frame in cis, independent of the sequence of the latter. Published ribosome footprinting results and the analysis of a frame-shifted uORF, in which the repression capability was lost, indicated that the uORF causes ribosome stalling. The regulation exerted by the CPuORF was tissue specific and did not act in the absence of light. Moreover, a photosynthetic signal is needed for the CPuORF action, since plants with uncoupled chloroplasts did not show uORF-dependent repression. Plants transformed with the native AtHB1 promoter driving AtHB1 expression did not show differential phenotypes, whereas those transformed with a construct in which the uORF was mutated exhibited serrated leaves, compact rosettes, and, most significantly, short nondehiscent anthers and siliques containing fewer or no seeds. Thus, we propose that the uncontrolled expression of AtHB1 is deleterious for the plant and, hence, finely repressed by a translational mechanism.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Sistemas de Lectura Abierta/genética , Especificidad de Órganos/genética , Factores de Transcripción/metabolismo , Regiones no Traducidas 5'/genética , Secuencia de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Codón/genética , Secuencia Conservada/genética , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Homocigoto , Mutación/genética , Especificidad de Órganos/efectos de la radiación , Fenotipo , Biosíntesis de Proteínas , Ribosomas/metabolismo , Factores de Transcripción/química , Factores de Transcripción/genética , Zea mays/genéticaRESUMEN
COX17 is a soluble protein from the mitochondrial intermembrane space that participates in the transfer of copper for cytochrome c oxidase (COX) assembly in eukaryotic organisms. In this work, we studied the function of both Arabidopsis thaliana AtCOX17 genes using plants with altered expression levels of these genes. Silencing of AtCOX17-1 in a cox17-2 knockout background generates plants with smaller rosettes and decreased expression of genes involved in the response of plants to different stress conditions, including several genes that are induced by mitochondrial dysfunctions. Silencing of either of the AtCOX17 genes does not affect plant development or COX activity but causes a decrease in the response of genes to salt stress. In addition, these plants contain higher reactive oxygen and lipid peroxidation levels after irrigation with high NaCl concentrations and are less sensitive to abscisic acid. In agreement with a role of AtCOX17 in stress and abscisic acid responses, both AtCOX17 genes are induced by several stress conditions, abscisic acid and mutation of the transcription factor ABI4. The results indicate that AtCOX17 is required for optimal expression of a group of stress-responsive genes, probably as a component of signalling pathways that link stress conditions to gene expression responses.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimología , Arabidopsis/fisiología , Proteínas de Transporte de Catión/metabolismo , Complejo IV de Transporte de Electrones/metabolismo , Estrés Fisiológico , Adaptación Fisiológica/efectos de los fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Transporte de Catión/genética , Análisis por Conglomerados , Proteínas Transportadoras de Cobre , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Silenciador del Gen/efectos de los fármacos , Genes de Plantas , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Estrés Oxidativo/efectos de los fármacos , Estrés Oxidativo/genética , Desarrollo de la Planta/efectos de los fármacos , Desarrollo de la Planta/genética , Plantas Modificadas Genéticamente , Transporte de Proteínas/efectos de los fármacos , Cloruro de Sodio/farmacología , Estrés Fisiológico/efectos de los fármacos , Estrés Fisiológico/genética , Factores de Transcripción/metabolismoRESUMEN
We studied the role of Arabidopsis thaliana TCP15, a member of the TEOSINTE BRANCHED1-CYCLOIDEA-PCF (TCP) transcription factor family, in gynoecium development. Plants that express TCP15 from the 35S CaMV promoter (35S:TCP15) develop flowers with defects in carpel fusion and a reduced number of stigmatic papillae. In contrast, the expression of TCP15 fused to a repressor domain from its own promoter causes the development of outgrowths topped with stigmatic papillae from the replum. 35S:TCP15 plants show lower levels of the auxin indoleacetic acid and reduced expression of the auxin reporter DR5 and the auxin biosynthesis genes YUCCA1 and YUCCA4, suggesting that TCP15 is a repressor of auxin biosynthesis. Treatment of plants with cytokinin enhances the developmental effects of expressing TCP15 or its repressor form. In addition, treatment of a knock-out double mutant in TCP15 and the related gene TCP14 with cytokinin causes replum enlargement, increased development of outgrowths, and the induction of the auxin biosynthesis genes YUCCA1 and YUCCA4. A comparison of the phenotypes observed after cytokinin treatment of plants with altered expression levels of TCP15 and auxin biosynthesis genes suggests that TCP15 modulates gynoecium development by influencing auxin homeostasis. We propose that the correct development of the different tissues of the gynoecium requires a balance between auxin levels and cytokinin responses, and that TCP15 participates in a feedback loop that helps to adjust this balance.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Citocininas/metabolismo , Ácidos Indolacéticos/metabolismo , Factores de Transcripción/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas/genética , Regulación de la Expresión Génica de las Plantas/fisiología , Factores de Transcripción/genéticaRESUMEN
Arabidopsis thaliana HomeoBox 1 (AtHB1) is a homeodomain-leucine zipper transcription factor described as a transcriptional activator with unknown function. Its role in A. thaliana development was investigated. AtHB1 expression was analyzed in transgenic plants bearing its promoter region fused to reporter genes. Knock-down mutant and overexpressor plant phenotypes were analyzed in different photoperiod regimes. AtHB1 was mainly expressed in hypocotyls and roots and up-regulated in seedlings grown under a short-day photoperiod. AtHB1 knock-down mutants and overexpressors showed shorter and longer hypocotyls, respectively, than wild type (WT). AtHB1 transcript levels were lower in PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) mutants than in controls, suggesting that AtHB1 is regulated by PIF1 in hypocotyls. ß-glucuronidase (GUS) activity in Nicotiana benthamiana leaves cotransformed with PromAtHB1::GUS and 35S::PIF1 indicated that PIF1 induces AtHB1 expression. Hypocotyl lenght was measured in seedlings of athb1, pif1, or double athb1/pif1 mutants and PIF1 or AtHB1 overexpressors in WT, athb1 or pif1 backgrounds, both in short- or long-day. These analyses allowed us to determine that AtHB1 is a factor acting downstream of PIF1. Finally, a transcriptome analysis of athb1 mutant hypocotyls revealed that AtHB1 regulates genes involved in cell wall composition and elongation. The results suggest that AtHB1 acts downstream of PIF1 to promote hypocotyl elongation, especially in response to short-day photoperiods.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Hipocótilo/crecimiento & desarrollo , Hipocótilo/metabolismo , Factores de Transcripción/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Hipocótilo/genética , Modelos Biológicos , Datos de Secuencia Molecular , Raíces de Plantas/metabolismo , Factores de Transcripción/genéticaRESUMEN
Different members of the HD-Zip I family of transcription factors exhibit differential AHA-like activation motifs, able to interact with proteins of the basal transcriptional machinery. Homeodomain-leucine zipper proteins are transcription factors unique to plants, classified in four subfamilies. Subfamily I members have been mainly associated to abiotic stress responses. Several ones have been characterized using knockout or overexpressors plants, indicating that they take part in different signal transduction pathways even when their expression patterns are similar and they bind the same DNA sequence. A bioinformatic analysis has revealed the existence of conserved motifs outside the HD-Zip domain, including transactivation AHA motifs. Here, we demonstrate that these putative activation motifs are functional. Four members of the Arabidopsis family were chosen: AtHB1, AtHB7, AtHB12 and AtHB13. All of them exhibited activation activity in yeast and in plants but with different degrees. The protein segment necessary for such activation was different for these four transcription factors as well as the role of the tryptophans they present. When interaction with components of the basal transcription machinery was tested, AtHB1 was able to interact with TBP, AtHB12 interacted with TFIIB, AtHB7 interacted with both, TBP and TFIIB while AtHB13 showed weak interactions with any of them, in yeast two-hybrid as well as in pull-down assays. Transient transformation of Arabidopsis seedlings confirmed the activation capacity and specificity of these transcription factors and showed some differences with the results obtained in yeast. In conclusion, the differential activation functionality of these transcription factors adds an important level of functional divergence of these proteins, and together with their expression patterns, these differences could explain, at least in part, their functional divergence.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Factores de Transcripción/genética , Activación Transcripcional , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Secuencia de Bases , Regulación de la Expresión Génica de las Plantas , Proteínas de Homeodominio/genética , Proteínas de Homeodominio/metabolismo , Leucina Zippers , Estructura Terciaria de Proteína , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Plantones/genética , Plantones/metabolismo , Proteína de Unión a TATA-Box/genética , Proteína de Unión a TATA-Box/metabolismo , Factor de Transcripción TFIIB/genética , Factor de Transcripción TFIIB/metabolismo , Factores de Transcripción/metabolismo , Técnicas del Sistema de Dos HíbridosRESUMEN
Plants deal with cold temperatures via different signal transduction pathways. The HD-Zip I homologous transcription factors HaHB1 from sunflower and AtHB13 from Arabidopsis were identified as playing a key role in such cold response. The expression patterns of both genes were analyzed indicating an up-regulation by low temperatures. When these genes were constitutively expressed in Arabidopsis, the transgenic plants showed similar phenotypes including cell membrane stabilization under freezing treatments and cold tolerance. An exploratory transcriptomic analysis of HaHB1 transgenic plants indicated that several transcripts encoding glucanases and chitinases were induced. Moreover, under freezing conditions some proteins accumulated in HaHB1 plants apoplasts and these extracts exerted antifreeze activity in vitro. Three genes encoding two glucanases and a chitinase were overexpressed in Arabidopsis and these plants were able to tolerate freezing temperatures. All the obtained transgenic plants exhibited cell membrane stabilization after a short freezing treatment. Finally, HaHB1 and AtHB13 were used to transiently transform sunflower and soybean leading to the up-regulation of HaHB1/AtHB13-target homologues thus indicating the conservation of cold response pathways. We propose that HaHB1 and AtHB13 are involved in plant cold tolerance via the induction of proteins able to stabilize cell membranes and inhibit ice growth.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiología , Glucano Endo-1,3-beta-D-Glucosidasa/metabolismo , Proteínas de Homeodominio/metabolismo , Proteínas de Plantas/metabolismo , Factores de Transcripción/metabolismo , Proteínas Anticongelantes/genética , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Membrana Celular/metabolismo , Quitinasas/genética , Frío , Congelación , Regulación de la Expresión Génica de las Plantas , Glucano Endo-1,3-beta-D-Glucosidasa/genética , Helianthus/genética , Proteínas de Homeodominio/genética , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Regiones Promotoras Genéticas , Factores de Transcripción/genética , Regulación hacia ArribaRESUMEN
BACKGROUND: Plant HD-Zip transcription factors are modular proteins in which a homeodomain is associated to a leucine zipper. Of the four subfamilies in which they are divided, the tested members from subfamily I bind in vitro the same pseudopalindromic sequence CAAT(A/T)ATTG and among them, several exhibit similar expression patterns. However, most experiments in which HD-Zip I proteins were over or ectopically expressed under the control of the constitutive promoter 35S CaMV resulted in transgenic plants with clearly different phenotypes. Aiming to elucidate the structural mechanisms underlying such observation and taking advantage of the increasing information in databases of sequences from diverse plant species, an in silico analysis was performed. In addition, some of the results were also experimentally supported. RESULTS: A phylogenetic tree of 178 HD-Zip I proteins together with the sequence conservation presented outside the HD-Zip domains allowed the distinction of six groups of proteins. A motif-discovery approach enabled the recognition of an activation domain in the carboxy-terminal regions (CTRs) and some putative regulatory mechanisms acting in the amino-terminal regions (NTRs) and CTRs involving sumoylation and phosphorylation. A yeast one-hybrid experiment demonstrated that the activation activity of ATHB1, a member of one of the groups, is located in its CTR. Chimerical constructs were performed combining the HD-Zip domain of one member with the CTR of another and transgenic plants were obtained with these constructs. The phenotype of the chimerical transgenic plants was similar to the observed in transgenic plants bearing the CTR of the donor protein, revealing the importance of this module inside the whole protein. CONCLUSIONS: The bioinformatical results and the experiments conducted in yeast and transgenic plants strongly suggest that the previously poorly analyzed NTRs and CTRs of HD-Zip I proteins play an important role in their function, hence potentially constituting a major source of functional diversity among members of this subfamily.
Asunto(s)
Proteínas de Homeodominio/metabolismo , Leucina Zippers , Filogenia , Proteínas de Plantas/metabolismo , Factores de Transcripción/metabolismo , Secuencia de Aminoácidos , Arabidopsis/genética , Arabidopsis/metabolismo , Biología Computacional , Secuencia Conservada , ADN de Plantas/genética , Proteínas de Homeodominio/genética , Datos de Secuencia Molecular , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , Análisis de Secuencia de Proteína , Factores de Transcripción/genéticaRESUMEN
Transcription factors are clue elements in the regulation of signal transduction pathways in living organisms. These proteins are able to recognize and bind specific sequences in the promoter regions of their targets and subsequently activate or repress entire metabolic or developmental processes. About 1500 TFs were informatically identified in plants, analysis mainly based in the presence of DNA-binding domains in the translated sequences. However, only a few of these 1500 were functionally characterized and clearly classified as TFs. Among these, several seem to be powerful biotechnological tools in order to improve agronomic crops via the obtaining of transgenic plants or as molecular markers. Such TFs have become the objects of patents presentations in the whole world. The assigned uses present a variety of purposes including the improvement in yield, abiotic and biotic stresses tolerances as well as a combination of them. Some examples are commented in the present overview. Most of these TFs confer to transgenic plants complex phenotypes due to a combination of different regulated pathways. In this sense, the use of inducible promoters instead of constitutive ones seems in some cases to be useful to limit the changed phenotype to the desired one, avoiding lateral effects. None of these TFs was converted up to now in a market product since time-consuming experiments and regulation permits are required to arrive to such point. Moreover, a considerable money investment must be done, not justified in all cases. However, it is likely that these molecules will become in the near future the first choice for breeders since it was demonstrated that TFs are very efficient conferring desired traits to transgenic plants. Additionally, for the public perception the over or ectopic expression of a plant gene should be more accepted than the use of molecules from other species.
Asunto(s)
Biotecnología/tendencias , Patentes como Asunto , Proteínas de Plantas/biosíntesis , Proteínas de Plantas/genética , Ingeniería de Proteínas/tendencias , Factores de Transcripción/biosíntesis , Factores de Transcripción/genéticaRESUMEN
Hahb-4 is a member of the Helianthusannuus (sunflower) subfamily I of HD-Zip proteins that is transcriptionally regulated by water availability and abscisic acid. Transgenic Arabidopsis thaliana plants overexpressing this transcription factor (TF) exhibit a characteristic phenotype that includes a strong tolerance to water stress. Here we show that this TF is a new component of ethylene signalling pathways, and that it induces a marked delay in senescence. Plants overexpressing Hahb-4 are less sensitive to external ethylene, enter the senescence pathway later and do not show the typical triple response. Furthermore, transgenic plants expressing this gene under the control of its own inducible promoter showed an inverse correlation between ethylene sensitivity and Hahb-4 levels. Potential targets of Hahb-4 were identified by comparing the transcriptome of Hahb-4-transformed and wild-type plants using microarrays and quantitative RT-PCR. Expression of this TF has a major repressive effect on genes related to ethylene synthesis, such as ACO and SAM, and on genes related to ethylene signalling, such as ERF2 and ERF5. Expression studies in sunflower indicate that Hahb-4 transcript levels are elevated in mature/senescent leaves. Expression of Hahb-4 is induced by ethylene, concomitantly with several genes homologous to the targets identified in the transcriptome analysis (HA-ACOa and HA-ACOb). Transient transformation of sunflower leaves demonstrated the action of Hahb-4 in the regulation of ethylene-related genes. We propose that Hahb-4 is involved in a novel conserved mechanism related to ethylene-mediated senescence that functions to improve desiccation tolerance.