Widespread Translational Inhibition by Plant miRNAs and siRNAs Brodersen, Peter; Sakvarelidze-Achard, Lali; Bruun-Rasmussen, Marianne ...
Science (American Association for the Advancement of Science),
05/2008, Letnik:
320, Številka:
5880
Journal Article
Recenzirano
Odprti dostop
High complementarity between plant microRNAs (miRNAs) and their messenger RNA targets is thought to cause silencing, prevalently by endonucleolytic cleavage. We have isolated Arabidopsis mutants ...defective in miRNA action. Their analysis provides evidence that plant miRNA-guided silencing has a widespread translational inhibitory component that is genetically separable from endonucleolytic cleavage. We further show that the same is true of silencing mediated by small interfering RNA (siRNA) populations. Translational repression is effected in part by the ARGONAUTE proteins AGO1 and AGO10. It also requires the activity of the microtubule-severing enzyme katanin, implicating cytoskeleton dynamics in miRNA action, as recently suggested from animal studies. Also as in animals, the decapping component VARICOSE (VCS)/Ge-1 is required for translational repression by miRNAs, which suggests that the underlying mechanisms in the two kingdoms are related.
In Arabidopsis (Arabidopsis thaliana) the root apex is protected from aluminum (Al) rhizotoxicity by excretion of malate, an Al chelator, by ALUMINUM-ACTIVATED MALATE TRANSPORTER1 (AtALMT1). AtALMT1 ...expression is fundamentally regulated by the SENSITIVE TO PROTON RHIZOTOXICITY1 (STOP1) zinc finger protein, but other transcription factors have roles that enable Al-inducible expression with a broad dynamic range. In this study, we characterized multiple cis-elements in the AtALMT1 promoter that interact with transcription factors. In planta complementation assays of AtALMT1 driven by 5' truncated promoters of different lengths showed that the promoter region between -540 and 0 (the first ATG) restored the Al-sensitive phenotype of atalm1 and thus contains cis-elements essential for AtALMT1 expression for Al tolerance. Computation of overrepresented octamers showed that eight regions in this promoter region contained potential cis-elements involved in Al induction and STOP1 regulation. Mutation in a position around -297 from the first ATG completely inactivated AtALMT1 expression and Al response. In vitro binding assays showed that this region contained the STOP1 binding site, which accounted for the recognition by four zinc finger domains of the protein. Other positions were characterized as cis-elements that regulated expression by repressors and activators and a transcription factor that determines root tip expression of AtALMT1. From the consensus of known cis-elements, we identified CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR2 to be an activator of AtALMT1 expression. Al-inducible expression of AtALMT1 changed transcription starting sites, which increased the abundance of transcripts with a shortened 5' untranslated region. The present analyses identified multiple mechanisms that regulate AtALMT1 expression.
Alternative promoter usage is a proteome-expanding mechanism that allows multiple pre-mRNAs to be transcribed from a single gene. The impact of this mechanism on the proteome and whether it is ...positively exploited in normal organismal responses remain unclear. We found that the plant photoreceptor phytochrome induces genome-wide changes in alternative promoter selection in Arabidopsis thaliana. Through this mechanism, protein isoforms with different N termini are produced that display light-dependent differences in localization. For instance, shade-grown plants accumulate a cytoplasmic isoform of glycerate kinase (GLYK), an essential photorespiration enzyme that was previously thought to localize exclusively to the chloroplast. Cytoplasmic GLYK constitutes a photorespiratory bypass that alleviates fluctuating light-induced photoinhibition. Therefore, phytochrome controls alternative promoter selection to modulate protein localization in response to changing light conditions. This study suggests that alternative promoter usage represents another ubiquitous layer of gene expression regulation in eukaryotes that contributes to diversification of the proteome.
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•Phytochrome induces genome-wide changes in alternative promoter selection•Phytochrome-mediated alternative promoter selection modulates protein localization•This mechanism produces a cytoplasmic isoform of glycerate kinase (cytGLYK)•cytGLYK accumulates in shade to alleviate fluctuating light-induced photoinhibition
Light signaling through phytochrome receptors changes protein localization through alternative promoter selection, allowing plants to metabolically respond to changing light conditions.
Redox Responsive Transcription Factor1 （RRTF1） in Arabidopsis is rapidly and transiently upregulated by H202, as well as biotic- and abiotic-induced redox signals. RRTF1 is highly conserved in angio- ...sperms, but its physiological role remains elusive. Here we show that inactivation of RRTF1 restricts and overexpression promotes reactive oxygen species （ROS） accumulation in response to stress. Transgenic lines overexpressing RRTF1 are impaired in root and shoot development, light sensitive, and susceptible to Alternaria brassicae infection. These symptoms are diminished by the beneficial root endophyte Piriformospora indica, which reduces ROS accumulation locally in roots and systemi- cally in shoots, and by antioxidants and ROS inhibitors that scavenge ROS. More than 800 genes were detected in mature leaves and seedlings of transgenic lines overexpressing RRTF1; ∽40% of them have stress-, redox-, ROS-regulated-, ROS-scavenging-, defense-, cell death- and related functions. Bioinformatic analyses and in vitro DNA binding assays demonstrate that RRTF1 binds to GCC-box-like sequences in the promoter of RRTFl-responsive genes. Upregulation of RRTF1 by stress stimuli and H202 requires WRKY18/40/60. RRTF1 is co-regulated with the phylogenet- ically related RAP2.6, which contains a GCC-box-like sequence in its promoter, but transgenic lines overexpressing RAP2.6 do not accumulate higher ROS levels. RRTF1 also stimulates systemic ROS accumulation in distal non-stressed leaves. We conclude that the elevated levels of the highly conserved RRTF1 induce ROS accumulation in response to ROS and ROS-producing abiotic and biotic stress signals.
Genes are transcribed from transcription start sites (TSSs), and their position in a genome is strictly controlled to avoid mis-expression of undesired regions. In this study, we designed and ...developed a methodology for the evaluation of promoter context, which detects proximal promoter regions from - 200 to - 60 bp relative to a TSS, in Arabidopsis and rice genomes. The method positively evaluates spacer sequences and Regulatory Element Groups, but not core promoter elements like TATA boxes, and is able to predict the position of a TSS within a width of 200 bp. An important feature of the evaluation/prediction method is its independence of the core promoter elements, which was demonstrated by successful prediction of all the TATA, GA, and coreless types of promoters without notable differences in the accuracy of prediction. The positive relationship identified between the evaluation scores and gene expression levels suggests that this method is useful for the evaluation of promoter maturity.
Plants tailor immune responses to defend against pathogens with different lifestyles. In this process, antagonism between the immune hormones salicylic acid (SA) and jasmonic acid (JA) optimizes ...transcriptional signatures specifically to the attacker encountered. Antagonism is controlled by the transcription cofactor NPR1. The indispensable role of NPR1 in activating SA-responsive genes is well understood, but how it functions as a repressor of JA-responsive genes remains unclear. Here, we demonstrate that SA-induced NPR1 is recruited to JA-responsive promoter regions that are co-occupied by a JA-induced transcription complex consisting of the MYC2 activator and MED25 Mediator subunit. In the presence of SA, NPR1 physically associates with JA-induced MYC2 and inhibits transcriptional activation by disrupting its interaction with MED25. Importantly, NPR1-mediated inhibition of MYC2 is a major immune mechanism for suppressing pathogen virulence. Thus, NPR1 orchestrates the immune transcriptome not only by activating SA-responsive genes but also by acting as a corepressor of JA-responsive MYC2.
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•NPR1 physically interacts with JA-induced MYC2 and its homologs•NPR1 is distributed to the JA-responsive promoters occupied by MYC2 and MED25•NPR1 dissociates the MYC2-MED25 interaction to repress JA-responsive gene expression•NPR1 suppresses MYC-mediated susceptibility of virulent Pseudomonas syringae
Nomoto et al. demonstrate the mechanistic details of crosstalk signaling between the phytohormones salicylic acid (SA) and jasmonic acid (JA). The SA-induced immune cofactor NPR1 directly inhibits JA-induced MYC activators, suppressing the virulent effect of the phytotoxin coronatine (COR) secreted from Pseudomonas syringae.
The transcription factor sensitive to proton rhizotoxicity 1 (STOP1) regulates multiple stress tolerances. In this study, we confirmed its involvement in NaCl and drought tolerance. The root growth ...of the T-DNA insertion mutant of STOP1 (stop1) was sensitive to NaCl-containing solidified MS media. Transcriptome analysis of stop1 under NaCl stress revealed that STOP1 regulates several genes related to salt tolerance, including CIPK23. Among all available homozygous T-DNA insertion mutants of the genes suppressed in stop1, only cipk23 showed a NaCl-sensitive root growth phenotype comparable to stop1. The CIPK23 promoter had a functional STOP1-binding site, suggesting a strong CIPK23 suppression led to NaCl sensitivity of stop1. This possibility was supported by in planta complementation of CIPK23 in the stop1 background, which rescued the short root phenotype under NaCl. Both stop1 and cipk23 exhibited a drought tolerant phenotype and increased abscisic acid-regulated stomatal closure, while the complementation of CIPK23 in stop1 reversed these traits. Our findings uncover additional pleiotropic roles of STOP1 mediated by CIPK23, which regulates various ion transporters including those regulating K+-homeostasis, which may induce a trade-off between drought tolerance and other traits.
Perception of pathogen-derived ligands by corresponding host receptors is a pivotal strategy in eukaryotic innate immunity. In plants, this is complemented by circadian anticipation of infection ...timing, promoting basal resistance even in the absence of pathogen threat. Here, we report that trichomes, hair-like structures on the epidermis, directly sense external mechanical forces, including raindrops, to anticipate pathogen infections in Arabidopsis thaliana. Exposure of leaf surfaces to mechanical stimuli initiates the concentric propagation of intercellular calcium waves away from trichomes to induce defence-related genes. Propagating calcium waves enable effective immunity against pathogenic microbes through the CALMODULIN-BINDING TRANSCRIPTION ACTIVATOR 3 (CAMTA3) and mitogen-activated protein kinases. We propose an early layer of plant immunity in which trichomes function as mechanosensory cells that detect potential risks.
The SENSITIVE TO PROTON RHIZOTOXICITY 1 (STOP1) transcription factor regulates gene expression associated with multiple stress tolerances in plant roots. In this study, we investigated the mechanism ...responsible for the sensitivity of the stop1 mutant to low-oxygen stress in Arabidopsis. Transcriptomic analyses revealed that two genes involved in low-oxygen tolerance, namely GLUTAMATE DEHYDROGENASE 1 (GDH1) and GDH2, showed lower expression levels in the stop1 mutant than in the wild-type. Sensitivity of the gdh1gdh2 double-mutant to low-oxygen conditions was partly attributable to the low-oxygen sensitivity of the stop1 mutant. Two transcription factors, STOP2 and HEAT SHOCK FACTOR A2 (HsfA2), were expressed at lower levels in the stop1 mutant. An in planta complementation assay indicated that CaMV35S::STOP2 or CaMV35S::HsfA2 partially rescued the low-oxygen tolerance of the stop1 mutant, which was concomitant with recovered expression of genes regulating low-pH tolerance and genes encoding molecular chaperones. Prediction of cis-elements and in planta promoter assays revealed that STOP1 directly activated the expression of HsfA2. Similar STOP1-dependent low-oxygen sensitivity was detected in tobacco. Suppression of NtSTOP1 induced low-oxygen sensitivity, which was associated with lower expression levels of NtHsfA2 and NtGDHs compared with the wild-type. Our results indicated that STOP1 pleiotropically regulates low-oxygen tolerance by transcriptional regulation.
Abstract
Malate efflux from roots, which is regulated by the transcription factor STOP1 (SENSITIVE-TO-PROTON-RHIZOTOXICITY1) and mediates aluminum-induced expression of ...ALUMINUM-ACTIVATED-MALATE-TRANSPORTER1 (AtALMT1), is critical for aluminum resistance in Arabidopsis thaliana. Several studies showed that AtALMT1 expression in roots is rapidly observed in response to aluminum; this early induction is an important mechanism to immediately protect roots from aluminum toxicity. Identifying the molecular mechanisms that underlie rapid aluminum resistance responses should lead to a better understanding of plant aluminum sensing and signal transduction mechanisms. In this study, we observed that GFP-tagged STOP1 proteins accumulated in the nucleus soon after aluminum treatment. The rapid aluminum-induced STOP1-nuclear localization and AtALMT1 induction were detected in the presence of a protein synthesis inhibitor, suggesting that post-translational regulation is involved in these events. STOP1 also regulated rapid aluminum-induced expression for other genes that carry a functional/high-affinity STOP1-binding site in their promoter, including STOP2, GLUTAMATE-DEHYDROGENASE1 and 2 (GDH1 and 2). However STOP1 did not regulate Al resistance genes which have no functional STOP1-binding site such as ALUMINUM-SENSITIVE3, suggesting that the binding of STOP1 in the promoter is essential for early induction. Finally, we report that GDH1 and 2 which are targets of STOP1, are novel aluminum-resistance genes in Arabidopsis.
STOP1 nuclear-localization and its high affinity binding to target gene promoters are essential for early aluminum-induced gene expression, with GDH1/2 being novel Arabidopsis Al-tolerance genes.
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