An inhibitory effect of the sequence-conserved upstream open-reading frame on the translation of the main open-reading frame of HsfB1 transcripts in Arabidopsis.
ABSTRACT Plants have as many as 20 heat shock factors (Hsfs) grouped into three classes, A, B and C, based on sequence similarity and modular structures. Through screening for cell death-inducing factor(s) in Nicotiana benthamiana, we identified Arabidopsis HsfB2b and thus subjected all other members of Arabidopsis Hsf class B (HsfB1, HsfB2a, HsfB2b, HsfB3 and HsfB4) to the same cell death assay. When expressed in N. benthamiana leaves, only HsfB1 and HsfB2b elicited mild cell death. Simultaneously we found that HsfB1 has a post-transcriptional control mechanism, in which a sequence-conserved upstream open-reading frame (sc-uORF) is involved. The known repressor function of the respective HsfBs was confirmed and the difference in cell death-inducing activity of HsfBs was explained by the fact that HsfB1 and HsfB2b are transcriptional repressors but the others are not. Indeed, the cell death symptom by HsfB1 and HsfB2b required not only their repression activity but also their nuclear localization activity. HsfB1 expression was drastically and transiently induced by heat shock (HS) and the intactness of sc-uORF was required for its HS response. Based on the results, the physiological significance of cell death-inducing activity of HsfB1 and HsfB2b and the sc-uORF in the HsfB1 transcript during HS response is discussed.
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ABSTRACT: The sequence elements that mediate post-transcriptional gene regulation often reside in the 5' and 3' untranslated regions (UTRs) of mRNAs. Using six different families of dicotyledonous plants, we developed a comparative transcriptomics pipeline for the identification and annotation of deeply conserved regulatory sequences in the 5' and 3' UTRs. Our approach was robust to confounding effects of poor UTR alignability and rampant paralogy in plants. In the 3' UTR, motifs resembling PUMILIO-binding sites form a prominent group of conserved motifs. Additionally, Expansins, one of the few plant mRNA families known to be localized to specific subcellular sites, possess a core conserved RCCCGC motif. In the 5' UTR, one major subset of motifs consists of purine-rich repeats. A distinct and substantial fraction possesses upstream AUG start codons. Half of the AUG containing motifs reveal hidden protein-coding potential in the 5' UTR, while the other half point to a peptide-independent function related to translation. Among the former, we added four novel peptides to the small catalog of conserved-peptide uORFs. Among the latter, our case studies document patterns of uORF evolution that include gain and loss of uORFs, switches in uORF reading frame, and switches in uORF length and position. In summary, nearly three hundred post-transcriptional elements show evidence of purifying selection across the eudicot branch of flowering plants, indicating a regulatory function spanning at least 70 million years. Some of these sequences have experimental precedent, but many are novel and encourage further exploration.RNA 03/2012; 18(3):368-84. · 5.09 Impact Factor
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ABSTRACT: Metabolic profiling analyses were performed to determine metabolite temporal dynamics associated with the induction of acquired thermotolerance in response to heat shock and acquired freezing tolerance in response to cold shock. Low-M(r) polar metabolite analyses were performed using gas chromatography-mass spectrometry. Eighty-one identified metabolites and 416 unidentified mass spectral tags, characterized by retention time indices and specific mass fragments, were monitored. Cold shock influenced metabolism far more profoundly than heat shock. The steady-state pool sizes of 143 and 311 metabolites or mass spectral tags were altered in response to heat and cold shock, respectively. Comparison of heat- and cold-shock response patterns revealed that the majority of heat-shock responses were shared with cold-shock responses, a previously unknown relationship. Coordinate increases in the pool sizes of amino acids derived from pyruvate and oxaloacetate, polyamine precursors, and compatible solutes were observed during both heat and cold shock. In addition, many of the metabolites that showed increases in response to both heat and cold shock in this study were previously unlinked with temperature stress. This investigation provides new insight into the mechanisms of plant adaptation to thermal stress at the metabolite level, reveals relationships between heat- and cold-shock responses, and highlights the roles of known signaling molecules and protectants.Plant physiology 01/2005; 136(4):4159-68. · 6.56 Impact Factor
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ABSTRACT: Sugars have been shown to regulate transcription of numerous genes in plants. Sucrose controls translation of the group S basic region leucine zipper (bZIP)-type transcription factor ATB2/AtbZIP11 (Rook et al., 1998a). This control requires the unusually long 5' untranslated region (UTR) of the gene. Point mutations and deletions of the 5'UTR have uncovered the sequences involved. A highly conserved upstream open reading frame (uORF) coding for 42 amino acids is essential for the repression mechanism. It is conserved in 5'UTRs of bZIP transcription factors from other Arabidopsis thaliana genes and many other plants. ATB2/AtbZIP11 is normally expressed in association with vascular tissues. Ectopic expression of a 5'UTR construct shows that the sucrose repression system is functional in all tissues. AtbZIP2 is another Arabidopsis bZIP transcription factor gene harboring the conserved uORF, which is regulated similarly via sucrose-induced repression of translation. This suggests a general function of the conserved uORF in sucrose-controlled regulation of expression. Our findings imply the operation of a sucrose-sensing pathway that controls translation of several plant bZIP transcription factor genes harboring the conserved uORF in their 5'UTRs. Target genes of such transcription factors will then be regulated in sucrose-dependent way.The Plant Cell 08/2004; 16(7):1717-29. · 9.25 Impact Factor