Biology subjects

Hiragori, Y.

Publications and source records attributed to Hiragori, Y..

3 recordsLinked to original sources

bioRxiv2026

Putrescine-responsive post-transcriptional feedback regulation of Arabidopsis ADC2 mediated by 5'-UTR elements

Putrescine (Put) is a bioactive polyamine that contributes to plant growth, development, and stress responses, whereas excessive Put accumulation impairs growth. However, how plants maintain Put levels within an appropriate range remains poorly understood. In Arabidopsis thaliana, expression of the arginine decarboxylase 2 (ADC2) gene is a major determinant of Put abundance. Here, we show that the 5' untranslated region (5'-UTR) of ADC2 mediates Put-responsive feedback regulation and contributes to Put homeostasis in Arabidopsis. In transient expression assays using an emerald luciferase (Eluc) gene placed downstream of the ADC2 5'-UTR (ADC2 5'-UTR:Eluc), Eluc activity was reduced by exogenously applied Put but increased when endogenous Put biosynthesis was impaired by adc2 mutations or treatment with an arginine decarboxylase inhibitor. In transgenic plants carrying ADC2 5'-UTR:Eluc, Put treatment modestly decreased Eluc mRNA abundance but substantially reduced Eluc activity and translation efficiency, suggesting that this Put-responsive repression occurs mainly at the translational level. Among the cis-regulatory elements in the ADC2 5'-UTR, mutations affecting either the conserved AUU/CUG-initiated upstream ORF or the predicted RNA secondary structure in the ADC-box, a conserved GC-rich motif, abolished Put-responsive repression, indicating that these elements are required for this regulation. Two genome-edited lines carrying deletions spanning these elements exhibited delayed germination and impaired growth, and the more severely affected line showed increased Put accumulation. Together, these findings reveal a feedback mechanism that regulates ADC2 expression through its 5'-UTR and support a role for this mechanism in Put homeostasis in Arabidopsis.

plant biology↗

bioRxiv2022

The conserved upstream ORF of the Arabidopsis ANAC082 gene mediates translational upregulation in response to nucleolar stress

Perturbations in ribosome biogenesis cause a type of cellular stress called nucleolar or ribosomal stress, which triggers adaptive responses in both animal and plant cells. The Arabidopsis ANAC082 transcription factor has been identified as a key mediator of the plant nucleolar stress response. The 5'-untranslated region (5'-UTR) of ANAC082 mRNA contains an upstream ORF (uORF) encoding an evolutionarily conserved amino acid sequence. Here, we report that this uORF mediates the upregulation of ANAC082 translation in response to nucleolar stress. When transgenic Arabidopsis plants containing a luciferase reporter gene under the control of the ANAC082 promoter and 5'-UTR were treated with reagents that induced nucleolar stress, translation of the reporter gene was enhanced in a uORF sequence-dependent manner. Additionally, we examined the effect of an endoplasmic reticulum (ER) stress-inducing reagent on reporter gene expression because the closest homolog of ANAC082 in Arabidopsis, ANAC103, is involved in the ER stress response. However, the ANAC082 uORF did not respond to ER stress. Interestingly, although ANAC103 has a uORF with an amino acid sequence similar to that of the ANAC082 uORF, the C-terminal sequence critical for regulation is not well conserved among ANAC103 homologs in Brassicaceae. Transient expression assays revealed that unlike the ANAC082 uORF, the ANAC103 uORF does not exert a sequence-dependent regulatory effect. Altogether, our findings suggest that the ANAC082 uORF is important for the nucleolar stress response but not for the ER stress response, and that for this reason, the uORF sequence-dependent translational regulation was lost in ANAC103 during evolution.

plant biology↗

bioRxiv2021

Genome-wide identification of Arabidopsis non-AUG-initiated upstream ORFs with evolutionarily conserved regulatory sequences that control protein expression levels

Upstream open reading frames (uORFs) are short ORFs found in the 5'-UTRs of many eukaryotic transcripts and can influence the translation of protein-coding main ORFs (mORFs). Recent genome-wide ribosome profiling studies have revealed that thousands of uORFs initiate translation at non-AUG start codons. However, the physiological significance of these non-AUG uORFs has so far been demonstrated for only a few of them. It is conceivable that physiologically important non-AUG uORFs are evolutionarily conserved across species. In this study, using a combination of bioinformatics and experimental approaches, we searched the Arabidopsis genome for non-AUG-initiated uORFs with conserved sequences that control the expression of the mORF-encoded proteins. As a result, we identified four novel regulatory non-AUG uORFs. Among these, two exerted repressive effects on mORF expression in an amino acid sequence-dependent manner. These two non-AUG uORFs are likely to encode regulatory peptides that cause ribosome stalling, thereby enhancing their repressive effects. In contrast, one of the identified regulatory non-AUG uORFs promoted mORF expression by alleviating the inhibitory effect of a downstream AUG-initiated uORF. These findings provide insights into the mechanisms that enable non-AUG uORFs to play regulatory roles despite their low translation initiation efficiencies.

genomics↗