Biology subjects

Ichida, H.

Publications and source records attributed to Ichida, H..

6 recordsLinked to original sources

bioRxiv2026

Rice Jumonji706 confers the photoperiod sensitivity in rice by distinct regulation of short-day and long-day flowering time regulatory pathways.

Photoperiod sensitivity (PS) is a key biological response in plants as they adapt to specific environments. Rice (Oryza sativa L.) exhibits a clear PS, as it implements critical phase transition decisions based on PS signals. In this study, we identified a novel PS gene, JMJ706, that is expected to deliver photoperiod-related signals to the flowering-time regulatory network in a day-length-dependent manner. The JMJ706 mutants exhibit early flowering under LD and later flowering under SD compared to WT plants. The gene encodes an H3K9me2 demethylase, and under long-day (LD) conditions, its demethylase activity facilitates the expression of Grain number, Plant height, and Heading-date7 (Ghd7). Since Ghd7 is a floral repressor in LD, it promotes the vegetative phase by delaying flowering. Under short-day conditions (SD), H3K9me2 demethylase activity facilitates Early heading-date 1 (Ehd1) expression, and it acts as a floral accelerator by inducing Heading date 3 (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1). Furthermore, we propose that the daylength-dependent promotion of target genes (Ghd7 and Ehd1) occurs through demethylation of specific promoter regions at a crucial time window. In addition, JMJ706 may play an important role in regulating plant architecture, including plant height. The natural variation in JMJ706 alleles shows high frequencies across major rice subpopulations, suggesting that JMJ706 could play an important role in the geographical distribution and adaptation of rice cultivars. Our results may add a new layer to the rice flowering-time regulatory pathway, supporting regional adaptation and potential for future breeding.

plant biology↗

bioRxiv2025

Mycobacterial DNA-binding protein 1 (MDP1) induces RNA condensation as revealed by high-speed AFM

Mycobacterial DNA-binding protein 1 (MDP1) is a histone-like protein in Mycobacterium tuberculosis (Mtb) that contributes to genome organization and dormancy adaptation. MDP1 consists of a structured HU-like region (HUR), and a post-translational modifications (PTMs)-enriched intrinsically disordered region (IDR), that regulate its function. While its role in DNA condensation is well established, how MDP1 interacts with RNA remains unclear, despite growing recognition of transcriptional regulation during dormancy. Here, by using total RNA from E. coli as a model substrate, we investigated whether MDP1 induces RNA condensation. Our high-speed AFM and optical microscopy analysis shows that native MDP1 from Mtb, rich in PTMs, forms globular RNA condensates. In contrast, MDP1 expressed in E. coli, which lacks PTMs, induces chain-like RNA condensates. Domain-specific analysis revealed that the IDR, the synergy between the IDR and HUR, and PTMs are essential for MDP1-induced RNA condensation. These findings suggest that MDP1 mediates RNA organization during dormancy.

biophysics↗

bioRxiv2025

Identification of an early-heading mutant in Indonesian native rice cultivar: 'Gemdjah Beton'

Rice is one of the worlds most widely cultivated field crops and a short-day adapted plant. It possesses a complex genetic regulatory mechanism for heading date determination. Gemdjah Beton (GB) is an Indonesian rice cultivar that takes approximately 17 weeks to flower after being transplanted into a rice field in Japan. We isolated early-heading mutant line GB-10 (flowers around two to three weeks early in the field). Under long-day (LD) conditions, GB-10 flowered approximately two weeks earlier than GB. Under short-day conditions, the heading date between GB-10 and GB plants shows no apparent difference. In agreement with the heading date, Hd3a and RFT1 expressions show around a 10-time relative transcript quantity difference under LD conditions in GB-10 compared to GB. Interestingly, Ghd7 expression was significantly reduced in GB-10, which may trigger the Hd3a and RFT1 activation. A bulk segregation analysis indicated that a single nucleotide variant on chromosome 7 was genetically linked to the early heading phenotype of GB-10 lines. Taken together, we reported the successful isolation of GB-10 as an early-heading mutant.

plant biology↗

bioRxiv2023

Complete de novo assembly of Tricholoma bakamatsutake chromosomes revealed the structural divergence and differentiation of Tricholoma genomes

Tricholoma bakamatsutake, which is an edible ectomycorrhizal fungus associated with Fagaceae trees, may have diverged before the other species in Tricholoma section Caligata. We generated a highly contiguous whole-genome sequence for T. bakamatsutake SF-Tf05 isolated in an oak (Quercus salicina) forest in Japan. The assembly of high-fidelity long reads, with a median read length of 12.3 kb, resulted in 13 chromosome-sized contigs comprising 142,068,211 bases with an average GC content of 43.94%. The 13 chromosomes were predicted to encode 11,060 genes. A contig (122,566 bases) presumably containing the whole circular mitochondrial genome was also recovered. The chromosome-wide comparison of T. bakamatsutake and T. matsutake (TMA_r1.0) indicated that the basic number of chromosomes (13) was conserved, but the structures of the corresponding chromosomes diverged, with multiple inversions and translocations. Gene conservation and cluster analyses revealed at least three groups in Tricholoma. Specifically, all T. bakamatsutake strains belonged to the "bakamatsutake" clade, which is most proximal to the "caligatum" clade consisting of T. caligatum and T. fulvocastaneum. The constructed highly contiguous telomere-to-telomere genome sequence of a T. bakamatsutake isolate will serve as a fundamental resource for future research on the evolution and differentiation of Tricholoma species.

genomics↗

bioRxiv2022

The mitochondrial genome of Oryza sativa L. cv. Taichung 65 (Poaceae)

A complete mitochondrial genome sequence was determined by a hybrid approach with long- and short-read sequences in a japonica rice cultivar Taichung 65. The assembled mitochondrial genome was 401,060 bases in length and an overall GC content of 43.88% and predicted to harbor 57 protein-encoding, 18 transfer RNA, and 3 ribosomal RNA genes. Phylogenetic and sequence polymorphism analysis indicated that Taichung 65 is classified as typical japonica. The mitochondrial genome resource would serve as a fundamental tool to investigate cytoplasmic male sterility in rice.

genomics↗

bioRxiv2019

Exome sequencing of ion-beam-induced mutants facilitates the detection of candidate genes responsible for phenotypes of mutants in rice

Ion beams are physical mutagens used for plant and microbe breeding that cause mutations via a distinct mechanism from those of chemical mutagens or gamma rays. We utilized whole-exome sequencing of rice DNA in order to understand the properties of ion beam-induced mutations in a genome-wide manner. DNA libraries were constructed from selected carbon-ion-beam-induced rice mutants by capturing with a custom probes covering 66.3 M bases of nearly all exons and miRNAs predicted in the genome. A total of 56 mutations, including 24 single nucleotide variations, 23 deletions, and 5 insertions, were detected in five mutant rice lines (two dwarf and three early-heading-date mutants). The mutations were distributed among all 12 chromosomes, and the average mutation frequency in the M1 generation was estimated to be 2.7 x 10-7 per base. Many single base insertions and deletions were associated with homopolymeric repeats, whereas larger deletions up to seven base pairs were observed at polynucleotide repeats in the DNA sequences of the mutation sites. Of the 56 mutations, six were classified as high-impact mutations that caused a frame shift or loss of exons. A gene that was functionally related to the phenotype of the mutant was disrupted by a high-impact mutation in four of the five lines tested, suggesting that whole-exome sequencing of ion-beam-irradiated mutants could facilitate the detection of candidate genes responsible for the mutant phenotypes.

plant biology↗