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Homodimerization of Ehd1 Is Required to Induce Flowering in Rice
Cho, Lae-Hyeon,Yoon, Jinmi,Pasriga, Richa,An, Gynheung American Society of Plant Biologists 2016 Plant Physiology Vol.170 No.4
<P>In plants, flowering time is elaborately controlled by various environment factors. Ultimately, florigens such as FLOWERING LOCUS T (FT) or FT-like molecules induce flowering. In rice (Oryza sativa), Early heading date 1 (Ehd1) is a major inducer of florigen gene expression. Although Ehd1 is highly homologous to the type-B response regulator (RR) family in the cytokinin signaling pathway, its precise molecular mechanism is not well understood. In this study, we showed that the C-terminal portion of the protein containing the GARP DNA-binding (G) domain can promote flowering when overexpressed. We also observed that the N-terminal portion of Ehd1, carrying the receiver (R) domain, delays flowering by inhibiting endogenous Ehd1 activity. Ehd1 protein forms a homomer via a 16-amino acid region in the inter domain between R and G. From the site-directed mutagenesis analyses, we demonstrated that phosphorylation of the Asp-63 residue within the R domain induces the homomerization of Ehd1, which is crucial for Ehd1 activity. A type-A RR, OsRR1, physically interacts with Ehd1 to form a heterodimer. In addition, OsRR1-overexpressing plants show a late-flowering phenotype. Based on these observations, we conclude that OsRR1 inhibits Ehd1 activity by binding to form an inactive complex.</P>
Histone Deacetylase 701 (HDT701) Induces Flowering in Rice by Modulating Expression of OsIDS1
Cho, Lae-Hyeon,Yoon, Jinmi,Wai, Antt Htet,An, Gynheung Korean Society for Molecular and Cellular Biology 2018 Molecules and cells Vol.41 No.7
Rice is a facultative short-day (SD) plant in which flowering is induced under SD conditions or by other environmental factors and internal genetic programs. Overexpression of Histone Deacetylase 701 (HDT701) accelerates flowering in hybrid rice. In this study, mutants defective in HDT701 flowered late under both SD and long-day conditions. Expression levels of florigens Heading date 3a (Hd3a) and Rice Flowering Locus T1 (RFT1), and their immediate upstream floral activator Early heading date 1 (Ehd1), were significantly decreased in the hdt701 mutants, indicating that HDT701 functions upstream of Ehd1 in controlling flowering time. Transcript levels of OsINDETERMINATE SPIKELET 1 (OsIDS1), an upstream repressor of Ehd1, were significantly increased in the mutants while those of OsGI and Hd1 were reduced. Chromatin-immunoprecipitation assays revealed that HDT701 directly binds to the promoter region of OsIDS1. These results suggest that HDT701 induces flowering by suppressing OsIDS1.
KNOX Protein OSH15 Induces Grain Shattering by Repressing Lignin Biosynthesis Genes
Yoon, Jinmi,Cho, Lae-Hyeon,Antt, Htet Wai,Koh, Hee-Jong,An, Gynheung American Society of Plant Biologists 2017 Plant Physiology Vol.174 No.1
<P>Seed shattering is an agronomically important trait. Two major domestication factors are responsible for this: qSH1 and SH5. Whereas qSH1 functions in cell differentiation in the abscission zone (AZ), a major role of SH5 is the repression of lignin deposition. We have determined that a KNOX protein, OSH15, also controls seed shattering. Knockdown mutations of OSH15 showed reduced seed-shattering phenotypes. Coimmunoprecipitation experiments revealed that OSH15 interacts with SH5 and qSH1, two proteins in the BELL homeobox family. In transgenic plants carrying the OSH15 promoter-GUS reporter construct, the reporter gene was preferentially expressed in the AZ during young spikelet development. The RNA in situ hybridization experiment also showed that OSH15 messenger RNAs were abundant in the AZ during spikelet development. Analyses of osh15 SH5-D double mutants showed that SH5 could not increase the degree of seed shattering when OSH15 was absent, indicating that SH5 functions together with OSH15. In addition to the seed-shattering phenotype, osh15 mutants displayed dwarfism and accumulated a higher amount of lignin in internodes due to increased expression of the genes involved in lignin biosynthesis. Knockout mutations of CAD2, which encodes an enzyme for the last step in the monolignol biosynthesis pathway, caused an easy seed-shattering phenotype by reducing lignin deposition in the AZ. This indicated that the lignin level is an important determinant of seed shattering in rice (Oryza sativa). Chromatin immunoprecipitation assays demonstrated that both OSH15 and SH5 interact directly with CAD2 chromatin. We conclude that OSH15 and SH5 form a dimer that enhances seed shattering by directly inhibiting lignin biosynthesis genes.</P>
Pasriga, Richa,Cho, Lae-Hyeon,Yoon, Jinmi,An, Gynheung Korean Society for Molecular and Cellular Biology 2018 Molecules and cells Vol.41 No.4
Flowering time is determined by florigens. These genes include, Heading date 3a (Hd3a) and Rice FT 1 (RFT1) in rice, which are specifically expressed in the vascular tissues of leaves at the floral transition stage. To study the cis-regulatory elements present in the promoter region of Hd3a, we generated transgenic plants carrying the 1.75-kb promoter fragment of Hd3a that was fused to the ${\beta}$-glucuronidase (GUS) reporter gene. Plants expressing this construct conferred a vascular cell-specific expression pattern for the reporter gene. However, GUS was expressed in leaves at all developmental stages, including the early seedling stage when Hd3a was not detected. Furthermore, the reporter was expressed in roots at all stages. This suggests that the 1.75-kb region lackings cis-elements that regulate leaf-specific expression at the appropriate developmental stages. Deletion analyses of the promoter region indicated that regulatory elements determining vascular cell-specific expression are present in the 200-bp region between -245 bp and -45 bp from the transcription initiation site. By transforming the Hd3a-GUS construct to rice cultivar 'Taichung 65' which is defective in Ehd1, we observed that Ehd1 is the major regulatory element that controls Hd3a promoter activity.
Chromatin interacting factor Os VIL 2 increases biomass and rice grain yield
Yang, Jungil,Cho, Lae‐,Hyeon,Yoon, Jinmi,Yoon, Hyeryung,Wai, Antt Htet,Hong, Woo‐,Jong,Han, Muho,Sakakibara, Hitoshi,Liang, Wanqi,Jung, Ki‐,Hong,Jeon, Jong‐,Seong,Koh, Hee John Wiley and Sons Inc. 2019 Plant biotechnology journal Vol.17 No.1
<P><B>Summary</B></P><P>Grain number is an important agronomic trait. We investigated the roles of chromatin interacting factor <I>Oryza sativa </I>VIN3‐LIKE 2 (OsVIL2), which controls plant biomass and yield in rice. Mutations in <I>OsVIL2</I> led to shorter plants and fewer grains whereas its overexpression (OX) enhanced biomass production and grain numbers when compared with the wild type. RNA‐sequencing analyses revealed that 1958 genes were up‐regulated and 2096 genes were down‐regulated in the region of active division within the first internodes of OX plants. Chromatin immunoprecipitation analysis showed that, among the downregulated genes, OsVIL2 was directly associated with chromatins in the promoter region of <I>CYTOKININ OXIDASE/DEHYDROGENASE2</I> (<I>OsCKX2</I>), a gene responsible for cytokinin degradation. Likewise, active cytokinin levels were increased in the OX plants. We conclude that OsVIL2 improves the production of biomass and grain by suppressing <I>OsCKX2</I> chromatin.</P>
Chromatin Interacting Factor OsVIL2 Is Required for Outgrowth of Axillary Buds in Rice
Yoon, Jinmi,Cho, Lae-Hyeon,Lee, Sichul,Pasriga, Richa,Tun, Win,Yang, Jungil,Yoon, Hyeryung,Jeong, Hee Joong,Jeon, Jong-Seong,An, Gynheung Korean Society for Molecular and Cellular Biology 2019 Molecules and cells Vol.42 No.12
Shoot branching is an essential agronomic trait that impacts on plant architecture and yield. Shoot branching is determined by two independent steps: axillary meristem formation and axillary bud outgrowth. Although several genes and regulatory mechanism have been studied with respect to shoot branching, the roles of chromatin-remodeling factors in the developmental process have not been reported in rice. We previously identified a chromatin-remodeling factor OsVIL2 that controls the trimethylation of histone H3 lysine 27 (H3K27me3) at target genes. In this study, we report that loss-of-function mutants in OsVIL2 showed a phenotype of reduced tiller number in rice. The reduction was due to a defect in axillary bud (tiller) outgrowth rather than axillary meristem initiation. Analysis of the expression patterns of the tiller-related genes revealed that expression of OsTB1, which is a negative regulator of bud outgrowth, was increased in osvil2 mutants. Chromatin immunoprecipitation assays showed that OsVIL2 binds to the promoter region of OsTB1 chromatin in wild-type rice, but the binding was not observed in osvil2 mutants. Tiller number of double mutant osvil2 ostb1 was similar to that of ostb1, suggesting that osvil2 is epistatic to ostb1. These observations indicate that OsVIL2 suppresses OsTB1 expression by chromatin modification, thereby inducing bud outgrowth.
Moon, Sunok,Cho, Lae-Hyeon,Kim, Yu-Jin,Gho, Yun-Shil,Jeong, Ho Young,Hong, Woo-Jong,Lee, Chanhui,Park, Hyon,Jwa, Nam‐,Soo,Dangol, Sarmina,Chen, Yafei,Park, Hayeong,Cho, Hyun-Soo,An, Gynheung,Jun American Society of Plant Biologists 2019 PLANT PHYSIOLOGY - Vol.179 No.2
<P>Root Hair Defective Six Like (RSL) Class II family proteins regulate root hair development by mediating RHL1 import into the nucleus.</P><P>Root hairs are important for absorption of nutrients and water from the rhizosphere. The Root Hair Defective-Six Like (RSL) Class II family of transcription factors is expressed preferentially in root hairs and has a conserved role in root hair development in land plants. We functionally characterized the seven members of the RSL Class II subfamily in the rice (<I>Oryza sativa</I>) genome. In root hairs, six of these genes were preferentially expressed and four were strongly expressed. Phenotypic analysis of each mutant revealed that <I>Os07g39940</I> plays a major role in root hair formation, based on observations of a short root hair phenotype in those mutants. Overexpression (OX) for each of four family members in rice resulted in an increase in the density and length of root hairs. These four members contain a transcription activation domain and are targeted to the nucleus. They interact with rice Root Hairless1 (OsRHL1), a key regulator of root hair development. When heterologously expressed in epidermal cells of <I>Nicotiana benthamiana</I> leaves, OsRHL1 was predominantly localized to the cytoplasm. When coexpressed with each of the four RSL Class II members, however, OsRLH1 was translocated to the nucleus. Transcriptome analysis using <I>Os07g39940-</I>OX plants revealed that 86 genes, including Class III peroxidases, were highly up-regulated. Furthermore, reactive oxygen species levels in the root hairs were increased in <I>Os07g39940-</I>OX plants but were drastically reduced in the <I>os07g39940</I> and <I>rhl1</I> mutants. Our results demonstrate that RSL Class II members function as essential regulators of root hair development in rice.</P>