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>

Structure and Expression of OsUBP6, an Ubiquitin-Specific Protease 6 Homolog in Rice (Oryza sativa L.)

Yea Kyung Moon,Jong-Pil Hong,Young-Chan Cho,Sae-Jun Yang,Gynheung An,김우택 한국분자세포생물학회 2009 Molecules and cells Vol.28 No.5

Although the possible cellular roles of several ubiquitin-specific proteases (UBPs) were identified in Arabidopsis, almost nothing is known about UBP homologs in rice, a monocot model plant. In this report, we searched the rice genome database (http://signal.salk.edu/cgi-bin/RiceGE) and identified 21 putative UBP family members (OsUBPs) in the rice genome. These OsUBP genes each contain a ubiquitin carboxyl-terminal hydrolase (UCH) domain with highly conserved Cys and His boxes and were subdivided into 9 groups based on their sequence identities and do-main structures. RT-PCR analysis indicated that rice OsUBP genes are expressed at varying degrees in differ-ent rice tissues. We isolated a full-length cDNA clone for OsUBP6, which possesses not only a UCH domain, but also an N-terminal ubiquitin motif. Bacterially expressed OsUBP6 was capable of dismantling K48-linked tetra-ubiquitin chains in vitro. Quantitative real-time RT-PCR indicated that OsUBP6 is constitutively expressed in dif-ferent tissues of rice plants. An in vivo targeting experi-ment showed that OsUBP6 is predominantly localized to the nucleus in onion epidermal cells. We also examined how knock-out of OsUBP6 affects developmental growth of rice plants. Although homozygous T3 osubp6 T-DNA insertion mutant seedlings displayed slower growth rela-tive to wild type seedlings, mature mutant plants appeared to be normal. These results raise the possibility that loss of OsUBP6 is functionally compensated for by an as-yet unknown OsUBP homolog during later stages of devel-opment in rice plants.

Rice transcription factor OsMYB102 delays leaf senescence by down-regulating abscisic acid accumulation and signaling

Piao, Weilan,Kim, Suk-Hwan,Lee, Byoung-Doo,An, Gynheung,Sakuraba, Yasuhito,Paek, Nam-Chon Oxford University Press 2019 Journal of experimental botany Vol.70 No.10

<▼1><P><B>Abstract</B></P><P>MYB-type transcription factors (TFs) play important roles in plant growth and development, and in the responses to several abiotic stresses. In rice (<I>Oryza sativa</I>), the roles of MYB-related TFs in leaf senescence are not well documented. Here, we examined rice MYB TF gene <I>OsMYB102</I> and found that an <I>OsMYB102</I> T-DNA activation-tagged line (termed <I>osmyb102-D</I>), which constitutively expresses <I>OsMYB102</I> under the control of four tandem repeats of the 35S promoter, and <I>OsMYB102</I>-overexpressing transgenic lines (<I>35S:OsMYB102</I> and <I>35S:GFP-OsMYB102</I>) maintain green leaves much longer than the wild-type under natural, dark-induced, and abscisic acid (ABA)-induced senescence conditions. Moreover, an <I>osmyb102</I> knockout mutant showed an accelerated senescence phenotype under dark-induced and ABA-induced leaf senescence conditions. Microarray analysis showed that a variety of senescence-associated genes (SAGs) were down-regulated in the <I>osmyb102-D</I> line. Further studies demonstrated that overexpression of <I>OsMYB102</I> controls the expression of SAGs, including genes associated with ABA degradation and ABA signaling (<I>OsABF4</I>, <I>OsNAP</I>, and <I>OsCYP707A6</I>), under dark-induced senescence conditions. OsMYB102 inhibits ABA accumulation by directly activating the transcription of <I>OsCYP707A6</I>, which encodes the ABA catabolic enzyme ABSCISIC ACID 8′-HYDROXYLASE. OsMYB102 also indirectly represses ABA-responsive genes, such as <I>OsABF4</I> and <I>OsNAP</I>. Collectively, these results demonstrate that OsMYB102 plays a critical role in leaf senescence by down-regulating ABA accumulation and ABA signaling responses.</P></▼1><▼2><P>Rice transcription factor OsMYB102 delays leaf senescence by decreasing ABA accumulation through up-regulation of <I>OsCYP707A6,</I> which encodes an ABA catalytic enzyme. </P></▼2>

Chromatin remodelling factors OsVIL2 and OsVIL4 control flowering time and yield in rice

Gynheung An 한국육종학회 2013 한국육종학회 심포지엄 Vol.2013 No.07

Flowering is exquisitely regulated by both promotive and inhibitory factors. Molecular genetic studies with Arabidopsis have verified several epigenetic repressors that regulate flowering time. However, the roles of chromatin remodeling factors in developmental processes have not been well explored in rice. We identified a chromatin remodeling factor OsVIL2 (O. sativa VIN3-LIKE 2) that promotes flowering. OsVIL2 contains a plant homeodomain (PHD) finger, which is a conserved motif of histone binding proteins. Insertion mutations in OsVIL2 caused late flowering under both long and short days. In osvil2 mutants OsLFL1 expression was increased, but that of Ehd1, Hd3a and RFT1 was reduced. We demonstrated that OsVIL2 is bound to native histone H3 in vitro. Chromatin immunoprecipitation analyses showed that OsVIL2 was directly associated with OsLFL1 chromatin. We also observed that H3K27me3 was significantly enriched by OsLFL1 chromatin in the wild type, but that this enrichment was diminished in the osvil2 mutants. These results indicated that OsVIL2 epigenetically represses OsLFL1 expression. We showed that OsVIL2 physically interacts with OsEMF2b, a component of polycomb repression complex 2. As observed from osvil2, a null mutation of OsEMF2b caused late flowering by increasing OsLFL1 expression and decreasing Ehd1 expression. Thus, we conclude that OsVIL2 functions together with PRC2 to induce flowering by repressing OsLFL1. Transgenic plants over-expressing OsVIL2 flowered early. In addition, they were taller and ticker due to increased in cell number, resulting in yield increase. The same phenotypes were observed from OsVIL4 knockout mutants. These indicate that OsVIL4 represses OsVIL2 function by directly binding to the protein.

Molecular Genetics Using T-DNA in Rice

An, Gynheung,Lee, Shinyoung,Kim, Sung-Hyun,Kim, Seong-Ryong Oxford University Press 2005 Plant & cell physiology Vol.46 No.1

<P>Now that sequencing of the rice genome is nearly completed, functional analysis of its large number of genes is the next challenge. Because rice is easy to transform, T-DNA has been used successfully to generate insertional mutant lines. Collectively, several laboratories throughout the world have established at least 200,000 T-DNA insertional lines. Some of those carry the <I>GUS</I> or <I>GFP</I> reporters for either gene or enhancer traps. Others are activation tagging lines for gain-of-function mutagenesis when T-DNA is inserted in the intergenic region. A forward genetic approach showed limited success because of somaclonal variations induced during tissue culture. To utilize these resources more efficiently, tagged lines have been produced for reverse genetics approaches. DNA pools of the T-DNA-tagged lines have been prepared for polymerase chain reaction (PCR) screening of insertional mutants in a given gene. Appropriate T-DNA insertion sites are determined by sequencing the region flanking the T-DNA. This information is then used to make databases that are shared with the scientific community. International efforts on seed amplification and maintenance are needed to exploit these valuable materials efficiently.</P>

Roles of Sugars in Controlling Flowering Time

Gynheung An,전종성,조래현,Richa Pasriga,Jinmi Yoon 한국식물학회 2018 Journal of Plant Biology Vol.61 No.3

Flowering time is influenced by environmentalfactors such as photosynthesis, temperature, nutrition, andwater. The main products of photosynthesis are sugars thatare mobilized to sink tissues to support plant growth anddifferentiation. They also function as signals to controlvarious types of metabolism and developmental processes. One of the most important transitions in the plant life cycleis from the vegetative to reproductive phase. During thattransition, sucrose levels rise rapidly but transiently in thephloem and shoot apexes. For several species, the addition ofexogenous sucrose promotes flowering, possibly by acting asa main signal. Although other sugars, including glucose, alsoappear to be involved in this transition, evidence for theirroles in flowering is limited. In Arabidopsis thaliana,trehalose-6-phosphate serves as a signal to induce flowering. However, its roles in other plants have not been reported. Sucrose seems to function primarily in the leaf phloem toenhance the generation of florigens such as Flowering LocusT (FT) while trehalose-6-phosphate functions in the shootapical meristem to promote the flowering signal pathwaydownstream of those florigens.

Overriding Photoperiod Sensitivity of Flowering Time by Constitutive Expression of a MADS Box Gene

An, Kyungsook,An, Gynheung 한국식물학회 2000 Journal of Plant Biology Vol.43 No.1

Most plants sense changes in environmental signals, such as day length or temperature. Here, we report the identification of a regulatory gene, OsMADS1, which controls the photoperiod sensitivity of flowering time. Constitutive expression of OsMADS1 in a long-day flowering plant, Nicotiana sylvestris, resulted in flowering under both short-day and long-day conditions. Similarly, ectopic expression of the gene in a short-day flowering plant, Nicotiana tabacum cv. Maryland Mammoth, also induced flowering, regardless of day length. Transition time depended on the level of the OsMADS1 transcript in transgenic plants. These suggest that OsMADS1 is a key regulatory factor that determines the transition from shoot apex to floral meristem, and that it may be used for controlling flowering time in a variety of plant species.

Chromatin Interacting Factor OsVIL2 Is Required for Outgrowth of Axillary Buds in Rice

Gynheung An,Jinmi Yoon,조래현,이시철,Richa Pasriga,윈툰,Jungil Yang,Hyeryung Yoon,Hee Joong Jeong,전종성 한국분자세포생물학회 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.

Analysis of the early-flowering mechanisms and generation of T-DNA tagging lines in Kitaake, a model rice cultivar

Kim, Song Lim,Choi, Minkyung,Jung, Ki-Hong,An, Gynheung Oxford University Press 2013 Journal of experimental botany Vol.64 No.14

<P>As an extremely early flowering cultivar, rice cultivar Kitaake is a suitable model system for molecular studies. Expression analyses revealed that transcript levels of the flowering repressor <I>Ghd7</I> were decreased while those of its downstream genes, <I>Ehd1</I>, <I>Hd3a</I>, and <I>RFT1</I>, were increased. Sequencing the known flowering-regulator genes revealed mutations in <I>Ghd7</I> and <I>OsPRR37</I> that cause early translation termination and amino acid substitutions, respectively. Genetic analysis of F2 progeny from a cross between cv. Kitaake and cv. Dongjin indicated that those mutations additively contribute to the early-flowering phenotype in cv. Kitaake. Because the short life cycle facilitates genetics research, this study generated 10 000 T-DNA tagging lines and deduced 6758 flanking sequence tags (FSTs), in which 3122 were genic and 3636 were intergenic. Among the genic lines, 367 (11.8%) were inserted into new genes that were not previously tagged. Because the lines were generated by T-DNA that contained the promoterless <I>GUS</I> reporter gene, which had an intron with triple splicing donors/acceptors in the right border region, a high efficiency of <I>GUS</I> expression was shown in various organs. Sequencing of the GUS-positive lines demonstrated that the third splicing donor and the first splicing acceptor of the vector were extensively used. The FST data have now been released into the public domain for seed distribution and facilitation of rice research.</P>

사과의 분자육종학적 연구

안진흥(Gynheung An),김우택(Woo Taek Kim),김성룡(Seong Ryong Kim) 한국원예학회 1998 원예과학기술지 Vol.16 No.3