• Molecules and Cells
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• 제43권5호
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• pp.448-458
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• 2020

T-DNA insertional mutations in Arabidopsis genes have conferred huge benefits to the research community, greatly facilitating gene function analyses. However, the insertion process can cause chromosomal rearrangements. Here, we show an example of a likely rearrangement following T-DNA insertion in the Anti-Silencing Function 1B (ASF1B) gene locus on Arabidopsis chromosome 5, so that the phenotype was not relevant to the gene of interest, ASF1B. ASF1 is a histone H3/H4 chaperone involved in chromatin remodeling in the sporophyte and during reproduction. Plants that were homozygous for mutant alleles asf1a or asf1b were developmentally normal. However, following self-fertilization of double heterozygotes (ASF1A/asf1a ASF1B/asf1b, hereafter AaBb), defects were visible in both male and female gametes. Half of the AaBb and aaBb ovules displayed arrested embryo sacs with functional megaspore identity. Similarly, half of the AaBb and aaBb pollen grains showed centromere defects, resulting in pollen abortion at the bi-cellular stage of the male gametophyte. However, inheritance of the mutant allele in a given gamete did not solely determine the abortion phenotype. Introducing functional ASF1B failed to rescue the AaBb- and aaBb-mediated abortion, suggesting that heterozygosity in the ASF1B gene causes gametophytic defects, rather than the loss of ASF1. The presence of reproductive defects in heterozygous mutants but not in homozygotes, and the characteristic all-or-nothing pollen viability within tetrads, were both indicative of commonly-observed T-DNA-mediated translocation activity for this allele. Our observations reinforce the importance of complementation tests in assigning gene function using reverse genetics.

• 한국산림과학회지
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• 제3권1호
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• pp.1-4
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• 1963

개나리 단주화개체(短柱花個體)를 사용(使用)하여 자성배우체발육(雌性配偶體發育)의 지연(遲延) 및 이상(異常), 임성(稔性)과의 관계(關係)를 조사(調査)한바 그 결과(結果)를 요약(要略)하면 다음과 같다. 1. 도생배주(倒生胚珠)의 주피(珠皮)는 대단(大端)히 두텁고 주심(珠心)은 반대(反對)로 극(極)히 작다. 2. 소포자모세포(小胞子母細胞)의 감수분열(減數分裂)은 9월하순(月下旬)~10월초순경(月初旬頃)인데 대포자모세포(大胞子母細胞)는 3월중하순경(月中下旬頃)에야 일어 난다. 3. 대포자모세포기(大胞子母細胞期)는 대단(大端)히 길다. 4. 성열배낭(成熱胚囊)은 개화약(開花約) 1개월후(個月後)인 5월초(月初)에 형성(形成)된다. 5. 정상배낭(正常胚囊)은 많지 않고 대부분(大部分)의 경우 배낭(胚囊)이 없는 공허(空虛)한 주심조직(珠心組織)만 생(生)긴다.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.20-20
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• 2017

Plant genomes include heterochromatic loci that consist of repetitive sequences and transposable elements. LTR retrotransposon is the major class of transposons in advanced plants in terms of proportion in plant genome. The elements contribute not only to genome size but also to genome stability and gene expression. A number of cases have been reported transposon insertions near genic regions affect crop traits such as fruit pigments, stress tolerance, and yields. Functional LTR retrotransposons produce extrachromosomal DNA from genomic RNA by reverse transcription that takes place within virus-like-particles (VLPs). DECREASED DNA METHYLATION 1 (DDM1) plays important roles in maintaining DNA methylation of heterochromatin affecting all sequence contexts, CG, CHG, and CHH. Previous studies showed that ddm1 mutant exhibits massive transcription of retrotransposons in Arabidopsis, but only few of them were able to create new insertions into the genome. RNA-dependent RNA POLYMERASE 6 (RDR6) is known to function in restricting accumulation of transposon RNA by processing the transcripts into 21-22 nt epigenetically activated small interfering RNA (easiRNA). We purified VLPs and sequence cDNA to identify functional LTR retrotransposons in Arabidopsis ddm1 and ddm1rdr6 plants. Over 20 LTR copia and gypsy families were detected in ddm1 and ddm1rdr6 sequencing libraries and most of them were not reported for mobility. In ddm1rdr6, short fragments of ATHILA gypsy elements were detected. It suggests easiRNAs might regulate reverse transcription steps. The highest enriched element among transposon loci was previously characterized EVADE element. It has been reported that active EVADE element is more efficiently silenced through female germline than male germline. By genetic analyses, we found ddm1 and rdr6 mutation affect maternal silencing of active EVADE elements. DDM1-GFP protein accumulated in megaspore mother cell but was not found in mature egg cell. The fusion protein was also found in early embryo and maternal DDM1-GFP allele was more dominantly expressed in the embryo. We observed localization of DDM1-GFP in Arabidopsis and DDM1-YFP in maize and found the proteins accumulated in dividing zone of root tips. Currently we are looking at cell cycle dependency of DDM1 expression using maize system. Among 10 AGO proteins in Arabidopsis, AGO9 is specifically expressed in egg cell and shoot meristematic cells. In addition, mutation of AGO9 and RDR6 caused failure in maternal silencing, implying 21-22 nt easiRNA pathway is important for retrotransposon silencing in female gametophyte or/and early embryo. On the other hand, canonical 24 nt sRNA-directed DNA methylation (RdDM) pathways did not contribute to maternal silencing as confirmed by this study. Heat-activated LTR retrotransposon, ONSEN, was not silenced by DDM1 but the silencing mechanisms require RdDM pathways in somatic cells. We will propose distinct mechanisms of LTR retrotransposons in germline and somatic stages.

• 한국작물학회:학술대회논문집
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• 한국작물학회 2017년도 9th Asian Crop Science Association conference
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• pp.97-97
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• 2017

Plant genomes include heterochromatic loci that consist of repetitive sequences and transposable elements. LTR retrotransposon is the major class of transposons in advanced plants in terms of proportion in plant genome. The elements contribute not only to genome size but also to genome stability and gene expression. A number of cases have been reported transposon insertions near genic regions affect crop traits such as fruit pigments, stress tolerance, and yields. Functional LTR retrotransposons produce extrachromosomal DNA from genomic RNA by reverse transcription that takes place within virus-like-particles (VLPs). DECREASED DNA METHYLATION 1 (DDM1) plays important roles in maintaining DNA methylation of heterochromatin affecting all sequence contexts, CG, CHG, and CHH. Previous studies showed that ddm1 mutant exhibits massive transcription of retrotransposons in Arabidopsis, but only few of them were able to create new insertions into the genome. RNA-dependent RNA POLYMERASE 6 (RDR6) is known to function in restricting accumulation of transposon RNA by processing the transcripts into 21-22 nt epigenetically activated small interfering RNA (easiRNA). We purified VLPs and sequence cDNA to identify functional LTR retrotransposons in Arabidopsis ddm1 and ddm1rdr6 plants. Over 20 LTR copia and gypsy families were detected in ddm1 and ddm1rdr6 sequencing libraries and most of them were not reported for mobility. In ddm1rdr6, short fragments of ATHILA gypsy elements were detected. It suggests easiRNAs might regulate reverse transcription steps. The highest enriched element among transposon loci was previously characterized EVADE element. It has been reported that active EVADE element is more efficiently silenced through female germline than male germline. By genetic analyses, we found ddm1 and rdr6 mutation affect maternal silencing of active EVADE elements. DDM1-GFP protein accumulated in megaspore mother cell but was not found in mature egg cell. The fusion protein was also found in early embryo and maternal DDM1-GFP allele was more dominantly expressed in the embryo. We observed localization of DDM1-GFP in Arabidopsis and DDM1-YFP in maize and found the proteins accumulated in dividing zone of root tips. Currently we are looking at cell cycle dependency of DDM1 expression using maize system. Among 10 AGO proteins in Arabidopsis, AGO9 is specifically expressed in egg cell and shoot meristematic cells. In addition, mutation of AGO9 and RDR6 caused failure in maternal silencing, implying 21-22 nt easiRNA pathway is important for retrotransposon silencing in female gametophyte or/and early embryo. On the other hand, canonical 24 nt sRNA-directed DNA methylation (RdDM) pathways did not contribute to maternal silencing as confirmed by this study. Heat-activated LTR retrotransposon, ONSEN, was not silenced by DDM1 but the silencing mechanisms require RdDM pathways in somatic cells. We will propose distinct mechanisms of LTR retrotransposons in germline and somatic stages.

• 한국수산과학회지
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• 제14권1호
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• pp.24-28
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• 1981

1980년 6월 20일부터 14일간, 어 청도산 미역을 모조로 유주자를 착생시킨 후, Keinetin, IAA및 2.4-D의 농도별배지에서 배양하여 배우체의 생장에 미치는 영향을 조사하였파. 그 결과를 간추리면 다음과 같다. 1. 발아율은 거의 $100\%$였으나 2.4-D 0.1 mg/l 또는 Keinetin 0.1, 1.0 또는 5.0 mg/1 배지에서는 발아관이 신장하지 않고 착생육자에서 바로 신생세포가 형성되었다. 2. 전체적 생장효과는 Keinetin 0.1 mg/l 배지에서 대조대비 $248.9\%$를 기록, 최고치를 표시하였고, IAA 1.0 mg/1($243.3\%$) 2.4-D에서는 0.05mg/l ($205.6\%$)가 가장 좋았다. 3. 웅성배우체에 미친 생장효과는 IAA 1.0mg/l가 $276.8\%$로서 최고치를 나타냈고 Keinetin 0.1mg/l($263.6\%$), 0.5mg/1($248.3\%$), 2.4-D 0.05mg/1($227.8\%$)의 순이 었다. 4. 자성배우체에서는 Keinetin이 효과적으로 작용하여 5.0mg/1($239.0\%$), 0.1mg/l ($222.0\%$), 0.05mg/l ($209.8\%$)를 기록 현저한 공률을 보여주고 있으나 IAA에서는 0.5mg/l($195.1\%$), 2.4-D에서는 0.05mg/1($164.6\%$)가 최고지를 기록하고 있어 대체로 웅성배우체에 비해 저조하고 배우체의 성에 따라 식물Hormone의 생장효과는 그 종류와 농도를 달리한다. 5. 생장조해농도는 2.4-D 0.5mg/l이상, IAA 0.5mg/1이상이고, Keinetin은 10.0mg/l 이상의 농도에서 생장이 크게 억제하고 있다. 6. 유효농도범의는 Keinetinol 0.01mg/1-5.0mg/l로 가장 넓고 공률곡선이 대단히 완만하며 IAA도 비교적 넓어 0.02mg/1와 1.0mg/l를 정점으로 생장효율 곡선이 S자형을 보여주고 있으나 2.4-D는 극히 좁아 0.05mg/1를 중심으로 급격히 저하하여 삼각곡선을 표시한다.