• The Plant Pathology Journal
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• 제24권3호
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• pp.296-304
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• 2008

The transient and rapid expression system of a foreign protein in planta is a very useful technique in biotechnology application. We have investigated optimum condition of Agrobacterium-infiltration technique in which expression level of foreign proteins were maximized without detrimental effects on plants using GFP and Cucumber mosaic virus 2b protein, which is known as an enhancer of gene expression and a suppressor of post-transcriptional gene silencing(PTGS). The optimum expression level of both RNA and protein of GFP with minimum leaf impairment was obtained at $OD_{600}$=0.2 of Agrobactrium inocula. The steady-state levels of GFP RNA and protein generally peaked at 3 and 7 days post-infiltration(dpi), respectively. In the presence of 2b, both the magnitude and duration of GFP expression was highly increased and we could detect GFP level until 17 dpi. On the other hands, the 2b-mediated higher accumulation of foreign proteins resulted in the repression of normal leaf growth, possibly due to the limitation of supply of energy or materials required for growth maintenance. Using this Agrobacterium-infiltration system with 2b and GFP, we tested a hypothesis for the threshold model of PTGS initiation. Four GFP transgenic lines of N. benthamiana, which shows different expression level of GFP were tested to determine the threshold level for PTGS initiation. Agrobacterium-infiltration of GFP into those GFP-transgenic plants resulted in the co-silencing of the transgenic GFP. It was found that very low concentration of Agrobacterium with GFP and GFP+2b($OD_{600}$=0.002-0.02) which could not phenotypically induce an additive GFP expression, was enough to trigger PTGS pathway in all GFP transgenic plants. This strongly indicates that each GFP-transgenic plant should be expressing the transgenic GFP at its own pre-determined level and there was no buffer zone of additive GFP-expression to the threshold. In other words, the PTGS seems to be immediately activated as a self-defensive mechanism if an internal balance of gene expression is broken.

• 식물병연구
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• 제21권3호
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• pp.186-192
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• 2015

오이모자이크바이러스 2b 유전자는 전사후유전자침묵(PTGS)을 억제하는 기능을 가진 억제인자이다. 식물체내 2b 유전자 기능을 분석하기 위해 Nicotiana benthamiana에 형질전환하였고 형태변화와 유전자 발현변화를 분석하였다. 8계통의 2b 유전자 형질전환체 중에서 1개의 유전자가 T0 개체에 삽입된 계통은 3개였다. 2b 유전자 형질전환체는 일반적으로 종자 확보가 어려웠지만 다행히 일부 배수화되지 않은 계통(hemizygote)에서는 소량의 종자가 확보되어 계통유지가 가능하였다. 고정계통의 전사체를 해독하여 대조와 비교분석한 바, 2b 유전 자는 특정유전자의 발현을 선택적으로 증대시키는 것이 아닌 다수의 유전자를 비선택적으로 발현을 증대시키는 것으로 판단되었다. 이러한 결과는 2b 유전자가 세포질에 존재하는 다양한 RNA의 대사중 분해를 억제하여 세포질내 RNA가 축적되고 이로 인해 단백질 합성도 증대되어 정상적 생장발달이 저해되고 기형적인 형태의 식물체가 되는 요인으로 판단된다.

• Plant Biotechnology Reports
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• 제5권3호
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• pp.273-281
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• 2011

Diverse epigenetic phenotypes are frequently found during research on transgenic plants. To understand the factors underlying such diversity, hundreds of independent 35S-GFP transgenic N. benthamiana plants were analyzed. The diverse GFP-expression phenotypes of the transgenic plants were classified into three major types based on the GFP expression patterns and their response to 35S-GFP agroinfiltration: steady-green, silenced and non-uniform phenotype. The non-uniform phenotype was further sub-divided into five minor phenotypes: variegated, red-dropped, on-silencing, partitioned and misty, according to the distribution of GFP expression on the leaves. Many of transgenic plants continuously generated diverse phenotypes over several generations despite the transgene identity. Such epigenetic GFP phenotyping was found to be the result of spontaneous transgene silencing mediated by either or both of post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS). This finding was verified by the detection of 21- and 24-nt small interfering RNA (siRNA) molecules, and DNA methylation in the transgenic plants that showed repeated epigenetic variation. Agroinfiltration demonstrated that irregular distribution of GFP on a leaf was the result of erratic transgene silencing, and the technique also proved to be a rapid and effective method for selecting fully silenced plants within 3 days. Furthermore, two novel phenotypes described are potential materials for in-depth investigations into the genes and mechanisms responsible for spontaneous transgene silencing.