Enhancement of Chloroplast Transformation Frequency by Using Mesophyll Cells Containing a Few Enlarged Chloroplasts from Nuclear Transformed Plants in Tobacco
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Abstract:
엽록체 형질전환된 식물체를 얻으려면 먼저 세포수준에서 모든 엽록체가 형질전환되어야 하는데, 세포내에는 많은 수의 엽록체가 존재하므로, 엽록체 형질전환 벡터가 전이되어 형질전환된 엽록체는 선발배지에서 선택적으로 분열을 계속하고 형질전환되지 않은 엽록체들은 분열을 하지 못하게 되어, 결국 해당 세포내의 모든 엽록체가 형질전환된 상태에 이르게 된다. 따라서 만일 해당 세포내에 엽록체의 수가 적으면 그만큼 효율적으로 엽록체 형질전환을 할 수 있을 것이다. 본 연구에서는 담배의 FtsZ 유전자를 핵형질전환법으로 과잉 발현시킴으로써 엽록체의 분열이 저해되어 엽육세포내에 거대한 엽록체 3-5개를 가진 담배식물체의 엽육조직을 이용하여, 엽록체 형질전환을 한 결과, 엽록체 형질전환 빈도가 약 40% 증가되었다. In the chloroplast transformation process, a chloroplast containing transformed chloroplast genome copies should be selected over wild-type chloroplasts on selection medium. It is more effective for a cell to become homoplasmic if the cell contains smaller number of chloroplasts. Therefore, to reduce the number of chloroplasts in mesophyll cells in tobacco, we overexpressed FtsZ to generate transgenic plants, of which mesophyll cell contained a few enlarged chloroplasts contrast to a wild-type mesophyll cell containing approximately 100 chloroplasts. It was demonstrated that transgenic leaf tissues comprising cells with a few enlarged chloroplasts gave rise to approximately 40% higher frequency of chloroplast-transformed adventitious shoots.Keywords:
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Nuclear gene
Solanum tuberosum
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During plant evolution, some plastid genes have been moved to the nuclear genome. These transferred genes are now correctly expressed in the nucleus, their products being transported into the chloroplast. We compared the base compositions, the distributions of some dinucleotides and codon usages of transferred, nuclear and chloroplast genes in two dicots and two monocots plant species. Our results indicate that transferred genes have adjusted to nuclear base composition and codon usage, being now more similar to the nuclear genes than to the chloroplast ones in every species analyzed.
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Chloroplasts are unique organelles within the plant cells and are responsible for sustaining life forms on the earth due to their ability to conduct photosynthesis. Multiple functional genes within the chloroplast are responsible for a variety of metabolic processes that occur in the chloroplast. Considering its fundamental role in sustaining life on the earth, it is important to identify the level of diversity present in the chloroplast genome, what genes and genomic content have been lost, what genes have been transferred to the nuclear genome, duplication events, and the overall origin and evolution of the chloroplast genome. Our analysis of 2511 chloroplast genomes indicated that the genome size and number of coding DNA sequences (CDS) in the chloroplasts genome of algae are higher relative to other lineages. Approximately 10.31% of the examined species have lost the inverted repeats (IR) in the chloroplast genome that span across all the lineages. Genome-wide analyses revealed the loss of the Rbcl gene in parasitic and heterotrophic plants occurred approximately 56 Ma ago. PsaM, Psb30, ChlB, ChlL, ChlN, and Rpl21 were found to be characteristic signature genes of the chloroplast genome of algae, bryophytes, pteridophytes, and gymnosperms; however, none of these genes were found in the angiosperm or magnoliid lineage which appeared to have lost them approximately 203-156 Ma ago. A variety of chloroplast-encoded genes were lost across different species lineages throughout the evolutionary process. The Rpl20 gene, however, was found to be the most stable and intact gene in the chloroplast genome and was not lost in any of the analyzed species, suggesting that it is a signature gene of the plastome. Our evolutionary analysis indicated that chloroplast genomes evolved from multiple common ancestors ~1293 Ma ago and have undergone vivid recombination events across different taxonomic lineages.
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The role of chloroplast (cp) DNA in plastid and chloroplast function is discussed, particularly in relation to the interaction with nuclear DNA. The evolution of the chloroplast genome and the endosymbiont hypothesis are related to our results and those of others which show the occurrence of cpDNA sequences common to the nuclear and chloroplast genome.
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The presence of chloroplast-related DNA sequences in the nuclear genome is generally regarded as a relic of the process by which genes have been transferred from the chloroplast to the nucleus. The remaining chloroplast encoded genes are not identical across the plant kingdom indicating an ongoing transfer of genes from the organelle to the nucleus. This review focuses on the active processes by which the nuclear genome might be acquiring or removing DNA sequences from the chloroplast genome. Present knowledge of the contribution to the nuclear genome of DNA originating from the chloroplast will be reviewed. In particular, the possible effects of stressful environments on the transfer of genetic material between the chloroplast and nucleus will be considered. The significance of this research and suggestions for the future research directions to identify drivers, such as stress, of the nuclear incorporation of plastid sequences are discussed. The transfer to the nuclear genome of most of the protein-encoding functions for chloroplast-located proteins facilitates the control of gene expression. The continual transfer of fragments, including complete functional genes, from the chloroplast to the nucleus has been observed. However, the mechanisms by which the loss of functions and physical DNA elimination from the chloroplast genome following the transfer of those functions to the nucleus remains obscure. The frequency of polymorphism across chloroplast-related DNA fragments within a species will indicate the rate at which these DNA fragments are incorporated and removed from the chromosomes.
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Chloroplasts are plant cell organelles whose main role is carrying out photosynthetic processes that originated by an endosymbiotic event between autotrophic bacteria and a eukaryotic ancestor that already possessed mitochondria. Due to their prokaryotic origin, chloroplasts still contain numerous characteristics of their ancestors, and one of the most important is the chloroplast genome. This seminar presents the chloroplast genome content and fundamental genetic mechanisms that take place in chloroplasts. Gene structure and regulation of gene expression in chloroplasts closely resembles that of prokaryotes, but during evolution chloroplast genome also acquired numerous eukaryotic characteristics, which is why it is a chimeric genetic system. During the evolution, the chloroplast genome suffered a large reduction in size. The reduction of its content is the result of gene transfer from chloroplast to the nucleus genome and consequent functional replacement of chloroplast copy by the nuclear one. Consequently, chloroplast proteins synthesized in cytosol are routed into chloroplast by specific signalling sequences or acquire new functions in cytosol or mitochondria. This process increased the complexity of eukaryotic genome and led to functional novelties that enabled better selection advantages. In algae and lower plants, the chloroplast genome content is large and by moving towards the more advanced plant lineages, increasing reduction in chloroplast genome is observed. However, the question arises to why there has not been a complete reduction in chloroplast genome, which is explained by a number of theories, but none of which was able to fully clarify the phenomenon of retaining multiple separate genetic systems in a single cell, which leaves room for further research that will shed light on the evolutionary significance of the chloroplast genome.
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Nuclear gene
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