In case of genetic transformation (either Agrobacterium mediated or by particle bombardment), we will get transformed plant cells which may be either stably transformed or chimeric transformed cells. What is mean by chimeric transformation (at molecular level or gene/DNA level)?
A chimera (also spelled chimaera) is a single organism composed of genetically distinct cells. Animal chimeras are produced by the merger of multiple fertilized eggs; the result is an organism with two sets of parents, giving them tissues that are a mixture of different genetic inheritance. This can result in male and female organs, two different blood types, or subtle variations in form. In plant chimeras, the distinct types of tissue may originate from the same zygote, and the difference is often due to mutation during ordinary cell division. Normally, chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage.
Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from two different genomes. For example, a bone marrow transplant can change someone's blood type
In plant transformation, chimeras arise due to the characteristics of plant regeneration. Usually plants regenerate from a group of cells, except when regeneration is through somatic embryogenesis, where the embryo is produced from a single cell. After transformation, not all of the cells that give rise to the regenerated tissue are transformed, or can contain independent transformation events, thus resulting in a plant with genetically distinct regions in terms of the introduced construct.
@ Gustavo,
Do you know any publication(s) which confirms that some 'transgenic' plants regenerated from a group of cells (mixed with transgenic cells and non-transgenic cells from cross-protection)? I have heard about that, but I was unable to locate a paper about it. I am interested to know. Thanks!
@Gustavo, you said "after transformation the regenerated tissue can contain independent transformation events". I wonder if I have many regenerative plantlets from a single explant (material for transformation), whether some among them are independent transformation events
@ Nguyen Thuy Linh,
Of course, you should have some independent transformation events among them.
If a single explant with many regenerated plantlets (in your case), some plantlets can be the same 'clones' (in other words, same transgenic evet). This especially true when you collect two plantlets which cluster together. They can derive from a same transgenic callus. To ensure that you obtain lines with independent transgenic events, harvest those 'putative' transgenic lines which are separated (with a distance). Ultimately, you still have to check whether they are the same clones or are independent transgenic events with Southern assay.
@ Dickson Adom,
That is an interesting paper. I like the statement in the paper saying:
"The high frequency of chimeras was probably the result of efficient protection from the hygromycin of non-transformed cells by adjacent transformed ones. The non-transformed cells were removed by multiple rounds of successive shoot regenerations."
It is possible that the transformed cells and the non-transformed cells together develope into a single chimeric transgenic plant.
@ Atul Sathe,
You compared: "stably transformed vs. chimeric transformed" cells.
I think it is more proper to compare things like:
1. Stably transformation vs. transient transformation (ie. transgene is stably integrated vs. transgene is not integrated in the genome)
2. Transgenic line with some cells are not transformed (chimeric) vs. transgenic line with all cells are transformed (non-chimeric)
In the chimeric transgenic line, some cells are transformed, and in those cells, the transgene is stably integrated in the genome.
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