Somatic fusion

 Somatic fusion, also called protoplast fusion, is a type of genetic modification in plants by which two distinct species of plants are fused together to form a new hybrid plant with the characteristics of both, a somatic hybrid.^[1] Hybrids have been produced either between different varieties of the same species (e.g. between non-flowering potato plants and flowering potato plants) or between two different species (e.g. between wheat Triticum and rye Secale to produce Triticale).

Fused protoplast (left) with chloroplasts (from a leaf cell) and coloured vacuole (from a petal).

Uses of somatic fusion include making potato plants resistant to potato leaf roll disease.^[2] Through somatic fusion, the crop potato plant Solanum tuberosum – the yield of which is severely reduced by a viral disease transmitted on by the aphid vector – is fused with the wild, non-tuber-bearing potato Solanum brevidens, which is resistant to the disease. The resulting hybrid has the chromosomes of both plants and is thus similar to polyploid plants. Somatic hybridization was first introduced by Carlson et al. in Nicotiana glauca.^[3]

Process for plant cellsEdit

The somatic fusion process occurs in four steps:^[4]

1. The removal of the cell wall of one cell of each type of plant using cellulase enzyme to produce a somatic cell called a protoplast
2. The cells are then fused using electric shock (electrofusion) or chemical treatment to join the cells and fuse together the nuclei. The resulting fused nucleus is called heterokaryon.
3. The formation of the cell wall is then induced using hormones
4. The cells are then grown into calluses which then are further grown to plantlets and finally to a full plant, known as a somatic hybrid.

The procedure for seed plants describe above, fusion of moss protoplasts can be initiated without electric shock but by the use of polyethylene glycol (PEG). Further, moss protoplasts do not need phytohormones for regeneration, and they do not form a callus.^[5] Instead, regenerating moss protoplasts behave like germinating moss spores.^[6] Of further note sodium nitrate and calcium ion at high pH can be used, although results are variable depending on the organism.^[7]

Applications of hybrid cells

Characteristics of somatic hybridization and cybridizationEdit

1. Somatic cell fusion appears to be the only means through which two different parental genomes can be recombined among plants that cannot reproduce sexually (asexual or sterile).
2. Protoplasts of sexually sterile (haploid, triploid, and aneuploid) plants can be fused to produce fertile diploids and polyploids.
3. Somatic cell fusion overcomes sexual incompatibility barriers. In some cases somatic hybrids between two incompatible plants have also found application in industry or agriculture.
4. Somatic cell fusion is useful in the study of cytoplasmic genes and their activities and this information can be applied in plant breeding experiments.

Inter-specific and inter-generic fusion achievementsEdit

Cross	Crossed with
Oat	Maize
Brassica sinensis	B. oleracea
Torrentia fourneri	T. bailloni
Brassica oleracea	B. campestris
Datura innoxia	Atropa belladonna
Nicotiana tabacum	N. glutinosa
Datura innoxia	D. candida
Arabidopsis thaliana	Brassica campestris
Petunia hybrida	Vicia faba

Table: Reference #5 Note: The table only lists a few examples, there are many more crosses. The possibilities of this technology are great; however, not all species are easily put into protoplast culture.

This article uses material from the Wikipedia article  Metasyntactic variable, which is released under the  Creative Commons Attribution-ShareAlike 3.0 Unported License.