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Terminology and historical aspects

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Somaclonal variation [1][2][3] is one of the terms used to describe the variability of regenerated plants issued from calluses obtained by in vitro tissue culture.

After initiation of plant regeneration through in vitro tissue cultures summarized by Gautheret since the 1950's [4][5][6], the first observations of unexpected variability were essentially reported since the end of 1969's[7] and the beginning of 1970's[8][9]. It was showed modifications at many biological levels as external or phenotypic traits, but also biochemical functioning and sometimes in chromosome numbers or organisation.

Not only regenerated plants from calluses or cells of somatic tissues of homozygous material [10] showed this variability, but also plants issued from somatic embryos obtained on anther diploid tissues [11], and gametophytic plants from pollen[12] or unfertilized ovaries[13][14][15]. So in vitro regenerants from most tissues are concerned with this variability, and the term "vitrovariation"[16] is also used sometimes.

The genetic heredities of the new characteristics of the vitroplants originated from tissues of homozygous plants have thus been analyzed. In some cases, they showed to be transmitted through either successive selfings or after reciprocal crosses [17][18][19]. Futhermore, beyond mutations phenomenon, chromosome numbers or structural chromosomic modifications concerning some of these changing, for others, all the heredities studies through data associated with statistical analyses of either qualitative (morphological, biochemical) or quantitative characters (developmental), led consistently to epigenetic behaviours[20][21].

Biological bases of somaclonal variations

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High mutation levels were often observed in plants issued from long duration in vitro calluses cultures, and in some species modifications concerning karyotypic abnormalities (aneuploidy, polyploidy) were dectected by chromosome countings in the cells of the strains or in the roots tips of the regenerated plants. Chromosomal rearrangements, as translocations, deletions, insertions or duplications, can also be one of the cause of variation, and all these are summarized in many review publications[22][23][24]. But one must not forget that more surprising modifications can appear supported by epigenetic bases[25]. One of the epigenetics-related event might be gene methylation[26][27], but small interfering RNA (related to microRNA) should well also be concerned[28].

Duration of in vitro culture and variability

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It has long ago been demonstrated that duration of in vitro callus stage shows to be related to an increase of mutation frequencies and variabilities of the regenerated plants (Skirvin, Janick, Deshayes, Buiatti, and many others), while epigenetics modifications seem to appear right from the start of the in vitro cycles, and their frequencies show to be stabilized by the third or even second transfer (-)

Experiments to clarify the location of the genetic bases of the modifications

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If no visual, morphogenic changes are apparent, other plant screening procedures must be applied. There are both benefits and disadvantages to somaclonal variation. The phenomenon of high variability in individuals from plant cell cultures or adventitious shoots has been named somaclonal variation.

Advantages

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The major likely benefit of somaclonal variation is plant/crop improvement. Somaclonal variation leads to the creation of additional genetic variability. Characteristics for which somaclonal mutants can be enriched during in vitro culture includes resistance to disease pathotoxins, herbicides, high salt concentration, mineral toxicity and tolerance to environmental or chemical stress, as well as for increased production of secondary metabolites.

suitable for breeding of new species

Disadvantages

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A serious disadvantage of somaclonal variation occurs in operations which require clonal uniformity, as in the horticulture and forestry industries where tissue culture is employed for rapid propagation of elite genotypes.

  • Sometimes leads to undesirable results
  • Selected variants are random and genetically unstable
  • Require extensive and extended field trials
  • Not suitable for complex agronomic traits like yield, quality etc.
  • May develop variants with pleiotropic effects which are not true.

Reducing somaclonal variation

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Different steps can be used to reduce somaclonal variation. It is well known that increasing numbers of subculture increases the likelihood of somaclonal variation, so the number of subcultures in micropropagation protocols should be kept to a minimum. Regular reinitiation of clones from new explants might reduce variability over time. Another way of reducing somaclonal variation is to avoid 2,4-D in the culture medium, as this hormone is known to introduce variation. Vitrification, commonly referred to as hyperhydricity in the tissue culture world, may be a problem in some species. Hyperhydricity is a physiological malformation that results in excessive hydration, low lignification, impaired stomatal function and reduced mechanical strength of tissue culture-generated plants. In case of forest trees, mature elite trees can be identified and rapidly cloned by this technique.[citation needed]

High production cost has limited the application of this technique to more valuable ornamental crops and some fruit trees.

See also

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Wikimedia Commons has media related to Epigeny/sandbox.

References

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  1. ^ Larkin, PJ; Scowcroft, WR (1981). "Somaclonal variation - a novel source of variability from cell cultures for plant improvement". Theor. Appl. Genet. 60: 197-214.
  2. ^ Orton, TJ (1980). "Chromosomal variability in tissue cultures and regenerated plants of Hordeum". Theor. Appl. Genet. 56: 102-112.
  3. ^ Orton, TJ (1984). "Somaclonal variation - theoretical and practical considerations". In: Manipulation in Plant Improvement (Gustafson JP ed.). New York: Plenum. p. 427-468.
  4. ^ Gautheret, RJ (1954). "Catalogue des tissus végétaux". Rev. Gén. Bot. 61: 672-702.
  5. ^ Gautheret, RJ (1959). La culture des tissus végétaux. Paris: Masson, 863 p.
  6. ^ Gautheret, RJ (1964). "Catalogue des tissus végétaux: son histoire, ses tendances". Rev. Cytol. Biol. Vég. 27: 99-220.
  7. ^ Lutz, A (1969). "Etude des aptitudes morphogénétiques des cultures de tissus. Analyse par la méthode des clones d'origine unicellulaire". Rev. Gén. Bot. 76: 309-359.
  8. ^ Heinz, DJ; Mee, GWP (1971). "Morphologic, cytogenetic and enzymatic variation in Saccharum species hybrid clones derived from callus tissue". Amer. J. Bot. 58: 257-262.
  9. ^ Sibi, M (1971). Création de variabilité par culture de tissus in vitro chez Lactuca sativa. DEA d'Amélioration des Plantes, Univ. Paris-Sud, 91405 Orsay, 95p.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  10. ^ Sibi, M (1976). "La notion de programme génétique chez les végétaux supérieurs II- Aspect expérimental - Obtention de variants par culture de tissus sur Lactuca sativa L. Apparition de vigueur chez les croisements". Ann. Amélior. Pl. 26 (4): 523-547.
  11. ^ Meynet, J (1990). "Culture in vitro de la renoncule des fleuristes (Ranunculus asiaticus L.). III Étude des plantes produites par embryogenèse somatique à partir des tissus superficiels de l'anthère". Agronomie. 10: 285-290.
  12. ^ Burk, LG; Matzinger, DF (1976). "Variation among anther-derived doubled haploids from an inbred line of tobacco". J. Hered. 67: 381-384.
  13. ^ San Nœum, H; Ahmadi, N (1982). Variability of doubled haploids from in vitro androgenesis and gynogenesis in Hordeum vulgare L. In: Variability in plants regenerated from tissue culture (Earle ED, Demarly Y ed.). New York, Praeger pp 273-283.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  14. ^ Evans, DA; Sharp, WR; Medina-Filho, HP (1984). "Somaclonal and gametoclonal variation". Amer. J. Bot. 71: 759-774.
  15. ^ Picard, E; Rode, A; Benslimane, A; Parisi, L (1982). Gametoclonal variations in doubled haploids of wheat: biometrical and molecular aspects. In: Somaclonal variation and crop improvement (Semal J ed.). New York, Praeger pp 136-147.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  16. ^ Sibi, M (1981). Hérédité de variants épigéniques obtenus par culture in vitro chez les végétaux supérieurs. Thèse de Doctorat ès-Sciences, Univ. Paris-Sud, 91405 Orsay, 280p.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  17. ^ Sibi, M (1976). "La notion de programme génétique chez les végétaux supérieurs II- Aspect expérimental - Obtention de variants par culture de tissus sur Lactuca sativa L. Apparition de vigueur chez les croisements". Ann. Amélior. Pl. 26 (4): 523-547.
  18. ^ Matzinger, DF; Burk, LG (1984). "Cytoplasmic modification by anther culture in Nicotiana tabacum L". Heredity. 75: 167-170.
  19. ^ Sibi, M (1990). Genetic bases of variation from in vitro tissue culture. In: Somaclonal variation in crop improvement (Bajaj YPS ed.). Berlin, Heidelberg, Springer-Verlag pp 112-133.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  20. ^ Jablonka, E; Raz, G (2009). "Transgenerational epigenetic inheritance prevalence mechanisms and implications for the study of heredity and evolution". The Quaterly Review of Biology. 84 (2): 131-176.
  21. ^ Sibi, ML. "Les vitrovariations et leurs hérédités". Commons. Retrieved 3 September 2017.
  22. ^ D'amato, F (1985). "Cytogenetics of plant cell and tissue cultures and their regenerates". CRC Crit. Rev. Plant Sci. 3: 73-112.
  23. ^ Reisch, B (1983). Genetic variability in regenerated plants. In: Handbook of plant cell cultures. Vol I (Evans DA, Sharp NR, Ammirato PV, Yamada Y ed.). New York, Macmillan, pp 748-769.{{cite book}}: CS1 maint: location (link) CS1 maint: location missing publisher (link)
  24. ^ Karp, A; Bright, SWJ (1985). "On the causes and origins of somaclonal variation". Oxford Surv. Plant Mol. Cell Biol. 2: 199-234.
  25. ^ Sibi, M (1986). Non-mendelian heredity. Genetic analysis of variant plants regenerated from in vitro culture: Epigenetics and Epigenics. In: Somaclonal variation and crop improvement (J. Semal ed.). CR CEC Symposium 1985, Gembloux, Belgique: Dordrecht, Boston, Lancaster. Martinus Nijhof pp. 53-83.{{cite book}}: CS1 maint: location (link)
  26. ^ Miguel, C; Marum, L (Jul 2011). "An epigenetic view of plant cells cultured in vitro: somaclonal variation and beyond". J Exp Bot. 62 (11): 3713–25. doi:10.1093/jxb/err155. PMID 21617249.
  27. ^ Jaligot, E; Adler, S; Debladis, É; Beulé, T; Richaud, F; Ilbert, P; Finnegan, EJ; Rival, A (Dec 2011). "Epigenetic imbalance and the floral developmental abnormality of the in vitro-regenerated oil palm Elaeis guineensis". Ann. Bot. 108 (8): 1453–62. doi:10.1093/aob/mcq266. PMC 3219487. PMID 21224269.
  28. ^ Fire, A; Xu, S; Montgomery, M; Kostas, SA; Driver, SE; Mello, CC (1998). "Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans". Nature. 391: 806-811.


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