Somaclonal variation : Somaclonal variation N.KANAGARAJ
BSF-06-007
Slide 2: Somaclonal variation
It is the term used to describe the variation seen in plants that have been produced by plant tissue culture.
Chromosomal rearrangements are an important source of this variation.
Slide 3: Regeneration from callus, leaf explants or plant protoplasts leads to the generation of considerable variation, described as somaclonal variation.
Different Steps Involved in Utilization of Somatic Variation Flow Chart : Different Steps Involved in Utilization of Somatic Variation Flow Chart
Slide 5: The variations can be
A] genotypic
B] epigenetic in origin
Slide 6: A] Genetic alterations are:
1.changes in chromosome
2.chromosome structure
3.DNA sequence
Slide 7: 1.changes in chromosome numbers;
Euploidy- changes in whole chromosome sets
Aneuploidy- changes in parts of chromosome sets
Ploidy: number of basic chromosome sets (a diploid has 2 sets; a hexaploid has 6 sets)
Euploid: organism containing multiples of the basic chromosome set
Monoploid: organisms with one chromosome set (in essentially diploid taxa)
Polyploid: organism containing more than two chromosome sets
2.Structural Changes in Chromosomes : 2.Structural Changes in Chromosomes Deletion Inversion Duplication Translocation
Slide 9: 3.DNA sequence (base mutations).
Change at DNA level
Detected using restriction enzyme analysis (altered fragment size)
Changes at protein levels
Loss or gain of protein band
Altered levels of specific proteins
DNA methylation
Methylation of a gene inactivates its transcription
Slide 10: B] Epigenetic change
Due to gene expression not gene alteration
Often temporary
Some examples
Morphological change - leaf shape
Earlier flowering
Improved adventitious rooting
Increased vigor
Plageotropic growth
Slide 11: Specific epigenetic processes
Paramutation
Imprinting
Gene silencing
Cellular differentiation
X chromosome inactivation
Position effect
Reprogramming
Transvection
Regulation of histone modifications
Maintain different characteristics
Slide 12: Advantages :
Benefit of somaclonal variation is in plant improvement
It is leads to the creation of additional genetic variability
Increased production of secondary metabolites
Characteristics for which somaclonal mutants can be enriched during in vitro culture include resistance to disease pathotoxins, herbicides and tolerance to environmental or chemical stress.
Slide 13: Somaclonal variation in trees
Somatic variation may be a better mans for tree improvement
Direct gene insertion or agrobacteruim –mediated transformation have many technical difficulties that must be overcome with this methods.
It have the potential to significantly change tree breeding programs by reducing the time required for selecting and improving desired traits .
Slide 14: Applying soma clonal technology to forest trees offers an even greater advantage
because of the long generation times of trees and the opportunity to introduce desired traits not possible through traditional breeding.
Somaclonal technology is simpler to exploit than other types of genetic engineering.
Slide 15: To Increase Somaclonal Variation:
Callus and suspension cultures for several cycles
Regeneration of large number of plants from long-term cultures
Testing of selected somaclones for genetic stability
Multiplication of genetically stable somaclones for developing new cultivars
Slide 16: Disadvantages:
No control - may change in undesirable direction
Variations are random in nature
May not be genetically stable
Require extensive field testing
May not occur for complex agronomic traits
Slide 17: Control of Somaclonal Variation:
Regular reinitiation of clones from new explants might reduce variability over time.
Avoid 2,4-D in the culture medium, as this hormone is known to introduce variation.
The duration of the culture cycle may influence the variability.
Slide 18: References:
http://belgian.plant.biotechnology.assoc.googlepages.com/symposium november23,2007
en.wikipedia.org/wiki/Somaclonal_variation - 20k
www.amazon.co.uk/Somaclonal-Variation-Crop-Improvement-Biotechnology
http://www.studentsguide.in/plant-biotechnology-genomics/tissue-culture-micropropagation-somaclonal-variation
Slide 19: Thank you