Effects of Mutagenesis on Crops
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Mutagenesis is the change in genetic information of organism by use of different mutagens like physical or chemical mutagens.
Mutagenesis is the process in which mutations are induced. Mutations can be occur due to exposure of natural mutagens e.g uv light.
Mutagenesis is important because it tells about genetic mechanisms of heredity and gene expression. Protein functioning is also studied by mutations.
Mutagenesis term is firstly invented by Charlotte Auerbach.
Types of Mutagenesis:
There are different types of mutagenesis:
- Directed Mutagenesis
- Random Mutagenesis
- Insertional Mutagenesis
- PCR Mutagenesis
Directed Mutagenesis is change in amino acid code at level of DNA. 3D structure of protein by using X-ray crystallography or by some other analytical procedure help to determine which amino acid should change to get specific property.
There are many types of mutagenesis:
- Oligonucleotide directed mutagenesis with plasmid DNA
- Oligonucleotide directed mutagenesis with M13 DNA
- PCR amplified oligonucleotide directed mutagenesis
- Rate of mutation is high
- All mutations are induced
- Targeted mutation have detailed & systematic investigation
Insertional mutagenesis can be produced by inserting one or more bases. Or it can be produce by
- Natural method
- Artificial in lab for research
- By virus or transposon
Virus insertional Mutagenesis:
Virus insertional mutagenesis is caused by virus. Virus insert its oncogene in cellular myc gene which usually turn off in cell. When it is turn on it push the cell in G1 phase, where it cause the replication of even the viral gene. After many replications latent tumors are produced at the site of gene. Eg Avian Leukosis virus is the cause of disease by using insertional mutagenesis.
Signature Tagged Mutagenesis:
It use transposons for study the function of genes. A transposon like Drosophila melanogaster P- element is use to randomly integrate in organism’s genome. Then unusual phenotype is identified by mutant screening. Such kind of phenotype suggest that phenotypic inactivation of that gene is caused by transposon. Than transposon sequence is known, whole genome sequenced to identify that specific gene. PCR is used ti amplify that gene.
Greater number of mutatnts are produce at low cost & high speed.
Easily trackable mutations are produced.
Random mutagenesis also called Directed evolution & Molecular breeding. At one or more codon level gene is non specifically change to produce mutated genes which is then select and screen for desired catalytic activity genes.
Some other useful proteins can be generated because of the production of range of mutants.
Amino acid role is not required in protein working.
In the mutagenesis nucleotide sequence is changed. It is use to change the amino acid sequence to check the function of protein.
There are different methods of inducing mutations in PCR:
It focus on single amino acid it used to check missense mutation in a gene of disease. Function of amino acid is also determine in a protein by Mismatched mutatgenesis.
Site directed Mutagenesis:
It induce mutation at specific location on strand of DNA. The primers that are used alter at one or more nucleotide.
5’add on Mutagenesis:
In this mutagenesis, a new sequence or chemical group is add on 5 end. Primer are produce in special manner:
- Primer’s 3 end should match PCR product sequence.
- 5 end should contain novel sequence
- A suitable restriction site
- Promoter sequence
- Modified nucleotide
Multiple mutations are introduced in DNA sequence. In this mutagenesis, a DNA fragment having sequence of desired mutant is replaced the sequence in wild type. It uses blunt end of DNA for insertion.
It is used for protein function.
It is less expensive than site directed mutagenesis because in this primer is not needed.
Types of Mutagens:
There are several types of mutagens:
Ionizing radiation e.g gamma rays, neutrons, ultraviolet light and x-rays. These high energy radiations cause break in double strand of DNA. Cellular repair system repair the broken pieces simultaneously when DNA pieces are broken. Only low radiations are handled by DNA repair system,permanent mutations are caused by increase exposure to these radiation. These cause deletion of nucleotides from the sequence. These cause inactive protein formation, wrong transcripts and frame shift. This is causing null mutations, in which specific gene is inactivated.
Transposable elements are the self replicating parts of DNA which inset or excise themselves in genome. These are also called transposons. These were first discovered by Barbara McClintock while working on Maize. These elements do not act upon in genme in random way, although they have ‘hot spots’ in which they cause insertion or deletion. Transposable elements cause alteration in protein product, disruptions in gene and genome rearrangement. Transcriptional inefficiency is caused if these are inserted into an intron.
Chemical mutagens cause chemical reactions in genome and affect DNA. Base analogs have same properties like bases of DNA. They replace the proper bases by incorporating into the genome. Alkylating agent like ethyl methane sulphonate with bases like guanine and thymine by adding ethyl group into them and it cause recognition of modify bases as adenine or cytosine. It causes changes in triplet codon sequence. Single base change in codon cause formation of non sense codon which stop the transcription or alter codon may change the amino acid, which may result in production of faulty or new protein.
Nitrous acid, it remove amino group from bases e.g adenine and cytosine. When this area is replicated, it matches cytosine to deaminated adenine and vice versa. It has same effect like alkylating agent.
Effect of mutagenesis in germination, pollen sterility in M1 generation of Soyabean:
Soyabean is the important source of edible oil throughout the world. It is 60 % of total oil production. Productivity of Soyabean is low in India. Productivity is low because of low genetic diversity, short growth period.
Flower of soyabean are small that is why hybridization is difficult. So, classical breeding is limited in soyabean improvement. Induced Mutagenesis is the only method to enhance genetic variability in short period of time. That is why it is proved to be a best method for crop improvement.
In this method, genetic variability is induced and the useful mutants are screened and use for the improvement of soyabean. However, pollen sterility, germination and survival are the important factors as initial indicators.
Method of Induced Mutagenesis in Soyabean:
Two varities of soyabean were taken and there sentivity is checked by different mutagens, chemical or physical. Firstly, gamma (physical mutagen) irradiation by cobalt-60 in gamma chamber. Than Ethyl Methane Sulphonate (chemical mutagen) was use for the treatment of soyabean seeds.
In EMS treatment, in distilled water seeds were presoaked for six hours. EMS is dissolved in distilled water. Treatment is done at room temperature of 22â-¦ C in early morning. After this treatment, seeds were washed with tap water for half an hour in order to remove chemical residues. Extra moisture is removed by using blotting paper. Than seeds sow in experimental field and check the results on germination.
After checking the generation, it may be conclude that both mutagens have an inhibitory effect on survival, pollen sterility and germination. It is effective in producing a range of mutant.
Induced Mutagenesis in Wheat for the improvement of drought and heat tolerance:
Environmental stresses the wheat production.
Use of Mutation in Plant Breeding:
Mutagenesis is widely use in plant breeding for the improve of crops. Barley was the first crop which is mutagenised by using x-ray by LJ Stadler. Early work is done with physical or chemical mutagens to describe doses and exposure of such agents to affect mutations without any harm. Rates and doses vary greatly depending upon species, genotype and conditions of the treatment.
There are several factors which can be checked before choosing dose for a crop.
- Safety issues
- Type and mechanism of mutagen
- Specific tissue reactions
- Ploidy level and species
Mutagenesis effect of sodium azide on crops:
It is a chemical mutagen and it produce point mutation in plant genome by producing metabolites and produced protein in mutant plants which is having different function than in normal plants. Mutant plants which are produced by using sodium azide have capacity to survive in adverse conditions, greater stress tolerance, increase shelf life, improved yield, lesser agronomic input as compare to normal plants. Plant growth is inhibited if the concentration of sodium azide is higher ror if the treatment duration is increased.
Sodium azide impact is observed in tomato plants in which it induce mutation which is related to seedling height, root length, germination percentage, yield and number of branches.
Spathoglottis plicata Blume, it is terrestrial orchid having purple pinkish flower. It is important commercially. When its seeds were treated with sodium azide, they produce modified flowers which are more attractive having milky white flowers. These modified flowers considered as new variety of horticulture.
Halianthus annus-sunflower, it is the most important oil seed crop throughout the world. In conventional sunflower 90% fatty acid is unsaturated which affacts its oil production. When it is treated with sodium azide, it altered its fatty acid composition in a significant way and improve its yield and quality.
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