Application Of Genomics In Plants

IntroductionRequirement of fruits vegetables and cereals

is increasing proportionally.Although conventional plant breeding

techniques considerably progressed in the development of improved varieties.

They are unable to keep pace with the increasing demand for vegetables fruits  and cereals.

So there is a need to integrate genomics to speed up the crop improvement programmes.

Conti.......Genomic tools have revolutionized the entire

crop improvement programmes by providing:New strains of plants, Supply  of planting material,More efficient pesticides,Improved fertilizers,

Conti…. The major areas of genomics which are

adopted for improvement of crops are:Tissue CultureGenetic Engineering Molecular diagnostics Molecular markers Development of Beneficial microbes

 

Tissue CultureIt is one of the most widely used techniques

for rapid asexual in vitro propagation. It is economical in time and space affords

greater output and provides disease free and elite propagules.

Can produce millions of uniformly flowering and yielding plants.

Can produce virus free planting material using meristem culture.

Conti…..Plants regenerated by tissue culture exhibits

phenotypic variation atypical of the original phenotype.

Such variation, termed somaclonal variation.Heritable i.e. genetically stable and passed

on to the next generation.These heritable variation are potentially

useful to plant breeders.

Genetic Engineering of Plants

Genetic Engineering involves three major steps:i) Identification and isolation of suitable genes for transferii)Delivery system to insert desired gene into recipient cells.iii)Expression of new genetic information in recipient cells.

Many transgenic plants have been developed. 

Conti….Genes for the following traits have been

introduced to the crop plants.Herbicide toleranceEngineering  pathogen resistanceStress resistance Fruit QualityPest resistance Male sterility and Fertility restoration

Herbicide toleranceHerbicides tolerant plants allow farmers to

spray crops so as to kill only weeds but not their crops.

Tomato, tobacco, potato, soybean, cotton, corn oilseed rape,  petunia, etc.

Glyphosate is one of the most potent broad spectrum environment friendly herbicide .

Glyphosate kills plants by blocking the action of an enzyme EPSPS.

EPSPS is an essential enzyme in the biosynthesis of tyrosine, phenylalanine and tryptophan.

Conti….Transgenic plants resistant to Glyphosate have

been developed.A number of detoxifying enzymes have been

identified in plants.These include glutathione-s-transferase or GST

in maize and other plants which detoxifies the herbicide.

Phosphinothricin acetyl transferase (PAT) detoxifies the herbiside PPT (L-phosphinothricine).

Herbicide tolerant plants reduce the use of weeding labour,  farmers cost  and increase yield. 

Engineering  pathogen resistanceViruses are the major pests of crop plants which cause

considerable yield losses. Many strategies have been applied to control virus

infection.Use of viral coat protein as a transgene for producing

virus resistant plants is successfully achieved in plant genomics.

Coat protein gene from TMV has been transferred to tobacco, making it nearly resistant against TMV.

Conti……Nucelocapsid protein resistance gene has

been introduced in crops against  tomato spotted wilt virus.

Use of satellite RNA makes many transgenic plants resistant to Cucumber Mosaic Virus (CMV).

Transgenic resistant plants have also been developed against

alfalfa mosaic virus, potato virus X, Rice tungro virus, tobacco rattle virus, Papaya ring spot virus.

 

Resistance Against Bacterial DiseasesGene of Acetyl transferase is introduced in

tobacco making it resistant to Pseudomonas syringea, a causal agent of wild fire disease.   

Resistance Against Fungal Disease Many of the antifungal compounds are

synthesized by plants which combat fungal infections have been identified. 

Chitinase  gene from bean plants in tobacco and Brassica napus showed enhanced resistance to Rhizoctonia solani.

Chitinase gene obtained from Serratia marcescens is introduced in tobacco making it resistant to Alternaria longipes.

Stress Resistance A number of genes responsible for providing

resistance against stresses have been identified.

Resistance against chilling was introduced into tobacco by introducing gene for glycerol-1-phosphate acyl-transferase enzyme from Arabidopsis.

Many plants respond to drought stress by synthesizing polyols (Mannitol, Sorbitol and Sion).

Using a bacterial gene capable of synthesizing mannitols it is possible to make plants resistant to drought. 

Fruit QualityTomatoes exhibiting delayed ripening have

been produced by using decreasing amount of enzymes involved in  ethylene production.

This increases the shelf  life of tomatoes.

These tomatoes can stay on the plant long giving more time for accumulation of sugars and acids for improving flavour.

Starch content in potatoes has been increased by using a bacterial ADP glucose pyrophosphorylase gene.

Pest Resistance The insecticidal bt gene has been isolated

from Bacillus thuringiensis bacteria and transferred to plants like cotton, tobacco, tomato, soybean, potato, etc.

These genes produce insecticidal crystal proteins which affect a range of insects.

These crystals upon ingestion by the insect larva  are solubilised in the highly alkaline midgut into individual protoxins.

Insecticidal crystal protein  produced during vegetative growth of the cells are  also found to be highly effective  against insect control.

Male sterility and Fertility Restoration

This is helpful in hybrid seed production.Transgenic plants with male sterility and

fertility restoration genes have become available in Brassica napus.

Molecular Diagnostics

Nucleic acid probes:It is now possible to detect the plant diseases

even before onset of symptoms by using cDNA probes.

cDNA probes can be generated using standard recombinant DNA technique.

 

Conti….Monoclonal Antibodies (MCAB): Hybridoma technology has provided methods

for the production of homologous and biochemically defined immunological reagents.

These are of identical specificity and produced by a single cell line directed against a unique epitope of the immunizing antigen.

Molecular Markers Molecular makers has made the job of

breeder easier.It has been possible to score the plants for

different traits or disease resistance at the seedling stage.

In plant breeding the use of following techniques is numerous. 

RFLP (Restriction Fragment Length polymorphism),

RAPD (Random Amplified Polymorphic DNA) ,AFLP (Amplified Fragment Length

Polymorphism)