Genetic transformation in Maize .

What is plant genetic transformation ....?

INTRODUCTION :-

Plant genetic transformation is a way to insert DNA from another organism - normally another organism /plant ,into the genome of the plant of interest .

Maize (Zea mays L.) or corn is the principal crop of the world and stands first among the grain crops in terms of production.

It is primarily used as animal feed and raw materials for various industries, and only a minor proportion is used as direct human food. The ever increasing human population and consumption of animal-derived foods is leading to enhanced demand for maize grains.

However, various biotic and abiotic stresses are the bottleneck in enhancing maize production, productivity, and quality in the limited cultivable land available.

To overcome these challenges, genetic engineering of maize with desired target genes have been extensively employed to produce transgenic maize cultivars with improved traits. The first transgenic maize cultivars were launched commercially 20 years ago in 1996 in the USA. Since then, maize has become the main target crop for plant genetic engineering.

Among the monocotyledonous grain ,maize has been one of the leading targets for genetic engineering through biotechnological technique , such as particle bombardment technique and others.

( Immature embryos used as target tissue for particle bombardment mediated transformation of

cry 1 Ab gene by Koziel et al. in 1993)

PRINCIPLE :-

Isolation of the gene to be cloned.

Insertion of the gene into another piece of DNA called vector which will allow it to be taken by bacteria and replicated within them as the cells grow and divide.

Transfer of the recombinant vector into bacterial cells, either by transformation or by infection using viruses.

METHODOLOGY :-

Plant transformation was first describe in tobacco in 1984 by Horsch et al .since that time ,rapid development in transformation technology have resulted in the genetic modification in many plant .

1)Gene transformation :-

Several gene transformation techniques utilize DNA uptake into isolated protoplasts mediated by chemical procedures, electroporation, or the use of high-velocity particles (particle bombardment). Direct DNA uptake is useful for both stable transformation and transient gene expression. However, the frequency of stable transformation is low, and it takes a long time to regenerate whole transgenic plants.

2) Chemical procedure :-

Plant protoplasts treated with polyethylene glycol more readily take up DNA from their surrounding medium, and this DNA can be stably integrated into the plant’s chromosomal DNA (Mathur&Koncz, 1997). Protoplasts are then cultured under conditions that allowed them to grow cell walls, start dividing to form a callus, develop shoots and roots, and regenerate whole plants.

3) Electroporation :-

Plant cell electroporation generally utilizes the protoplast because thick plant cell walls restrict macromolecule movement (Bates, 1999). Electrical pulses are applied to a suspension of protoplasts with DNA placed between electrodes in an electroporation cuvette. Short high-voltage electrical pulses induce the formation of transient micropores in cell membranes allowing DNA to enter the cell and then the nucleus.

4) Particle (microprojectile) bombardment :-

Particle bombardment is a technique used to introduce foreign DNA into plant cells .Gold or tungsten particles (1–2 µm) are coated with the DNA to be used for transformation. The coated particles are loaded into a particle gun and accelerated to high speed either by the electrostatic energy released from a droplet of water exposed to high voltage or using pressurized helium gas; the target could be plant cell suspensions, callus cultures, or tissues. The projectiles penetrate the plant cell walls and membranes. As the microprojectiles enter the cells, transgenes are released from the particle surface for subsequent incorporation into the plant’s chromosomal DNA.

5) Using Agrobacterium for plant transformation :-

Agrobacherium mediated transformation is the most commonly used method for plant . The pathogenic soil bacteria Agrobacterium tumefaciens that causes crown gall disease has the ability to introduce part of its plasmid DNA (called transfer DNA or T-DNA) into the nuclear genome of infected plant cells.