Microbial biotechnology enables the introduction of foreign genes into crop plants through techniques like Agrobacterium-mediated gene transfer. This allows for traits like herbicide and insect resistance by introducing genes for Bt toxins or genes that confer tolerance. Transgenic plants can also be engineered for abiotic stress tolerance by introducing genes for compatible solutes like trehalose. Additionally, transgenic plants have been developed with resistance to viral and fungal diseases by introducing genes for viral coat proteins or chitinases. Genetic engineering also aims to enable nitrogen fixation in non-leguminous plants by transferring nodulation genes to plants.

1. 1
Agriculture
Microbial biotechnology enabled scientists to produce crop varieties by introduction of foreign
genes . Transgenic plants are produced by inserting foreign genes that are as stable as other
genes in the plant nuclei and can be inherited normally. Transgenic plants are most commonly
generated by using a plasmid vector carried by Agro bacterium tumefaciens. Foreign DNA
carrying from one to 50 genes can be introduced into plants with the donor DNA from different
plant species, animal cells, or microorganisms. The control sequence(s) can be inserted into
transgenic plants to confine the expression of foreign genes to specific organelles or tissues and
also the initiation and duration of such expression
Ability to grow in harsh environments
Tolerances toward environmental stresses (cold, heat, and drought tolerance; ability to withstand
high moisture or high salt concentrations) are polygenic traits and it is difficult to transfer them
from one kind of organism to another. Some success has been done for example. Trehalose, a
disaccharide of glucose, acts as a compatible solute stabilizing and protecting proteins and
biological membranes in bacteria, fungi, and invertebrates from damage during desiccation. E.
coli fusion genes otsA and otsB for trehalose are used for its biosynthesis and introduced into
indica rice. Secondly to obtain either tissue-specific or stress-inducible expression, two different
constructs were made.
1. OtsA gene was equipped with a transit peptide and under the control of the promoter of
ribulose bisphosphate carboxylase which express the gene product in chloroplast.
2. OtsB gene was placed under the control of an abscisic acid which is an inducible
promoter.
The constructs were then introduced into rice using Agrobacterium-mediated gene transfer.
Which resulted sustained plant growth under drought, salt, or low temperature stress conditions.
trehalose level did not exceed 1 mg/g wet weight of tissue.trehalose must exert its protective
effect without affecting the bulk properties of water within the plant cells. The plant acquired
greater ability to control K+/Na+ balance in the roots under the stress conditions. trehalose acts
as a regulatory molecule affecting the expression of genes linked with carbon metabolism and
also with ion uptake.
Herbicide tolerance

2. 2
Modified crop plants that are resistant to particular herbicides and when applied to a field having
weeds it acts as selective weed killer.
Resistance to insect pests
Specific strains of the bacterium Bacillus thuringiensis produce protein endotoxins which
permeabilize the epithelial cells in the gut of the larvae of lepidopteran insects, moths, and
butterflies. Genes encoding particular B. thuringiensis endotoxins are transferred and expressed
in tobacco, cotton, and tomato. B. thuringiensis cry genes are also introduced in maize and cotton
which encode insecticidal proteins and it constituted 26% of the global area of transgenic crops
in 2003.secondly for the same purpose B. thuringiensis endotoxin gene was transfered into
bacteria such as Clavibacter xyli subsp. cynodontis, whichmake colonies in plants and is
inoculated into corn.
Control of pathogenic bacteria, fungi, and parasitic nematodes
The cell walls of plant pests (insects and fungi) contain chitin (poly-N-acetylglucosamine) and
most bacteria (species of Serratia, Streptomyces, and Vibrio) produce chitin degrading enzymes
(chitinases) which can be introduce in plants to control fungal diseases.
Bacillus subtilis strains as broad-spectrum microbial pesticides
B. subtilis strains secrete a formidable array of compounds that combinely perform antifungal,
antibacterial, and also insecticidal activities. Large amounts of a B. subtilis strain capable of
producing mixture of lipopeptides (iturins and plipastatins) obtained by solid state fermentation
and when the mixture of cells and metabolites obtained by the solid-state fermentation are
applied to soil growth of various plant pathogens is supressed. When this bio fungicide is applied
to plants, pathogens cannot be attached to plants because it coats leaf surfaces.
Resistance to viral diseases
Research showed that transgenic tobacco expressing the coat protein (capsid) gene of tobacco
mosaic virus (TMV) is resistant to TMV, and it was speculated that the resistance is the result of
the interference with virus uncoating by the expressed coat protein. The protection is now known
to be the result of RNA silencing, a cell-based sequence specific posttranscriptional RNA
degradation system that is programmed by the transgene-encoded RNA sequence. The
introduction in 1998 of transgenic papaya cultivars with a transgene that expressed a PRSV coat
protein saved the Hawaiian papaya industry from PRSV.

3. 3
Nitrogen fixation
In order to increase the the expression of genes involve in nitrogen fixation Strains of
Bradyrhizobium japonicum and Rhizobium meliloti are engineered. To initiate nodulation on
non-legumes Transfer of the genes to Agrobacterium enables nitrogen fixation to non-
leguminous plants.