Stratagies to Improve Bactrial Disease Resistance in Plants through Genetic Engineering

1. Production of Anti Bacterial Proteins of Non-Plant Origin

• Lytic Peptides from Insects
• Lysozymes
• Other antibacterial Peptides

2. Inhibition of Bacterial Pathogenicity or Virulence Factors

• Inhibition of Bacterial toxins
• Other Approached

3. Enhancement of Natural Plant Defenses

• Enhanced Production of Elicitors 
• Expression of cloned resistant genes
• Enhanced production of reactive oxygen species
• Expression of plant defense genes 

4. Artificially Induced Programmed Cell Death at the site of infection

• R and avr genes
• Barnase and Barstar genes
• Bacterio-opsin gene

Production of anti-Bacterial Proteins of Non-Plant Origin:

a) Lytic Peptides from Insects:

•  Small Proteins with alpha helices
• Causes pores in bacteria
  Example: Cecropins, attacins – giant silk moth 

Cecropins

•  Synthetic analogs of cecropin gene – Potato, Tobacco. 
•  Transgenic tobacco – bacterial wilt – delayed mortality. 
•  Limitation: Degradation of cecropins by plant proteases. 

b) Lysozyme

•  Lysozymes are ubiquitous enzymes. 
• Hydrolytic bacterial cell wall containing peptidoglycan. 

Examples

•  Transgenic tobacco- hen egg lysozyme – resistance to several species. 
•  Transgenic potato – T4 Bacteriophage – Partial resistance to Erwinia. 
•  Transgenic tobacco- human lysozyme – Partial resistance to P.syringae. 

c) Other antibacterial peptides

Lactoferin:

• Iron binding glycoprotein
• Bactericidal properties

Transgenic Tobacco

• Human Lactoferin gene
• Delayed symptoms on Rhizoctonia solanaceae

Trachyplesin: 

• Codes for lytic peptides
• Horseshoe crab.

Transgenic potato:

• genes from horseshoe crab - partial resistance.
• Limitation: Expressed reduced amount of tuber.

Inhibition of Bacterial Pathogenicity or Virulence Factors

a) Inhibition of bacterial toxins

Pathogen protects itself against toxin by expressing tabtoxin resistant genes (ttr), transgenic tobacco with genes show resistance towards many bacteria.

b) Other Approaches

3. Enhancement of Natural Plant Defenses

a) Enhanced Production of Elicitors

b) Expression of cloned resistant genes

c) Enhanced production of reactive oxygen species

A glucose oxidase gene from A.niger is cloned into potato plants resulted in resistance. This enzyme induce large amount of hydrogen peroxide. transgenic potato results in increased level of resistance.

d) Expression of plant defense genes

In certain cases resistance was not seen though high level of thionin is produced. This may be due to thionin is secreted into intracellular space, where bacteria are generally found.

Plant defense mechanism is due to battery of synergetic reactions. Hence the expression of combination of heterologous genes would be more promising

4. Artificially Induced Programmed Cell Death at the site of infection

• R and avr genes applied to fungus
• Barnase and Barstar genes
• Barnase - Bacterial ribonuclease gene
• Barstar - Inhibitor of barnase
• Bacterial opsin gene

Limitations

• Efficacy, durability, absence of toxicity and low environmental impact
• Gene silencing