In this article we will discuss about the bacterial resistance in plants.
T4 Lysozyme:
Several bacterial pathogens are responsible for enormous losses in cultivated and stored crops. Therefore, protection of plants from pathogenic bacteria is also a primary concern among plant scientists.
Genetic engineering offers some good protection against bacterial attack. In one of the classic case studies, a novel gene encoding T4 lysozyme was successfully expressed in many model plants. Overexpression of T4 lysozyme can combat bacteria during infection. T4 lysozyme is very effective against wide range of gram-positive and gram-negative bacteria which specifically degrade peptidoglycan of bacterial cell wall.
Cecropin Melittin:
Another example is the production of transgenic plants strongly exhibits resistant to broad-spectrum bacterial phytopathogens by the expression by Cationic antimicrobial peptides (CAPs). Over the past two decades persistent effort have been made in the discovery of large group of natural antimicrobial peptides.
Although CAPs are structurally divided, they are generally a two classes one is a-helical peptides, such as cecropins and magainins and second is β-sheet peptides, such as defensins, protegrins and tachyplasins. These natural peptide exhibit greater degree of broader biological activity killing bacteria, fungi and even protozoas at concentrations from 0.25 to 4 µg/ml.
With all these plus points, earlier endeavour on the expression of CAPs in plants have focused on antibacterial natural products of limited spectrum such as barley-α or β-hordothionin cecropin β or even a cecropin A/B chimera but results were seems to be disappointed due to their weak antimicrobial activity.
When researchers are looking for different options, insect cecropins show much promising antimicrobial activity. It represents a family of small, highly basic a-helical antimicrobial peptides that forms an important component in the immune response of insects. Cecropins precured from the giant silk moth, Hyalopthora ceropa, and containing-35 amino acid residues with amphipathic N termini and hydrophobic C termini.
In addition, 26-amino acid antibacterial peptide, Melittin, is the major component of bee venom and has a predominently hydrophobic N-terminus with an amphipathic C terminus. However, due to its powerful hemolytic activity makes it unsuitable for transgenic applications.
In order to exploit animal derived cecropin and melittin for transgenic work against phytophathogens, molecular modeling and engineering of their peptides were attempted to weaponise transgenic plants against bacteria. An example of this approach is the creation of antibacterial chimeric peptide, CEMA, which contain eight amino acid residue from the antimicrobial peptides cecropin A and a modified melittin sequence.
Expression of modified CEMA exhibit strong antimicrobial activity and highly reduced haemolytic activity making it successful candidate for transgenic work in order to fight pathogenic bacteria. A modified version of CEMA synthetic gene msrA, was expressed in potato tuber and considerably increased their resistance to both bacterial and fungal pathogens.
Sarcotoxin:
Sarcotoxin 1A is an antibacterial peptide of Sarcophaga peregrina (freshly). As self defence system in insects it protects wounded larvae from bacterial attack. To generate resistant plant to pathogenic bacteria. Sarcotoxin 1A gene was introduced into tobacco driven by PR-1 a promoter, activated by salicylic acid or pathogen infection provided protection against Pseudomonas syringae, Erwinia ceretovora and Xanthomonas campestris.