Resistance to Bacterial Pathogens

Pathogenic bacteria have developed pathogenicity or virulence factors which allow the pathogen to multiply in infected tissues. As indicated above for fungal pathogens, in which R-genes resistant to bacterial pathogens are also given, host R-genes recognize some of these factors, encoded by avr genes, which trigger a similar range of defence responses.
Approaches to engineer resistance to bacterial pathogens include:
(i) production of anti-bacterial proteins of non-plant origin (e.g. antibacterial proteins Shival, MB39, Attacin E from the giant silk moth, lysozymes of various origins, lactoferrin and tachyplesin from the horseshoe crab);
(ii) inhibition of bacterial pathogenicity or virulence factors (e.g. tab toxin-resistance protein, phaseolotoxin-insensitive ornithine carbamoyltransferase from P. syringae);
(iii) enhanced plant defences e.g. pectate lyase, R-genes Xa21 and Pto, glucose oxidase, thionins);
(iv) artificial induction of the hypersensitive response.
The insect lytic peptides (e.g. cecropins from the giant silk moth and synthetic analogues) form pores in bacterial membranes. Transgenic potato, tobacco and apples with genes for these lytic peptides have been generated, which confer some protection against bacterial wilt and fireblight (Erwinia amylovora). Lysozymes digest bacterial cell wall peptidoglycans and expression of different lysozyme genes can give partial resistance to E. caratova atroseptica and P. syringae pv tabaci in potato and tobacco, respectively.
The R-gene Xa21 confers resistance to bacterial leaf blight (Xantho- monas oryzae pv oryzae) and has been transferred into susceptible rice genotypes to confer resistance to X. oryzae and overexpression of the resistance conferred by the R-gene Pto to Pseudomonas syringae pv in tomato confers resistance to other pathogens.