ABSTRACT
ABSTRACT Plant pathogenic bacteria stimulate disease symptoms in plants using various pathways. Pathogenicity factors encoded by pathogenicity genes and disease-specic genes are involved in steps that are crucial for the establishment of disease. Many plant bacterial pathogens require different types of secretion systems to mount successful invasions of susceptible host-plant species. Quorum sensing is known to be involved in the regulation of important physiological functions of bacteria such as symbiosis, conjugation, and virulence. The expression of the extracellular polysaccharides in host cells is known to play a central role by providing resistance to oxidative stress during pathogenesis. Basal resistance is elicited in plants by pathogen-associated or microbial-associated molecular patterns. The overproduction of reactive oxygen species is an early event that characterizes the HR (Hypersensitive response) induced by bacteria; this induction, at least in part, may generate unfavorable conditions for bacterial multiplication in the apoplast. Aside from hydrogen peroxide, plant antibacterial molecules could be responsible for the restriction of bacterial growth observed during HR. Induced plant defenses (SAR and ISR) against pathogens are regulated by networks of interconnecting signaling pathways in which the primary components are the plant-signal molecules (salicylic acid, jasmonic acid, ethylene, and nitric oxide). In many host-pathogen interactions, plants react to attack by pathogens with enhanced production of these substances; at the same time,
2.1 Introduction ............................................................................................................................ 18 2.2 Pathogenicity .......................................................................................................................... 19
2.2.1 Bacterial Secretion Systems .......................................................................................20 2.2.1.1 Type I ...........................................................................................................20 2.2.1.2 Type II ..........................................................................................................20 2.2.1.3 Type III ........................................................................................................ 21 2.2.1.4 Type IV ........................................................................................................27
