Ralstonia solanacearum – a plant pathogen in touch with its host
Denny. T. P
Trends in Microbiology ; 2000 [Vol.8] Pages:486-489
Abstract
Ralstonia solanacearum, one of the world's most important phytopathogenic bacteria, causes lethal wilting diseases of.200 plant species. Its agronomically important hosts include peanut, potato, tomato, tobacco and banana. Although most troublesome in the tropics and subtropics, R. solanacearum continues to be a threat in cooler climates, especially on potato. A part-time soil inhabitant, R. solanacearum enters plant roots via wounds or where secondary roots emerge, colonizes the root cortex, invades xylem vessels and rapidly spreads throughout the vascular system. Efficient systemic colonization requires production of a high molecular mass extracellular polysaccharide (EPS) and multiple extracellular proteins (EXPs). Some EXPs, like the enzymes that attack plant cell walls, transit the main terminal branch of the general secretory pathway (type II secretion) and enhance the rate and severity of wilting. Other EXPs, which have more subtle (and so-far enigmatic) roles in causing disease and eliciting defense responses, are delivered to host cells via a type III secretion system (secreton). Wilting is a result of vascular dysfunction caused by high bacterial cell densities [>1010 colony forming units (CFU) per gram fresh weight] and the large amount of EPS these bacteria produce. Over the past 50 years, extensive fundamental and applied research has established R. solanacearum as a model system for studying bacterial pathogenesis of plants. In addition, R. solanacearum will be one of the first plant pathogens to have its genome completely sequenced. Extending the cutting-edge research on R. solanacearum, Aldon et al.[8] recently provided the first example of host-cell-contact-mediated type III secretion by a plant pathogen.
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