Genetics of Phytopathogenic Bacteria

Abstract

Only a small proportion of bacteria are plant pathogenic and have developed mechanisms to invade and colonize their host plants and cause disease. However, resistant host-plant cultivars and certain non-host plants are able to recognize and combat phytopathogenic bacteria. These resistant plants react with a localized induced cell death at the site of infection; this is termed hypersensitive response (HR) and is induced by so-called elicitors, such as avirulence proteins (Avr proteins). These are recognized by corresponding receptor proteins in the plant. It has been shown that the ability to cause disease in compatible interactions with host plants and the induction of HR in incompatible interactions both depend on the ability of the bacteria to express a cluster of genes termed hrp. (hypersensitive reaction and pathogenicity; Lindgren et al. 1986). Thus, hrp. mutants of plant pathogenic bacteria cause no detectable reactions in either host or non-host plants. Hrp genes seem to be a common feature of all Gram-negative plant pathogenic bacteria. Some of the hrp. genes encode a protein-secretion mechanism known from animal pathogenic bacteria (the type III secretion system) which apparently enables them to direct proteins into plant cells. The type III secretion system differs markedly from the earlier discovered type I protein secretion [which involves adenosine triphosphate (ATP)-binding cassette transporters] and the signal-peptide/sec-dependent type II secretion system (Salmond and Reeves 1993; Lee 1997).KeywordsHypersensitive ResponseSecretion SystemXanthomonas CampestrisPlant Pathogenic BacteriumPhytopathogenic BacteriumThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.