期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1995
卷号：92
期号：10
页码：4197-4201
DOI：10.1073/pnas.92.10.4197
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Genetic resistance in plants to root diseases is rare, and agriculture depends instead on practices such as crop rotation and soil fumigation to control these diseases. "Induced suppression" is a natural phenomenon whereby a soil due to microbiological changes converts from conducive to suppressive to a soilborne pathogen during prolonged monoculture of the susceptible host. Our studies have focused on the wheat root disease "take-all," caused by the fungus Gaeumannomyces graminis var. tritici, and the role of bacteria in the wheat rhizosphere (rhizobacteria) in a well-documented induced suppression (take-all decline) that occurs in response to the disease and continued monoculture of wheat. The results summarized herein show that antibiotic production plays a significant role in both plant defense by and ecological competence of rhizobacteria. Production of phenazine and phloroglucinol antibiotics, as examples, account for most of the natural defense provided by fluorescent Pseudomonas strains isolated from among the diversity of rhizobacteria associated with take-all decline. There appear to be at least three levels of regulation of genes for antibiotic biosynthesis: environmental sensing, global regulation that ties antibiotic production to cellular metabolism, and regulatory loci linked to genes for pathway enzymes. Plant defense by rhizobacteria producing antibiotics on roots and as cohabitants with pathogens in infected tissues is analogous to defense by the plant's production of phytoalexins, even to the extent that an enzyme of the same chalcone/stilbene synthase family used to produce phytoalexins is used to produce 2,4-diacetylphloroglucinol. The defense strategy favored by selection pressure imposed on plants by soilborne pathogens may well be the ability of plants to support and respond to rhizosphere microorganisms antagonistic to these pathogens.
