Plant responses to plant growth-promoting rhizobacteria |
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Authors: | L C van Loon |
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Institution: | (1) Department of Biology, Section Phytopathology, Institute of Environmental Biology, Faculty of Science, Utrecht University, P.O. Box 800.84, 3508 TB Utrecht, The Netherlands |
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Abstract: | Non-pathogenic soilborne microorganisms can promote plant growth, as well as suppress diseases. Plant growth promotion is
taken to result from improved nutrient acquisition or hormonal stimulation. Disease suppression can occur through microbial
antagonism or induction of resistance in the plant. Several rhizobacterial strains have been shown to act as plant growth-promoting
bacteria through both stimulation of growth and induced systemic resistance (ISR), but it is not clear in how far both mechanisms
are connected. Induced resistance is manifested as a reduction of the number of diseased plants or in disease severity upon
subsequent infection by a pathogen. Such reduced disease susceptibility can be local or systemic, result from developmental
or environmental factors and depend on multiple mechanisms. The spectrum of diseases to which PGPR-elicited ISR confers enhanced
resistance overlaps partly with that of pathogen-induced systemic acquired resistance (SAR). Both ISR and SAR represent a
state of enhanced basal resistance of the plant that depends on the signalling compounds jasmonic acid and salicylic acid,
respectively, and pathogens are differentially sensitive to the resistances activated by each of these signalling pathways.
Root-colonizing Pseudomonas bacteria have been shown to alter plant gene expression in roots and leaves to different extents, indicative of recognition
of one or more bacterial determinants by specific plant receptors. Conversely, plants can alter root exudation and secrete
compounds that interfere with quorum sensing (QS) regulation in the bacteria. Such two-way signalling resembles the interaction
of root-nodulating Rhizobia with legumes and between mycorrhizal fungi and roots of the majority of plant species. Although ISR-eliciting rhizobacteria
can induce typical early defence-related responses in cell suspensions, in plants they do not necessarily activate defence-related
gene expression. Instead, they appear to act through priming of effective resistance mechanisms, as reflected by earlier and
stronger defence reactions once infection occurs. |
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Keywords: | Arabidopsis Disease suppression Induced systemic resistance Plant growth promotion Signal transduction Systemic acquired resistance |
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