Rhizosphere interactions: the root microbiome
Hawes, Martha , Curlango-Rivera, Gilberto , Huskey, David , Xiong, Zhongguo .
The rhizosphere microbiome and border cell extracellular 'trapping:' new insight into an old conundrum.
The rhizosphere, by Hiltner's definition, is a region where microbial growth is stimulated by the release of nutrient-rich exudates from roots and plant health in turn is influenced by associated microflora. The root apex has been shown to be the primary site of exudation in healthy young seedlings of diverse species, with >90% of the total exudate weight delivered by the root cap of cereals and legumes. It would therefore be reasonable to expect most microbial colonization to occur in this nutrient-rich region. Yet the root cap repeatedly has been shown to remain free of infection and colonization by most pathogenic and symbiotic bacteria and fungi. Recent insight into the function of root border cells, a population of specialized living cells programmed to detach from the root cap into the soil environment, may shed light on this longstanding mystery. Border cells have been found to be functionally analogous to mammalian cells functioning in innate defense. In neutrophils, histone-linked extracellular DNA (exDNA) and antimicrobial proteins operate as extracellular traps which chemotactically attract and immobilize pathogens. Group A Streptococcus can escape these traps via pathogen-derived extracellular DNases. exDNA also is a component of root cap defense. Experiments have confirmed work by Phillips and Torrey in 1971 (Plant Physiol 48:213, 1971) documenting that DNA is synthesized and exported into the extracellular matrix of root cap peripheral cells. This exDNA is a component of the surrounding mucilage which attracts, traps and immobilizes pathogens in a host-microbe specific manner. As in neutrophils, this 'trapping' process is reversed by DNase treatment. Moreover, when root cap exDNA is degraded concurrently with inoculation by root-rotting fungal pathogens including Nectria haematococca, Thielaviopsis basicola, and Phoma medicaginis, the normal resistance of the root cap to infection is abolished and infection increases from <3% to 100%. Our progress in defining the dynamics and mechanisms of border cell trapping of soilborne bacteria will be presented.
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1 - University of Arizona, Soil, Water and Environmental Science, Shantz Building, Tucson, AZ, 85721, USA
2 - University of Arizona, Plant Science, Division of Plant Pathology and Microbiolosy, Tucson, AZ, 85721, USA
root border cells
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware D/Hyatt
Date: Tuesday, July 10th, 2012
Time: 8:45 AM