PLANT PHYSIOLOGY , Vol 115, Issue 4 1691-1698, Copyright © 1997 by American Society of Plant Biologists
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PLANT-MICROBE AND PLANT-INSECT INTERACTIONS |
Induction of Microbial Genes for Pathogenesis and Symbiosis by Chemicals from Root Border Cells
Y. Zhu, L. S. Pierson III and M. C. Hawes
Departments of Plant Pathology and Molecular and Cellular Biology, 204 Forbes Building, University of Arizona, Tucson, Arizona 85721
Reporter strains of soil-borne bacteria were used to test the hypothesis
that chemicals released by root border cells can influence the expression
of bacterial genes required for the establishment of plant-microbe
associations. Promoters from genes known to be activated by plant factors
included virE, required for Agrobacterium tumefaciens pathogenesis, and
common nod genes from Rhizobium leguminosarum bv viciae and Rhizobium
meliloti, required for nodulation of pea (Pisum sativum) and alfalfa
(Medicago sativum), respectively. Also included was phzB, an autoinducible
gene encoding the biosynthesis of antibiotics by Pseudomonas aureofaciens.
The virE and nod genes were activated to different degrees, depending on
the source of border cells, whereas phzB activity remained unaffected. The
homologous interaction between R. leguminosarum bv viciae and its host,
pea, was examined in detail. Nod gene induction by border cells was dosage
dependent and responsive to environmental signals. The highest levels of
gene induction by pea (but not alfalfa) border cells occurred at low
temperatures, when little or no bacterial growth was detected. Detached
border cells cultured in distilled water exhibited increased nod gene
induction (ini) in response to signals from R. leguminosarum bv viciae.
