© 2005 Heron Publishing—Victoria, Canada
Activation of stress-responsive mitogen-activated protein kinase pathways in hybrid poplar (Populus trichocarpa × Populus deltoides)
Louis-Philippe Hamel (1, 2), Godfrey P. Miles (3), Marcus A. Samuel (3), Brian E. Ellis (3), Armand Séguin (1) and Nathalie Beaudoin (2, 4)
1. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du PEPS, P.O. Box 3800, QC G1V 4C7, Canada / 2. Département de Biologie, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada / 3. Biotechnology Laboratory, University of British Columbia, 6174 University Boulevard, Vancouver, BC V6T 1Z3, Canada / 4. Corresponding author (nathalie.beaudoin@usherbrooke.ca) / Received July 22, 2004; accepted October 2, 2004; published online January 4, 2005
Summary
Plant mitogen-activated protein kinase (MAPK) cascades are important amplifying modules that can rapidly transduce stress
signals into various appropriate intracellular responses. Several extracellular regulated kinase (ERK)-type MAPKs involved
in plant defense signaling have been identified in herbaceous species, but no MAPK cascade has yet been characterized in a
tree species. We examined the signal transduction events that lead to activation of defense mechanisms in poplar, a major
forest species of economic and ecological importance which is becoming the model tree system for studying stress and adaptation
responses. We show that, in poplar cell suspensions and leaf tissue, chitosan, a non-host-specific elicitor, and ozone, a
strong oxidant and atmospheric pollutant, induce rapid and transient activation of at least two myelin basic protein (MBP)
kinases with apparent molecular masses of 44 and 47 kD. The chitosan- and ozone-activated kinases have characteristics of
MAPKs—they preferentially phosphorylate MBP, require tyrosine and threonine phosphorylation to be activated and are specifically
recognized by anti-ERK and anti-pERK antibodies. Moreover, activation of these poplar MAPKs by chitosan or ozone is dependent
on the production of reactive oxygen species; the influx of calcium ions via membrane channels; the activation of an upstream,
membrane-localized component; and a cognate MAPK kinase (MAPKK). These data suggest that biotic and abiotic challenges activate
MAPKs in poplar, as in herbaceous species, which then function as a convergence point for pathogen defense and oxidant stress
signaling cascades.
Keywords:
chitosan, MAPK, ozone, Populus, stress-signaling pathways.
