Planta

, Volume 225, Issue 6, pp 1535–1546

Changes in extracellular pH are neither required nor sufficient for activation of mitogen-activated protein kinases (MAPKs) in response to systemin and fusicoccin in tomato

  • Rebecca Higgins
  • Thomas Lockwood
  • Susan Holley
  • Roopa Yalamanchili
  • Johannes W. Stratmann
Original Article

DOI: 10.1007/s00425-006-0440-8

Cite this article as:
Higgins, R., Lockwood, T., Holley, S. et al. Planta (2007) 225: 1535. doi:10.1007/s00425-006-0440-8

Abstract

Leaf wounding and the wound signaling peptide systemin induce expression of wound response genes while the fungal toxin fusicoccin (FC) induces expression of pathogenesis-related genes. Consistent with their functional differences, FC and systemin regulate the extracellular pH in opposite ways, with systemin inducing an alkalinization and FC an acidification response. Here we show that systemin, wounding and FC activate the same mitogen-activated protein kinases (MAPKs; MPKs) MPK1 and 2 in tomato (Lycopersicon esculentum) leaves and L. peruvianum suspension-cultured cells. Wounding and FC activated an additional MAPK, MPK3. Pronounced differences were observed with regard to MAPK activation kinetics. FC induced prolonged, and systemin transient activity of the MAPKs. This shows that functionally different elicitors engage the same signaling components, yet induce signal-specific activation dynamics. A comparative analysis of pH effects and MAPK activity in response to specific treatments revealed that the kinetics of pH changes and MAPK activation did not correlate. Simultaneous application of FC and systemin did not lead to immediate pH changes but resulted in rapid increases in MAPK activity. Furthermore, changes in extracellular pH could be induced without concomitant MAPK activation by exchanging conditioned medium with fresh medium. This shows that changes in the extracellular pH are neither required nor sufficient for MAPK activation, suggesting that signaling pathways involving MAPKs and extracellular pH changes operate in parallel and are not part of the same linear pathway.

Keywords

Fusicoccin MAPK LeMPK Plant stress responses Plasma membrane proton ATPase Systemin Tomato 

Abbreviations

ΔpHmax

Maximal change in medium pH

DES

Diethyl stilbestrol

FC

Fusicoccin

MAPK and MPK

Mitogen-activated protein kinase

PMA

Plasma membrane proton ATPase

PR genes

Pathogenesis-related genes

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Rebecca Higgins
    • 1
  • Thomas Lockwood
    • 1
    • 2
  • Susan Holley
    • 1
  • Roopa Yalamanchili
    • 1
  • Johannes W. Stratmann
    • 1
  1. 1.Department of Biological SciencesUniversity of South CarolinaColumbiaUSA
  2. 2.Department of Molecular GeneticsUSDA, ARS, NFSPRCCorvallisUSA

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