Plant Molecular Biology

, Volume 70, Issue 5, pp 603–616

The tomato brassinosteroid receptor BRI1 increases binding of systemin to tobacco plasma membranes, but is not involved in systemin signaling

  • Robert Malinowski
  • Rebecca Higgins
  • Yuan Luo
  • Laverne Piper
  • Azka Nazir
  • Vikramjit S. Bajwa
  • Steven D. Clouse
  • Paul R. Thompson
  • Johannes W. Stratmann
Article

Abstract

The tomato wound signal systemin is perceived by a specific high-affinity, saturable, and reversible cell surface receptor. This receptor was identified as the receptor-like kinase SR160, which turned out to be identical to the brassinosteroid receptor BRI1. Recently, it has been shown that the tomato bri1 null mutant cu3 is as sensitive to systemin as wild type plants. Here we explored these contradictory findings by studying the responses of tobacco plants (Nicotiana tabacum) to systemin. A fluorescently-labeled systemin analog bound specifically to plasma membranes of tobacco suspension-cultured cells that expressed the tomato BRI1-FLAG transgene, but not to wild type tobacco cells. On the other hand, signaling responses to systemin, such as activation of mitogen-activated protein kinases and medium alkalinization, were neither increased in BRI1-FLAG-overexpressing tobacco cells nor decreased in BRI1-silenced cells as compared to levels in untransformed control cells. Furthermore, in transgenic tobacco plants BRI1-FLAG became phosphorylated on threonine residues in response to brassinolide application, but not in response to systemin. When BRI1 transcript levels were reduced by virus-induced gene silencing in tomato plants, the silenced plants displayed a phenotype characteristic of bri1 mutants. However, their response to overexpression of the Prosystemin transgene was the same as in control plants. Taken together, our data suggest that BRI1 can function as a systemin binding protein, but that binding of the ligand does not transduce the signal into the cell. This unusual behavior and the nature of the elusive systemin receptor will be discussed.

Keywords

Systemin SR160 BRI1 Wound response Wound signaling Brassinosteroids 

Supplementary material

11103_2009_9494_MOESM1_ESM.doc (442 kb)
Supplementary material 1 (DOC 26,773 kb)

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Robert Malinowski
    • 1
    • 4
  • Rebecca Higgins
    • 1
  • Yuan Luo
    • 2
    • 5
  • Laverne Piper
    • 1
    • 6
  • Azka Nazir
    • 1
  • Vikramjit S. Bajwa
    • 3
  • Steven D. Clouse
    • 3
  • Paul R. Thompson
    • 2
  • Johannes W. Stratmann
    • 1
  1. 1.Department of Biological SciencesUniversity of South CarolinaColumbiaUSA
  2. 2.Department of Chemistry and BiochemistryUniversity of South CarolinaColumbiaUSA
  3. 3.Department of Horticultural ScienceNorth Carolina State UniversityRaleighUSA
  4. 4.Department of Animal and Plant SciencesUniversity of SheffieldSheffieldUK
  5. 5.Department of Internal MedicineUniversity of Texas Southwestern Medical CenterDallasUSA
  6. 6.Dutch Fork High SchoolIrmoUSA

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