In the complex family of heat stress transcription factors, HsfA1 has a unique role as master regulator of thermotolerance in tomato

  1. Shravan Kumar Mishra,
  2. Joanna Tripp,
  3. Sybille Winkelhaus,
  4. Bettina Tschiersch1,
  5. Klaus Theres2,
  6. Lutz Nover3, and
  7. Klaus-Dieter Scharf
  1. Biocenter of the Goethe University, D-60439 Frankfurt am Main, Germany

Abstract

We generated transgenic tomato plants with altered expression of heat stress transcription factor HsfA1. Plants with 10-fold overexpression of HsfA1 (OE plants) were characterized by a singleHsfA1 transgene cassette, whereas plants harboring a tandem inverted repeat of the cassette showed cosuppression (CS plants) by posttranscriptional silencing of the HsfA1 gene connected with formation of small interfering RNAs. Under normal growth conditions, major developmental parameters were similar for wild-type (WT), OE, and CS plants. However, CS plants and fruits were extremely sensitive to elevated temperatures, because heat stress-induced synthesis of chaperones and Hsfs was strongly reduced or lacking. Despite the complexity of the plant Hsf family with at least 17 members in tomato, HsfA1 has a unique function as master regulator for induced thermotolerance. Using transient reporter assays with mesophyll protoplasts from WT tomato, we demonstrated that plasmid-encoded HsfA1 and HsfA2 were well expressed. However, in CS protoplasts the cosuppression phenomenon was faithfully reproduced. Only transformation with HsfA2 expression plasmid led to normal expression of the transcription factor and reporter gene activation, whereas even high amounts of HsfA1 expression plasmids were silenced. Thermotolerance in CS protoplasts was restored by plasmid-borne HsfA2, resulting in expression of chaperones, thermoprotection of firefly luciferase, and assembly of heat stress granules.

Keywords

Footnotes

  • Present addresses: 1SunGene GmbH & Co., Corrensstr.3, D-06466 Gatersleben, Germany; 2MPI für Züchtungsforschung, Carl-von-Linne-Weg 10, D-50829 Köln, Germany.

  • 3 Corresponding author.

  • E-MAIL nover{at}cellbiology.uni-frankfurt.de; FAX 49-69-798-29286.

  • Article and publication are at http://www.genesdev.org/cgi/doi/10.1101/gad.228802.

    • Received February 25, 2002.
    • Accepted May 3, 2002.
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