Expression of an active tobacco mitogen-activated protein kinase kinase kinase enhances freezing tolerance in transgenic maize

doi:10.1073/pnas.0308095100

Expression of an active tobacco mitogen-activated protein kinase kinase kinase enhances freezing tolerance in transgenic maize

^†Plant Transformation Facility, Department of Agronomy, Iowa State University, Ames, IA 50011-1010; ^§Illumina Inc., 9885 Towne Centre Drive, San Diego, CA 92121; and ^¶Department of Molecular Biology, Massachusetts General Hospital, and Department of Genetics, Harvard Medical School, Boston, MA 02114

Communicated by Luis Herrera-Estrella, National Polytechnic Institute, Guanajuato, Mexico, December 9, 2003 (received for review October 9, 2003)

Abstract

Cold acclimation is the major process that prepares plants for freezing tolerance. In addition to extensive transcription regulation by cold-inducible master transcription factors, oxidative stress signaling has been postulated to play a role in freezing tolerance. Activation of oxidative signaling through the expression of an active mitogen-activated protein kinase kinase kinase provided benefits in transgenic tobacco at freezing temperature bypassing cold acclimation. Because involvement of the mitogen-activated protein kinase cascade in oxidative stress signaling is evolutionarily conserved in eukaryotes from yeast to mammals, we tested the effect of expressing a heterologous tobacco mitogen-activated protein kinase kinase kinase (Nicotiana PK1), which can mimic H₂O₂ signaling, in a major cereal crop. We demonstrate that low-level but constitutive expression of the Nicotiana PK1 gene enhances freezing tolerance in transgenic maize plants that are normally frost sensitive. Our results suggest that a new molecular approach can be designed to genetically enhance freezing tolerance in important crops.

Footnotes

↵ ∥ To whom correspondence should be addressed. E-mail: kanwang{at}iastate.edu.
↵ ‡ Present address: College of Life Science, Zhejiang University, Hangzhou 310029, China.
Abbreviations: DREB, dehydration-responsive element binding; MAPK, mitogen-activated protein kinase; CBF, cold-inducible master transcription factor; NPK1, Nicotiana PK1; PH, plant height, LN, leaf number; EL, electrolyte leakage; TSC, total soluble carbohydrate; NA, nonacclimated; CA, cold-acclimated; HSP, heat shock protein.