Redox-dependent structural switch and CBF activation confer freezing tolerance in plants

Abstract

CBF transcription factors are central to cold stress responses. The authors show that only monomeric reduced forms can induce target genes. The redox status of CBFs is controlled by thioredoxin, isotype-h2, Trx-h2. The activities of cold-responsive C-repeat-binding transcription factors (CBFs) are tightly controlled as they not only induce cold tolerance but also regulate normal plant growth under temperate conditions(1-4). Thioredoxin h2 (Trx-h2)-a cytosolic redox protein identified as an interacting partner of CBF1-is normally anchored to cytoplasmic endomembranes through myristoylation at the second glycine residue(5,6). However, after exposure to cold conditions, the demyristoylated Trx-h2 is translocated to the nucleus, where it reduces the oxidized (inactive) CBF oligomers and monomers. The reduced (active) monomers activate cold-regulated gene expression. Thus, in contrast to the Arabidopsis trx-h2 (AT5G39950) null mutant, Trx-h2 overexpression lines are highly cold tolerant. Our findings reveal the mechanism by which cold-mediated redox changes induce the structural switching and functional activation of CBFs, therefore conferring plant cold tolerance.