DREB1A/CBF3 is repressed by transgene-induced DNA methylation in the Arabidopsis ice1-1 mutant
Satoshi Kidokoro†, June-Sik Kim†, Tomona Ishikawa, Takamasa Suzuki, Kazuo Shinozaki, Kazuko Yamaguchi-Shinozaki*
DREB1/CBFs are key transcription factors involved in plant cold stress adaptation. The expression of DREB1/CBFs triggers a cold-responsive transcriptional cascade, after which many stress tolerance genes are expressed. Thus, elucidating the mechanisms of cold stress-inducible DREB1/CBF expression is important to understand the molecular mechanisms of plant cold stress responses and tolerance. We analyzed the roles of a transcription factor, ICE1 (INDUCER OF CBF EXPRESSION 1), that is well known as an important transcriptional activator in the cold-inducible expression of DREB1A/CBF3. ice1-1 is a widely accepted mutant allele known to abolish cold-inducible DREB1A expression, and this evidence has strongly supported ICE1-DREB1A regulation for many years. However, in ice1-1 outcross descendants, we unexpectedly discovered that ice1-1 DREB1A repression was genetically independent of the ice1-1 allele, ICE1(R236H). Moreover, neither ICE1 overexpression nor double loss-of-function mutation of ICE1 and its homologous SCRM2 altered DREB1A expression. Instead, a transgene locus harboring a reporter gene in the ice1-1 genome was responsible for altering DREB1A expression. The DREB1A promoter was hypermethylated due to the transgene. We showed that DREB1A repression in ice1-1 results from transgene-induced silencing and not genetic regulation by ICE1. The ICE1(R236H) mutation has also been reported as scrm-D, which confers constitutive stomatal differentiation. The scrm-D phenotype and the expression of a stomatal differentiation marker gene were confirmed to be linked to the ICE1(R236H) mutation. We propose that the current ICE1-DREB1 regulatory model should be revalidated without the previous assumptions.
- : The Plant Cell
- : 10.1105/tpc.19.00532
- : http://www.plantcell.org/content/early/2020/02/07/tpc.19.00532