<i><scp>RDM</scp>4</i> modulates cold stress resistance in <i>Arabidopsis</i> partially through the <i><scp>CBF</scp></i>‐mediated pathway

Summary The C‐ REPEAT ‐ BINDING FACTOR ( CBF ) pathway has important roles in plant responses to cold stress. How the CBF genes themselves are activated after cold acclimation remains poorly understood. In this study, we characterized cold tolerance of null mutant of RNA ‐ DIRECTED DNA METHYLATION 4 ( RDM 4 ), which encodes a protein that associates with RNA polymerases Pol V and Pol II , and is required for RNA ‐directed DNA methylation (Rd DM ) in Arabidopsis . The results showed that dysfunction of RDM 4 reduced cold tolerance, as evidenced by decreased survival and increased electrolyte leakage. Mutation of RDM 4 resulted in extensive transcriptomic reprogramming. CBF s and CBF regulon genes were down‐regulated in rdm4 but not nrpe1 (the largest subunit of PolV) mutants, suggesting that the role of RDM 4 in cold stress responses is independent of the Rd DM pathway. Overexpression of RDM 4 constitutively increased the expression of CBF s and regulon genes and decreased cold‐induced membrane injury. A great proportion of genes affected by rdm4 overlapped with those affected by CBF s . Chromatin immunoprecipitation results suggested that RDM 4 is important for Pol II occupancy at the promoters of CBF 2 and CBF 3 . We present evidence of a considerable role for RDM 4 in regulating gene expression at low temperature, including the CBF pathway in Arabidopsis .