Novel aspects of transcriptional regulation in the winter survival and maintenance mechanism of poplar.

Temperate woody plants have developed sophisticated winter survival and maintenance mechanisms that enable them to adapt rapidly to the annual cycle of environmental changes. Here, we demonstrate notable aspects of the transcriptional regulation adopted by poplar in winter/dormancy, employing biochemical and whole transcriptome analysis, and showing high levels of transcriptional activity in a broad spectrum of genes during the dormancy period. A total of 3237 probe sets upregulated more than threefold in winter/dormancy stems over summer/active-growth stems were identified. As expected, genes related to cold hardiness and defense were over-represented. Carbohydrate biosynthesis and transport-related genes were also actively expressed in winter/dormancy stems. Further biochemical analyses verified the dormancy/winter transcription phenotype. More than 60% of the winter upregulated transcription factors (TFs) were related to either biotic or abiotic stress. This finding substantiates that the major transcriptional network of winter/dormancy stems is related to stress tolerance, such as dehydration, cold tolerance and defense. Furthermore, during winter/dormancy, preferential expression of genes involved in cell wall biosynthesis or modification, indirect transcriptional regulation (RNA metabolism) and chromatin modification/remodeling were observed. Taken together, these findings show that regulation of gene expression associated with winter survival and maintenance extends beyond control by promoter-binding TFs to include regulation at the post-transcriptional and chromatin levels.