Abstract
Cold acclimation in plants is a complex phenomenon involving numerous
stress-responsive transcriptional and metabolic pathways. Existing gene
expression studies have primarily addressed cold acclimation responses
in herbaceous plants, and few have focused on perennial evergreens, such
as conifers, that survive extremely low temperatures during winter.
Relative to Arabidopsis leaves, the main transcriptional response of
Norway spruce (Picea abies (L.) H. Karst) needles exposed to cold was
delayed, and this delay was associated with slower development of
freezing tolerance. Despite this difference in timing, our results
indicate that, similar to herbaceous species, Norway spruce principally
utilizes early response transcription factors (TFs) of the APETALA
2/ethylene-responsive element binding factor (AP2/ERF) superfamily and
NAM (no apical meristem)/ATAF (Arabidopsis Transcription Factors)/CUC
(cup shaped cotyledon) (NACs). The needles and root of Norway spruce
showed contrasting results, in keeping with their different metabolic
and developmental states. Regulatory network analysis identified
conserved TFs, including a root-specific bHLH101 homolog, and other
members of the same TF family with a pervasive role in cold regulation,
such as homologs of ICE1 and AKS3, and also homologs of the NAC (anac47
and anac28) and AP2/ERF superfamilies (DREB2 and ERF3), providing new
functional insights into cold stress response strategies in Norway
spruce.