We have characterized the seasonal accumulation of transcripts and proteins in peach (Prunuspersica), particularly a 60 kDa dehydrin (PCA60; PpDhn1). Recently, we have isolated another dehydrin gene (PpDhn2). The present report compares the structural organization of the two dehydrin genes, their promoters, and the response of the genes to temperature, photoperiod, and water deficit. Trees were exposed for 3 or 5 weeks to either short day (SD) or long day (LD) photoperiods at either 25 or 5 °C. Additional experiments exposed trees to a period of water deficit followed by recovery. Transcript abundance of both genes, as assessed by RT-PCR, was determined, in response to the different photoperiods and temperatures as well as a prolonged SD/5 °C regime, from monthly-collected field samples, and trees subjected to water deficit. Results indicated that water deficit increased transcript abundance of both genes, but their abundance differed dramatically in response to low temperature and seasonal cues. Surprisingly, neither gene exhibited a significant elevation in transcript abundance in response to SD conditions. The lack of response of PpDhn1to SD is problematical given the observation that transcript levels in field-collected samples begin to increase substantially in September, prior to the onset of cold temperatures. Analysis of the promoter regions and cis-acting elements suggest that ABA may play an important role in seasonal expression, interacting with photoperiod in field conditions. Two CRT/DRE elements are present in the promoter region of PpDhn1, but absent in the promoter of PpDhn2.
Metabolic responses to water deficit in two Eucalyptus globulus clones with contrasting drought sensitivity
