|Farrell, Jr., Robert|
|Artlip, Timothy - Tim|
Submitted to: Tree Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2005
Publication Date: 2/1/2006
Citation: Wisniewski, M.E., Bassett, C.L., Renaut, J., Farrell, Jr., R., Tworkoski, T., Artlip, T.S. 2006. Differential regulation of two dehydrin genes from peach (prunus persica) by photoperiod, low temperature and water deficit. Tree Physiology. 26:575-584. Interpretive Summary: Unfavorable environmental conditions result in reduced crop yields and loss of vigor for perennial plants, such as fruit trees. Freeze damage to fruit crops results in reductions in annual yields and sometimes the loss of entire orchards. As an example, it was estimated that in New York State alone, 25,000 apple trees were lost to winter damage during 2003-2004 at a valued cost of 2.5 million dollars. In order to develop new strategies to overcome the genetic limitations of stress resistance in fruit crops, a better understanding of the regulation of stress-induced genes is needed. In previous research, we identified a gene (Ppdhn1) in peach belonging to the dehydrin family of genes, which was associated with cold hardiness. In the current research, we have identified a new dehydrin gene (Ppdhn1) in peach and characterized the expression of these genes in response to low temperatures, short daylengths, and water deficit (drought). In trees, short daylengths are an environmental cue that induces them to stop growing and become dormant. The results of the current research indicated that neither gene was responsive to short daylength. Furthermore, Ppdhn1 was more responsive to cold than Ppdhn2, which was mostly responsive to drought. An analysis of the promoter region of each gene, i.e., the region responsible for regulating the expression of the gene, indicated that Ppdhn1 had two specific areas that were responsive to cold, whereas, these regions were absent in Ppdhn2. Both genes had regions that are responsive to water deficit, but Ppdhn2 had more of these regions. This research will greatly increase our knowledge of how fruit trees acclimate and become tolerant of low temperatures without being injured. Future research will focus on how the promoter regions of these genes perceive and respond to environmental cues, such as low temperature and water deficit.
Technical Abstract: Seasonal expression of genes and the proteins they encode is a feature of temperate woody plant species. The selective expression of specific proteins is felt to be a pre-requisite for dormancy and cold acclimation, and is thought to be largely controlled by photoperiod and temperature. A previously described dehydrin, PCA60/ PpDhn1 from peach (Prunus persica [L.] Batsch) is an example of this expression pattern, reaching a maximum in late autumn and not declining until mid-spring. It was also shown to respond to dehydration, which is another consequence of low or freezing temperatures. However, it has been difficult to separate dormancy-related effects on PpDhn1 expression from low temperature effects. In an attempt to further understand the regulation of PpDhn1, a discrete system to separate photoperiod from temperature was created in which peach trees were exposed for three or five weeks to either short day (SD) or long day (LD) photoperiods with either a growth-promoting temperature (25 deg C) or a non-freezing, low temperature (5 deg C). To provide contrast, a previously unreported second dehydrin, PpDhn2 was also examined. Transcript abundance of both genes, as assessed by RT-PCR, was determined under the varying photoperiods and temperatures, as well as from monthly-collected field samples, trees subjected to water deficit, as well as a prolonged SD/ 5 deg C regime. The new dehydrin, PpDhn2, was found to differ from PpDhn1 in terms of sequence, and had near identity to a dehydrin from almond. As is common for dehydrins, water deficit increased the transcript abundance of both genes. However, the genes differed radically in their response to natural seasonal abundance and low temperature. They were quite similar in response to photoperiod, i.e., no significant elevation in transcript abundance in response to SD conditions. The lack of response of PpDhn1 to SD was surprising, given its seasonal expression pattern. 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.