Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2015
Publication Date: 2/5/2015
Publication URL: http://handle.nal.usda.gov/10113/60476
Citation: Wisniewski, M.E., Norelli, J.L., Artlip, T.S. 2015. Overexpression of a peach CBF gene in apple: a model for understanding the integration of growth, dormancy, and cold hardiness in woody plants. Frontiers in Plant Science. DOI: 10.3389/fpls.2015.00085.
Interpretive Summary: The timing of when fruit trees and other woody plants go dormant, acclimate and become cold hardy, break dormancy, and resume growth is critical to the survival of overwintering plants. These parameters are important not only in midwinter but also in the spring time when early growth and flowering can result in devastating injury and thus result in losses in fruit production for that year and even subsequent years if the injury is extensive. Current trends in climate change represent an additional burden since trees are receiving mixed signals due to dramatic and unseasonable changes in temperature. Dormancy, cold hardiness, and the timing of bud break are all under genetic control, so understanding how these events are controlled and how their regulation is integrated will allow researchers and breeders to develop management practices and new cultivars, respectively, which are adapted to our changing climate. USDA-ARS researchers have developed a transgenic line of apple trees in which cold hardiness has been increased, dormancy is prolonged, and growth is modified. These trees have been field-planted and monitored for three years and are being used as a model system for studying the integration of growth, dormancy, and cold hardiness in woody plants. The present study identified members of several different families of genes whose expression is associated with differences in dormancy and cold hardiness exhibited in the transgenic lines. The identified genes will serve as candidate genes for further exploring how dormancy, cold hardiness, and growth are integrated.
Technical Abstract: The timing of cold acclimation and de-acclimation, dormancy, and bud break play an integral role in the life cycle of woody plants. The molecular events that regulate these parameters have been the subject of much study, however, in most studies these events have been investigated independently of each other. Ectopic expression of a peach CBF (PpCBF1) in apple increases the level of both non-acclimated and acclimated freezing tolerance relative to the non-transformed control, and also inhibits growth, induces early bud set and leaf senescence, and delays bud break in the spring. The current study examined differences in the seasonal expression of genes (CBF, DAM, RGL, and EBB) that have been reported to be associated with freezing tolerance, dormancy, growth, and bud break, respectively, in the PpCBF1 T166 transgenic apple line and the non-transformed M.26 control. Results indicated that expression of several of these key genes, including MdDAM, MdRGL, and MdEBB was altered in transgenic T166 trees relative to non-transformed M.26 trees. In particular, several putative MdDAM genes, associated with the dormancy-cycle in other species of woody plants in the Rosaceae exhibited different patterns of expression in the T166 vs. M.26 trees. Additionally, for the first time a putative APETALA2/Ethylene-responsive transcription factor, originally described in poplar and shown to regulate the timing of bud break, was shown to be associated with the timing of bud break in apple. Since the overexpression of PpCBF1 in apple results in a dramatic alteration in cold acclimation, dormancy, and growth, this transgenic line (T166) may represent a useful model for studying the integration of these seasonal life-cycle parameters.