Field Evaluation of Apple Overexpressing a Peach CBF Gene Confirms its Effect on Cold Hardiness, Dormancy, and Growth

The role of CBF genes in cold response and acclimation has been well documented in both herbaceous and woody plants.  Our initial research demonstrated that overexpression of a peach CBF gene (PpCBF1) in ‘M.26’ apple increases freezing tolerance of non-acclimated plants and unexpectedly also results in short-day induced dormancy (Wisniewski, et al.  2010. Planta 233: 971-983).  Transcriptomic studies indicated that PpCBF1-Regulated genes represent approximately 8.5% of the total gene set induced during normal cold acclimation of apple.  Cold-acclimation-Regulated genes are also more diverse than PpCBF1-Regulated genes. Field performance of transgenic ‘M.26’ apple overexpressing a peach CBF gene (T166) and transgenic ‘M.26’ apple in which the expression of a native CBF gene was silenced (T186) has also been conducted. Results indicate that the T166 line has improved cold hardiness, reduced growth, earlier leaf senescence, and later budbreak.  The reduced growth would be advantageous as ‘M.26’ is a rootstock and the delayed budbreak would help trees avoid late spring frosts, a problem that is expected to become more significant due to climate change.  Preliminary data on reciprocal grafting experiments under field conditions will also be presented. In summary, it appears that overexpression of a peach CBF gene in apple has significant, long-term effects on apple physiology, development, and response to environmental cues.