2017 ASHS Annual Conference

CBF or DREB transcription factors are involved in plant adaptation to low temperatures and osmotic stress (drought and salt) in plants. Overexpression of these transcription factors in plants has been to shown to affect other developmental processes, such as growth, flowering, and dormancy. Several laboratory and field studies have been conducted on the overexpression of a peach, and native apple CBF genes in apple. Results have demonstrated that overexpression of a peach CBF gene in apple improves cold hardiness but also has a significant impact on, shoot growth, the onset of dormancy and leaf senescence, and the timing of spring bud break. Interestingly, similar effects have not been observed when native, apple CBF genes have been overexpressed in apple, despite high levels of homology between the apple and peach CBF genes. RT-qPCR analysis has indicated that several genes related to growth and dormancy are impacted by the overexpression of CBF and that promoters from these genes contain C-repeats (the binding site for CBF) and other stress and environmental-associated motifs. Reciprocal grafting studies of transgenic and non-transgenic rootstock/scion combinations have revealed that when transgenic ‘M.26’ is used as a rootstock it does not impact cold hardiness or dormancy of non-transgenic ‘Royal Gala’ scions but does impact growth. Collective studies indicate that the functional role of CBF in fruit trees is complex and impacts several developmental processes. Overexpression of CBF in apple may serve as a model for studying the integration of cold hardiness, dormancy, and growth in fruit trees.