Title: Field evaluation of apple overexpressing a peach CBF gene confirms its effect on cold hardiness, dormancy, and growth Authors
Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2013
Publication Date: December 15, 2013
Citation: Artlip, T.S., Wisniewski, M.E., Norelli, J.L. 2013. Field evaluation of apple overexpressing a peach CBF gene confirms its effect on cold hardiness, dormancy, and growth. Environmental and Experimental Botany. DOI: 10.1016/j.envexbot.2013.12.008. Interpretive Summary: Erratic conditions such as early spring warming followed by frosts or freezing events are particularly devastating to fruit and vegetable growers. If chilling requirements have been met in a fruit tree, warm spells permit the tree to deacclimate from a cold tolerant condition, and foster bud break. Blossoms and nascent fruit are particularly susceptible to freeze damage. Several genes in apple and peach that respond to low temperature have been investigated in an effort to better understand the mechanisms behind cold acclimation and deacclimation. The CBF (c-repeat binding factor) family encodes transcription factors that act as higher-level “on switches” for many genes known for their importance in cold acclimation and tolerance. We have constitutively over-expressed a CBF gene in apple and have followed growth and phenological characteristics in a field planting for three years. The CBF-overexpressing apple trees have delayed vegetative bud break in the spring. While the exact mechanism is unknown, the CBF gene appears to provide a novel sensitivity to daylength that apple is not known to have. This improved knowledge may provide a means by which damage from frosts during bloom or early fruit set can be mitigated. In addition, reduced growth (stem diameter and height) was observed. Reduced growth in apple may be advantageous. Since the apple cultivar used in this study (‘M.26’) is a rootstock variety, the reduction in growth may not be detrimental but rather beneficial if the reduced growth can be transferred to grafted scion varieties.
Technical Abstract: In recent years, the scientific literature has become replete with examples of the improvement of abiotic stress tolerance by overexpression of specific genes. Few studies, however, have evaluated transgenic plants under field conditions or the impact of overexpression on non-target traits. We previously reported that constitutive overexpression of a peach (Prunus persica) CBF (C-Repeat Binding Factor)/ DREB1 (Dehydration Response Element Binding) gene in an apple (Malus X domestica) rootstock variety (‘M.26’) resulted in a modest increase in cold hardiness of acclimated and non-acclimated leaves but also unexpectedly resulted in apple plants that were subject to short-day–induced dormancy. In the present study, a transgenic apple line constitutively overexpressing a peach CBF gene were evaluated under field conditions for two years to determine the impact of the CBF overexpression growth, phenology, and cold hardiness compared to untransformed apple. One-year-old seedling trees were planted in an orchard in autumn 2010, and data recorded over two growing seasons. Results indicated significantly reduced growth, early leaf senescence, delayed bud break, temporal changes in pigment accumulation, and enhanced freezing tolerance in the transgenic line (T166) compared to un-transformed ’M.26’. Results highlight the importance of conducting long-term field studies on transgenic plants modified to increase abiotic stress tolerance.