Overexpression of a blueberry-derived CBF gene enhances cold tolerance in a southern highbush blueberry cultivar

Blueberry cultivars are subject to freezing damage in the winter and early spring. C-repeat binding factor (CBF) genes are transcription factors known to induce the expression of genes associated with cold acclimation and freezing tolerance. A CBF-encoding gene (BB-CBF) was isolated from the northern highbush blueberry Bluecrop (a cold-tolerant cultivar) and introduced into the southern highbush blueberry Legacy (a more cold-sensitive cultivar) to determine the effects on cold tolerance. The BB-CBF coding sequence was linked to the cauliflower mosaic virus 35S promoter and the 35S polyA terminator and was subsequently introduced into Legacy using Agrobacterium-mediated transformation of leaf explants. Fifty-seven transgenic events were obtained. Non-acclimated mature leaves, dormant flower buds, and flowers at various developmental stages from transformants and nontransgenic plants were subjected to electrolyte leakage assays over the course of 3 years, 2009-2011. Transgenic lines showed an increase in freezing tolerance in leaves and dormant buds. Expression of putative downstream components of the blueberry CBF regulon was increased in non-acclimated transgenic lines, and, in some cases, to a level similar to that of acclimated control plants. Following low temperature exposure, BB-CBF-overexpressing transgenics and controls expressed these genes at similar levels.