The CBF/DREB 1 increases freezing tolerance in woody plants but is associated with dwarfed plants and delayed flowering. These same changes were observed when Arabidopsis DWARF AND DELAYED FLOWERING 1 (DDF1) was overexpressed. However, DDF1 orthologs have not been studied in woody plants.

Michigan State University's Guo-qing Song investigated the overexpression of blueberry (Vaccinium corymbosum) DDF1, named VcDDF1. The VcDDF1 overexpression resulted in enhanced freezing tolerance in tetraploid blueberry plants and did not result in significant changes in plant size and flowering time. Analysis revealed differentially expressed (DE) genes in the pathways of cold-response, plant flowering, DELLA proteins, and plant phytohormones between the transgenic and non-transgenic blueberry.

The increase in freezing tolerance was associated to the expression of cold-regulated genes and the ethylene pathway genes. The unchanged plant size, dormancy and flowering were due to the minimal effect of the VcDDF1-OX on the expression of DELLA proteins, flowering pathway genes, and the other phytohormone genes. The differentially expressed genes in auxin and cytokinin pathways also suggest altered plant tolerance to drought and high salinity.

The overexpression of VcDDF1 or its orthologues can be a new approach to increase freezing tolerance of woody plant species.

For more on this study, read the article in BMC Plant Biology.