ENHANCEMENT OF BLUEBERRY, STRAWBERRY, AND BRAMBLES THROUGH MOLECULAR APPROACHES
Title: Functional identification of a blueberry CBF/DREB-like element associated with cold acclimation and freezing tolerance
Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 12, 2010
Publication Date: February 17, 2010
Citation: Polashock, J.J., Arora, R., Peng, Y., Dhananjay, N., Rowland, L.J. 2010. Functional identification of a blueberry CBF/DREB-like element associated with cold acclimation and freezing tolerance. Journal of the American Society for Horticultural Science. 135(1)40-48.
Interpretive Summary: Freezing and frost injury in blueberry can reduce yield due to damage to flower buds and vegetative tissues. Resistance to cold injury is complex and varies among blueberry varieties and throughout the year. The blueberry plants become more cold tolerant in the fall and winter and revert to less tolerant as growing resumes in the spring. To better understand development of cold tolerance, we monitored expression of a gene thought to be involved in ‘turning on’ this process in two blueberry varieties with differing resistances to cold damage. Expression of the gene was highest in the fall when temperatures begin to decline and the less tolerant variety had lower expression of the gene than the more tolerant variety. We isolated the gene from the more cold tolerant variety and expressed it in the model plant Arabidopsis. The gene ‘turned on’ some the cold tolerance genes in Arabidopsis and increased tolerance to freezing damage, confirming its involvement in the process of cold tolerance development. This information will be useful to plant breeders working on developing cold tolerant blueberry varieties and to research scientists studying the onset of the complex process of cold tolerance in plants.
Highbush blueberry (Vaccinium corymbosum L.) is susceptible to winter freezing injury and frost damage in the spring. As part of an ongoing project to understand the process of cold acclimation, we isolated a CBF/DREB-like (C-repeat binding factor/dehydration-responsive element binding protein) gene coding region from the highbush blueberry cultivar Bluecrop. Expression of the blueberry CBF gene was compared in floral buds of the cold tolerant northern highbush cultivar Bluecrop and the more cold-sensitive southern rabbiteye cultivar Tifblue (V. virgatum Ait.). Relative gene expression was higher in ‘Bluecrop’ than in ‘Tifblue’. Expression in both cultivars was highest at the earliest time point in the fall (coincident with the first stage of cold acclimation), declined during the later fall and winter, and in ‘Bluecrop’, increased again as buds deacclimated, when temperatures tend to fluctuate. To confirm the putative identity of the gene as a member of the CBF-gene family, and to determine if expression in a heterologous system could enhance freezing tolerance, the blueberry gene coding sequence was overexpressed in transgenic Arabidopsis thaliana under the control of the CAMV 35S promoter. Transgenic plants expressing the putative blueberry CBF gene exhibited induced expression of the Arabidopsis cold-regulated (COR) genes COR78 and COR6.6, under non-acclimating conditions, however, expression of two other COR genes was unaffected. Transgenic plants also exhibited enhanced freezing tolerance under non-acclimating conditions, but not to the level of acclimated control plants. Transgenic plants did not exhibit enhanced dehydration tolerance when drought stressed. Thus, both the expression pattern in floral buds and the ability of the isolated gene to turn on a subset of COR genes and increase freezing tolerance in a heterologous system suggest it is a functional member of the CBF gene family in blueberry.