1Dept. of Biological Sciences, The George Washington Univ., Washington, DC 20052; 2Dept. of Horticulture, Univ. of Georgia, Athens, GA 30602;3 USDA-ARS, Fruit Laboratory, Beltsville Agricultural Research Center, Beltsville, MD 20705
The blueberry industry experiences significant losses every year due to environmental factors with a dehydrative component, such as drought and freezing stress. In a recent survey of blueberry research and extension scientists in the United States, lack of cold hardiness and susceptibility to spring frosts were identified as the most important genetic limitations of current cultivars. For these reasons, cloning and characterization of expression of dehydration-responsive genes (dehydrins) have been ongoing in our laboratory. To date, one full-length (2.0 kb bbdhn1 gene) and four partial-length dehydrin cDNAs have been cloned and sequenced. Very high homology at the DNA and protein levels were found among the blueberry dehydrin clones, particularly at the 3' ends. From DNA blots, it appears that blueberry dehydrins are encoded by about three genes with high homology to the full-length 2.0 kb bbdhn1 cDNA clone and a few other less related genes. The 2.0 kb bbdhn1 gene was mapped in a blueberry population segregating for cold hardiness and chilling requirement. Expression studies indicated that dehydrins are induced by cold and drought stress. In general, dehydrins were induced in all organs examined in response to cold stress, including floral buds, leaves, stems, and roots. Under drought conditions, dehydrins were induced primarily in stems and their levels declined in roots. Some of the induced dehydrins were the same for drought and cold stress, whereas others were unique to a given stress. Levels of dehydrin accumulation correlated positively with cold hardiness; however, levels of dehydrins did not correspond precisely to the degree of drought avoidance.