The path to dormancy induction, maintenance, and release is a continuum and has been the topic of thousands of research articles to date. It would be an impossible task and indeed presumptuous of us to imagine that we could review all the research conducted on dormancy in the past century in this article. The multiple and complex nature of the dormancy phenomenon would require not one review but a series of in-depth reviews to cover the research on individual subdisciplines that come under the umbrella of dormancy. Its complexity and multiplicity of various subdisciplines stem from the fact that dormancy affects diverse plant structures (buds, seeds, bulbs, etc.) distinctly and that these dormant structures maintain distinct anatomical and physiological relations with neighboring parts. We, therefore, have chosen to discuss here only one, nevertheless highly significant, aspect of dormancy, i.e., bud dormancy in woody plants.As one reflects over nearly a century of work, it is apparent that, as with other disciplines, dormancy research has evolved as different aspects of bud dormancy (e.g., site of dormancy; photoperiod and environmental induction of dormancy; physiology of dormancy control, particularly phytohormones; chilling requirement-effective temperatures, bud differences, modification of chilling requirement by environment and/or cultural practices, models for calculating chilling requirement; dormancy-breaking chemicals and/or stress treatments) catching the fancy of horticulturists at different periods on the temporal curve of dormancy research. This research was extensively reviewed during the ), followed by more recent reviews and workshop proceedings in the among others). To appreciate the continuity of significant research developments in this field, we recommend them as a must-read for students of plant dormancy.Although many significant mileposts have been reached in our understanding of the induction and release of bud dormancy in the past 50 to 60 years (reviewed in the above citations), research published up until the 1980s includes little information on experimental systems and approaches for studying the genetics of bud dormancy and the cellular and molecular events-gene expression and regulation, signaling mechanism(s), or mechanistic aspects-associated with regulation of bud dormancy. Many of us must wonder how H. Muller-Thurgau had already confirmed in 1885 that a shortened growth period of the shoots caused by water stress promotes early inception of bud dormancy and shortens its duration, i.e., reduces the chilling requirement. This observation was further supported by Chandler and Tufts in 1934 based on their observation that an extended growth period of shoots delays budbreak the following spring if there is insufficient chilling. Despite these early observations, today we still do not clearly understand the cellular biology of how environmental stress regulates bud dormancy. dormancy induction and release in the past century has been, in part, due to the preoccupation with the linear ...

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An expressed sequence tag (EST) analysis approach was undertaken to identify major genes involved in cold acclimation of Rhododendron, a broad-leaf, woody evergreen species. Two cDNA libraries were constructed, one from winter-collected (cold-acclimated, CA; leaf freezing tolerance -53 degrees C) leaves, and the other from summer-collected (non-acclimated, NA; leaf freezing tolerance -7 degrees C) leaves of field-grown Rhododendron catawbiense plants. A total of 862 5'-end high-quality ESTs were generated by sequencing cDNA clones from the two libraries (423 from CA and 439 from NA library). Only about 6.3% of assembled unique transcripts were shared between the libraries, suggesting remarkable differences in gene expression between CA and NA leaves. Analysis of the relative frequency at which specific cDNAs were picked from each library indicated that four genes or gene families were highly abundant in the CA library including early light-induced proteins (ELIP), dehydrins/late embryogenesis abundant proteins (LEA), cytochrome P450, and beta-amylase. Similarly, seven genes or gene families were highly abundant in the NA library and included chlorophyll a/b-binding protein, NADH dehydrogenase subunit I, plastidic aldolase, and serine:glyoxylate aminotransferase, among others. Northern blot analyses for seven selected abundant genes confirmed their preferential expression in either CA or NA leaf tissues. Our results suggest that osmotic regulation, desiccation tolerance, photoinhibition tolerance, and photosynthesis adjustment are some of the key components of cold adaptation in Rhododendron.

BackgroundThere has been increased consumption of blueberries in recent years fueled in part because of their many recognized health benefits. Blueberry fruit is very high in anthocyanins, which have been linked to improved night vision, prevention of macular degeneration, anti-cancer activity, and reduced risk of heart disease. Very few genomic resources have been available for blueberry, however. Further development of genomic resources like expressed sequence tags (ESTs), molecular markers, and genetic linkage maps could lead to more rapid genetic improvement. Marker-assisted selection could be used to combine traits for climatic adaptation with fruit and nutritional quality traits.ResultsEfforts to sequence the transcriptome of the commercial highbush blueberry (Vaccinium corymbosum) cultivar Bluecrop and use the sequences to identify genes associated with cold acclimation and fruit development and develop SSR markers for mapping studies are presented here. Transcriptome sequences were generated from blueberry fruit at different stages of development, flower buds at different stages of cold acclimation, and leaves by next-generation Roche 454 sequencing. Over 600,000 reads were assembled into approximately 15,000 contigs and 124,000 singletons. The assembled sequences were annotated and functionally mapped to Gene Ontology (GO) terms. Frequency of the most abundant sequences in each of the libraries was compared across all libraries to identify genes that are potentially differentially expressed during cold acclimation and fruit development. Real-time PCR was performed to confirm their differential expression patterns. Overall, 14 out of 17 of the genes examined had differential expression patterns similar to what was predicted from their reads alone. The assembled sequences were also mined for SSRs. From these sequences, 15,886 blueberry EST-SSR loci were identified. Primers were designed from 7,705 of the SSR-containing sequences with adequate flanking sequence. One hundred primer pairs were tested for amplification and polymorphism among parents of two blueberry populations currently being used for genetic linkage map construction. The tetraploid mapping population was based on a cross between the highbush cultivars Draper and Jewel (V. darrowii is also in the background of 'Jewel'). The diploid mapping population was based on a cross between an F1 hybrid of V. darrowii and diploid V. corymbosum and another diploid V. corymbosum. The overall amplification rate of the SSR primers was 68% and the polymorphism rate was 43%.ConclusionsThese results indicate that this large collection of 454 ESTs will be a valuable resource for identifying genes that are potentially differentially expressed and play important roles in flower bud development, cold acclimation, chilling unit accumulation, and fruit development in blueberry and related species. In addition, the ESTs have already proved useful for the development of SSR and EST-PCR markers, and are currently being used for construction of genetic linkage maps in bl...

l h e level of three major polypeptides of 65, 60, and 14 kD increased in response to chilling unit accumulation in floral buds of a woody perennial, blueberry (Vaccinium, section Cyanococcus). The level of the polypeptides increased most dramatically within 300 h of chilling and decreased to the prechilling level with the initiation of budbreak. Cold-hardiness levels were assessed for dormant buds of Vaccinium corymbosum and Vaccinium ashei after different chilling treatments until the resumption of growth. lhese levels coincided with the level of the chilling-responsive polypeptides. Like some other previously described cold-induced proteins in annual plants, the level of the chilling-induced polypeptides also increased in leaves in response to cold treatment; the chilling-induced polypeptides were heat stable, resisting aggregation after incubation at 95°C for 15 min. By fradionating bud proteins first by isoelectric point (pl) and then by molecular mass, the p l values of the 65-and 60-kD polypeptides were found to be 7.5 to 8.0 and the p l value of the 14-kD polypeptide was judged to be 8.5. Purification of the 65-and 60-kD polypeptides, followed by digestion with endoproteinase Lys-C and sequencing of seleded fragments, revealed similarities in amino acid composition between the 65-and 60-kD polypeptides and dehydrins. Indeed, antiserum to the lysine-rich consensus sequence EKKCIMDKIKEKLPC of dehydrin proteins cross-reacted to all three of the major chillingresponsive polypeptides of blueberry, identifying these as dehydrins or dehydrin-like proteins.