Changes in gene expression associated with the end of dormancy in Vitis vinifera L.

Toni-Louise Pacey-Miller

Temperate zone deciduous plants undergo the process of bud dormancy in preparation for environmental change which is unfavourable to growth. Dormancy is a general term to indicate that no visible growth is occurring within the plant. Although many studies have been undertaken in the past into the processes involved in the onset and release from dormancy no satisfactory conclusions have yet been reached. These studies have mainly been morphological and physiological. There has been a considerable lack of knowledge on gene involvement in the process of dormancy prior to this study. Using a genetic approach this work finds that in the dormant state bud tissue is very physiologically and biochemically active. A grape bud EST library was constructed from Vitis vintfera cv. Purple Cornichon and 4,270 EST's were sequenced. The library clones were arrayed for the purpose of investigating the level of gene expression over time, particularly leading up to the buds' release from dormancy. The arrays were hybridized with P33 labelled probes produced from samples of buds collected at weekly intervals. These probes covered the time from nine weeks prior to bud burst until just after the emergence of the shoots. Expression patterns from these genes have been examined. It was found that 74% of the genes in the data set encoded products that were homologous to known proteins. Genes were assigned to functional categories according to their primary BLAST match. 13% of these were involved with photosynthesis, 13% with disease resistance and defense, 5% energy, 12% metabolism, 20% protein production and processing, 25% cell structure and plant growth and the remaining 12% were unclassified. These values were compared to a previous study of transcript levels in leaf and berry tissue of Vitis vinifera cv. Chardonnay. The expression patterns of a selection of "candidate" genes identified from the literature as having involvement in dormancy were examined. On close investigation most of these genes were found to relate to the oxidative processes and stress responses within the cell. These results show that even in the dormant state, gene expression in the buds is high, not only for particular categories of genes, but for the gene pool as a whole. A subset of the total gene pool, relating only to those genes which showed a substantial change in expression in the first three time points of sampling was examined in detail. This subset described two distinct patterns of expression, one with a decrease in expression to time point three; the second showed a significant peak in the first three time points. Both data subsets had considerably different proportions of transcripts when compared with the total gene pool. Of particular interest were the high proportions of defense related genes in the subset that had decreased early expression, and the high proportion of photosynthesis related transcripts in the subset that showed a considerable peak in expression in the first three time points. This study has expanded the knowledge available on the genetic processes involved in dormancy. It has examined a large number of transcripts expressed leading up to dormancy release and increased the number of transcripts identified in the grape genome by more than one hundred fold.

Changes in gene expression associated with the end of dormancy in Vitis vinifera L.

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Changes in gene expression associated with the end of dormancy in Vitis vinifera L.

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