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Dehydration response of different grapevine genotypes and organs
AuthorHopper, Daniel W.
AdvisorCramer, Grant R.
Biochemistry and Molecular Biology
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Drought has one of the greatest impacts on crop production. Wine grapes in particular are very sensitive to climate changes. Field studies on grapes can take years for vineyard establishment therefore; therefore, a simple and reliable way of phenotyping for plant response to water loss was developed. Fully developed mature leaves were detached and placed in a closed plastic container with a solution of NaCl to control the water potential of the atmosphere within the container. Application of the plant hormone abscisic acid (ABA) prior to leaf detachment caused a decrease in the amount of water loss indicating that the assay was able to detect differences based on a stomatal response to dehydration. Five different Vitis genotypes (V. riparia, V. champinii, V. vinifera cv. Shiraz, V. vinifera cv. Grenache and V. vinifera cv. Cabernet Sauvignon) with known differences in drought tolerance were screened for their dehydration response and the data collected corresponded to previous reports of stomatal responses in the vineyard.Using the newly developed rapid dehydration assay on Cabernet Sauvignon leaves and shoot tips, we tested the hypothesis that the dehydration response of a “source” and “sink” organ is different over time. Using whole-genome microarrays, statistical analysis revealed nearly 19,000 genes changing significantly due to treatment and over 7,000 transcripts changing with respect to the treatment x time x organ interaction, indicating notable changes in gene expression. Significant expression level changes of genes involved in the production, degradation, storage, transport, and downstream signaling of ABA indicate differences in the regulation of key genes in this “central hub” of drought signaling. Proteomic investigation of leaf samples also indicated changes in the protein abundance of a bZIP transcription factor, an ABA-responsive kinase substrate, occurring as early as 1 h after the start of dehydration with a similar response at the transcript level. Overall, ABA metabolism and signaling, transcription factor expression, and glycolysis highlight key differences in the response between the two organs, thus providing key targets for further investigation.Finally, rootstocks are routinely used in viticulture and are known to have differences in their response to dehydration. A better understanding of the rootstock genotypes response to dehydration is needed. Microarray analysis of Cabernet Sauvignon, Riparia Gloire, and Ramsey leaves revealed significant differences in the leaf response to dehydration at the transcript level. Differences between the genotypes in response to dehydration were observed. Statistical analysis revealed over 14,000 transcripts changing significantly with respect to the genotype x treatment interaction term and 10,000 transcripts changed significantly according to the genotype x treatment x time interaction term indicating massive changes in gene expression. Transcripts responding to dehydration were involved in the metabolism and signaling of ABA and ethylene. In particular, VviNCED6 was shown to increase in the North American rootstocks with little response in Cabernet Sauvignon leaves suggesting differences in the regulation of this gene. Also, a number of AP2/ERF transcription factors known to be involved in drought tolerance increased in Riparia leaves with little response in Cabernet Sauvignon and Ramsey. These data provide further insights into the dehydration response at the transcript level of different grapevine genotypes and organs providing for further hypothesis-driven research focused on improving drought tolerance