Simone Castellarin

Associate Professor

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Master's Student Supervision (2010 - 2018)
Compositional changes of the grape berry (Vitis vinifera L.) cuticle during fruit development in response to water deficit stress (2018)

The cuticle is a layer found on the surface of plant aerial parts mostly composed of cutin polymer and aliphatic waxes, and provides protection from biotic and abiotic environmental stresses. In fruits, cuticular waxes are also rich in triterpenoids. The cuticular waxes of the grapevine (Vitis vinifera L.) berry and the related biosynthetic pathways are poorly characterized. It is not understood how the berry cuticle responds to water deficit (WD) stress, a stress that commonly occurs in vineyards. We hypothesized that under severe WD stress, the cuticular aliphatic wax biosynthetic pathway of developing grape berries would be upregulated, resulting in an increased wax load in the fruit’s cuticle and a decrease in the transpiration rate through the berry cuticle. Candidate genes for the cuticular wax biosynthetic pathway were identified by phylogenetic analyses and surveys of publicly available grapevine transcriptomic datasets. Analyses of these transcriptomes also showed that a number of wax-related genes are significantly upregulated in response to WD stress, and are also modulated by other environmental stresses. A greenhouse experiment was performed in order to test the impact of water deficit on wax composition, expression of candidate biosynthetic genes, and water transpiration in Merlot grapes. A significant increase in aliphatic wax and a decrease in the ratio of triterpenoids:aliphatic wax was observed under WD stress. The increase in aliphatic wax was due to an upregulation of the aliphatic wax biosynthetic pathway, with an increase in expression seen in fatty acid elongation, the alkane forming, and the alcohol forming genes. The transpiration rate of the berry was not significantly affected by WD; however, a marginally significant (P = 0.051) reduction of the rate was observed in WD berries. The study also revealed that cuticular aliphatic wax composition changed over the course of berry development, with very long chain (VLC)-aldehydes and VLC- primary alcohols predominating before veraison (the onset of berry ripening), and VLC-fatty acids and wax esters mainly accumulating after veraison.

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