The evaluation of the impact of microclimatic factors on grapevine berries in a vineyard setting through molecular profiling

[摘要] ENGLISH SUMMARY: Grape composition is considered to be the result of the grapevine genotype, the environmental factors thegrapes are exposed to and the management practices implemented during their development. However,elucidating how each of these components contributes to the outcome is notoriously difficult under fieldconditions due to the myriad confounding variables that grapes are influenced by. One of the viticulturalmanagement practices frequently implemented in the vineyard is the removal of leaves in the berry bunchzone in order to alter the microclimate of the developing grapes with various potentially advantageousoutcomes. However, this common viticultural practice of leaf removal very rarely affects levels of lightwithout elevating bunch temperatures as well. Moreover, definitive links between this treatment and theunderlying grape molecular responses are currently lacking, particularly in cause and effect relationships.Utilizing a highly characterized Sauvignon Blanc vineyard, a leaf removal treatment was implementedaccording to a field-omics experimental approach, in which it was established that light exposure to thedeveloping grapes was the predominant factor modulated by the treatment. A preceding studycharacterized the physical growth parameters of the developing grapes and targeted specific metabolitesin order to determine how elevated light would affect grape development. The results revealed that thegrowth and development of the grapes were not affected by the treatment, but that specific secondarymetabolites with photoprotective abilities were elevated. These results showed that the grapes acclimatedto the elevated light exposure, providing the possibility to study the molecular mechanisms associatedwith this acclimated state in the berries.The aim of this study was therefore to explore the transcriptional responses of the developing grapeberries to elevated light exposure to understand how primary metabolism and growth was maintaineddespite the implementation of stress mitigation strategies. The approach taken to study this transcriptionalresponse involved RNA sequencing (RNASeq) analysis in order to generate a transcriptional snapshot ofall the genes expressed in control and light exposed grapes sampled at four developmental stagesthroughout berry development. This analysis revealed that the green grapes implemented severalphotoprotective mechanisms simultaneously. Some of these mechanisms involved non-photochemicalquenching and the rapid turnover of the proteins of the photosynthetic machinery, much like other foliarphotosynthetic tissues, despite the profound differences in photosynthesis dynamics between these tissuetypes. Additionally, the genes associated with the synthesis of flavonoid compounds were significantlyupregulated and these findings were further corroborated by the accumulation of high levels of flavonolsthat are known to have both light absorbing and antioxidant abilities. In combination, through thesephotoprotective mechanisms, as well as the synthesis of higher levels of carotenoids in green berries andsubsequent apocarotenoids in ripe berries these grapes achieved a state of acclimation. Furthermore, thecatabolism of amino acids provided energy precursors and substrates towards the redistribution of energythat contributed to the maintenance of these energetically costly stress mitigation mechanisms. To thisend, green, photosynthesizing grapes maintain growth and development at all costs to protect thedevelopment and maturation of the grape seed. Therefore, when the berries achieved ripeness, thephotoprotective mechanisms associated with photosynthesis had ceased and the upregulation ofapocarotenoids and flavonols were no longer effectively mitigating the light stress.A subsequent investigation explored the role that grapevine heat shock factor (Hsf) genes may haveplayed in achieving this acclimated state. The consistent upregulation of three grapevine Hsfs wasestablished and for one of these genes, VviHsfA7a, a unique putative role in photoprotection underelevated light was identified. Furthermore, by utilizing these results, the first putative working model ofthe expression and regulation of the Hsfs in grapevine berries were proposed.This study further identified two groups of putative developmental stage-specific molecular biomarkers ingrape berries. The first group of genes contributed to the current understanding of the underlyingmolecular mechanisms associated with the coordinated progression of berry development, whereas theother group of genes represented putative light-responsive molecular biomarkers that are developmentallyregulated under non-stressed conditions, but that become significantly upregulated by light stress.Further investigation into the effect that the elevated light exposure may have had on the pathwaysassociated with the synthesis of Sauvignon Blanc impact odorants was conducted. These findingsprovided insights into how leaf removal and elevated light exposure may lower green aromacharacteristics in wine by modulating berry metabolism on a molecular level.Taken together, the findings presented in this study provided definitive insights into how light exposureeffects grape berry development on a molecular level and the mechanisms that these berries implement inorder to ameliorate the potentially harmful affects of light stress. This study further contributed by puttingforward the first de novo assembled transcriptome for the Sauvignon Blanc grapevine genotype that canbe utilized in future studies in order to draw more conclusive links between genotypic and/or treatmentspecific expression in grapevine.

[发布机构] Stellenbosch University