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Abstract

Viticulture faces production challenges from multiple environmental factors, ranging from changing weather patterns and nutrient deficiencies to pathogen pressure. In this thesis, we deepened the understanding of how grapevine responds to water deficit, increased soil salinity, different aspects of iron deficiency, and infection by 'Candidatus Phytoplasma solani', by investigating transcriptomic responses in various genotypes. A multifactorial linear model was used to combine transcriptomic and metabolomic data with midday stem water potential to evaluate the responses of Cabernet Volos and Fleurtai, both cultivars originally bred for disease resistance, to prolonged water deficit. The responses were categorized into three groups. The most numerous were core responses shared by both genotypes, including osmoprotectant accumulation and downregulation of biotic defense. The other two categories comprised the gene expression and metabolite abundance signatures unique to each genotype. Salinity stress was evaluated in the leaves and berry skins of Tempranillo vines grafted onto rootstocks M1, M4, and 1103 Paulsen. At the gene expression level, all tested rootstocks protected the scion from the effects of increased salinity. Rootstocks Couderc 3309 and Fercal were used to investigate iron deficiency responses. The effects of iron deficiency were first studied in combination with different nitrogen sources; the response was more severe when only nitrate was supplied, compared to the application of equal amounts of nitrate and ammonium. This held true for both rootstocks; however, the more susceptible 3309 C consistently showed a lower capacity to engage core Fe acquisition-related genes and lower induction of auxin responses and root growth. Iron deficiency was induced by two different mechanisms: directly, through low-Fe treatments, or indirectly, by adding bicarbonate to Fe-sufficient media. For both genotypes, indirect Fe deficiency presented a greater challenge, and the more tolerant Fercal exhibited a greater ability to engage genes related to Fe acquisition, transport, and root development. Gene expression changes in grapevines infected with 'Ca. P. solani' were detected in the early growing season, before symptom onset, and included major shifts in photosynthesis and energy metabolism, protein synthesis, and disturbances in lignification-related genes, which persisted into the late growing season as symptoms appeared. Two genes involved in salicylic acid response regulation, VviDMR6-1 and VviDLO1, were found to be significantly regulated in this investigation and were chosen as targets to reduce Chardonnay and Zweigelt susceptibility to this pathogen. DNA-free genome editing was performed on protoplasts isolated from embryogenic callus, using polyethylene glycol-mediated transfection to deliver in vitro-assembled Cas9-gRNA ribonucleoprotein complexes into the cells. Plants were successfully regenerated from both Chardonnay and Zweigelt. Zweigelt showed a much higher propensity to regenerate into whole plants than Chardonnay, while successful editing was more frequent in Chardonnay than in Zweigelt. Seven of the eight edited lines obtained in our experiments carried a small insertion resulting in a frameshift and a premature stop codon. However, all edited lines were heterozygous, having been edited on only one chromosome.