Physiological performance and targeted gene expression dynamics in ‘Italia’ table grapevine under prolonged water deficit

Abstract

Water availability constraints are becoming a defining factor in Mediterranean viticulture, which requires a deeper understanding of cultivar-specific adaptive mechanisms to sustain yield and fruit quality. The widely cultivated table grape (Vitis vinifera L.) cv. ‘Italia’ is particularly relevant in this context, yet its integrated physiological and molecular responses to prolonged water deficit remain insufficiently characterized.

This study evaluated the response of ‘Italia’ grapevine subjected to 37 days of controlled drought stress, combining ecophysiological measurements with targeted gene expression analysis. Leaf water potential, transpiration rate, and net CO₂ assimilation were monitored to assess plant water status and photosynthetic performance. In parallel, the expression of six drought-responsive genes was quantified by qRT-PCR: VvPP2C4 and VvPP2C8, involved in abscisic acid (ABA) signaling; VvGolS1 and VvGolS2, associated with osmoprotectant biosynthesis; VvHSP18, encoding a small heat- shock protein linked to cellular protection; and VvRD26, a NAC transcription factor implicated in dehydration responses.

Water deficit progressively reduced leaf water potential and gas-exchange parameters, indicating a conservative strategy based on stomatal limitation to minimize water loss, albeit at the expense of carbon assimilation. Gene expression profiling revealed significant upregulation of VvPP2C4, VvGolS2, VvHSP18, and particularly VvRD26, which exhibited up to a 60-fold increase at the end of the stress period. Conversely, VvPP2C8 and VvGolS1 showed limited modulation, suggesting differential regulatory roles within the same functional pathways.

These findings highlight a coordinated adjustment between physiological regulation and selective activation of ABA- dependent signaling, osmoprotection, and stress-responsive transcriptional control. The identified expression patterns provide potential molecular indicators of drought responsiveness in ‘Italia’ and contribute to the development of targeted strategies for improving resilience in Mediterranean table grape production systems.