Understanding the morpho-functional strategies of grapevine rootstocks under controlled conditions

The gap

Evidence profile

Sourced from the future work of the source papers, classified as general, spanning 2 journals.

Supporting evidence — 8 representative gaps

• Scion-Rootstock interactions shape early transcriptional responses to controlled water deficit in newly selected table grape genotypes (2026) · BMC Plant Biology · doi

  This study highlights the role of rootstock–scion inter- actions in shaping grapevine responses to controlled water deficit, revealing genotype-dependent differences in early molecular responsiveness across grafting combi- nations. Differences in transcriptional responses suggest that combinations vary in their molecular sensitivity to water limitation. Coordinated modulation of hormonal Maggiolini et al. BMC Plant Biology (2026) 26:891 Page 18 of 20 signaling, aquaporins, phenylpropanoid metabolism, and cytoskeletal components indicates the complex- ity of regulatory networks underlying early water-deficit responses. Notably, the combined modulation of cyto- skeletal genes and aquaporins represents a relatively underexplored aspect of scion–rootstock interactions under reduced water availability. Unlike most previous studies focusing on established cultivars, this work evaluates newly selected table grape genotypes across different rootstock combinations dur- ing early selection stages. The candidate genes identi- fied (Table  2; Supplementary Figs.  5 and 6) represent potential molecular markers for discriminating scion– rootstock combinations based on their sensitivity to reduced irrigation, providing a useful framework for breeding programs aimed at optimizing table grape per- formance under moderate water limitation [5]. Notably, the two scion genotypes displayed distinct transcrip- tional responsiveness patterns: Maula generally showed stronger transcriptional reprogramming under reduced irrigation, whereas Genusia exhibited comparatively moderated responses. These results suggest that scion– rootstock combinations may differ in their molecu- lar sensitivity thresholds to irrigation reduction. More broadly, this study shows how transcriptomic profiling can complement physiological screening to support early evaluation of scion–rootstock combinations in table grape breeding. Future studies integrating transcriptomic data with physiological analyses and field validation will be essential to support the development of climate-resil- ient grapevine cultivars under variable water availability. number of enriched genes. Supplementary Material 4: Supplementary Figure 4. Gene Ontology enrichment between genotypes. A. GO enrichment analysis of DEGs at WS in Maula compared to Genusia grafted on 1103P; B. GO enrichment analysis of DEGs at WS in Maula compared to Genusia grafted on SO4. For each functional category (BP= Biological process; CC=Cellular component; MF= molecular function) Down-regulated genes and up-regulated genes are reported by green and red bars respectively. The length of each bar is proportional to the number of enriched genes. Supplementary Material 5: Supplementary Figure 5. Plant hormone signal- ling pathway- vvi04075. KE

  generalfuture workevidence 5/5
  Keywords: rootstock scion water genes combinations supplementary responses early molecular sensitivity reduced grape genotypes irrigation maula
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  Fig. 1 | Theoretical kinetics of stomatal conductance (gs) and leaf water potential (ψleaf) over 10 days of absence of water supply under optimal transpiration conditions. a from day 2 to day 11 the grapevine exhibits a response dominated by stomatal control, which allows to maintain an isohydric leaf status (stable midday Ψ leaf and slight progressive decline in the predawn values). This is the theoretical representation of a pure drought avoidance response. b from day 2 to day 11 the plant shows a progressive activation of osmotic adjustment, leading to lower midday Ψ leaf, sustained transpirational dissipation, and a pronounced reduction in predawn Ψ leaf, reflecting the gradual depletion of soil water. This is the theoretical repre- sentation of a pure drought tolerance response. In grapevine, these two behaviours have not evolved as mutually exclusive but rather as coexisting strategies. The broad platform provided by cultivars and rootstocks adapted to diverse climates has produced a continuous gradient between avoidance and tolerance mechanisms9. By plotting the maximum gs values and the minimum daily leaf water potential (midday Ψ leaf) over the ten days of the incipient-drought kinetics described in Fig. 1, it becomes possible to visualize this continuum. On one end lies a strictly ‘vertical’ response, representing the theoretical response of complete avoidance and a purely isohydric behaviour (days 2i–11i). On the opposite end is a strictly ‘horizontal’ response, fully tolerant of continuous transpirative dissipation, corresponding to a purely anisohydric behaviour (days 2a–11a) (Fig. 2). In a meta-analysis describing the factors gov- erning stomatal conductance in relation to water availability4, real- world behaviours consistently fall between these two extremes: more vertical when the plant is more evasive (i.e. a stress avoider), and more horizontal when it is more tolerant. Main mechanisms controlling water stress avoidance in grapevine The definitive mechanism for avoiding water stress is stomatal closure. For decades, grapevine has served as a strong model for how stomatal control is regulated through both ABA-mediated and hydraulic factors10. The ABA pathway exemplifies i) root-to-shoot signalling via the xylem, ii) chemical modulation of hormonal signals, iii) foliar regulation of signal intensity, and iv) stomatal sensitivity to the transmitted signal. i. The root biosynthesizes ABA when its water potential declines, that is, when water in the soil, and therefore at the soil-root interface, becomes progressively less available11. Rootstocks that strongly induce stomatal closure synthesize ABA at less negative potentials than those associated with anisohydric regulation (tolerant root- stocks, see next paragraph). Soil water availability certainly depends on its absolute quantity, which underlies both the historical associations between grapevine cultivars and their native rainfalls regimes, and the principles of irrigation s

  generalfuture workevidence 5/5
  Keywords: water leaf stomatal response grapevine theoretical days avoidance soil root potential midday drought tolerant stress
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  Fig. 2 | Interrelationship between maximum daily stomatal conductance (gs) and corresponding minimum leaf water potential (midday ψleaf). The plot illustrates the two theoretical extremes: a pure ‘vertical’ response, representing complete drought avoidance and strictly isohydric behaviour (days 2–11, 2i–11i, red empty squares), in contrast with a pure ‘horizontal’ response, totally tolerant of continuous transpiration dissipation and descriptive of a strictly anisohydric behaviour (days 2–11, 2a–11a, red crosses). Intermediate situations between the two theoretical extremes are modelled to represent real cases, based on a meta-analysis of 718 data points from 26 different Vitis vinifera varieties investigated as scions, 15 non-V. vinifera rootstock genotypes and 11 own-rooted V. vinifera varieties. Linearised data were analysed using the univariate general linear model (GLM), following Lavoie- Lamoureux et al.4. In addition, other root-to-shoot signals complementary and synergistic to the ABA signal have been identified in grapevine, through exchange of miRNAs19 or small peptides20. Conversely, in hydraulic mechanisms, the turgor-driven water status of guard cells overrides hormonal signalling. In this case, stomatal regulation is linked to the declining leaf water potential, which may result from limited soil water availability, limited root absorption capacity, and/or xylem sys- tems with low hydraulic conductivity (e.g. high incidence of embolism). The drop in leaf water potential also triggers local ABA biosynthesis, which supports stomatal closure long after the initial hydraulic signal21. This hydraulic signal, which directly induces stomatal closure, will be discussed further in the next section. When stomata close, reduced transpiration helps conserve water, but the evaporative cooling system of the plant (its only mechanism for heat dissipation) loses effectiveness. As a result, severe water stress accompanied by prolonged stomatal closure causes physiological dysfunction due to leaf overheating. In many wine-growing regions worldwide, water stress thus leads to heat stress22, also because arid envir- onments are often simultaneously hot23. How does the vine defend itself? The response involves a complex interplay of photorespiration and pho- toinhibition. In short: high temperatures in the chloroplast shift Rubisco activity toward oxygenation rather than carboxylation. This means the diversion of ribulose-6-phosphate into C2 compounds that enter the pho- torespiratory pathway, instead of C3 intermediates used for the biosynthesis of primary sugars in the Calvin-Benson cycle. Photorespiration consumes ATP and dissipates excess energy, an important function when high light adds to heat. Since the sun is the source of both heat and light, photo- respiration acts as a safety mechanism protecting the leaf from photo- inhibition (often irreversible). Protection against photoinhibition also relies on photoprotective and antioxidant systems.

  generalfuture workevidence 5/5
  Keywords: water leaf stomatal hydraulic heat potential response vinifera signal high closure stress theoretical extremes pure
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  Fig. 3 | Schematic summary of the main strategies for grapevine acclimation to water stress. This diagram illustrates contrasting isohydric (stress avoidance) and anisohydric (stress tolerance) mechanisms. Isohydric genotypes rely on rapid ABA biosynthesis, ABA/pH regulation, and stomatal closure to conserve water, with soil texture strongly influencing signal intensity. In contrast, anisohydric genotypes sustain transpiration under declining water potentials, relying on hydraulic sig- nalling, osmotic adjustment, aquaporin activity, and embolism recovery. Differences in ABA sensitivity and metabolite accumulation highlight how genotype, soil con- ditions, and physiological trade-offs collectively shape drought acclimation and underpin grapevine’s role as a model for perennial crops. tolerance strategies correlate with deep reductions in water potential along the root-stem-leaf axis, which in turn promote xylem embolism. Grapevine has long been studied as a model species for understanding the control of xylem embolism6. Both passive resistance to embolism formation and efficient embolism repair have been suggested as key factors controlling anisohydric response behaviour (i.e., drought tolerance). In general, vessels with smaller diameters are less prone to embolism, whereas larger vessels, because of their greater lumen area and volume, are more susceptible to air seeding and bubble formation, processes that ultimately lead to embolization32. Recently, however, calls have been made for a more nuanced assessment of the vessel diameter-vulnerability relationship, to gain a better mechanistic understanding of the nanoscale biophysical processes that drive embolism initiation and spread33,34. This issue is particularly important in vineyard research, where a progressive acclimation to embolism is observed as the growing season advances35. Much of the literature on rootstocks and scions examines the anatomy of the xylem system, drawing on both traditional microscopic analyses and, more recently, on X-ray tomographic measurements (micro-CT)36. Fur- thermore, in grapevine, embolism recovery in the late afternoon or at night has been described as a common and effective mechanism37. Thus, biolo- gical control of the hydraulic system does not depend solely on avoiding embolism formation (which results from declining water potential and increasing hydrostatic tension in the xylem), but also on the ability to repair embolized vessels. Embolism recovery is based on two concurrent processes. The first is the transfer of osmoregulatory sugars from the phloem into the xylem, which draws water from the perivascular cells and the apoplast back into the embolized conduits. Recent studies have proposed a role for non- structural carbohydrates (NSCs) in generating the osmotic pressure required for refilling38,39. Moreover, different cultivars appear to adopt dis- tinct NSC-use strategies during drought: in ‘Grenache’, sucrose accumula- tion is closely associated with embolism formation and may help sustain refilling; in ‘Barbera’, NSCs may contribute to a conduit-recovery strategy via the formation of cell-wall hydrogels, which likely explain the reduction of conduit lumen detected by micro-CT40. The second phenomenon involves npj Science of Plants | (2026) 2:14 4 https://doi.org/10.1038/s44383-026-00028-6

  generalfuture workevidence 5/5
  Keywords: embolism water xylem formation grapevine recovery strategies acclimation stress anisohydric tolerance drought vessels processes isohydric
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  the regulation of membrane aquaporins in perivascular cells, which increases cell permeability and accelerates water movement during the recovery phases of xylem embolism41. In rootstocks derived from Vitis rupestris, this aquaporin-mediated activity is closely associated with suc- cessful recovery from embolisms28. The decrease in water potential that triggers tolerance mechanisms also serves as an important signal for stomatal closure, as mentioned in the previous section. In this case, roots transmit hydraulic signals upward (decreasing the water potential of the entire plant system), while ABA can be synthesized locally in the leaves42. This makes it impossible to frame grapevine behaviour within a strict binary of isohydry versus anisohydry, as recently unequivocally demonstrated on 30 own-rooted winegrape cultivars originating from different European regions, tested in the same investiga- tion site by Obiero and Keller43. Instead, stomatal control can be activated following a drop in water potential, with different vine species or cultivars responding more or less readily also depending on their genetics, rootstock and soil type4. The plant hydraulic system, especially in the root, thus becomes the first point of sensing for decreased water potential. Importantly, this sen- sitivity is not limited to the root tissues themselves: the root-soil interface can act as a critical control point. In this region, Schuldt et al. 42 emphasized the need to reconsider classical concepts of root xylem vulnerability (the “root- as-hydraulic-fuse” hypothesis). Their updated hypothesis proposes that hydraulic disconnection may instead originate at the root-soil interface, when the cortex shrinks during moderate soil drying, a situation commonly experienced by grapevines. Another “fuse” for controlling embolism damage, one that grapevines can sacrifice relatively easily, has often been identified in the leaf, through a mechanism leading to petiole abscission. This idea is the basis of the hydraulic segmentation hypothesis, according to which cavitation occurs at less negative water potentials in the petiole than in the stem44–47. Through this mechanism, the vine can tolerate substantial drops in water potential near the leaves. However, its effectiveness has recently been questioned by direct measurements in grapevine48,49. Indeed, growing evidence indicates that measurement artifacts have historically overestimated embolism vulnerability, suggesting that plants may not experience severe drought-induced embolism events under natural field conditions33,42,50. These con- siderations, now extended to all tree species, are supported by more than fifteen years of in vivo evidence collected by micro-CT tech- nology across grapevine species and cultivars. In this field, in situ and in vivo demonstrations of intra- or inter-species-specific hydraulic tolerance factors during drought acclimationin grapevine is a benchmark of the literature on the subject51–61. Another i

  generalfuture workevidence 5/5
  Keywords: water hydraulic root potential embolism grapevine species soil cultivars hypothesis recovery xylem tolerance stomatal plant
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  context-specific microbial functions. Mechanistically, beneficial micro- organisms enhance grapevine resilience to water deficit in several ways. They fine-tune hormonal balances, for instance by reducing stress-induced ethylene through ACC deaminase activity, thereby sustaining root growth and water uptake under limiting conditions. They also promote the accu- mulation of compatible solutes such as proline and soluble sugars, strengthening osmotic adjustment, and enhancing antioxidant defences through the accumulation of superoxide dismutase, catalase, peroxidase and melatonin, which collectively mitigate oxidative damage. At the transcrip- tional level, microbial inoculation triggers a complex network of stress- responsive genes involved in ABA biosynthesis (e.g., VvNCED1), proline and sugar metabolism, and the phenylpropanoid pathway, while activating signalling cascades mediated by WRKY, MYB, and GRAS transcription factors. In addition, AMF have been shown to influence small RNA reg- ulation (e.g., the miR156/miR529/miR535 superfamily) and secondary metabolism, stimulating the production of flavonoids and stilbenes with recognized antioxidant and protective functions81. Collectively, these find- ings underscore the importance of integrating plant–microbe interactions into grapevine drought acclimation studies: the microbiome is not merely a passive passenger but an active co-determinant of host stress responses. The grapevine biological platform also provides opportunities to explore long-term acclimation strategies, including stress memory and transgenerational effects in woody crops. Evidence suggests that recurrent drought exposure can prime grapevine physiological and molecular responses, leading to faster or stronger activation of protective mechanisms upon subsequent stress events. Such stress imprinting may involve epige- netic modifications, metabolic reallocation, and shifts in microbiome composition that persist beyond a single stress episode. In particular, epi- genetic mechanisms have emerged as major players contributing to the primed state of plants after stress exposure82. The study by Rodriguez- Izquierdo et al83. conducted on cultivated and wild accessions of Vitis, provides evidence of genome-wide differential methylation related to stress- response and metabolic pathways in Vitis. Other recent studies have also addressed the epigenetic adaptive capacities of vines in relation to different environments84–86, under different possible stressors, as reviewed by Tan and Rodríguez López87. Understanding how the processes underlying stress memory operate in grapevine could reveal new targets for enhancing resi- lience to abiotic stress88–90. To do this, the scientific community should move beyond the numerous studies in the literature that analyse single events of water stress and recovery in grapevine, and instead focus on experimental trials involving repeated exposure to long-lasting water stress events, ideally over multiple years, ca

  generalfuture workevidence 5/5
  Keywords: stress grapevine water exposure events microbial functions proline enhancing antioxidant collectively metabolism protective drought acclimation
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  Fig. 4 | Schematic summary of the multi-layered investigative approaches underway aimed at optimizing grapevine responses to drought. This scheme summarizes three complementary layers of grapevine responses and improvement strategies. On the left, the root-associated microbiome enhances tolerance through multiple processes, including bacterial ACC deaminase activity that lowers stress- induced ethylene, while arbuscular mycorrhizal fungi (AMF) that mitigate oxidative stress, collectively sustaining ABA biosynthesis and activating stress-responsive transcriptional networks (e.g., WRKY, MYB, GRAS). These responses promote the accumulation of protective metabolites such as stilbenes, flavonols, phenylpropa- noids, soluble sugars, and proline. In the centre, plant-intrinsic acclimation involves drought- and heat-induced modulation of secondary metabolism, including the activation of the phenylpropanoid pathway (VvCHS, VvUFGT, VvF3’5’H, VvOMT), stilbene biosynthesis, and acyltransferase-driven anthocyanin acylation (VvGAT1, VvSCP5, VvSCP31), alongside cultivar-specific alterations in flavonol profiles. On the right, conventional breeding is constrained by the need to preserve historical cultivars, whereas New Plant Breeding Techniques (NPBTs) including genome editing can specifically target traits such as stomatal behaviour (VvEPF9-1, OST2, GID1), biochemical and hormonal responses (VvGST40, VvbZIP36, ERA1, AREB1, TRE1, LBD), and microbial recruitment (VvNPR3). This integrative view highlights how combining plant physiology, microbial symbioses, and biotechnology can advance sustainable viticulture under climate change. conclusions. Genotypes identified as resilient under drought alone may fail when heat waves coincide with water scarcity, which represents the actual selective pressure faced in Mediterranean vineyards. Ignoring this simul- taneity risks overlooking germplasm that is well adapted to real-world field conditions. Finally, framing viticulture through a Mediterranean lens offers a unifying conceptual structure. It connects environmental constraints, plant physiological responses, and berry metabolic outcomes into a coherent system, providing a basis for predictive approaches. This shift toward mechanistic integration is essential for forecasting cultivar performance, guiding the selection of resilient plant material, and ensuring the long-term sustainability of viticulture in a rapidly changing climate23. In this context, understanding how grapevines perceive, regulate, and ultimately adapt to water deficit becomes central, as drought responses constitute the physiological backbone upon which resilience to more complex Mediterranean stress scenarios is built. Exploitable target genes in breeding approaches aimed at improving avoidance/tolerance to water stress The viticultural agro-ecosystem is seriously impacted by climate-change- induced abiotic stresses and by the intensification of fungal diseases101. Grapevine cultivation relies heavily on

  generalfuture workevidence 5/5
  Keywords: responses stress plant drought approaches grapevine including induced breeding viticulture climate water mediterranean aimed tolerance
• The grapevine as a model plant to describe intra- and interspecific mechanisms of drought acclimation (2026) · npj Science of Plants · doi

  analyses show that AMF recruiting is enhanced in VvNPR3-edited Char- donnay lines, with a positive impact on performances under drought111. Beyond grapevine-specific breeding approaches, several candidate genes identified in other species112 could provide promising targets for improving water stress avoidance and tolerance in grapevine. For instance, the CRISPR/Cas9 system was successfully used in Arabidopsis to create novel alleles of OPEN STOMATA 2 (OST2), a stomatal proton pump, and the resulting genome-edited lines displayed enhanced performances via altered stomatal closure under drought stress113. Another target acting at the stomatal level is the ENHANCED RESPONSE TO ABA1 (ERA1) gene, encoding the β-subunit of farnesyltransferase and regulating ABA signalling and dehydration responses. era1 mutant plants showed enhanced ABA- induced stomatal closure, making it a promising candidate for increasing drought tolerance in a variety of crops114. A further promising target is again related to ABA signalling: the overexpression of ABA-responsive element- binding protein 1 (AREB1) improved Arabidopsis physiological perfor- mances under severe drought. This result was achieved by CRISPR acti- vation (CRISPRa), a technique that could be potentially applied to other ABA-related genes for drought-targeted breeding strategies115. Targets outside the ABA pathway are also promising. In tomato, the editing of the GIBBERELLIN-INSENSITIVE DWARF1 (GID1) gibberellin receptor suc- cessfully reduced whole-plant transpiration under water-deficit conditions without impairing growth. Reduced gibberellin activity inhibited leaf growth, promoted stomatal closure, and reduced xylem vessel proliferation and expansion, therefore decreasing hydraulic conductivity and limiting water loss116. The jasmonate pathway also offers potential targets. The LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors are plant-specific regulators of various processes, including organ devel- opment and response to stress. In tomato, LBD40 expression is jasmonate- dependent and its CRISPR/Cas9 targeted mutagenesis improved drought tolerance by enhancing the water-holding capacity of the plant. Notably, grapevine is known to possess five LBD genes responsive to salt, mannitol, heat, and cold stresses117, making them promising candidates for genome editing aimed at multi-stress tolerance. An interesting gene target for enhancing tolerance mechanisms in anisohydric grapevine varieties is related to the trehalose catabolic pathway, given the osmoprotective role of this metabolite. Arabidopsis gene-edited mutants of TRE1, which encodes the trehalase enzyme responsible for trehalose hydrolysis, exhibited enhanced drought tolerance118. Finally, the accumulation of anthocyanins, key metabolites that contribute both to grapevine berry quality and defence responses, is known to confer tolerance to various abiotic stresses in multiple plant species119. Under prolonged stomatal closure in the contex

  generalfuture workevidence 5/5
  Keywords: drought tolerance stomatal enhanced grapevine promising water stress closure plant edited genes targets crispr arabidopsis

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