Drought tolerance of the grapevine, Vitis champinii cv. Ramsey, is associated with higher photosynthesis and greater transcriptomic responsiveness of abscisic acid biosynthesis and signaling

Multi-hormonal analysis and aquaporins regulation reveal new insights on drought tolerance in grapevine

Disentangling the factors that foster the tolerance to water stress in plants could provide great benefits to crop productions. In a two-year experiment, two new PIWI (fungus resistant) grapevine varieties, namely Merlot Kanthus and Sauvignon Kretos (Vitis hybrids), grown in the field, were subjected to two different water regimes: weekly irrigated (IR) or not irrigated (NIR) for two months during the summer. The two varieties exhibited large differences in terms of performance under water-limiting conditions. In particular, Merlot Kanthus strongly decreased stem water potential (Ψs) under water shortage and Sauvignon Kretos maintained higher Ψs values accompanied by generally high stomatal conductance and net carbon assimilation, regardless of the treatment. We hypothesized differences in the hormonal profile that mediate most of the plant responses to stresses or in the regulation of the aquaporins that control the water transport in the leaves. In general, substantial differences were found in the abundance of different hormonal classes, with Merlot Kanthus reporting higher concentrations of cytokinins while Sauvignon Kretos higher concentrations of auxins, jasmonate and salicylic acid. Interestingly, under water stress conditions ABA modulation appeared similar between the two cultivars, while other hormones were differently modulated between the two varieties. Regarding the expression of aquaporin encoding genes, Merlot Kanthus showed a significant downregulation of VvPIP2;1 and VvTIP2;1 in leaves exposed to water stress. Both genes have probably a role in influencing leaf conductance, and VvTIP2;1 has been correlated with stomatal conductance values. This evidence suggests that the two PIWI varieties are characterized by different behaviour in response to drought. Furthermore, the findings of the study may be generalized, suggesting the involvement of a complex hormonal cross-talk and aquaporins in effectively influencing plant performance under water shortage.

Deciphering the regulatory networks involved in mild and severe salt stress responses in the roots of wild grapevine Vitis vinifera spp. sylvestris

Transcriptional regulatory networks are pivotal components of plant's response to salt stress. However, plant adaptation strategies varied as a function of stress intensity, which is mainly modulated by climate change. Here, we determined the gene regulatory networks based on transcription factor (TF) TF_gene co-expression, using two transcriptomic data sets generated from the salt-tolerant "Tebaba" roots either treated with 50 mM NaCl (mild stress) or 150 mM NaCl (severe stress). The analysis of these regulatory networks identified specific TFs as key regulatory hubs as evidenced by their multiple interactions with different target genes related to stress response. Indeed, under mild stress, NAC and bHLH TFs were identified as central hubs regulating nitrogen storage process. Moreover, HSF TFs were revealed as a regulatory hub regulating various aspects of cellular metabolism including flavonoid biosynthesis, protein processing, phenylpropanoid metabolism, galactose metabolism, and heat shock proteins. These processes are essentially linked to short-term acclimatization under mild salt stress. This was further consolidated by the protein-protein interaction (PPI) network analysis showing structural and plant growth adjustment. Conversely, under severe salt stress, dramatic metabolic changes were observed leading to novel TF members including MYB family as regulatory hubs controlling isoflavonoid biosynthesis, oxidative stress response, abscisic acid signaling pathway, and proteolysis. The PPI network analysis also revealed deeper stress defense changes aiming to restore plant metabolic homeostasis when facing severe salt stress. Overall, both the gene co-expression and PPI network provided valuable insights on key transcription factor hubs that can be employed as candidates for future genetic crop engineering programs.

Arbuscular Mycorrhizal Fungi Improve the Performance of Tempranillo and Cabernet Sauvignon Facing Water Deficit under Current and Future Climatic Conditions

Climate change (CC) threatens Mediterranean viticulture. Rhizospheric microorganisms may be crucial for the adaptation of plants to CC. Our objective was to assess whether the association of two grapevine varieties with arbuscular mycorrhizal fungi (AMF) increases grapevine's resilience to environmental conditions that combine elevated atmospheric CO2, increased air temperatures, and water deficit. Tempranillo (T) and Cabernet Sauvignon (CS) plants, grafted onto R110 rootstocks, either inoculated (+M) or not (-M) with AMF, were grown in temperature-gradient greenhouses under two environmental conditions: (i) current conditions (ca. 400 ppm air CO2 concentration plus ambient air temperature, CATA) and (ii) climate change conditions predicted by the year 2100 (700 ppm of CO2 plus ambient air temperature +4 °C, CETE). From veraison to maturity, for plants of each variety, inoculation treatment and environmental conditions were also subjected to two levels of water availability: full irrigation (WW) or drought cycles (D). Therefore, the number of treatments applied to each grapevine variety was eight, resulting from the combination of two inoculation treatments (+M and -M), two environmental conditions (CATA and CETE), and two water availabilities (WW and D). In both grapevine varieties, early drought decreased leaf conductance and transpiration under both CATA and CETE conditions and more markedly in +M plants. Photosynthesis did not decrease very much, so the instantaneous water use efficiency (WUE) increased, especially in drought +M plants under CETE conditions. The increase in WUE coincided with a lower intercellular-to-atmospheric CO2 concentration ratio and reduced plant hydraulic conductance. In the long term, mycorrhization induced changes in the stomatal anatomy under water deficit and CETE conditions: density increased in T and decreased in CS, with smaller stomata in the latter. Although some responses were genotype-dependent, the interaction of the rootstock with AMF appeared to be a key factor in the acclimation of the grapevine to water deficit under both current and future CO2 and temperature conditions.

Insights into the cell-wall dynamics in grapevine berries during ripening and in response to biotic and abiotic stresses

The cell wall (CW) is the dynamic structure of a plant cell, acting as a barrier against biotic and abiotic stresses. In grape berries, the modifications of pulp and skin CW during softening ensure flexibility during cell expansion and determine the final berry texture. In addition, the CW of grape berry skin is of fundamental importance for winemaking, controlling secondary metabolite extractability. Grapevine varieties with contrasting CW characteristics generally respond differently to biotic and abiotic stresses. In the context of climate change, it is important to investigate the CW dynamics occurring upon different stresses, to define new adaptation strategies. This review summarizes the molecular mechanisms underlying CW modifications during grapevine berry fruit ripening, plant-pathogen interaction, or in response to environmental stresses, also considering the most recently published transcriptomic data. Furthermore, perspectives of new biotechnological approaches aiming at modifying the CW properties based on other crops' examples are also presented.

Potential of UV-B radiation in drought stress resilience: A multidimensional approach to plant adaptation and future implications

The escalating impact of climate change and ultraviolet (UV) radiation is subjecting plants to unique combinations of UV-B and drought stress. These combined stressors could have additive, synergistic, or antagonistic effects, but the precise nature of these impacts remains uncertain, hampering our ability to predict plant adaptations approach towards stressors. Our analysis of various studies shows that UV-B or drought conditions detrimentally influence plant growth and health metrics by the enhanced generation of reactive oxygen species causing damage to lipids, proteins, carbohydrates and DNA. Further reducing biomass accumulation, plant height, photosynthetic efficiency, leaf area, and water transpiration, while enhancing stress-related symptoms. In response to UV-B radiation and drought stress, plants exhibit a notable up-regulation of specific acclimation-associated metabolites, including proline, flavonoids, anthocyanins, unsaturated fatty acids, and antioxidants. These metabolites play a pivotal role in conferring protection against environmental stresses. Their biosynthesis and functional roles are potentially modulated by signalling molecules such as hydrogen peroxide, abscisic acid, jasmonic acid, salicylic acid, and ethylene, all of which have associated genetic markers that further elucidate their involvement in stress response pathways. In comparison to single stress, the combination of UV-B and drought induces the plant defence responses and growth retardation which are less-than-additive. This sub-additive response, consistent across different study environments, suggests the possibility of a cross-resistance mechanism. Our outlines imply that the adverse effects of increased drought and UV-B could potentially be mitigated by cross-talk between UV-B and drought regimes utilizing a multidimensional approach. This crucial insight could contribute significantly to refining our understanding of stress tolerance in the face of ongoing global climate change.

The Rootstock Genotypes Determine Drought Tolerance by Regulating Aquaporin Expression at the Transcript Level and Phytohormone Balance

Grapevine rootstocks may supply water to the scion according to the transpiration demand, thus modulating plant responses to water deficit, but the scion variety can alter these responses, as well. The rootstock genotypes' effect on the scion physiological response, aquaporin expression, and hormone concentrations in the xylem and the leaf was assessed under well watered (WW) and water stress (WS) conditions. Under WW, vines grafted onto 1103P and R110 rootstocks (the more vigorous and drought-tolerant) showed higher photosynthesis (A_N), stomatal conductance (g_s), and hydraulic conductance (Kh_plant) compared with the less vigorous and drought-sensitive rootstock (161-49C), while under WS, there were hardly any differences between vines depending on the rootstock grafted. Besides, stomatal traits were affected by drought, which was related to g_s, but not by the rootstock. Under WS conditions, all VvPIP and VvTIP aquaporins were up-regulated in the vines grafted onto 1103P and down-regulated in the ones grafted onto 161-49C. The 1103P capability to tolerate drought was enhanced by the up-regulation of all VvPIP and VvTIP aquaporins, lower ABA synthesis, and higher ACC/ABA ratios in leaves during WS compared with 161-49C. It was concluded that, under WW conditions, transpiration and stomatal control were rootstock-dependent. However, under WS conditions, alterations in the molecular components of water transport and hormone concentration of the scion resulted in similar gas exchange values in the studied scions grafted onto different rootstocks.

Comparative proteomic analysis of chromosome segment substitution lines of Thai jasmine rice KDML105 under short-term salinity stress

Heat shock proteins, ROS detoxifying enzymes, and ion homeostasis proteins, together with proteins in carbohydrate metabolism, cell structure, brassinosteroids, and carotenoid biosynthesis pathway were up-regulated in CSSLs under salinity stress. Rice is one of the most consumed staple foods worldwide. Salinity stress is a serious global problem affecting rice productivity. Many attempts have been made to select or produce salinity-tolerant rice varieties. Genetics and biochemical approaches were used to study the salinity-responsive pathway in rice to develop salinity tolerant strains. This study investigated the proteomic profiles of chromosome segment substitution lines (CSSLs) developed from KDML105 (Khao Dawk Mali 105, a Thai jasmine rice cultivar) under salinity stress. The CSSLs showed a clear resistant phenotype in response to 150 mM NaCl treatment compared to the salinity-sensitive line, IR29. Liquid chromatography-tandem mass spectrometry using the Ultimate 3000 Nano/Capillary LC System coupled to a Hybrid Quadrupole Q-Tof Impact II™ equipped with a nano-captive spray ion source was applied for proteomic analysis. Based on our criteria, 178 proteins were identified as differentially expressed proteins under salinity stress. Protein functions in DNA replication and transcription, and stress and defense accounted for the highest proportions in response to salinity stress, followed by protein transport and trafficking, carbohydrate metabolic process, signal transduction, and cell structure. The protein interaction network among the 75 up-regulated proteins showed connections between proteins involved in cell wall synthesis, transcription, translation, and in defense responses.

Metabolic adjustment and regulation of gene expression are essential for increased resistance to severe water deficit and resilience post-stress in soybean

Background

Soybean is the main oilseed crop grown in the world; however, drought stress affects its growth and physiology, reducing its yield. The objective of this study was to characterize the physiological, metabolic, and genetic aspects that determine differential resistance to water deficit in soybean genotypes.

Methods

Three soybean genotypes were used in this study, two lineages (L11644 and L13241), and one cultivar (EMBRAPA 48-C48). Plants were grown in pots containing 8 kg of a mixture of soil and sand (2:1) in a greenhouse under sunlight. Soil moisture in the pots was maintained at field capacity until the plants reached the stage of development V4 (third fully expanded leaf). At this time, plants were subjected to three water treatments: Well-Watered (WW) (plants kept under daily irrigation); Water Deficit (WD) (withholding irrigation until plants reached the leaf water potential at predawn of -1.5 ± 0.2 MPa); Rewatered (RW) (plants rehydrated for three days after reached the water deficit). The WW and WD water treatments were evaluated on the eighth day for genotypes L11644 and C48, and on the tenth day for L13241, after interruption of irrigation. For the three genotypes, the treatment RW was evaluated after three days of resumption of irrigation. Physiological, metabolic and gene expression analyses were performed.

Results

Water deficit inhibited growth and gas exchange in all genotypes. The accumulation of osmolytes and the concentrations of chlorophylls and abscisic acid (ABA) were higher in L13241 under stress. The metabolic adjustment of lineages in response to WD occurred in order to accumulate amino acids, carbohydrates, and polyamines in leaves. The expression of genes involved in drought resistance responses was more strongly induced in L13241. In general, rehydration provided recovery of plants to similar conditions of control treatment. Although the C48 and L11644 genotypes have shown some tolerance and resilience responses to severe water deficit, greater efficiency was observed in the L13241 genotype through adjustments in morphological, physiological, genetic and metabolic characteristics that are combined in the same plant. This study contributes to the advancement in the knowledge about the resistance to drought in cultivated plants and provides bases for the genetic improvement of the soybean culture.

Rootstock influences the effect of grapevine leafroll-associated viruses on berry development and metabolism via abscisic acid signalling

Grapevine leafroll-associated virus (GLRaV) infections are accompanied by symptoms influenced by host genotype, rootstock, environment, and which individual or combination of GLRaVs is present. Using a dedicated experimental vineyard, we studied the responses to GLRaVs in ripening berries from Cabernet Franc grapevines grafted to different rootstocks and with zero, one, or pairs of leafroll infection(s). RNA sequencing data were mapped to a high-quality Cabernet Franc genome reference assembled to carry out this study and integrated with hormone and metabolite abundance data. This study characterized conserved and condition-dependent responses to GLRaV infection(s). Common responses to GLRaVs were reproduced in two consecutive years and occurred in plants grafted to different rootstocks in more than one infection condition. Though different infections were inconsistently distinguishable from one another, the effects of infections in plants grafted to different rootstocks were distinct at each developmental stage. Conserved responses included the modulation of genes related to pathogen detection, abscisic acid (ABA) signalling, phenylpropanoid biosynthesis, and cytoskeleton remodelling. ABA, ABA glucose ester, ABA and hormone signalling-related gene expression, and the expression of genes in several transcription factor families differentiated the effects of GLRaVs in berries from Cabernet Franc grapevines grafted to different rootstocks. These results support that ABA participates in the shared responses to GLRaV infection and differentiates the responses observed in grapevines grafted to different rootstocks.

Grapevine aquaporins: Diversity, cellular functions, and ecophysiological perspectives

High-scored premium wines are typically produced under moderate drought stress, suggesting that the water status of grapevine is crucial for wine quality. Aquaporins greatly influence the plant water status by facilitating water diffusion across the plasma membrane in a tightly regulated manner. They adjust the hydraulic conductance of the plasma membrane rapidly and reversibly, which is essential in specific physiological events, including adaptation to soil water scarcity. The comprehension of the sophisticated plant-water relations at the molecular level are thus important to optimize agricultural practices or to assist plant breeding programs. This review explores the recent progresses in understanding the water transport in grapevine at the cellular level through aquaporins and its regulation. Important aspects, including aquaporin structure, diversity, cellular localization, transport properties, and regulation at the cellular and whole plant level are addressed. An ecophysiological perspective about the roles of grapevine aquaporins in plant response to drought stress is also provided.

VviERF6Ls: an expanded clade in Vitis responds transcriptionally to abiotic and biotic stresses and berry development

Background

VviERF6Ls are an uncharacterized gene clade in Vitis with only distant Arabidopsis orthologs. Preliminary data indicated these transcription factors may play a role in berry development and extreme abiotic stress responses. To better understand this highly duplicated, conserved clade, additional members of the clade were identified in four Vitis genotypes. A meta-data analysis was performed on publicly available microarray and RNA-Seq data (confirmed and expanded with RT-qPCR), and Vitis VviERF6L1 overexpression lines were established and characterized with phenotyping and RNA-Seq.

Results

A total of 18 PN40024 VviERF6Ls were identified; additional VviERF6Ls were identified in Cabernet Sauvignon, Chardonnay, and Carménère. The amino acid sequences of VviERF6Ls were found to be highly conserved. VviERF6L transcripts were detected in numerous plant organs and were differentially expressed in response to numerous abiotic stresses including water deficit, salinity, and cold as well as biotic stresses such as red blotch virus, N. parvum, and E. necator. VviERF6Ls were differentially expressed across stages of berry development, peaking in the pre-veraison/veraison stage and retaining conserved expression patterns across different vineyards, years, and Vitis cultivars. Co-expression network analysis identified a scarecrow-like transcription factor and a calmodulin-like gene with highly similar expression profiles to the VviERF6L clade. Overexpression of VviERF6L1 in a Seyval Blanc background did not result in detectable morphological phenotypes. Genes differentially expressed in response to VviERF6L1 overexpression were associated with abiotic and biotic stress responses.

Conclusions

VviERF6Ls represent a large and distinct clade of ERF transcription factors in grapevine. The high conservation of protein sequence between these 18 transcription factors may indicate these genes originate from a duplication event in Vitis. Despite high sequence similarity and similar expression patterns, VviERF6Ls demonstrate unique levels of expression supported by similar but heterogeneous promoter sequences. VviERF6L gene expression differed between Vitis species, cultivars and organs including roots, leaves and berries. These genes respond to berry development and abiotic and biotic stresses. VviERF6L1 overexpression in Vitis vinifera results in differential expression of genes related to phytohormone and immune system signaling. Further investigation of this interesting gene family is warranted.