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Background: In viticulture, iron (Fe) chlorosis is a common abiotic stress that impairs plant development and leads to yield and quality losses. Under low availability of the metal, the applied N form (nitrate and ammonium) can play a role in promoting or mitigating Fe deficiency stresses. However, the processes involved are not clear in grapevine. Therefore, the aim of this study was to investigate the response of two grapevine rootstocks to the interaction between N forms and Fe uptake. This process was evaluated in a hydroponic experiment using two ungrafted grapevine rootstocks Fercal (Vitis berlandieri x V. vinifera) tolerant to deficiency induced Fe chlorosis and Couderc 3309 (V. riparia x V. rupestris) susceptible to deficiency induced Fe chlorosis. Results: The results could differentiate Fe deficiency effects, N-forms effects, and rootstock effects. Interveinal chlorosis of young leaves appeared earlier on 3309 C from the second week of treatment with NO3−/NH4+ (1:0)/-Fe, while Fercal leaves showed less severe symptoms after four weeks of treatment, corresponding to decreased chlorophyll concentrations lowered by 75% in 3309 C and 57% in Fercal. Ferric chelate reductase (FCR) activity was by trend enhanced under Fe deficiency in Fercal with both N combinations, whereas 3309 C showed an increase in FCR activity under Fe deficiency only with NO3−/NH4+ (1:1) treatment. With the transcriptome analysis, Gene Ontology (GO) revealed multiple biological processes and molecular functions that were significantly regulated in grapevine rootstocks under Fe-deficient conditions, with more genes regulated in Fercal responses, especially when both forms of N were supplied. Furthermore, the expression of genes involved in the auxin and abscisic acid metabolic pathways was markedly increased by the equal supply of both forms of N under Fe deficiency conditions. In addition, changes in the expression of genes related to Fe uptake, regulation, and transport reflected the different responses of the two grapevine rootstocks to different N forms. Conclusions: Results show a clear contribution of N forms to the response of the two grapevine rootstocks under Fe deficiency, highlighting the importance of providing both N forms (nitrate and ammonium) in an appropriate ratio in order to ease the rootstock responses to Fe deficiency. [ABSTRACT FROM AUTHOR]

Berry shrivel (BS) is one of the prominent and still unresolved ripening physiological disorders in grapevine. The causes of BS are unclear, and previous studies focused on the berry metabolism or histological studies, including cell viability staining in the rachis and berries of BS clusters. Herein, we studied the transcriptional modulation induced by BS in the rachis of pre-symptomatic and symptomatic clusters with a custom-made microarray qPCR in relation to a previous RNASeq study of BS berries. Gene set analysis of transcript expression in symptomatic rachis tissue determined suppression of cell wall biosynthesis, which could also be confirmed already in pre-symptomatic BS rachis by CESA8 qPCR analyses, while in BS berries, a high number of SWITCH genes were suppressed at veraison. Additionally, genes associated with the cell wall were differently affected by BS in berries. A high percentage of hydrolytic enzymes were induced in BS grapes in rachis and berries, while other groups such as, e.g., xyloglucan endotransglucosylase/hydrolase, were suppressed in BS rachis. In conclusion, we propose that modulated cell wall biosynthesis and cell wall assembly in pre-symptomatic BS rachis have potential consequences for cell wall strength and lead to a forced degradation of cell walls in symptomatic grape clusters. The similarity to sugar starvation transcriptional profiles provides a link to BS berries, which are low in sugar accumulation. However, further studies remain necessary to investigate the temporal and spatial coordination in both tissues. [ABSTRACT FROM AUTHOR]

The successful parasitisation of a plant by a phytophagous insect is dependent on the delivery of effector molecules into the host. Sedentary gall forming insects, such as grape phylloxera (Daktulosphaira vitifoliaeFitch, Phylloxeridae), secrete multiple effectors into host plant tissues that alter or modulate the cellular and molecular environment to the benefit of the insect. The identification and characterisation of effector proteins will provide insight into the host-phylloxera interaction specifically the gall-induction processes and potential mechanisms of plant resistance. Using proteomic mass spectrometry and in-silico secretory prediction, 420 putative effectors were determined from the salivary glands or the root-feeding D. vitifoliae larvae reared on Teleki 5C (V. berlandieri x V. riparia). Among them, 170 conserved effectors were shared between D. vitifoliae and fourteen phytophagous insect species. Quantitative RT-PCR analysis of five conserved effector candidates (protein disulfide-isomerase, peroxidoredoxin, peroxidase and a carboxypeptidase) revealed that their gene expression decreased, when larvae were starved for 24 h, supporting their assignment as effector molecules. The D. vitifoliae effectors identified here represent a functionally diverse group, comprising both conserved and unique proteins that provide new insight into the D. vitifoliae–Vitis spp. interaction and the potential mechanisms by which D. vitifoliae establishes the feeding site, suppresses plant defences and modulates nutrient uptake. [ABSTRACT FROM AUTHOR]

Overcoming host defensive traits is a prerequisite to establish compatible plant-parasite interactions. Following parasite perception, jasmonic (JA) and salicylic acid (SA) signalling pathways mediate biotic stress signals resulting in the activation of host defence responses. Piercing-sucking grape phylloxera (Daktulosphaira vitifoliae) infests Vitis spp. by the formation of organoid root galls. This study aims to investigate whether host defensive SA/JA signalling pathways are affected during D. vitifoliae infestation. We hypothesize that the JA signalling pathway is induced during larval probing (14 hai). Compatible root gall formation (24 hai − 14 dai) involves the reduction of the JA, but the induction of the SA signaling pathway. T5C (V. berlandieri x V. riparia) cuttings are infested with a D. vitifoliae single founder lineage (biotype C). Phytohormone quantification (HPLC-MS) and transcriptional alterations of JA/SA marker genes (qRT-PCR) are determined in root tissues from larval probing (14 hai) until gall formation (>14 dai). Non-infested root tips are considered controls. Our results show a significant induction of all analysed JA marker genes during insect probing (14 hai), but their significant reduction during early gall formation (24 hai). Following gall formation (5–14 dai) SA and JA-Ile increase. However, only the analysed SA marker genes are induced, whereas JA marker gene expression levels are significantly reduced. Based on this data we conclude that the observed suppression of the JA signalling pathway might represent an important step for the compatible D. vitifoliae – Vitis spp. root interaction. We discuss whether the induced SA defences protect nutritive root galls against soil microbes. • D. vitifoliae probing induces the JA signaling pathway on Vitis spp. roots. • Subsequent root gall formation involves the transcriptional suppression of the JA, but the induction of the SA signaling. • Induced SA defence responses might protect nutritive root gall tissue against soil microbes. [ABSTRACT FROM AUTHOR]

Gall forming phylloxera may compete for nutrients with meristematic tissues and develop heterotrophic structures that act as carbon sinks. In this work, we studied the underlying starch metabolism, sink-source translocation of soluble sugars towards and within root galls. We demonstrated that nodosities store carbohydrates by starch accumulation and monitored the expression of genes involved in the starch metabolic. Thereby we proved that the nodosity is symplastically connected to the source tissues through its development and that the starch metabolism is significantly affected to synthesize and degrade starch within the gall. Genes required for starch biosynthesis and degradation are up-regulated. Among the carbohydrate transporters the expression of a glucose-6-phosphate translocater, one sucrose transporter and two SWEET proteins were increases, whereas hexose transporters, tonoplast monosaccharide transporter and Erd6-like sugar transporters were decreased. We found general evidence for plant response to osmotic stress in the nodosity as previously suggested for gall induction processes. We conclude that nodosities are heterogenous plant organs that accumulate starch to serve as temporary storage structure that is gradually withdrawn by phylloxera. Phylloxera transcriptionally reprograms gall tissues beyond primary metabolism and included downstream secondary processes, including response to osmotic stress. [ABSTRACT FROM AUTHOR]

Cover crops in vineyards do provide many important ecosystem functions, however wine growers are often reluctant to incorporate cover crops into their vineyard management as they are concerned about competition regarding water and nutrient availability. The objective of this study was to define the effects of three standard inter-row vegetation management strategies on vine growth and grape quality in different European regions. We hypothesize that general patterns of responses to different inter-row management can be identified across European vine growing regions independent of local climate and soil conditions. Data were collected in 2016 and 2017 in commercial vineyards located in five European temperate wine growing regions directly comparing standard inter-row vegetation management strategies in parallel in vineyards ranging from cover crops to bare ground through tillage or herbicide application. Vegetation management strongly influenced leaf chlorophyll content, shoot pruning weight and yeast assimilable nitrogen (YAN) in grape juice. Across countries, grape varieties and varying soil conditions, YAN consistently showed higher values in grapes separated by bare ground inter-rows as compared to inter-rows with a permanent vegetation cover. Other grape quality parameters, total soluble solids, total titratable acidity and berry weight were not or inconsistently affected across countries, preventing the prediction of generalized trends. We also observed higher values of soil organic matter in complete vegetation inter-rows. In conclusion, we identified general effects of inter-row vegetation management on vine vigor and grape quality across countries and grape varieties in different pedo-climatic conditions. Our study provides general response patterns as a basis for functional studies to develop local inter-row vegetation management strategies. • Across European vineyards, inter-row vegetation decreased vine vigor and grape nitrogen. • Vine response was conserved across pedo-climatic conditions and grape varieties. • Pruning weight and leaf chlorophyll content increased with soil tillage. • Total soluble solids and titratable acidity were not influenced by inter-row management. • Soil organic matter decreased with soil tillage or herbicide application. [ABSTRACT FROM AUTHOR]

Grapevine (Vitis vinifera L.) is the most economically important deciduous fruit crop in the world. Iron (Fe) is an essential micronutrient for plant development since its active form is involved in several biochemical processes, e.g., chlorophyll synthesis. The uptake of the elements depends on individual elements' interactions. Iron (Fe) nutrition of plants can be significantly affected by different nitrogen (N) forms through altering the uptake ratio of cations and anions, and changing rhizosphere pH. It is known, that most crop species grow best with access to nitrate (NO3 -) as well as ammonium (NH4 +) nitrogen, but little attention has been paid to changes in iron uptake under supply of different nitrogen (N) forms. The presented study aimed to decipher the specific interaction of different nitrogen (N) forms on Iron uptake of different grapevine rootstocks on the physiological as well as on the biochemical and molecular level. Four NH4 +: NO3 - ratios (0:1,1:5, 1:3, 1:1) were tested with a modified half-strength Hoagland solution with and without FeNa(III)-EDTA, summing up to eight treatments within a hydroponic system (Kick-Brauckmann, 7.5 L) under semi-controlled climatic glasshouse conditions in 2021. Rooted woody cuttings of the rootstocks Fercal (V.berlandieri x V. vinifera) and Couderc 3309 (V. riparia x V. rupestris) were used for the experiment. The results could differentiate iron deficiency effects, nitrogen form effects and rootstock effects. Biomass of leaves was negatively influenced by iron absent in both rootstocks with nitrate as only N source. This effect was observed for 3309C for all NH4 +: NO3 -ratios, while with Fercal the biomass of leaves increased with increasing amount of NH4 +. A similar trend was overserved for root biomass, promoting in Fercal with increased NH4 + amount and not response in 3309C. The efficiency of the photsystem II (Y(II)) decreased under iron deficient conditions in both rootstocks showing the strongest effect with only nitrate as N source especially with rootstock 3309C. Increasing ammonium levels in the nutrient solution lead to a higher pH reduction by the rootstocks probably enhancing the Fe2+ availability and uptake. The ferric chelate reductase (FCR) activity was specifically increased in Fercal under irondeficient conditions, while no effect was observed for 3309C in comparison to control plants. These first results of the study indicate that rootstocks differ in their preference on both the physiological and molecular level depending on the nitrogen form and in interaction with iron deficiency stress. In a next step the molecular mechanism will be analysed. [ABSTRACT FROM AUTHOR]

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Simple Summary: Grape phylloxera is an American native insect pest that caused heavy damages to the vineyards worldwide since its spreading to wine regions since the 1850s. This insect, able to feed on leaves and roots, induces plant galls and manipulates the grapevine physiology leading to plant damage and may cause plant death. The most successful treatment was the use of mostly partially resistant rootstocks. The degree of resistance is affected by environment, grapevine management and the insect biotype. In this study, we analyse the interaction of insect biotypes feeding on particular host plants. Therefore we evaluated the gene expression of Phylloxera feeding on a susceptible host versus feeding on a rootstock in two different developmental stages. We discovered (mainly in advanced insect developmental stages) genes expressed in higher proportion in one insect compared to the other. These genes related to chemosensory; in plant physiology manipulation and root deformation and insect digestive traits may play a role in the plant-insect interaction determining plant resistance in response to the pest attack. Grape phylloxera is one of the most dangerous insect pests for worldwide viticulture. The leaf- and root-galling phylloxerid has been managed by grafting European grapevines onto American rootstock hybrids. Recent reports pinpoint the appearance of host-adapted biotypes, but information about the biomolecular characteristics underlying grape phylloxera biotypisation and its role in host performance is scarce. Using RNA-sequencing, we sequenced the transcriptome of two larval stages: L1 (probing) and L2-3 (feeding) larvae of two root-feeding grape phylloxera lineages feeding on the rootstock Teleki 5C (biotype C) and V. vinifera Riesling (biotype A). In total, 7501 differentially expressed genes (DEGs) were commonly modulated by the two biotypes. For the probing larvae, we found an increased number of DEGs functionally associated with insect chemoreception traits, such as odorant-binding proteins, chemosensory proteins, ionotropic, odorant, and gustatory receptors. The transcriptomic profile of feeding larvae was enriched with DEGs associated with the primary metabolism. Larvae feeding on the tolerant rootstock Teleki 5C exhibited higher numbers of plant defense suppression-associated DEGs than larvae feeding on the susceptible host. Based on the identified DEGs, we discuss their potential role for the compatible grape phylloxera–Vitis interaction belowground. This study was the first to compare the transcriptomes of two grape phylloxera lineages feeding on a tolerant and susceptible host, respectively, and to identify DEGs involved in the molecular interaction with these hosts. Our data provide a source for future studies on host adaptation mechanisms of grape phylloxera and help to elucidate grape phylloxera resistance further. [ABSTRACT FROM AUTHOR]

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 (Ψ s) under water shortage and Sauvignon Kretos maintained higher Ψ s 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. • Sauvignon Kretos exhibited higher Ψ s even in the presence of water shortage. • The observed different degree of tolerance is probably ABA independent. • Sauvignon Kretos hormonal profile is more suitable to cope with water limiting conditions. • VvPIP2;1 and VvTIP2;1 aquaporins might affect the hydraulic behaviour under water stress. [ABSTRACT FROM AUTHOR]