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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]

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]

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]

Abstract Many plants respond to herbivore attacks by the formation of secondary metabolites, such as polyphenols. Grape phylloxera (Daktulosphaira vitifoliae Fitch) induces organoid root galls on fibrous root tips of tolerant Vitis spp. rootstocks. We aim to understand if and how secondary metabolites are involved in the compatible interaction of D. vitifoliae and tolerant Vitis ssp. rootstocks belowground. We hypothise that D. vitifoliae infestation triggers the accumulation of phenolic key compounds in root gall tissue without preventing the compatible host-parasite interaction on two tolerant rootstocks with different genetic background: Teleki 5C (V. berlandieri x V. riparia) and Fercal (B.C. n°1B x 31 Richter). Plants and insects are grown in isolated climate chambers to sample root tips of non-infested plants (control) as well as root tips and galls of D. vitifoliae infested plants (5–14 dai). HPLC-MS-based analyses of phenolic key compounds are compared with gene expression levels of the biosynthetic phenylpropanoid pathway analysing temporal sequences of D. vitifoliae infested root tissue. The results show that the induction of the phenylpropanoid pathway by D. vitifoliae infestation plays an important role in the plant response. Concentrations of phenolic key compounds vary significantly among the rootstocks tested. Both rootstocks display an accumulation of flavan-3-ols and stilbenes in infested root gall tissue. Comparing the host responses of the two rootstocks Fercal shows a stronger accumulation of stilbenes locally in infested root galls, whereas Teleki 5C indicates elevated amounts of stilbenes in non-infested root tip tissue. Highlights • Flavan-3-ols are present in Vitis spp. root tips indicating their role in constitutive plant defence and root tip growth. • Gradual accumulations of stilbenes and flavan-3-ols predominate the host response in root galls upon D. vitifoliae exposure. • Polyphenols do not interfere with D. vitifoliae feeding, but might protect the feeding tissue against secondary infections. [ABSTRACT FROM AUTHOR]