Root-Zone Restriction Regulates Soil Factors and Bacterial Community Assembly of Grapevine.

Root-zone restriction induces physiological stress on roots, thus limiting the vegetative and enhancing reproductive development, which promotes fruit quality and growth. Numerous bacterial-related growth-promoting, stress-mitigating, and disease-prevention activities have been described, but none in root-restricted cultivation. The study aimed to understand the activities of grapevine bacterial communities and plant-bacterial relationships to improve fruit quality. We used High-throughput sequencing, edaphic soil factors, and network analysis to explore the impact of restricted cultivation on the diversity, composition and network structure of bacterial communities of rhizosphere soil, roots, leaves, flowers and berries. The bacterial richness, diversity, and networking were indeed regulated by root-zone restriction at all phenological stages, with a peak at the veraison stage, yielding superior fruit quality compared to control plants. Moreover, it also handled the nutrient availability in treated plants, such as available nitrogen (AN) was 3.5, 5.7 and 0.9 folds scarcer at full bloom, veraison and maturity stages, respectively, compared to control plants. Biochemical indicators of the berry have proved that high-quality berry is yielded in association with the bacteria. Cyanobacteria were most abundant in the phyllosphere, Proteobacteria in the rhizosphere, and Firmicutes and Bacteroidetes in the endosphere. These bacterial phyla were most correlated and influenced by different soil factors in control and treated plants. Our findings are a comprehensive approach to the implications of root-zone restriction on the bacterial microbiota, which will assist in directing a more focused procedure to uncover the precise mechanism, which is still undiscovered.

Transcriptome analysis revealed the expression levels of genes related to abscisic acid and auxin biosynthesis in grapevine (Vitis vinifera L.) under root restriction.

The root system is essential for the stable growth of plants. Roots help anchor plants in the soil and play a crucial role in water uptake, mineral nutrient absorption and endogenous phytohormone formation. Root-restriction (RR) cultivation, a powerful technique, confines plant roots to a specific soil space. In the present study, roots of one-year-old "Muscat Hamburg" grapevine under RR and control (nR) treatments harvested at 70 and 125 days after planting were used for transcriptome sequencing, and in total, 2031 (nR7 vs. nR12), 1445 (RR7 vs. RR12), 1532 (nR7 vs. RR7), and 2799 (nR12 vs. RR12) differentially expressed genes (DEGs) were identified. Gene Ontology (GO) enrichment analysis demonstrated that there were several genes involved in the response to different phytohormones, including abscisic acid (ABA), auxin (IAA), ethylene (ETH), gibberellins (GAs), and cytokinins (CTKs). Among them, multiple genes, such as PIN2 and ERF113, are involved in regulating vital plant movements by various phytohormone pathways. Moreover, following RR cultivation, DEGs were enriched in the biological processes of plant-type secondary cell wall biosynthesis, the defense response, programmed cell death involved in cell development, and the oxalate metabolic process. Furthermore, through a combined analysis of the transcriptome and previously published microRNA (miRNA) sequencing results, we found that multiple differentially expressed miRNAs (DEMs) and DEG combinations in different comparison groups exhibited opposite trends, indicating that the expression levels of miRNAs and their target genes were negatively correlated. Furthermore, RR treatment indeed significantly increased the ABA content at 125 days after planting and significantly decreased the IAA content at 70 days after planting. Under RR cultivation, most ABA biosynthesis-related genes were upregulated, while most IAA biosynthesis-related genes were downregulated. These findings lay a solid foundation for further establishing the network through which miRNAs regulate grapevine root development through target genes and for further exploring the molecular mechanism through which endogenous ABA and IAA regulate root architecture development in grapevine.

Comparative fungal diversity and dynamics in plant compartments at different developmental stages under root-zone restricted grapevines.

BACKGROUND: The root-zone restriction cultivation technique is used to achieve superior fruit quality at the cost of limited vegetative and enhanced reproductive development of grapevines. Fungal interactions and diversity in grapevines are well established; however, our knowledge about fungal diversity under the root-zone restriction technique is still unexplored. To provide insights into the role of mycobiota in the regulation of growth and fruit quality of grapevine under root-zone restriction, DNA from rhizosphere and plant compartments, including white roots (new roots), leaves, flowers, and berries of root-zone restricted (treatment) and conventionally grown plants (control), was extracted at three growth stages (full bloom, veraison, and maturity). RESULTS: Diversity analysis based on the ITS1 region was performed using QIIME2. We observed that the root-zone restriction technique primarily affected the fungal communities of the soil and plant compartments at different growth stages. Interestingly, Fusarium, Ilyonectria, Cladosporium and Aspergillus spp observed in the rhizosphere overlapped with the phyllosphere at all phenological stages, having distinctive abundance in grapevine habitats. Peak richness and diversity were observed in the rhizosphere at the full bloom stage of control plants, white roots at the veraison stage of treatment, leaves at the maturity stage of treatment, flowers at the full bloom stage and berries at the veraison stage of control plants. Except for white roots, the diversity of soil and plant compartments of treated plants tended to increase until maturity. At the maturity stage of the treated and control plants, the abundance of Aspergillus spp. was 25.99 and 29.48%, respectively. Moreover, the total soluble sugar content of berries was 19.03 obrix and 16 obrix in treated and control plants, respectively, at the maturity stage. CONCLUSIONS: This is the first elucidative study targeting the fungal diversity of conventional and root-restricted cultivation techniques in a single vineyard. Species richness and diversity are affected by stressful cultivation known as root zone restriction. There is an association between the abundance of Aspergillus spp. and fruit quality because despite causing stress to the grapevine, superior quality of fruit is retrieved in root-zone restricted plants.

Drying Treatments Change the Composition of Aromatic Compounds from Fresh to Dried Centennial Seedless Grapes.

Raisin aroma is a vital sensory characteristic that determines consumers' acceptance. Volatile organic compounds (VOCs) in fresh grapes, air-dried (AD), pre-treated air-dried (PAD), sun-dried (SD), and pre-treated sun-dried (PSD) raisins were analyzed, with 99 and 77 free- and bound-form compounds identified in centennial seedless grapes, respectively. The hexenal, (E)-2-hexenal, 1-hexanol, ethyl alcohol, and ethyl acetate in free-form while benzyl alcohol, ß-damascenone, gerenic acid in bound-form were the leading compounds. Overall, the concentration of aldehydes, alcohols, esters, acids, terpenoids, ketones, benzene, and phenols were abundant in fresh grapes but pyrazine and furan were identified in raisin. Out of 99 VOCs, 30 compounds had an odour active value above 1. The intensity of green, floral, and fruity aromas were quite higher in fresh grapes followed by AD-raisins, PAD-raisins, SD-raisins, and PSD-raisins. The intense roasted aroma was found in SD-raisins due to 2,6-diethylpyrazine and 3-ethyl-2,5-dimethylpyrazine. Among raisins, the concentration of unsaturated fatty acid oxidized and Maillard reaction volatiles were higher in SD-raisins and mainly contributed green, fruity and floral, and roasted aromas, respectively.

Small RNA Sequencing Analysis of miRNA Expression Reveals Novel Insihts into Root Formation under Root Restriction Cultivation in Grapevine (Vitis vinifera L.).

Root restriction cultivation (RRC) can influence plant root architecture, but its root phenotypic changes and molecular mechanisms are still unknown. In this study, phenotype observations of grapevine root under RRC and control cultivation (nRC) at 12 time points were conducted, and the root phenotype showed an increase of adventitious and lateral root numbers and root tip degeneration after RRC cultivation from 70 days after planting (DAP). The 70 and 125 DAP sampling of two different cultivations, named nR70, RR70, nR125, and RR125, were selected for small RNA sequencing. A total of 153 known miRNAs and 119 predicted novel miRNAs were obtained. Furthermore, BLAST was used to predict the novel miRNAs with miRBase databases using the default parameters; 96 of the 119 predicted novel miRNAs were similar to other species, and the remaining 23 grapevine-specific novel miRNAs were obtained. There were 26, 33, 26, and 32 miRNAs that were differentially expressed in different comparison groups (RR70 vs. nR70, RR125 vs. nR125, nR125 vs. nR70 and RR125 vs. RR70). Target genes prediction of differentially expressed miRNAs was annotated on a variety of biological processes, and 24 participated in root development. Moreover, multiple miRNAs were found to jointly regulate lateral root development under root restriction conditions. The miRNA expression pattern comparison between RRC and nRC may provide a framework for the future analysis of miRNAs associated with root development in grapevine.

Grapevine ABA receptor VvPYL1 regulates root hair development in Transgenic Arabidopsis.

Root architecture is very important for plant growth. In this study, we characterized the process of root formation in grapevine (Vitis vinifera L.). Continuous observation of root morphology during development revealed that the establishment of root system could be divided into five stages: initial cultivation (stage I), preliminary development (stage II), even change (stage III), root system formation (stage IV), and root architecture stability (stage V). The level of abscisic acid (ABA) increased from stages II to IV and was stable at stage V. Quantitative expression analysis of 11 genes encoding ABA-related rate-limiting enzymes in different tissues showed that the expression of VvPYL1 was the highest in roots. Spatiotemporal expression analysis showed that VvPYL1 was highly expressed during stages II and III. Furthermore, VvPYL1 was highly expressed in lateral roots of grapevine seedlings in tissue culture. Overexpression of VvPYL1 in Arabidopsis thaliana resulted in longer root hairs compared with wild-type plants. Moreover, the root hair length of transgenic lines was hypersensitive to exogenously applied ABA. Additionally, VvPYL1 overexpressing plants showed greater drought tolerance and longer root hairs than wild-type plants under osmotic stress. These results suggest that VvPYL1 may play a key role in root development and drought resistance.