Biochemical differences in the skin of two blueberries (Vaccinium corymbosum) varieties with contrasting firmness: Implication of ions, metabolites and cell wall related proteins in two developmental stages

Unraveling the genetic architecture of blueberry fruit quality traits: major loci control organic acid content while more complex genetic mechanisms control texture and sugar content

BACKGROUND

Fruit quality traits, including taste, flavor, texture, and shelf-life, have emerged as important breeding priorities in blueberry (Vaccinium corymbosum). Organic acids and sugars play crucial roles in the perception of blueberry taste/flavor, where low and high consumer liking are correlated with high organic acids and high sugars, respectively. Blueberry texture and appearance are also critical for shelf-life quality and consumers' willingness-to-pay. As the genetic mechanisms that determine these fruit quality traits remain largely unknown, in this study, an F1 mapping population was used to perform quantitative trait loci (QTL) mapping for pH, titratable acidity (TA), organic acids, total soluble solids (TSS), sugars, fruit size, and texture at harvest and/or post-storage and weight loss.

RESULTS

Twenty-eight QTLs were detected for acidity-related parameters (pH, TA, and organic acid content). Six QTLs for pH, TA, and citric acid, two for quinic acid, and two for shikimic acid with major effects were consistently detected across two years on the same genomic regions on chromosomes 3, 4, and 5, respectively. Putative candidate genes for these QTLs were also identified using comparative transcriptomic analysis. No QTL was detected for malic acid content, TSS, or individual sugar content. A total of 146 QTLs with minor effects were identified for texture- and size-related parameters. With a few exceptions, these QTLs were generally inconsistent over years and post-storage, indicating a highly quantitative nature.

CONCLUSIONS

Our findings enhance the understanding of the genetic basis underlying fruit quality traits in blueberry and guide future work to exploit DNA-informed selection strategies in blueberry breeding programs. The major-effect QTLs identified for acidity-related fruit characteristics could be potential targets to develop DNA markers for marker-assisted selection (MAS). On the other hand, genomic selection may be a more suitable approach than MAS when targeting fruit texture, sugars, or size.

Fruit Cuticle Thickness and Anatomical Changes in Pedicel Xylem Vessels Influence Fruit Transpiration and Calcium Accumulation in Cranberry Fruit

Ca is a key nutrient for fruit quality due to its role in bonding with pectin in the cell wall, providing strength through cell-to-cell adhesion, thus increasing fruit firmness and extending post-harvest life. However, Ca accumulation is mostly limited to the initial stages of fruit development due to anatomical and physiological changes that occur as fruits develop. The objective of this study was to evaluate fruit transpiration, cuticle thickness, and pedicel vessel changes during cranberry fruit development and the effect these parameters might have on Ca translocation. 'Stevens' cranberry fruits were collected weekly, starting seven days after full bloom (DAFB) until 70 DAFB. For each collection date, fruit transpiration was evaluated in the field, and samples were taken to analyze total fruit Ca content, stomata density, cuticle thickness, pedicel anatomical changes, and xylem functionality. Ca accumulation in the fruit exhibited a sigmoidal curve, beginning at 0.04 mg per berry at 7 DAFB, increasing to a maximum of 0.1 mg per berry at 28 DAFB, and remaining constant until harvest (70 DAFB). Fruit Ca accumulation was mostly explained by fruit transpiration, which exhibited a similar sigmoidal pattern. The rapid decline in fruit transpiration was largely modulated by increases in cuticle thickness, as well as anatomical changes in the pedicel xylem, thereby reducing the capacity to transport water and nutrients into the fruit. Thus, this research could help cranberry growers maximize fruit Ca content by prioritizing fertilization during the early stages of fruit development.

Transcriptomic and Metabolomic Profiling Reveals the Variations in Carbohydrate Metabolism between Two Blueberry Cultivars

Blueberry is a high-quality fruit tree with significant nutritional and economic value, but the intricate mechanism of sugar accumulation in its fruit remains unclear. In this study, the ripe fruits of blueberry cultivars 'Anna' and 'Misty' were utilized as experimental materials, and physiological and multi-omics methodologies were applied to analyze the regulatory mechanisms of the difference in sugar content between them. The results demonstrated that the 'Anna' fruit was smaller and had less hardness than the 'Misty' fruit, as well as higher sugar content, antioxidant capability, and lower active substance content. A total of 7067 differentially expressed genes (DEGs) (3674 up-regulated and 3393 down-regulated) and 140 differentially abundant metabolites (DAMs) (82 up-regulated and 58 down-regulated) were identified between the fruits of the two cultivars. According to KEGG analysis, DEGs were primarily abundant in phenylpropanoid synthesis and hormone signal transduction pathways, whereas DAMs were primarily enriched in ascorbate and aldarate metabolism, phenylpropanoid biosynthesis, and the pentose phosphate pathway. A combined multi-omics study showed that 116 DEGs and 3 DAMs in starch and sucrose metabolism (48 DEGs and 1 DAM), glycolysis and gluconeogenesis (54 DEGs and 1 DAM), and the pentose phosphate pathway (14 DEGs and 1 DAM) were significantly enriched. These findings suggest that blueberries predominantly increase sugar accumulation by activating carbon metabolism network pathways. Moreover, we identified critical transcription factors linked to the sugar response. This study presents new understandings regarding the molecular mechanisms underlying blueberry sugar accumulation and will be helpful in improving blueberry fruit quality through breeding.

Postharvest High-CO2 Treatments on the Quality of Soft Fruit Berries: An Integrated Transcriptomic, Proteomic, and Metabolomic Approach

Soft fruits are appreciated for their taste qualities and for being a source of health-promoting compounds. However, their postharvest is affected by their high respiratory rates and susceptibility to fungal decay. Our aim here is to provide a perspective on the application of short-term high-CO₂ treatments at a low temperature to maintain the postharvest quality of soft fruits. This work also suggests using a multi-omics approach to better understand the role of the cell wall and phenolic compounds in maintaining quality. Finally, the contribution of high-throughput transcriptomic technologies to understand the mechanisms modulated by the short-term gaseous treatments is also highlighted.

Pre-Anthesis Cytokinin Applications Increase Table Grape Berry Firmness by Modulating Cell Wall Polysaccharides

The use of plant growth regulators (PGRs) is widespread in commercial table grape vineyards. The synthetic cytokinin CPPU is a PGR that is extensively used to obtain higher quality grapes. However, the effect of CPPU on berry firmness is not clear. The current study investigated the effects of pre-anthesis applications (BBCH15 and BBCH55 stages) of CPPU on 'Thompson Seedless' berry firmness at harvest through a combination of cytological, morphological, and biochemical analyses. Ovaries in CPPU-treated plants presented morphological changes related to cell division and cell wall modification at the anthesis stage (BBCH65). Moreover, immunofluorescence analysis with monoclonal antibodies 2F4 and LM15 against pectin and xyloglucan demonstrated that CPPU treatment resulted in cell wall modifications at anthesis. These early changes have major repercussions regarding the hemicellulose and pectin cell wall composition of mature fruits, and are associated with increased calcium content and a higher berry firmness at harvest.