Molecular bases of strawberry fruit quality traits: Advances, challenges, and opportunities

Identification and characterization of SWEET gene family in passion fruit reveals the involvement of PeSWEET3 in soluble sugar accumulation

The sugars will eventually be exported transporters (SWEET) family is a class of sugar transporters that play crucial roles in plant growth, reproduction, and stresses response. The characteristics of 21 PeSWEETs, identified in passion fruit (Passiflora edulis Sims) and divided into four clades, were evaluated. Structural feature analysis showed that exon numbers ranged from 4 to 12, while motif 1, 2, and 3 were highly conserved. Analysis of RNA-seq from different tissues revealed that PeSWEETs showed tissue-specificity. Additionally, Cis-acting regulatory element analysis indicated that abundant hormone-response and stress response elements were enriched in promoters of PeSWEETs. Exogenous abscisic acid (ABA) treatment led to an increase in the soluble sugar accumulation and up-regulated the expression level of PeSWEET3. The PeSWEET3 protein localizes on the plasma membrane and exhibits transport activity of fructose, glucose, and mannose. Furthermore, ectopic expression of PeSWEET3 significantly enhanced soluble sugar accumulation in leaves of transgenic tobacco. Collectively, these results lay a solid foundation for further exploration on the role of PeSWEETs.

Exploring Postharvest Metabolic Shifts and NOX2 Inhibitory Potential in Strawberry Fruits and Leaves via Untargeted LC-MS/MS and Chemometric Analysis

Background/Objectives: Strawberries are highly appreciated for their rich phytochemical composition, but rapid postharvest deterioration limits their shelf life and nutritional quality. This study aimed to investigate the metabolic changes occurring in both strawberry fruits and leaves during storage and to evaluate the NADPH oxidase 2 (NOX2) inhibitory potential of strawberry-derived metabolites. Methods: Untargeted LC-MS/MS analysis was conducted on fruit and leaf tissues stored at 8 ± 0.5 °C. A total of 37 metabolites were identified, including organic acids, phenolic acids, flavonoids, and hydroxycinnamic acid derivatives. Multivariate statistical analyses (ANOVA, PLS-DA, and volcano plots) were used to assess temporal and tissue-specific metabolic shifts. Additionally, a machine learning-based predictive model was applied to evaluate the NOX2 inhibitory potential of 24 structurally characterized metabolites. Results: Storage induced significant and tissue-specific metabolic changes. In fruits, malic acid, caffeic acid, and quercetin-3-glucuronide showed notable variations, while ellagic acid aglycone and galloylquinic acid emerged as prominent markers in leaves. The predictive model identified 21 out of 24 metabolites as likely NOX2 inhibitors, suggesting potential antioxidant and anti-inflammatory bioactivity. Conclusions: These findings provide new insights into postharvest biochemical dynamics in both strawberry fruits and leaves. The results highlight the value of leaves as a source of bioactive compounds and support their potential valorization in functional food and nutraceutical applications.

Structure and release function of fragrance glands

Volatile compounds serve physiological, signaling, and defensive purposes in plants and have beneficial effects on the growth, reproduction, resistance, and yield of horticultural plants. They are released through fragrance glands and become gasses by passing through the plasma membrane, cell walls that contain water, and cuticle. Transporter proteins facilitate their transport and reduce the resistance of these barriers. They also regulate the rate of release and concentration of volatiles inside and outside of the membrane. However, there has been no summary of the structure and function of the fragrance glands of horticultural plants, as well as an introduction to the latest research progress on the mechanism of the transport of volatiles. This review focuses on the structure and function of the release of aromas in horticultural plants and explores the mechanism of the release of volatiles through a transporter model. Additionally, it considers the factors that affect their release and ecological functions and suggests directions for future research.

Use of Bacillus velezensis JNS-1 from vermicompost against strawberry root rot

China is the biggest producer of strawberry and has the largest strawberry cultivation area worldwide. This study adopted an experimental method to explore the effect of vermicompost addition on the yield and quality of strawberries and to investigate the influence of the composition and activity of microbial communities in soilless cultivation systems. The addition of vermicompost significantly increased the activity of three soil enzymes, namely cellulase, urease, and acid phosphatase. Furthermore, it significantly increased the nitrogen content of the strawberry-planted substrate, through NO3-N and alkaline-N contents and organic matter, as well as the available-K content and cation exchange capacity, but with no significant effect on the available-P content of the substrate. Vermicompost addition effectively improved the growth of strawberry plants by transforming microbial diversity and increasing the level of beneficial microbial transcription. The average plant yield of the first-crop fruit of vermicompost-treated plants was significantly higher than that of the control. Furthermore, a biocontrol strain named JNS-1 was isolated from the vermicompost, which showed a good direct inhibitory effect against the mycelial growth of Fusarium oxysporum and Neopestalotiopsis spp. According to its morphology and 16S rRNA gene sequences, JNS-1 strain was identified as Bacillus velezensis. In greenhouse pot experiments and field trials, B. velezensis JNS-1 was found to be effective in controlling strawberry root rot disease. This study focuses on using B. velezensis JNS-1 to enhance the health and quality of strawberries and providing a theoretical basis for the use of B. velezensis JNS-1 in strawberry fields.

Volatile aromatic substances analysis of different temperature stored 'Docteur Jules Guyot' pear (Pyrus communis L.)

During the post-ripening process of 'Docteur Jules Guyot' pear, the aroma of the fruit gradually becomes richer with increasing maturity. In this study, the volatile substances in 'Docteur Jules Guyot' pear fruits stored at room temperature (RT), low temperature (LT), and low temperature to room temperature (LT-RT) were identified and analyzed using solid-phase microextraction (SPME) with gas chromatography-mass spectrometry (GC-MS) at different ripening stages. The results showed that the volatile substances were mainly alcohols, aldehydes, esters, acids, ketones, alkanes, and terpenes. Esters are the main substances of fruit aroma; with an increase in fruit maturity, the ester content increases gradually. Ethyl acetate, hexyl acetate, heptyl acetate, and amyl acetate were the main volatile components of the fruit. The aroma content under LT was lower than that under RT, and after transferring from LT-RT, the ripening of the fruit was accelerated, and the aroma content increased rapidly. Among the genes involved in the lox pathway, the expression of PcHPL1, PcADH1, PcGLIP1, PcGLIP-like, PcLOX2, PcLIP2, and PcFAD2 were the most contributing to the changes of esters in 'Docteur Jules Guyot' pear. These results are helpful to provide basic data for the study of volatile in 'Docteur Jules Guyot' pear fruit under LT and RT storage.

HMGR Modulates Strawberry Fruit Coloration and Aroma Through Regulating Terpenoid and Anthocyanin Pathways

HMGR is a crucial enzyme in the biosynthesis of terpenoids. We cloned FaHMGR and found that FaHMGR expression in fruit was significantly higher than other tissues, especially during the coloring stage. Suppression of FaHMGR (FaHMGRR) promoted coloration by increasing anthocyanin content and produced five new components. In contrast, FaHMGR overexpression (FaHMGROE) downregulated most anthocyanin genes and reduced hexanoic acid methyl ester and linalool contents, thereby inhibiting coloring. Transcriptomic and metabolomic analyses showed that DEGs in HMGROE vs. HMGRC (pCAMBIA1302 empty vector transformant serving as a control) were significantly enriched in phenylpropanoid biosynthesis pathway and pathways related to terpenoid metabolism and MeJA, suggesting MeJA as a potential mediator of HMGR's influence on terpenoid pathways. Additionally, DEGs in HMGRR vs. HMGRC were enriched in anthocyanin biosynthesis, particularly keracyanin and pelargonidin, which may explain the promoted coloration observed in HMGRR. WGCNA analysis identified five module genes with distinct expression patterns in HMGRR and HMGROE, including ERF118 and WRKY12, which may impact fruit quality by regulating HMGR activity.

Multi-objective RGB-D fusion network for non-destructive strawberry trait assessment

Growing consumer demand for high-quality strawberries has highlighted the need for accurate, efficient, and non-destructive methods to assess key postharvest quality traits, such as weight, size uniformity, and quantity. This study proposes a multi-objective learning algorithm that leverages RGB-D multimodal information to estimate these quality metrics. The algorithm develops a fusion expert network architecture that maximizes the use of multimodal features while preserving the distinct details of each modality. Additionally, a novel Heritable Loss function is implemented to reduce redundancy and enhance model performance. Experimental results show that the coefficient of determination (R²) values ​​for weight, size uniformity and number are 0.94, 0.90 and 0.95 respectively. Ablation studies demonstrate the advantage of the architecture in multimodal, multi-task prediction accuracy. Compared to single-modality models, non-fusion branch networks, and attention-enhanced fusion models, our approach achieves enhanced performance across multi-task learning scenarios, providing more precise data for trait assessment and precision strawberry applications.

The bHLH transcription factor DlbHLH68 positively regulates DlSPS1 expression to promote sucrose biosynthesis in longan

Sucrose is an important factor affecting plant growth and fruit quality, but the molecular regulatory mechanism of sucrose biosynthesis in longan is not yet understood. Here, we characterized a transcription factor, DlbHLH68, positively regulates sucrose accumulation in longan. Subcellular localization and transcriptional activity analysis indicated that DlbHLH68 is a nuclear transcriptional activator. Overexpressing DlbHLH68 in Arabidopsis enhanced sucrose content, plant height, and the relative expression level of sucrose phosphate synthase genes (AtSPS1 and AtSPS2). Yeast one-hybrid and dual-luciferase reporter assays indicated that DlbHLH68 was able to activate the expression of DlSPS1, the homology gene of AtSPS1. As expected, overexpression of DlSPS1 significantly increased the sucrose content in transgenic Arabidopsis and longan fruits. Collectively, this study reveals that DlbHLH68 is a positive regulator in sucrose accumulation by activating DlSPS1 expression to mediate sucrose biosynthesis, which is helpful for understanding the molecular basis of sucrose biosynthesis and accumulation in longan fruit and provides candidate genes for further breeding.

Integrative transcriptomic and HS-SPME-GC-MS analysis reveals the influence mechanism of different altitude ecotypes on pulp aroma components and volatile metabolites in strawberry hybrid F1 and its parents

Strawberry (Fragaria × ananassa) is an important horticultural crop and is highly nutritious and valuable. However, several molecular mechanisms on the biosynthesis and metabolism of aroma compounds and the regulatory network that governs aromas remain unknown. This study investigated the influence of different altitude ecotypes on the components of pulp aroma and volatile metabolites in strawberry hybrid F1 and its parents. "Perilla alcohol" was found to be the major factor that regulated the aroma of strawberry pulp from plants at low altitudes, and "perilla alcohol, linalool, alpha-farnesene and E-2-hexenyl benzoate" were the major factors that regulated the aroma of strawberry pulp from plants at high altitudes. Furthermore, three key candidate genes were identified according to the criteria of |K.i| > 40 and |MM| > 0.90. This study will establish a theoretical foundation for the cultivation of novel varieties of strawberries characterized by superior quality and flavor.

Uncovering fruit flavor and genetic diversity across diploid wild Fragaria species via comparative metabolomics profiling

Wild Fragaria resources exhibit extensive genetic diversity and desirable edible traits, such as high soluble solid content and flavor compounds. However, specific metabolites in different wild strawberry fruits remain unknown. In this study, we characterized 1008 metabolites covering 11 subclasses among 13 wild diploid resources representing eight species, including F. vesca, F. nilgerrensis, F. viridis, F. nubicola, F. pentaphylla, F. mandschurica, F. chinensis, and F. emeiensis. Fifteen potential metabolite biomarkers were identified to distinguish fruit flavors among the 13 diploid wild Fragaria accessions. A total of nine distinct modules were employed to explore key metabolites related to fruit quality through weighted gene co-expression module analysis, with significant enrichment in amino acid biosynthesis pathway. Notably, the identified significantly different key metabolites highlighted the close association of amino acids, sugars, and anthocyanins with flavor formation. These findings offer valuable resources for improving fruit quality through metabolome-assisted breeding.

Chemical and Thermal Characteristics of PEF-Pretreated Strawberries Dried by Various Methods

By increasing the permeability of the cell membrane of the treated material, pulsed electric fields (PEF) enhance the internal transport of various chemical substances. Changing the distribution of these components can modify the chemical and thermal properties of the given material. This study aimed to analyze the impact of PEF (1 kV/cm; 1 and 4 kJ/kg) applied to strawberries prior to drying by various methods (convective, infrared-convective, microwave-convective, and vacuum) on the chemical and thermal properties of the obtained dried materials (sugars content, total phenolic content, and antioxidant capacity (ABTS and DPPH assays); thermal properties (TGA and DSC); and molecular composition (FTIR)). PEF could have induced and/or enhanced sucrose inversion because, compared to untreated samples, PEF-pretreated samples were characterized by a lower share of sucrose in the total sugar content but a higher share of glucose and fructose. Reduced exposure to oxygen and decreased drying temperature during vacuum drying led to obtaining dried strawberries with the highest content of antioxidant compounds, which are sensitive to these factors. All PEF-pretreated dried strawberries exhibited a lower glass transition temperature (Tg) than the untreated samples, which confirms the increased mobility of the system after the application of an electric field.

Fractionation of metals in soil for strawberry cultivation: Effect on metal migration in food chain and application in risk assessment

Although trace metals in strawberry production system have attracted growing attention, little is known about metal fractionation in soil for strawberry cultivation. We hypothesized that the metal fractions in soil influenced by strawberry production had significant effect on food chain transport of metals and their risk in soil. Here, samples of strawberries and soil were gathered in the Yangtze River Delta, China to verify the hypothesis. Results showed that the acid-soluble Cr, Cd, and Ni in soil for strawberry cultivation were 21.5%-88.3% higher than those in open field soil, which enhanced uptake and bioaccessible levels of these metals in strawberries. Overall, the ecological, mobility, and health risks of Pb, Zn, Ni, and Cu in soil were at a low level. However, the ecological risk of bioavailable Cd, mobility risk of Cd, and cancer risk of bioavailable Cr in over 70% of the soil samples were at moderate, high, and acceptable levels, respectively. Since the increased acid-soluble Cr and Ni in soil were related to soil acidification induced by strawberry production, nitrogen fertilizer application should be optimized to prevent soil acidification and reduce transfer of Cr and Ni. Additionally, as Cd and organic matter accumulated in soil, the acid-soluble Cd and the ecological and mobility risks of Cd in soil were enhanced. To decrease transfer and risk of Cd in soil, organic fertilizer application should be optimized to mitigate Cd accumulation, alter organic matter composition, and subsequently promote the transformation of bioavailable Cd into residual Cd in soil.

Development and Comparison of Visual LAMP and LAMP-TaqMan Assays for Colletotrichum siamense

Strawberry anthracnose caused by Colletotrichum spp. has resulted in significant losses in strawberry production worldwide. Strawberry anthracnose occurs mainly at the seedling and early planting stages, and Colletotrichum siamense is the main pathogen in North China, where mycelia, anamorphic nuclei, and conidia produced in the soil are the main sources of infection. The detection of pathogens in soil is crucial for predicting the prevalence of anthracnose. In this study, a visualized loop-mediated isothermal amplification (LAMP) assay and a loop-mediated isothermal amplification method combined with a TaqMan probe (LAMP-TaqMan) assay were developed for the β-tubulin sequence of C. siamense. Both methods can detect Colletotrichum siamense genomic DNA at very low concentrations (104 copies/g) in soil, while both the visualized LAMP and LAMP-TaqMan assays exhibited a detection limit of 50 copies/μL, surpassing the sensitivity of conventional PCR and qPCR techniques, and both methods showed high specificity for C. siamense. The two methods were compared: LAMP-TaqMan exhibited enhanced specificity due to the incorporation of fluorescent molecular beacons, while visualized LAMP solely necessitated uncomplicated incubation at a constant temperature, with the results determined by the color change; therefore, the requirements for the instrument are relatively straightforward and user-friendly. In conclusion, both assays will help monitor populations of C. siamense in China and control strawberry anthracnose in the field.

Advances in genomics and genome editing for improving strawberry (Fragaria ×ananassa)

The cultivated strawberry, Fragaria ×ananassa, is a recently domesticated fruit species of economic interest worldwide. As such, there is significant interest in continuous varietal improvement. Genomics-assisted improvement, including the use of DNA markers and genomic selection have facilitated significant improvements of numerous key traits during strawberry breeding. CRISPR/Cas-mediated genome editing allows targeted mutations and precision nucleotide substitutions in the target genome, revolutionizing functional genomics and crop improvement. Genome editing is beginning to gain traction in the more challenging polyploid crops, including allo-octoploid strawberry. The release of high-quality reference genomes and comprehensive subgenome-specific genotyping and gene expression profiling data in octoploid strawberry will lead to a surge in trait discovery and modification by using CRISPR/Cas. Genome editing has already been successfully applied for modification of several strawberry genes, including anthocyanin content, fruit firmness and tolerance to post-harvest disease. However, reports on many other important breeding characteristics associated with fruit quality and production are still lacking, indicating a need for streamlined genome editing approaches and tools in Fragaria ×ananassa. In this review, we present an overview of the latest advancements in knowledge and breeding efforts involving CRISPR/Cas genome editing for the enhancement of strawberry varieties. Furthermore, we explore potential applications of this technology for improving other Rosaceous plant species.

Biostimulatory Effects of Chlorella fusca CHK0059 on Plant Growth and Fruit Quality of Strawberry

Green algae have been receiving widespread attention for their use as biofertilizers for agricultural production, but more studies are required to increase the efficiency of their use. This study aimed to investigate the effects of different levels of Chlorella fusca CHK0059 application on strawberry plant growth and fruit quality. A total of 800 strawberry seedlings were planted in a greenhouse and were grown for seven months under different Chlorella application rates: 0 (control), 0.1, 0.2, and 0.4% of the optimal cell density (OCD; 1.0 × 107 cells mL-1). The Chlorella application was conducted weekly via an irrigation system, and the characteristics of fruit samples were monitored monthly over a period of five months. The growth (e.g., phenotype, dry weight, and nutrition) and physiological (e.g., Fv/Fm and chlorophylls) parameters of strawberry plants appeared to be enhanced by Chlorella application over time, an enhancement which became greater as the application rate increased. Likewise, the hardness and P content of strawberry fruits had a similar trend. Meanwhile, 0.2% OCD treatment induced the highest values of soluble solid content (9.3-12 °Brix) and sucrose content (2.06-2.97 g 100 g-1) in the fruits as well as fruit flavor quality indices (e.g., sugars:acids ratio and sweetness index) during the monitoring, whilst control treatment represented the lowest values. In addition, the highest anthocyanin content in fruits was observed in 0.4% OCD treatment, which induced the lowest incidence of grey mold disease (Botrytis cinerea) on postharvest fruits for 45 days. Moreover, a high correlation between plants' nutrients and photosynthetic variables and fruits' sucrose and anthocyanin contents was identified through the results of principal component analysis. Overall, C. fusca CHK0059 application was found to promote the overall growth and performance of strawberry plants, contributing to the improvement of strawberry quality and yield, especially in 0.2% OCD treatment.

Rosaceae fruit transcriptome database (ROFT)-a useful genomic resource for comparing fruits of apple, peach, strawberry, and raspberry

Rosaceae is a large plant family consisting of many economically important fruit crops including peach, apple, pear, strawberry, raspberry, plum, and others. Investigations into their growth and development will promote both basic understanding and progress toward increasing fruit yield and quality. With the ever-increasing high-throughput sequencing data of Rosaceae, comparative studies are hindered by inconsistency of sample collection with regard to tissue, stage, growth conditions, and by vastly different handling of the data. Therefore, databases that enable easy access and effective utilization of directly comparable transcript data are highly desirable. Here, we describe a database for comparative analysis, ROsaceae Fruit Transcriptome database (ROFT), based on RNA-seq data generated from the same laboratory using similarly dissected and staged fruit tissues of four important Rosaceae fruit crops: apple, peach, strawberry, and red raspberry. Hence, the database is unique in allowing easy and robust comparisons among fruit gene expression across the four species. ROFT enables researchers to query orthologous genes and their expression patterns during different fruit developmental stages in the four species, identify tissue-specific and tissue-/stage-specific genes, visualize and compare ortholog expression in different fruit types, explore consensus co-expression networks, and download different data types. The database provides users access to vast amounts of RNA-seq data across the four economically important fruits, enables investigations of fruit type specification and evolution, and facilitates the selection of genes with critical roles in fruit development for further studies.

The red/far-red light photoreceptor FvePhyB regulates tissue elongation and anthocyanin accumulation in woodland strawberry

Light is an important environmental signal that influences plant growth and development. Among the photoreceptors, phytochromes can sense red/far-red light to coordinate various biological processes. However, their functions in strawberry are not yet known. In this study, we identified an EMS mutant, named P8, in woodland strawberry (Fragaria vesca) that showed greatly increased plant height and reduced anthocyanin content. Mapping-by-sequencing revealed that the causal mutation in FvePhyB leads to premature termination of translation. The light treatment assay revealed that FvePhyB is a bona fide red/far-red light photoreceptor, as it specifically inhibits hypocotyl length under red light. Transcriptome analysis showed that the FvePhyB mutation affects the expression levels of genes involved in hormone synthesis and signaling and anthocyanin biosynthesis in petioles and fruits. The srl mutant with a longer internode is caused by a mutation in the DELLA gene FveRGA1 (Repressor of GA1) in the gibberellin pathway. We found that the P8 srl double mutant has much longer internodes than srl, suggesting a synergistic role of FvePhyB and FveRGA1 in this process. Taken together, these results demonstrate the important role of FvePhyB in regulating plant architecture and anthocyanin content in woodland strawberry.