The potassium channel FaTPK1 plays a critical role in fruit quality formation in strawberry (Fragaria × ananassa)

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.

Investigation of two-pore K+ (TPK) channels in Triticum aestivum L. suggests their role in stress response

Two-pore K+ (TPK) channels are voltage-independent and involved in stress response in plants. Herein, we identified 12 TaTPK genes located on nine chromosomes in the Triticum aestivum genome. The majority of TaTPK genes comprised two exons. Each TaTPK channel comprised four transmembrane (TM) helices, N- and C-terminal ion-channel domains, two EF-hand domains and one 14-3-3 binding site. Additionally, highly conserved 'GYGD' motif responsible for K+ ion specificity, was found in between the TMs in both the ion-channel domains. Nine TaTPK channels were predicted to be localised at the plasma membrane, while three were vacuolar. The protein-protein and protein-chemical interactions indicated the coordinated functioning of the TaTPK channels with the other K+ transporters and their possible interaction with the Ca2+-signaling pathway. Expression studies suggested their importance in both vegetative and reproductive tissues development. Significantly modulated expression of various TaTPK genes during heat, drought, combined heat and drought and salt stresses, and after fungal infestation, depicted their function in stress responses. The miRNAs and transcription factors interaction analyses suggested their role in the hormone, light, growth and development-related, and stress-responsive signaling cascades. The current study suggested vital functions of various TaTPK genes, especially in stress response, and would provide an opportunity for their detailed characterization in future studies.

Genome-wide identification and expression analysis of the glutamate receptor gene family in sweet potato and its two diploid relatives

Plant glutamate receptor (GLR) homologs are crucial calcium channels that play an important role in plant development, signal transduction, and response to biotic and abiotic stresses. However, the GLR gene family has not yet been thoroughly and systematically studied in sweet potato. In this study, a total of 37 GLR genes were identified in the cultivated hexaploid sweet potato (Ipomoea batatas), and 32 GLR genes were discovered in each of the two diploid relatives (Ipomoea trifida and Ipomoea triloba) for the first time. Based on their evolutionary relationships to those of Arabidopsis, these GLRs were split into five subgroups. We then conducted comprehensive analysis to explore their physiological properties, protein interaction networks, promoter cis-elements, chromosomal placement, gene structure, and expression patterns. The results indicate that the homologous GLRs of the cultivated hexaploid sweet potato and its two relatives are different. These variations are reflected in their functions related to plant growth, hormonal crosstalk, development of tuberous roots, resistance to root rot, and responses to abiotic stress factors, all of which are governed by specific individual GLR genes. This study offers a comprehensive analysis of GLR genes in sweet potato and its two diploid relatives. It also provides a theoretical basis for future research into their regulatory mechanisms, significantly influencing the field of molecular breeding in sweet potatoes.

The role of WRKY transcription factors, FaWRKY29 and FaWRKY64, for regulating Botrytis fruit rot resistance in strawberry (Fragaria × ananassa Duch.)

BACKGROUND

The cultivated strawberry (Fragaria × ananassa Duch.) is one of the most economically important horticultural crops worldwide. Botrytis fruit rot (BFR) caused by the necrotrophic fungal pathogen Botrytis cinerea is the most devasting disease of cultivated strawberries. Most commercially grown strawberry varieties are susceptible to BFR, and controlling BFR relies on repeated applications of various fungicides. Despite extensive efforts, breeding for BFR resistance has been unsuccessful, primarily due to lack of information regarding the mechanisms of disease resistance and genetic resources available in strawberry.

RESULTS

Using a reverse genetics approach, we identified candidate genes associated with BFR resistance and screened Arabidopsis mutants using strawberry isolates of B. cinerea. Among the five Arabidopsis T-DNA knockout lines tested, the mutant line with AtWRKY53 showed the greatest reduction in disease symptoms of BFR against the pathogen. Two genes, FaWRKY29 and FaWRKY64, were identified as orthologs in the latest octoploid strawberry genome, 'Florida Brilliance'. We performed RNAi-mediated transient assay and found that the disease frequencies were significantly decreased in both FaWRKY29- and FaWRKY64-RNAi fruits of the strawberry cultivar, 'Florida Brilliance'. Furthermore, our transcriptomic data analysis revealed significant regulation of genes associated with ABA and JA signaling, plant cell wall composition, and ROS in FaWRKY29 or FaWRKY64 knockdown strawberry fruits in response to the pathogen.

CONCLUSION

Our study uncovered the foundational role of WRKY transcription factor genes, FaWRKY29 and FaWRKY64, in conferring resistance against B. cinerea. The discovery of susceptibility genes involved in BFR presents significant potential for developing resistance breeding strategies in cultivated strawberries, potentially leveraging CRISPR-based gene editing techniques.

Recent updates on the physiology and evolution of plant TPK/KCO channels

Plant vacuoles are the main cellular reservoirs to store K+ . The vacuolar K+ channels play a pivotal role in K+ exchange between cytosol and vacuolar sap. Among vacuolar K+ transporters, the Two Pore Potassium Channels (TPKs) are highly selective K+ channels present in most or all plant vacuoles and could be involved in various plant stress responses and developmental processes. Although the majority of TPK members have a vacuolar specialisation, some TPKs display different membrane localisation including the plasma membrane, tonoplast of protein storage vacuoles and probably chloroplast membranes. The functional properties as well as physiological roles of TPKs remains largely unexplored. In this review, we have collected recent data about the physiology, structure, functionality and evolution of TPK/KCO3 channels. We also critically evaluate the latest findings on the biological role, physiological functions, and regulation of TPK/KCO3 channels in relation to their structure and phylogenetic position. The possible role of TPK/KCO3 channels in plant tolerance to various abiotic stresses is summarised, and the future priority directions for TPK/KCO3 studies are addressed.

Genomic & structural diversity and functional role of potassium (K+) transport proteins in plants

Potassium (K⁺) is an essential macronutrient for plant growth and productivity. It is the most abundant cation in plants and is involved in various cellular processes. Variable K⁺ availability is sensed by plant roots, consequently K⁺ transport proteins are activated to optimize K⁺ uptake. In addition to K⁺ uptake and translocation these proteins are involved in other important physiological processes like transmembrane voltage regulation, polar auxin transport, maintenance of Na⁺/K⁺ ratio and stomata movement during abiotic stress responses. K⁺ transport proteins display tremendous genomic and structural diversity in plants. Their key structural features, such as transmembrane domains, N-terminal domains, C-terminal domains and loops determine their ability of K⁺ uptake and transport and thus, provide functional diversity. Most K⁺ transporters are regulated at transcriptional and post-translational levels. Genetic manipulation of key K⁺ transporters/channels could be a prominent strategy for improving K⁺ utilization efficiency (KUE) in plants. This review discusses the genomic and structural diversity of various K⁺ transport proteins in plants. Also, an update on the function of K⁺ transport proteins and their regulatory mechanism in response to variable K⁺ availability, in improving KUE, biotic and abiotic stresses is provided.

Ethylene-induced potassium transporter AcKUP2 gene is involved in kiwifruit postharvest ripening

BACKGROUND

Potassium (K) is important in the regulation of plant growth and development. It is the most abundant mineral element in kiwifruit, and its content increases during fruit ripening. However, how K⁺ transporter works in kiwifruit postharvest maturation is not yet clear.

RESULTS

Here, 12 K⁺ transporter KT/HAK/KUP genes, AcKUP1 ~ AcKUP12, were isolated from kiwifruit, and their phylogeny, genomic structure, chromosomal location, protein properties, conserved motifs and cis-acting elements were analysed. Transcription analysis revealed that AcKUP2 expression increased rapidly and was maintained at a high level during postharvest maturation, consistent with the trend of K content; AcKUP2 expression was induced by ethylene, suggesting that AcKUP2 might play a role in ripening. Fluorescence microscopy showed that AcKUP2 is localised in the plasma membrane. Cis-elements, including DER or ethylene response element (ERE) responsive to ethylene, were found in the AcKUP2 promoter sequence, and ethylene significantly enhanced the AcKUP2 promoter activity. Furthermore, we verified that AcERF15, an ethylene response factor, directly binds to the AcKUP2 promoter to promote its expression. Thus, AcKUP2 may be an important potassium transporter gene which involved in ethylene-regulated kiwifruit postharvest ripening.

CONCLUSIONS

Therefore, our study establishes the first genome-wide analysis of the kiwifruit KT/HAK/KUP gene family and provides valuable information for understanding the function of the KT/HAK/KUP genes in kiwifruit postharvest ripening.

Insights into sugar metabolism during bilberry (Vaccinium myrtillus L.) fruit development

Bilberry fruit is regarded as one of the best natural sources of anthocyanins and is widely explored for its health-beneficial compounds. Besides anthocyanins, one of the major attributes that determine the berry quality is the accumulation of sugars that provide sweetness and flavor to ripening fruit. In this study, we have identified 25 sugar metabolism-related genes in bilberry, including invertases (INVs), hexokinases (HKs), fructokinases (FKs), sucrose synthases (SSs), sucrose phosphate synthases (SPSs), and sucrose phosphate phosphatases (SPPs). The results indicate that isoforms of the identified genes are expressed differentially during berry development, suggesting specialized functions. The highest sugar content was found in ripe berries, with fructose and glucose dominating accompanied by low sucrose amount. The related enzyme activities during berry development and ripening were further analyzed to understand the molecular mechanism of sugar accumulation. The activity of INVs in the cell wall and vacuole increased toward ripe berries. Amylase activity involved in starch metabolism was not detected in unripe berries but was found in ripe berries. Sucrose resynthesizing SS enzyme activity was detected upon early ripening and had the highest activity in ripe berries. Interestingly, our transcriptome data showed that supplemental irradiation with red and blue light triggered upregulation of several sugar metabolism-related genes, including α- and β-amylases. Also, differential expression patterns in responses to red and blue light were found across sucrose, galactose, and sugar-alcohol metabolism. Our enzymological and transcriptional data provide new understanding of the bilberry fruit sugar metabolism having major effect on fruit quality.

Impact of Potassium Pre-Harvest Applications on Fruit Quality and Condition of Sweet Cherry (Prunus avium L.) Cultivated under Plastic Covers in Southern Chile Orchards

In rainy locations, sweet cherry is cultivated under plastic covers, which are useful to prevent fruit cracking but decrease cherry quality such as firmness and acidity. Here we evaluate the impact of pre-harvest K foliar applications on harvest and post-harvest fruit quality and condition of sweet cherry cultivated under plastic covers in southern Chile orchards. The study was performed on two commercial orchards (cv. Regina), located in different regions, during two consecutive seasons. In all cases, a conventional K regime (four sprays) was compared to an intensive K regimen (seven sprays). Results showed that cherries from the most southern region revealed lower acidity but higher soluble solids content weight and size. The intensive K regime improved the firmness and acidity of fruits of covered trees at harvest and post-harvest. Moreover, we found that condition defects were higher in fruits from un-covered trees and that trees grown under intensive K regime showed lower levels of cracking at harvest and pitting at post-harvest compared to trees treated with the conventional K regime. Otherwise, pedicel browning was inconsistently affected by K sprays. Our results revealed that an intensive K regime could improve the quality and condition of fruits at harvest and post-harvest in covered orchards of sweet cherry cv. Regina; however, the impacts can significantly vary depending on season and locality.

Recent Advances in Genome-wide Analyses of Plant Potassium Transporter Families

Plants require potassium (K⁺) as a macronutrient to support numerous physiological processes. Understanding how this nutrient is transported, stored, and utilized within plants is crucial for breeding crops with high K⁺ use efficiency. As K⁺ is not metabolized, cross-membrane transport becomes a rate-limiting step for efficient distribution and utilization in plants. Several K⁺ transporter families, such as KUP/HAK/KT and KEA transporters and Shaker-like and TPK channels, play dominant roles in plant K⁺ transport processes. In this review, we provide a comprehensive contemporary overview of our knowledge about these K⁺ transporter families in angiosperms, with a major focus on the genome-wide identification of K⁺ transporter families, subcellular localization, spatial expression, function and regulation. We also expanded the genome-wide search for the K⁺ transporter genes and examined their tissue-specific expression in Camelina sativa, a polyploid oil-seed crop with a potential to adapt to marginal lands for biofuel purposes and contribution to sustainable agriculture. In addition, we present new insights and emphasis on the study of K⁺ transporters in polyploids in an effort to generate crops with high K⁺ Utilization Efficiency (KUE).

Resveratrol Alleviates the KCl Salinity Stress of Malus hupehensis Rhed

Applying large amounts of potash fertilizer in apple orchards for high apple quality and yield aggravates KCl stress. As a phytoalexin, resveratrol (Res) participates in plant resistance to biotic stress. However, its role in relation to KCl stress has never been reported. Herein we investigated the role of Res in KCl stress response of Malus hupehensis Rehd., a widely used apple rootstock in China which is sensitive to KCl stress. KCl-stressed apple seedlings showed significant wilting phenotype and decline in photosynthetic rate, and the application of 100 μmol Res alleviated KCl stress and maintained photosynthetic capacity. Exogenous Res can strengthen the activities of peroxidase and catalase, thus eliminating reactive oxygen species production induced by KCl stress. Moreover, exogenous Res can decrease the electrolyte leakage by accumulating proline for osmotic balance under KCl stress. Furthermore, exogenous Res application can affect K⁺/Na⁺ homeostasis in cytoplasm by enhancing K⁺ efflux outside the cells, inhibiting Na⁺ efflux and K⁺ absorption, and compartmentalizing K⁺ into vacuoles through regulating the expression of K⁺ and Na⁺ transporter genes. These findings provide a theoretical basis for the application of exogenous Res to relieve the KCl stress of apples.

RNA-Seq Provides New Insights into the Molecular Events Involved in "Ball-Skin versus Bladder Effect" on Fruit Cracking in Litchi

Fruit cracking is a disorder of fruit development in response to internal or external cues, which causes a loss in the economic value of fruit. Therefore, exploring the mechanism underlying fruit cracking is of great significance to increase the economic yield of fruit trees. However, the molecular mechanism underlying fruit cracking is still poorly understood. Litchi, as an important tropical and subtropical fruit crop, contributes significantly to the gross agricultural product in Southeast Asia. One important agricultural concern in the litchi industry is that some famous varieties with high economic value such as ‘Nuomici’ are susceptible to fruit cracking. Here, the cracking-susceptible cultivar ‘Nuomici’ and cracking-resistant cultivar ‘Huaizhi’ were selected, and the samples including pericarp and aril during fruit development and cracking were collected for RNA-Seq analysis. Based on weighted gene co-expression network analysis (WGCNA) and the “ball-skin versus bladder effect” theory (fruit cracking occurs upon the aril expanding pressure exceeds the pericarp strength), it was found that seven co-expression modules genes (1733 candidate genes) were closely associated with fruit cracking in ‘Nuomici’. Importantly, we propose that the low expression level of genes related to plant hormones (Auxin, Gibberellins, Ethylene), transcription factors, calcium transport and signaling, and lipid synthesis might decrease the mechanical strength of pericarp in ‘Nuomici’, while high expression level of genes associated with plant hormones (Auxin and abscisic acid), transcription factors, starch/sucrose metabolism, and sugar/water transport might increase the aril expanding pressure, thereby resulting in fruit cracking in ‘Nuomici’. In conclusion, our results provide comprehensive molecular events involved in the “ball-skin versus bladder effect” on fruit cracking in litchi.

Advances in Mineral Nutrition Transport and Signal Transduction in Rosaceae Fruit Quality and Postharvest Storage

Mineral nutrition, taken up from the soil or foliar sprayed, plays fundamental roles in plant growth and development. Among of at least 14 mineral elements, the macronutrients nitrogen (N), potassium (K), phosphorus (P), and calcium (Ca) and the micronutrient iron (Fe) are essential to Rosaceae fruit yield and quality. Deficiencies in minerals strongly affect metabolism with subsequent impacts on the growth and development of fruit trees. This ultimately affects the yield, nutritional value, and quality of fruit. Especially, the main reason of the postharvest storage loss caused by physiological disorders is the improper proportion of mineral nutrient elements. In recent years, many important mineral transport proteins and their regulatory components are increasingly revealed, which make drastic progress in understanding the molecular mechanisms for mineral nutrition (N, P, K, Ca, and Fe) in various aspects including plant growth, fruit development, quality, nutrition, and postharvest storage. Importantly, many studies have found that mineral nutrition, such as N, P, and Fe, not only affects fruit quality directly but also influences the absorption and the content of other nutrient elements. In this review, we provide insights of the mineral nutrients into their function, transport, signal transduction associated with Rosaceae fruit quality, and postharvest storage at physiological and molecular levels. These studies will contribute to provide theoretical basis to improve fertilizer efficient utilization and fruit industry sustainable development.

Elucidating the role of polygalacturonase genes in strawberry fruit softening

To disentangle the role of polygalacturonase (PG) genes in strawberry softening, the two PG genes most expressed in ripe receptacles, FaPG1 and FaPG2, were down-regulated. Transgenic ripe fruits were firmer than those of the wild type when PG genes were silenced individually. Simultaneous silencing of both PG genes by transgene stacking did not result in an additional increase in firmness. Cell walls from ripe fruits were characterized by a carbohydrate microarray. Higher signals of homogalacturonan and rhamnogalacturonan I pectin epitopes in polysaccharide fractions tightly bound to the cell wall were observed in the transgenic genotypes, suggesting a lower pectin solubilization. At the transcriptomic level, the suppression of FaPG1 or FaPG2 alone induced few transcriptomic changes in the ripe receptacle, but the amount of differentially expressed genes increased notably when both genes were silenced. Many genes encoding cell wall-modifying enzymes were down-regulated. The expression of a putative high affinity potassium transporter was induced in all transgenic genotypes, indicating that cell wall weakening and loss of cell turgor could be linked. These results suggest that, besides the disassembly of pectins tightly linked to the cell wall, PGs could play other roles in strawberry softening, such as the release of oligogalacturonides exerting a positive feedback in softening.

FaPAO5 regulates Spm/Spd levels as a signaling during strawberry fruit ripening

Polyamines are important for non-climacteric fruit ripening according to an analysis of the model plant strawberry. However, the molecular mechanism underlying the polyamine accumulation during ripening has not been fully elucidated. In this study, an examination of our proteome data related to strawberry fruit ripening revealed a putative polyamine oxidase 5, FaPAO5, which was localized in the cytoplasm and nucleus. Additionally, FaPAO5 expression levels as well as the abundance of the encoded protein continually decreased during ripening. Inhibiting FaPAO5 expression by RNAi promoted Spd, Spm, and ABA accumulation while inhibited H2O2 production, which ultimately enhanced ripening as evidenced by the ripening-related events and corresponding gene expression changes. The opposite effects were observed in FaPAO5-overexpressing transgenic fruits. Analyses of the binding affinity and enzymatic activity of FaPAO5 with Spm, Spd, and Put uncovered a special role for FaPAO5 in the terminal catabolism of Spm and Spd, with a K d of 0.21 and 0.29 µM, respectively. Moreover, FaPAO5 expression was inhibited by ABA and promoted by Spd and Spm. Furthermore, the RNA-seq analysis of RNAi and control fruits via differentially expressed genes (DEGs) indicated the six most enriched pathways among the differentially expressed genes were related to sugar, abscisic acid, ethylene, auxin, gibberellin, and Ca2+. Among four putative PAO genes in the strawberry genome, only FaPAO5 was confirmed to influence fruit ripening. In conclusion, FaPAO5 is a negative regulator of strawberry fruit ripening and modulates Spm/Spd levels as a signaling event, in which ABA plays a central role.

Strawberry tonoplast transporter, FaVPT1, controls phosphate accumulation and fruit quality

Phosphorus (P) is essential for plant growth and development, and the vacuole is an important organelle for phosphate storage. However, the tonoplast phosphate transporter in fleshy fruits remains unknown. In this study, based on the strawberry (Fragaria × ananassa) fruit transcriptome data, a tonoplast-localized vacuolar phosphate transporter with SPX and major facilitator superfamily domains, FaVPT1, was identified. FaVPT1 expression was highest in the fruits and could be induced by sucrose. Using transient transgenic systems in strawberry fruit, the downregulation and upregulation of FaVPT1 inhibited and promoted ripening, respectively, and affected phosphate contents, fruit firmness, sugar and anthocyanin contents, and ripening-related gene transcription. FaVPT1 could rescue Pi absorption in both yeast and the Arabidopsis atvpt1 mutant, confirming the similar function of FaVPT1 and AtVPT1, a previously identified tonoplast phosphate transporter in Arabidopsis. The Escherichia coli-expressed SPX domain of FaVPT1 could strongly bind to InsP₆ with a K_d of 3.5 μM. The results demonstrate that FaVPT1 is a tonoplast phosphate transporter and regulates strawberry fruit ripening and quality, to a large extent, via sucrose.

GhNAC83 inhibits corm dormancy release by regulating ABA signaling and cytokinin biosynthesis in Gladiolus hybridus

Corm dormancy is an important trait for breeding in many bulb flowers, including the most cultivated Gladiolus hybridus. Gladiolus corms are modified underground stems that function as storage organs and remain dormant to survive adverse environmental conditions. Unlike seed dormancy, not much is known about corm dormancy. Here, we characterize the mechanism of corm dormancy release (CDR) in Gladiolus. We identified an important ABA (abscisic acid) signaling regulator, GhPP2C1 (protein phosphatase 2C1), by transcriptome analysis of CDR. GhPP2C1 expression increased during CDR, and silencing of GhPP2C1 expression in dormant cormels delayed CDR. Furthermore, we show that GhPP2C1 expression is directly regulated by GhNAC83, which was identified by yeast one-hybrid library screening. In planta assays show that GhNAC83 is a negative regulator of GhPP2C1, and silencing of GhNAC83 promoted CDR. As expected, silencing of GhNAC83 decreased the ABA level, but also dramatically increased cytokinin (CK; zeatin) content in cormels. Binding assays demonstrate that GhNAC83 associates with the GhIPT (ISOPENTENYLTRANSFERASE) promoter and negatively regulates zeatin biosynthesis. Taken together, our results reveal that GhNAC83 promotes ABA signaling and synthesis, and inhibits CK biosynthesis pathways, thereby inhibiting CDR. These findings demonstrate that GhNAC83 regulates the ABA and CK pathways, and therefore controls corm dormancy.

An ETHYLENE RESPONSE FACTOR-MYB Transcription Complex Regulates Furaneol Biosynthesis by Activating QUINONE OXIDOREDUCTASE Expression in Strawberry

4-Hydroxy-2,5-dimethyl-3(2H)-furanone is a major contributor to the aroma of strawberry (Fragaria × ananassa) fruit, and the last step in its biosynthesis is catalyzed by strawberry quinone oxidoreductase (FaQR). Here, an ethylene response factor (FaERF#9) was characterized as a positive regulator of the FaQR promoter. Linear regression analysis indicated that FaERF#9 transcript levels were correlated significantly with both FaQR transcripts and furanone content in different strawberry cultivars. Transient overexpression of FaERF#9 in strawberry fruit significantly increased FaQR expression and furaneol production. Yeast one-hybrid assays, however, indicated that FaERF#9 by itself did not bind to the FaQR promoter. An MYB transcription factor (FaMYB98) identified in yeast one-hybrid screening of the strawberry cDNA library was capable of both binding to the promoter and activating the transcription of FaQR by ∼5.6-fold. Yeast two-hybrid assay and bimolecular fluorescence complementation confirmed a direct protein-protein interaction between FaERF#9 and FaMYB98, and in combination, they activated the FaQR promoter 14-fold in transactivation assays. These results indicate that an ERF-MYB complex containing FaERF#9 and FaMYB98 activates the FaQR promoter and up-regulates 4-hydroxy-2,5-dimethyl-3(2H)-furanone biosynthesis in strawberry.