Abscisic acid plays an important role in the regulation of strawberry fruit ripening

Unraveling the key step in the aroma puzzle: Insights into alcohol acyltransferases in strawberries

Alcohol acyltransferases (AATs) play a crucial role in catalyzing the transfer of acyl groups, contributing to the diverse aroma of fruits, including strawberries. In this research we identified nine AAT genes in strawberries through a comprehensive analysis involving phylogenetics, gene structure, conserved motifs, and structural protein model examinations. The study used the 'Camarosa' strawberry genome database, and experiments were conducted with fruits harvested at different developmental and ripening stages. The transcriptional analysis revealed differential expression patterns among the AAT genes during fruit ripening, with only four genes (SAAT, FaAAT2, FaAAT7, and FaAAT9) showing increased transcript accumulation correlated with total AAT enzyme activity. Additionally, the study employed in silico methods, including sequence alignment, phylogenetic analysis, and structural modeling, to gain insights into the AAT protein model structures with increase expression pattern during fruit ripening. The four modeled AAT proteins exhibited structural similarities, including conserved catalytic sites and solvent channels. Furthermore, the research investigated the interaction of AAT proteins with different substrates, highlighting the enzymes' promiscuity in substrate preferences. The study contributes with valuable information to unveil AAT gene family members in strawberries, providing scientific background for further exploration of their biological characteristics and their role in aroma biosynthesis during fruit ripening.

DNA methylation controlling abscisic acid catabolism responds to light to mediate strawberry fruit ripening

Phytohormones, epigenetic regulation and environmental factors regulate fruit ripening but their interplay during strawberry fruit ripening remains to be determined. In this study, bagged strawberry fruit exhibited delayed ripening compared with fruit grown in normal light, correlating with reduced abscisic acid (ABA) accumulation. Transcription of the key ABA catabolism gene, ABA 8'-hydroxylase FaCYP707A4, was induced in bagged fruit. With light exclusion whole genome DNA methylation levels were up-regulated, corresponding to a delayed ripening process, while DNA methylation levels in the promoter of FaCYP707A4 were suppressed, correlating with increases in transcript and decreased ABA content. Experiments indicated FaCRY1, a blue light receptor repressed in bagged fruit and FaAGO4, a key protein involved in RNA-directed DNA methylation, could bind to the promoter of FaCYP707A4. The interaction between FaCRY1 and FaAGO4, and an increased enrichment of FaAGO4 directed to the FaCYP707A4 promoter in fruit grown under light suggests FaCRY1 may influence FaAGO4 to modulate the DNA methylation status of the FaCYP707A4 promoter. Furthermore, transient overexpression of FaCRY1, or an increase in FaCRY1 transcription by blue light treatment, increases the methylation level of the FaCYP707A4 promoter, while transient RNA interference of FaCRY1 displayed opposite phenotypes. These findings reveal a mechanism by which DNA methylation influences ABA catabolism, and participates in light-mediated strawberry ripening.

A 5.2-kb insertion in the coding sequence of PavSCPL, a serine carboxypeptidase-like enhances fruit firmness in Prunus avium

Fruit firmness is an important trait in sweet cherry breeding because it directly positively influences fruit transportability, storage and shelf life. However, the underlying genes responsible and the molecular mechanisms that control fruit firmness remain unknown. In this study, we identified a candidate gene, PavSCPL, encoding a serine carboxypeptidase-like protein with natural allelic variation, that controls fruit firmness in sweet cherry using map-based cloning and functionally characterized PavSCPL during sweet cherry fruit softening. Genetic analysis revealed that fruit firmness in the 'Rainier' × 'Summit' F1 population was controlled by a single dominant gene. Bulked segregant analysis combined with fine mapping narrowed the candidate gene to a 473-kb region (7418778-7 891 914 bp) on chromosome 6 which included 72 genes. The candidate gene PavSCPL, and a null allele harbouring a 5244-bp insertion in the second exon that completely inactivated PavSCPL expression and resulted in the extra-hard-flesh phenotype, were identified by RNA-sequencing analysis and gene cloning. Quantitative RT-PCR analysis revealed that the PavSCPL expression level was increased with fruit softening. Virus-induced gene silencing of PavSCPL enhanced fruit firmness and suppressed the activities of certain pectin-degrading enzymes in the fruit. In addition, we developed functional molecular markers for PavSCPL and the Pavscpl5.2-k allele that co-segregated with the fruit firmness trait. Overall, this research identified a crucial functional gene for fruit firmness. The results provide insights into the genetic control and molecular mechanism of the fruit firmness trait and present useful molecular markers for molecular-assisted breeding for fruit firmness in sweet cherry.

Abscisic acid controls sugar accumulation essential to strawberry fruit ripening via the FaRIPK1-FaTCP7-FaSTP13/FaSPT module

Strawberry is considered as a model plant for studying the ripening of abscisic acid (ABA)-regulated non-climacteric fruits, a process in which sugar plays a fundamental role, while how ABA regulates sugar accumulation remains unclear. This study provides a direct line of physiological, biochemical, and molecular evidence that ABA signaling regulates sugar accumulation via the FaRIPK1-FaTCP7-FaSTP13/FaSPT signaling pathway. Herein, FaRIPK1, a red-initial protein kinase 1 previously identified in strawberry fruit, not only interacted with the transcription factor FaTCP7 (TEOSINTE BRANCHEN 1, CYCLOIDEA, and PCF) but also phosphorylated the critical Ser89 and Thr93 sites of FaTCP7, which negatively regulated strawberry fruit ripening, as evidenced by the transient overexpression (OE) and virus-induced gene silencing transgenic system. Furthermore, the DAP-seq experiments revealed that FvTCP7 bound the motif "GTGGNNCCCNC" in the promoters of two sugar transporter genes, FaSTP13 (sugar transport protein 13) and FaSPT (sugar phosphate/phosphate translocator), inhibiting their transcription activities as determined by the electrophoretic mobility shift assay, yeast one-hybrid, and dual-luciferase reporter assays. The downregulated FaSTP13 and FaSPT transcripts in the FaTCP7-OE fruit resulted in a reduction in soluble sugar content. Consistently, the yeast absorption test revealed that the two transporters had hexose transport activity. Especially, the phosphorylation-inhibited binding of FaTCP7 to the promoters of FaSTP13 and FaSPT could result in the release of their transcriptional activities. In addition, the phosphomimetic form FaTCP7S89D or FaTCP7T93D could rescue the phenotype of FaTCP7-OE fruits. Importantly, exogenous ABA treatment enhanced the FaRIPK1-FaTCP7 interaction. Overall, we found direct evidence that ABA signaling controls sugar accumulation during strawberry fruit ripening via the "FaRIPK1-FaTCP7-FaSTP13/FaSPT" module.

Ethylene promotes fruit ripening initiation by downregulating photosynthesis, enhancing abscisic acid and suppressing jasmonic acid in blueberry (Vaccinium ashei)

BACKGROUND

Blueberry fruit exhibit atypical climacteric ripening with a non-auto-catalytic increase in ethylene coincident with initiation of ripening. Further, application of ethephon, an ethylene-releasing plant growth regulator, accelerates ripening by increasing the proportion of ripe (blue) fruit as compared to the control treatment. To investigate the mechanistic role of ethylene in regulating blueberry ripening, we performed transcriptome analysis on fruit treated with ethephon, an ethylene-releasing plant growth regulator.

RESULTS

RNA-Sequencing was performed on two sets of rabbiteye blueberry ('Powderblue') fruit: (1) fruit from divergent developmental stages; and (2) fruit treated with ethephon, an ethylene-releasing compound. Differentially expressed genes (DEGs) from divergent developmental stages clustered into nine groups, among which cluster 1 displayed reduction in expression during ripening initiation and was enriched with photosynthesis related genes, while cluster 7 displayed increased expression during ripening and was enriched with aromatic-amino acid family catabolism genes, suggesting stimulation of anthocyanin biosynthesis. More DEGs were apparent at 1 day after ethephon treatment suggesting its early influence during ripening initiation. Overall, a higher number of genes were downregulated in response to ethylene. Many of these overlapped with cluster 1 genes, indicating that ethylene-mediated downregulation of photosynthesis is an important developmental event during the ripening transition. Analyses of DEGs in response to ethylene also indicated interplay among phytohormones. Ethylene positively regulated abscisic acid (ABA), negatively regulated jasmonates (JAs), and influenced auxin (IAA) metabolism and signaling genes. Phytohormone quantification supported these effects of ethylene, indicating coordination of blueberry fruit ripening by ethylene.

CONCLUSION

This study provides insights into the role of ethylene in blueberry fruit ripening. Ethylene initiates blueberry ripening by downregulating photosynthesis-related genes. Also, ethylene regulates phytohormone-metabolism and signaling related genes, increases ABA, and decreases JA concentrations. Together, these results indicate that interplay among multiple phytohormones regulates the progression of ripening, and that ethylene is an important coordinator of such interactions during blueberry fruit ripening.

For a Colorful Life: Recent Advances in Anthocyanin Biosynthesis during Leaf Senescence

Leaf senescence is the last stage of leaf development, and it is accompanied by a leaf color change. In some species, anthocyanins are accumulated during leaf senescence, which are vital indicators for both ornamental and commercial value. Therefore, it is essential to understand the molecular mechanism of anthocyanin accumulation during leaf senescence, which would provide new insight into autumn coloration and molecular breeding for more colorful plants. Anthocyanin accumulation is a surprisingly complex process, and significant advances have been made in the past decades. In this review, we focused on leaf coloration during senescence. We emphatically discussed several networks linked to genetic, hormonal, environmental, and nutritional factors in regulating anthocyanin accumulation during leaf senescence. This paper aims to provide a regulatory model for leaf coloration and to put forward some prospects for future development.

Molecular mechanism of abscisic acid signaling response factor VcbZIP55 to promote anthocyanin biosynthesis in blueberry (Vaccinium corymbosum)

A high content of anthocyanin in blueberry (Vaccinium corymbosum) is an important indicator to evaluate fruit quality. Abscisic acid (ABA) can promote anthocyanin biosynthesis, but since the molecular mechanism is unclear, clarifying the mechanism will improve for blueberry breeding and cultivation regulation. VcbZIP55 regulating anthocyanin synthesis in blueberry were screened and mined using the published Isoform-sequencing, RNA-Seq and qRT-PCR at different fruit developmental stages. Blueberry genetic transformation and transgenic experiments confirmed that VcbZIP55 could promote anthocyanin biosynthesis in blueberry adventitious buds, tobacco leaves, blueberry leaves and blueberry fruit. VcbZIP55 responded to ABA signals and its expression was upregulated in blueberry fruit. In addition, using VcbZIP55 for Yeast one hybrid assay (Y1H) and transient expression in tobacco leaves demonstrated an interaction between VcbZIP55 and a G-Box motif on the VcMYB1 promoter to activate the expression of VcMYB1. This study will lay the theoretical foundation for the molecular mechanisms of phytohormone regulation responsible for anthocyanin synthesis and provide theoretical support for blueberry quality improvement.

Ethylene biosynthesis and signal transduction during ripening and softening in non-climacteric fruits: an overview

In recent years, the ethylene-mediated ripening and softening of non-climacteric fruits have been widely mentioned. In this paper, recent research into the ethylene-mediated ripening and softening of non-climacteric fruits is summarized, including the involvement of ethylene biosynthesis and signal transduction. In addition, detailed studies on how ethylene interacts with other hormones to regulate the ripening and softening of non-climacteric fruits are also reviewed. These findings reveal that many regulators of ethylene biosynthesis and signal transduction are linked with the ripening and softening of non-climacteric fruits. Meanwhile, the perspectives of future research on the regulation of ethylene in non-climacteric fruit are also proposed. The overview of the progress of ethylene on the ripening and softening of non-climacteric fruit will aid in the identification and characterization of key genes associated with ethylene perception and signal transduction during non-climacteric fruit ripening and softening.

Analysis of Ethylene Signal Regulating Sucrose Metabolism in Strawberry Fruits Based on RNA-seq

Ethylene is a key hormone that regulates the maturation and quality formation of horticultural crops, but its effects on non-respiratory climacteric fruits such as strawberries are not yet clear. In this study, strawberry fruits were treated with exogenous ethephon (ETH) and 1-methylcyclopropene (1-MCP). It was found that ETH treatment increased the soluble solids and anthocyanin content of the fruits, reduced hardness, and decreased organic acid content, while 1-MCP treatment inhibited these processes. Transcriptome analysis revealed that differentially expressed genes (DEGs) were enriched in the starch-sucrose metabolism pathway. qRT-PCR results further showed significant changes in the expression levels of sucrose metabolism genes, confirming the influence of ethylene signals on soluble sugar accumulation during strawberry fruit development. This study elucidates the quality changes and molecular mechanisms of ethylene signal in the development of strawberry fruits, providing some key targets and theoretical support for guiding strawberry cultivation and variety improvement.

Multi-omics provide insights into the regulation of DNA methylation in pear fruit metabolism

BACKGROUND

Extensive research has been conducted on fruit development in crops, but the metabolic regulatory networks underlying perennial fruit trees remain poorly understood. To address this knowledge gap, we conduct a comprehensive analysis of the metabolome, proteome, transcriptome, DNA methylome, and small RNAome profiles of pear fruit flesh at 11 developing stages, spanning from fruitlet to ripening. Here, we systematically investigate the metabolic landscape and regulatory network involved.

RESULTS

We generate an association database consisting of 439 metabolites and 14,399 genes to elucidate the gene regulatory network of pear flesh metabolism. Interestingly, we detect increased DNA methylation in the promoters of most genes within the database during pear flesh development. Application of a DNA methylation inhibitor to the developing fruit represses chlorophyll degradation in the pericarp and promotes xanthophyll, β-carotene, and abscisic acid (ABA) accumulation in the flesh. We find the gradual increase in ABA production during pear flesh development is correlated with the expression of several carotenoid pathway genes and multiple transcription factors. Of these transcription factors, the zinc finger protein PbZFP1 is identified as a positive mediator of ABA biosynthesis in pear flesh. Most ABA pathway genes and transcription factors are modified by DNA methylation in the promoters, although some are induced by the DNA methylation inhibitor. These results suggest that DNA methylation inhibits ABA accumulation, which may delay fruit ripening.

CONCLUSION

Our findings provide insights into epigenetic regulation of metabolic regulatory networks during pear flesh development, particularly with regard to DNA methylation.

The Controlled Release of Abscisic Acid (ABA) Utilizing Alginate-Chitosan Gel Blends: A Synergistic Approach for an Enhanced Small-Molecule Delivery Controller

The integration of abscisic acid (ABA) into a chitosan-alginate gel blend unveils crucial insights into the formation and stability of these two substances. ABA, a key phytohormone in plant growth and stress responses, is strategically targeted for controlled release within these complexes. This study investigates the design and characterization of this novel controlled-release system, showcasing the potential of alginate-chitosan gel blends in ABA delivery. Computational methods, including molecular dynamics simulations, are employed to analyze the structural effects of microencapsulation, offering valuable insights into complex behavior under varying conditions. This paper focuses on the controlled release of ABA from these complexes, highlighting its strategic importance in drug delivery systems and beyond. This controlled release enables targeted and regulated ABA delivery, with far-reaching implications for pharmaceuticals, agriculture, and plant stress response studies. While acknowledging context dependency, the paper suggests that the liberation or controlled release of ABA holds promise in applications, urging further research and experimentation to validate its utility across diverse fields. Overall, this work significantly contributes to understanding the characteristics and potential applications of chitosan-alginate complexes, marking a noteworthy advancement in the field of controlled-release systems.

Epigenomic mechanism regulating the quality and ripeness of apple fruit with differing harvest maturity

Harvest maturity significantly affects the quality of apple fruit in post-harvest storage process. Although the regulatory mechanisms underlying fruit ripening have been studied, the associated epigenetic modifications remain unclear. Thus, we compared the DNA methylation changes and the transcriptional responses of mature fruit (MF) and immature fruit (NF). There were significant correlations between DNA methylation and gene expression. Moreover, the sugar contents (sucrose, glucose, and fructose) were higher in MF than in NF, whereas the opposite pattern was detected for the starch content. The expression-level differences were due to DNA methylations and ultimately resulted in diverse fruit textures and ripeness. Furthermore, the higher ethylene, auxin, and abscisic acid levels in MF than in NF, which influenced the fruit texture and ripening, were associated with multiple differentially expressed genes in hormone synthesis, signaling, and response pathways (ACS, ACO, ZEP, NCED, and ABA2) that were regulated by DNA methylations. Multiple transcription factor genes involved in regulating fruit ripening and quality via changes in DNA methylation were identified, including MIKCC-type MADS-box genes and fruit ripening-related genes (NAP, SPL, WRKY, and NAC genes). These findings reflect the diversity in the epigenetic regulation of gene expression and may be relevant for elucidating the epigenetic regulatory mechanism underlying the ripening and quality of apple fruit with differing harvest maturity.

PpAmy1 Plays a Role in Fruit-Cracking by Regulating Mesocarp Starch Hydrolysis of Nectarines

Nectarine [Prunus persica (L.) Batsch var.] fruits are highly susceptible to cracking during the ripening process, which significantly decreases their commercial value. In this study, we investigated the underlying mechanism of nectarine fruit-cracking using two nectarine varieties, namely, "Qiannianhong" (cracking-susceptible) and "CR1012" (cracking-resistant). Our findings indicate that nectarine fruit-cracking occurs during the second stage of fruit expansion. Despite no differences in epicarp cell size between "Qiannianhong" and "CR1012", the mesocarp cells of "Qiannianhong" were larger than those of "CR1012". Moreover, a comparison of starch hydrolysis between the two varieties revealed that "CR1012" had higher starch content in the mesocarp but lower soluble sugar content compared to "Qiannianhong". Additionally, by testing the α-amylase and β-amylase activity of the mesocarp, our results showed a difference only in α-amylase activity between the two varieties. Furthermore, qRT-PCR detection indicated a higher expression level of the PpAmy1 (α-amylase synthesis gene) in "Qiannianhong" compared to "CR1012". To further investigate the role of PpAmy1, we employed RNAi technology to suppress its expression in "Qiannianhong" fruits. The results showed a significant reduction in α-amylase activity, starch hydrolysis, soluble sugar content, cell size of the mesocarp, and fruit-cracking. These findings underscore the pivotal role of PpAmy1 in the occurrence of nectarine fruit cracking.

Structural and transcriptional characterization of pyruvate decarboxylase (PDC) gene family during strawberry fruit ripening process

Strawberry is one of the most popular fruits in the world, because their high fruit quality, especially with respect to the combination of aroma, flavor, color, and nutritional compounds. Pyruvate decarboxylase (PDC) is the first of two enzymes specifically required for ethanolic fermentation and catalyzes the decarboxylation of pyruvate to yield acetaldehyde and CO2. The ethanol, an important alcohol which acts as a precursor for the ester and other alcohols formation in strawberry, is produced by the PDC. The objective was found all different PDCs genes present in the strawberry genome and investigate PDC gene expression and ligand-protein interactions in strawberry fruit. Volatile organic compounds were evaluated during the development of the fruit. After this, eight FaPDC were identified with four genes that increase the relative expression during fruit ripening process. Molecular dynamics simulations were performed to analyze the behavior of Pyr and TPP ligands within the catalytic and regulatory sites of the PDC proteins. Results indicated that energy-restrained simulations exhibited minor fluctuations in ligand-protein interactions, while unrestrained simulations revealed crucial insights into ligand affinity. TPP consistently displayed strong interactions with the catalytic site, emphasizing its pivotal role in enzymatic activity. However, FaPDC6 and FaPDC9 exhibited decreased pyruvate affinity initially, suggesting unique binding characteristics requiring further investigation. Finally, the present study contributes significantly to understanding PDC gene expression and the intricate molecular dynamics underlying strawberry fruit ripening, shedding light on potential targets for further research in this critical biological pathway.

Transcription factor CsMYB77 negatively regulates fruit ripening and fruit size in citrus

MYB family transcription factors (TFs) play essential roles in various biological processes, yet their involvement in regulating fruit ripening and fruit size in citrus remains poorly understood. In this study, we have established that the R2R3-MYB TF, CsMYB77, exerts a negative regulatory influence on fruit ripening in both citrus and tomato (Solanum lycopersicum), while also playing a role in modulating fruit size in citrus. The overexpression of CsMYB77 in tomato and Hongkong kumquat (Fortunella hindsii) led to notably delayed fruit ripening phenotypes. Moreover, the fruit size of Hongkong kumquat transgenic lines was largely reduced. Based on DNA affinity purification sequencing and verified interaction assays, SEVEN IN ABSENTIA OF ARABIDOPSIS THALIANA4 (SINAT4) and PIN-FORMED PROTEIN5 (PIN5) were identified as downstream target genes of CsMYB77. CsMYB77 inhibited the expression of SINAT4 to modulate abscisic acid (ABA) signaling, which delayed fruit ripening in transgenic tomato and Hongkong kumquat lines. The expression of PIN5 was activated by CsMYB77, which promoted free indole-3-acetic acid decline and modulated auxin signaling in the fruits of transgenic Hongkong kumquat lines. Taken together, our findings revealed a fruit development and ripening regulation module (MYB77-SINAT4/PIN5-ABA/auxin) in citrus, which enriches the understanding of the molecular regulatory network underlying fruit ripening and size.

Regulation of carotenoid metabolism and ABA biosynthesis during blueberry fruit ripening

Carotenoids and their derivates play critical physiologic roles in plants. However, these substrates and their metabolism have not been elucidated in fruit of blueberry (Vaccinium corymbosum). In this study, carotenoids and ABA were investigated by LC-MS and their biosynthesis were subject to proteomic analysis during fruit ripening. Activity of CCD1 and NCED1/3 were studied in vivo or in vitro. Also, effects of ethephon and 1-MCP on biosynthesis of carotenoid and ABA were investigated through the expression of corresponding genes using qPCR. As a result, carotenoid biosynthesis was prominently mitigated whereas its metabolism was enhanced during fruit ripening, which resulted in a decrease in the carotenoids. VcCCD1 could both cleave β-carotene, zeaxanthin and lutein at positions of 9, 10 (9', 10'), which was mainly responsible for the degradation of these carotenoids. Interestingly, in the situation of mitigation of carotenoid biosynthesis, ABA still rapidly accumulated, which was mainly attributed to the upregulated expression of VcNCED1/3. Notably, VcNCED1/3 also showed a cleavage activity of all-trans-zeaxanthin and a stereospecific cleavage activity of 9-cis-carotene to generate C15-carotenal. The C15-carotenal could be potentially converted to ABA through ZEP-independent ABA biosynthetic pathway during blueberry fruit ripening. Similar to a nature natural maturation, ethylene accelerated the carotenoid degradation and ABA biosynthesis trough downregulating the expression of genes in carotenoid biosynthesis and upregulating the expression of genes in ABA biosynthesis. These information help understand the regulation of carotenoids and ABA, and effects of ethylene on the regulation during blueberry fruit ripening.

The dynamic changes in pigment metabolites provide a new understanding of the colouration of Pyracantha fortuneana at maturity

The type, content and accumulation characteristics of pigments are the material basis for fruit colour and the evaluation basis of the fruit maturity and nutritional value of P. fortuneana. However, little information is available on the changes in carotenoids, anthocyanins, procyanidins and major flavones during the ripening process of P. fortuneana fruits. Thus, this study investigated the colour conversion characteristics, the main changes in the above four metabolites and the association landscape with those metabolites. The results showed that thirty-nine kinds of carotenoids and derivatives, eighteen anthocyanins, five procyanidins and five flavone compounds were identified in the fruits of P. fortuneana. The total content and contents of most individual carotenoids, anthocyanins, procyanidins and flavones reached the highest values at the TS2, TS4, TS1 and TS1 stages, respectively. Among the variations, the contents of β-carotene and lutein increased first and then decreased, cyanidin-3-galactoside and cyanidin-3-glucoside accumulated, the concentrations of procyanidin C1 and procyanidin B2 decreased, and the contents of rutin and quercetin-3-O-glucoside also decreased; these changers were responsible for the main changes in carotenoids, anthocyanidin, procyanidins and flavones, respectively. For the correlation analysis results, there might be two modes of action that together affected the colour conversion of P. fortuneana fruits during ripening, i.e., (E/Z)-phytoene communicated with the carotenoid metabolic pathway that might promote the accumulated ABA content, which might cause the increased anthocyanidin (primarily through cyanidin-3-(6-malonyl-beta-d-glucoside) (C3MG)) at the final stage; most of the decreased flavone and procyanidin metabolites produced by the flavonoid metabolic pathway were another important factor affecting the accumulation of C3MG.

Integrating the multiple functions of CHLH into chloroplast-derived signaling fundamental to plant development and adaptation as well as fruit ripening

Chlorophyll (Chl)-mediated oxygenic photosynthesis sustains life on Earth. Greening leaves play fundamental roles in plant growth and crop yield, correlating with the idea that more Chls lead to better adaptation. However, they face significant challenges from various unfavorable environments. Chl biosynthesis hinges on the first committed step, which involves inserting Mg2+ into protoporphyrin. This step is facilitated by the H subunit of magnesium chelatase (CHLH) and features a conserved mechanism from cyanobacteria to plants. For better adaptation to fluctuating land environments, especially drought, CHLH evolves multiple biological functions, including Chl biosynthesis, retrograde signaling, and abscisic acid (ABA) responses. Additionally, it integrates into various chloroplast-derived signaling pathways, encompassing both retrograde signaling and hormonal signaling. The former comprises ROS (reactive oxygen species), heme, GUN (genomes uncoupled), MEcPP (methylerythritol cyclodiphosphate), β-CC (β-cyclocitral), and PAP (3'-phosphoadenosine-5'-phosphate). The latter involves phytohormones like ABA, ethylene, auxin, cytokinin, gibberellin, strigolactone, brassinolide, salicylic acid, and jasmonic acid. Together, these elements create a coordinated regulatory network tailored to plant development and adaptation. An intriguing example is how drought-mediated improvement of fruit quality provides insights into chloroplast-derived signaling, aiding the shift from vegetative to reproductive growth. In this context, we explore the integration of CHLH's multifaceted roles into chloroplast-derived signaling, which lays the foundation for plant development and adaptation, as well as fruit ripening and quality. In the future, manipulating chloroplast-derived signaling may offer a promising avenue to enhance crop yield and quality through the homeostasis, function, and regulation of Chls.

Nano-selenium repaired the damage caused by fungicides on strawberry flavor quality and antioxidant capacity by regulating ABA biosynthesis and ripening-related transcription factors

Recently, studies have shown that pesticides may have adverse effects on the flavor quality of the fruits, but there is still a lack of appropriate methods to repair the damage. This study investigated the effects and mechanism of applying the emerging material, nano‑selenium, and two fungicides (Boscalid and Pydiflumetofen) alone or together on the flavor quality and antioxidant capacity of strawberries. The results showed that the two fungicides had a negative impact on strawberry color, flavor, antioxidant capacity and different enzymatic systems. The color damage was mainly attributed to the impact on anthocyanin content. Nano‑selenium alleviated the quality losses by increasing sugar-acid ratio, volatiles, anthocyanin levels, enzyme activities and DPPH scavenging ability and reducing ROS levels. Results also showed that these damage and repair processes were related to the regulation of flavor and ripening related transcription factors (including FaRIF, FaSnRK1, FaMYB10, FaMYB1, FaSnRK2.6 and FaABI1), the upregulation of genes on sugar-acid, volatile, and anthocyanin synthesis pathways, as well as the increase of sucrose and ABA signaling molecules. In addition, the application of nano-Se supplemented the selenium content in fruits, and was harmless to human health. This information is crucial for revealing the mechanisms of flavor damage caused by pesticides to strawberry and the repaired of nano‑selenium, and broadens the researching and applying of nano‑selenium in repairing the damage caused by pesticides.

Effects of preharvest chitosan-Myrtus communis essential oil composite and postharvest nanocellulose on quality of strawberry

The objective of this study was to investigate the effects of preharvest chitosan-Myrtus communis essential oil composite (1.5 and 3.0 %) and postharvest nanocellulose (0.3 and 0.6 %) on the quality of strawberries. The gas chromatography-mass spectrometry (GC/MS) analysis led to identification of 32 compounds in the Myrtus communis essential oil. The study showed that using CHS-ES composite coating for foliar application could increase the lifespan of the fruit by up to 24 days. This is because it increases the levels of components, such as phenol content (TPC) total flavonoids content (TFC) vitamin C, firmness and SSC. It also enhances the effectiveness of enzymes such, as glutathione peroxidase (GSH POD) and polyphenol oxidase (PPO). The use of CHS-ES treatments reduced the weight loss of fruits between 50 and 80 %, which is very important from the commercial point of view and maintaining nutritional properties, marketability and appearance. The microscopic analysis further revealed that using CHS-ES composite + nanocellulose coating produced a more continuous and uniform surface than the control. In general, this method is both safe and environmentally friendly while also proving to be effective, in preserving and enhancing the quality of strawberries.

Abscisic acid biosynthesis, metabolism and signaling in ripening fruit

Fruits are highly recommended nowadays in human diets because they are rich in vitamins, minerals, fibers and other necessary nutrients. The final stage of fruit production, known as ripening, plays a crucial role in determining the fruit's quality and commercial value. This is a complex physiological process, which involves many phytohormones and regulatory factors. Among the phytohormones involved in fruit ripening, abscisic acid (ABA) holds significant importance. ABA levels generally increase during the ripening process in most fruits, and applying ABA externally can enhance fruit flavor, hasten softening, and promote color development through complex signal regulation. Therefore, gaining a deeper understanding of ABA's mechanisms in fruit ripening is valuable for regulating various fruit characteristics, making them more suitable for consumption or storage. This, in turn, can generate greater economic benefits and reduce postharvest losses. This article provides an overview of the relationship between ABA and fruit ripening. It summarizes the effects of ABA on ripening related traits, covering the biochemical aspects and the underlying molecular mechanisms. Additionally, the article discusses the interactions of ABA with other phytohormones during fruit ripening, especially ethylene, and provides perspectives for future exploration in this field.

The role of environmental stress in fruit pigmentation

For many fruit crops, the colour of the fruit outwardly defines its eating quality. Fruit pigments provide reproductive advantage for the plant as well as providing protection against unfavourable environmental conditions and pathogens. For consumers these colours are considered attractive and provide many of the dietary benefits derived from fruits. In the majority of species, the main pigments are either carotenoids and/or anthocyanins. They are produced in the fruit as part of the ripening process, orchestrated by phytohormones and an ensuing transcriptional cascade, culminating in pigment biosynthesis. Whilst this is a controlled developmental process, the production of pigments is also attuned to environmental conditions such as light quantity and quality, availability of water and ambient temperature. If these factors intensify to stress levels, fruit tissues respond by increasing (or ceasing) pigment production. In many cases, if the stress is not severe, this can have a positive outcome for fruit quality. Here, we focus on the principal environmental factors (light, temperature and water) that can influence fruit colour.

Environmental Stimuli and Phytohormones in Anthocyanin Biosynthesis: A Comprehensive Review

Anthocyanin accumulation in plants plays important roles in plant growth and development, as well as the response to environmental stresses. Anthocyanins have antioxidant properties and play an important role in maintaining the reactive oxygen species (ROS) homeostasis in plant cells. Furthermore, anthocyanins also act as a "sunscreen", reducing the damage caused by ultraviolet radiation under high-light conditions. The biosynthesis of anthocyanin in plants is mainly regulated by an MYB-bHLH-WD40 (MBW) complex. In recent years, many new regulators in different signals involved in anthocyanin biosynthesis were identified. This review focuses on the regulation network mediated by different environmental factors (such as light, salinity, drought, and cold stresses) and phytohormones (such as jasmonate, abscisic acid, salicylic acid, ethylene, brassinosteroid, strigolactone, cytokinin, and auxin). We also discuss the potential application value of anthocyanin in agriculture, horticulture, and the food industry.

Non-climacteric fruit development and ripening regulation: 'the phytohormones show'

Fruit ripening involves numerous physiological, structural, and metabolic changes that result in the formation of edible fruits. This process is controlled at different molecular levels, with essential roles for phytohormones, transcription factors, and epigenetic modifications. Fleshy fruits are classified as either climacteric or non-climacteric species. Climacteric fruits are characterized by a burst in respiration and ethylene production at the onset of ripening, while regulation of non-climacteric fruit ripening has been commonly attributed to abscisic acid (ABA). However, there is controversy as to whether mechanisms regulating fruit ripening are shared between non-climacteric species, and to what extent other hormones contribute alongside ABA. In this review, we summarize classic and recent studies on the accumulation profile and role of ABA and other important hormones in the regulation of non-climacteric fruit development and ripening, as well as their crosstalk, paying special attention to the two main non-climacteric plant models, strawberry and grape. We highlight both the common and different roles of these regulators in these two crops, and discuss the importance of the transcriptional and environmental regulation of fruit ripening, as well as the need to optimize genetic transformation methodologies to facilitate gene functional analyses.

Deciphering the regulatory network of the NAC transcription factor FvRIF, a key regulator of strawberry (Fragaria vesca) fruit ripening

The NAC transcription factor ripening inducing factor (RIF) was previously reported to be necessary for the ripening of octoploid strawberry (Fragaria × ananassa) fruit, but the mechanistic basis of RIF-mediated transcriptional regulation and how RIF activity is modulated remains elusive. Here, we show that FvRIF in diploid strawberry, Fragaria vesca, is a key regulator in the control of fruit ripening and that knockout mutations of FvRIF result in a complete block of fruit ripening. DNA affinity purification sequencing coupled with transcriptome deep sequencing suggests that 2,080 genes are direct targets of FvRIF-mediated regulation, including those related to various aspects of fruit ripening. We provide evidence that FvRIF modulates anthocyanin biosynthesis and fruit softening by directly regulating the related core genes. Moreover, we demonstrate that FvRIF interacts with and serves as a substrate of MAP kinase 6 (FvMAPK6), which regulates the transcriptional activation function of FvRIF by phosphorylating FvRIF at Thr-310. Our findings uncover the FvRIF-mediated transcriptional regulatory network in controlling strawberry fruit ripening and highlight the physiological significance of phosphorylation modification on FvRIF activity in ripening.

An arginine-to-histidine mutation in flavanone-3-hydroxylase results in pink strawberry fruits

Fruit color is a very important external commodity factor for consumers. Compared to the most typical red octoploid strawberry (Fragaria × ananassa), the pink strawberry often sells for a more expensive price and has a higher economic benefit due to its outstanding color. However, few studies have examined the molecular basis of pink-colored strawberry fruit. Through an EMS mutagenesis of woodland strawberry (Fragaria vesca), we identified a mutant with pink fruits and green petioles. Bulked-segregant analysis sequencing analysis and gene function verification confirmed that the responsible mutation resides in a gene encoding flavanone-3-hydroxylase (F3H) in the anthocyanin synthesis pathway. This nonsynonymous mutation results in an arginine-to-histidine change at position 130 of F3H. Molecular docking experiments showed that the arginine-to-histidine mutation results in a reduction of intermolecular force-hydrogen bonding between the F3H protein and its substrates. Enzymatic experiments showed a greatly reduced ability of the mutated F3H protein to catalyze the conversion of the substrates and hence a blockage of the anthocyanin synthesis pathway. The discovery of a key residue in the F3H gene controlling anthocyanin synthesis provides a clear target of modification for the molecular breeding of strawberry varieties with pink-colored fruits, which may be of great commercial value.

Transcriptomic and physiological comparison of Shatangju (Citrus reticulata) and its late-maturing mutant provides insights into auxin regulation of citrus fruit maturation

Previous studies have shown that abscisic acid (ABA) and ethylene are involved in pulp maturation and peel coloration in the nonclimacteric citrus fruits. There are also signs indicating that other plant hormones may play some roles in citrus fruit ripening. In this study, we compared profiles of genome-wide gene expression and changes in hormones and peel pigments between fruits of Shatangju mandarin (Citrus reticulata Blanco, designated WT) and its natural mutant, Yuenongwanju (designated MT). The MT fruit matures ~2 months later than the WT fruit. Significant differences in fruit diameter, total soluble solids, titratable acid content, chlorophylls and carotenoids were detected between the fruits of the two genotypes at the sampled time points. Genome-wide transcriptome profiling showed that many genes involved in auxin and ABA metabolism and/or signaling pathways were differentially expressed between the MT and the WT fruits. Importantly, the expression of CrYUCCA8 was significantly lower and the expression of CrNCED5 was significantly higher in WT than in MT fruits at 230 and 250 DPA, respectively. In addition, the indole-3-acetic acid (IAA) level in the MT fruit was significantly higher than that in the WT counterpart, whereas a significantly lower level of ABA was detected in the mutant. Treatment of the WT fruit with exogenous IAA significantly delayed fruit maturation. Our results provide experimental evidence supporting the notion that auxin is a negative regulator of fruit maturation in citrus.

A clathrin-related protein FaRRP1/SCD2 integrates ABA trafficking and signaling to regulate strawberry fruit ripening

Abscisic acid (ABA) is a critical regulator for nonclimacteric fruit ripening such as in the model plant of strawberry (Fragaria × ananassa). Although FaRRP1 is proposed to participate in clathrin-mediated endocytosis of ABA, its action molecular mechanisms in ABA signaling are not fully understood. Here, using our isolated FaRRP1 (ripening-regulation protein) and candidate ABA receptor FaPYL2 and FaABAR from strawberry fruit, a series of silico and molecular interaction analyses demonstrate that they all bind to ABA, and FaRRP1 binds both FaPYL2 and FaABAR; by contrast, the binding affinity of FaRRP1 to FaPYL2 is relatively higher. Interestingly, the binding of FaRRP1 to FaPYL2 and FaABAR affects the perception affinity to ABA. Furthermore, exogenous ABA application and FaRRP1 transgenic analyses confirm that FaRRP1 participates in clathrin-mediated endocytosis and vesicle transport. Importantly, FaRRP1, FaPYL2, and FaABAR all trigger the initiation of strawberry fruit ripening at physiological and molecular levels. In conclusion, FaRRP1 not only binds to ABA but also affects the binding affinity of FaPYL2 and FaABAR to ABA, thus promoting strawberry fruit ripening. Our findings provide novel insights into the role of FaRRP1 in ABA trafficking and signaling, at least in strawberry, a model plant for nonclimacteric fruit ripening.

ATP-binding cassette protein ABCC8 promotes anthocyanin accumulation in strawberry fruits

Anthocyanins are important health-promoting flavonoid compounds that substantially contribute to fruit quality. Anthocyanin biosynthesis and most regulatory mechanisms are relatively well understood. However, the functions of anthocyanin transport genes in strawberry fruit remain unclear. In this study, a gene encoding an ATP-binding cassette (ABC) protein of type C, ABCC8, was isolated from strawberry fruits. qRT-PCR analysis demonstrated that the transcript levels of FvABCC8 were the highest and were strongly correlated with anthocyanin accumulation during strawberry fruit ripening. Transient overexpression and RNAi of FvABCC8 led to an increase and decrease in anthocyanin content in strawberry fruits, respectively. Moreover, the ABCC8 promoter was activated by MYB and bHLH transcription factors MYB10, bHLH33, and MYC1. Sucrose enhanced anthocyanin accumulation in FvABCC8-overexpressing Arabidopsis, particularly at higher concentrations. FvABCC8-overexpressing lines were less sensitive to ABA during seed germination and seedling development. These results suggest that strawberry vacuolar anthocyanin transport may be mediated by the ABCC transporter ABCC8, the expression of which may be regulated by transcription factors MYB10, bHLH33, and MYC1.

ClSnRK2.3 negatively regulates watermelon fruit ripening and sugar accumulation

Watermelon (Citrullus lanatus) as non-climacteric fruit is domesticated from the ancestors with inedible fruits. We previously revealed that the abscisic acid (ABA) signaling pathway gene ClSnRK2.3 might influence watermelon fruit ripening. However, the molecular mechanisms are unclear. Here, we found that the selective variation of ClSnRK2.3 resulted in lower promoter activity and gene expression level in cultivated watermelons than ancestors, which indicated ClSnRK2.3 might be a negative regulator in fruit ripening. Overexpression (OE) of ClSnRK2.3 significantly delayed watermelon fruit ripening and suppressed the accumulation of sucrose, ABA and gibberellin GA4 . Furthermore, we determined that the pyrophosphate-dependent phosphofructokinase (ClPFP1) in sugar metabolism pathway and GA biosynthesis enzyme GA20 oxidase (ClGA20ox) could be phosphorylated by ClSnRK2.3 and thereby resulting in accelerated protein degradation in OE lines and finally led to low levels of sucrose and GA4 . Besides that, ClSnRK2.3 phosphorylated homeodomain-leucine zipper protein (ClHAT1) and protected it from degradation to suppress the expression of the ABA biosynthesis gene 9'-cis-epoxycarotenoid dioxygenase 3 (ClNCED3). These results indicated that ClSnRK2.3 negatively regulated watermelon fruit ripening by manipulating the biosynthesis of sucrose, ABA and GA4 . Altogether, these findings revealed a novel regulatory mechanism in non-climacteric fruit development and ripening.

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

The strawberry is one of the world's most popular fruits, providing humans with vitamins, fibers, and antioxidants. Cultivated strawberry (Fragaria × ananassa) is an allo-octoploid and highly heterozygous, making it a challenge for breeding, quantitative trait locus (QTL) mapping, and gene discovery. Some wild strawberry relatives, such as Fragaria vesca, have diploid genomes and are becoming laboratory models for the cultivated strawberry. Recent advances in genome sequencing and CRISPR-mediated genome editing have greatly improved the understanding of various aspects of strawberry growth and development in both cultivated and wild strawberries. This review focuses on fruit quality traits that are most relevant to the consumers, including fruit aroma, sweetness, color, firmness, and shape. Recently available phased-haplotype genomes, single nucleotide polymorphism (SNP) arrays, extensive fruit transcriptomes, and other big data have made it possible to locate key genomic regions or pinpoint specific genes that underlie volatile synthesis, anthocyanin accumulation for fruit color, and sweetness intensity or perception. These new advances will greatly facilitate marker-assisted breeding, the introgression of missing genes into modern varieties, and precise genome editing of selected genes and pathways. Strawberries are poised to benefit from these recent advances, providing consumers with fruit that is tastier, longer-lasting, healthier, and more beautiful.

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.

Induced Resistance in Fruit and Vegetables: A Host Physiological Response Limiting Postharvest Disease Development

Harvested fruit and vegetables are perishable, subject to desiccation, show increased respiration during ripening, and are colonized by postharvest fungal pathogens. Induced resistance is a strategy to control diseases by eliciting biochemical processes in fruits and vegetables. This is accomplished by modulating the progress of ripening and senescence, which maintains the produce in a state of heightened resistance to decay-causing fungi. Utilization of induced resistance to protect produce has been improved by scientific tools that better characterize physiological changes in plants. Induced resistance slows the decline of innate immunity after harvest and increases the production of defensive responses that directly inhibit plant pathogens. This increase in defense response in fruits and vegetables contributes to higher amounts of phenols and antioxidant compounds, improving both the quality and appearance of the produce. This review summarizes mechanisms and treatments that induce resistance in harvested fruits and vegetables to suppress fungal colonization. Moreover, it highlights the importance of host maturity and stage of ripening as limiting conditions for the improved expression of induced-resistance processes.

Sugar composition and transcriptome analysis in developing 'Fengtang' plum (Prunus salicina Lindl.) reveal candidate genes regulating sugar accumulation

Sweetness is an important attribute of fruit quality, which directly affects consumers' preference for fresh fruit and is mostly determined by carbohydrate composition. 'Fengtang' plum (Prunus salicina Lindl.) is recognized for its high soluble sugar content, but the sugar composition and the molecular mechanisms underlying sugar overproduction are not fully understood. In this work, the sugar components were analyzed using gas chromatography-mass spectrometry combined with transcription profiles from RNA-sequencing and Quantitative Real-time PCR during fruit development. The target metabolic group showed that sucrose was the dominant sugar component in mature fruit, followed by glucose, fructose, and sorbitol. Based on the transcriptome data and qRT-PCR validation, we identified 12 key structural genes that significantly responded to corresponding component accumulation: sucrose synthase (PsSUS4), sucrose phosphate synthase (PsSPS2), neutral invertase (PsNINV1/3/4), phosphoglucomutase (PsPGM1), UTP-glucose-1-phosphate uridylyl transferase (PsUGP1/2), hexose kinase (PsHXK1/3), sugar transport protein (PsSTP1), and Sugars Will Eventually be Exported Transporter (PsSWEET4). In which PsSUS4 and PsSPS2, whose encoding proteins immediately catalyze sucrose synthesis, were selected to be silenced using the virus-induced gene silencing technology. Silencing of PsSUS4 or PsSPS2 resulted in decreased sucrose content by 27.6% and 8%, respectively, compared with the control, verifying their important roles in sucrose accumulation. Subsequently, sugar metabolism networks in this high-sugar plum were constructed with 12 key structural genes, 72 putative transcription factors, and 4 major sugar components. These results might facilitate a better understanding of the molecular mechanisms of sugar accumulation in 'Fengtang' plum and provide a framework for future fruit quality improvement.

MaABI5 and MaABF1 transcription factors regulate the expression of MaJOINTLESS during fruit abscission in mulberry (Morus alba L.)

Mulberry holds significant economic value. However, during the ripening stage of its fruit, the phenomenon of abscission, resulting in heavy fruit drop, can severely impact the yield. The formation of off-zone structures is a critical factor in the fruit abscission process, and this process is regulated by multiple transcription factors. One such key gene that plays a significant role in the development of the off-zone in the model plant tomato is JOINTLESS, which promotes the expression of abscission-related genes and regulates the differentiation of abscission zone tissue cells. However, there is a lack of information about fruit abscission mechanism in mulberry. Here, we analyzed the MaJOINTLESS promoter and identified the upstream regulators MaABF1 and MaABI5. These two regulators showed binding with MaJOINTLESS promoter MaABF1 (the ABA Binding Factor/ABA-Responsive Element Binding Proteins) activated the expression of MaJOINTLESS, while MaABI5 (ABSCISIC ACID-INSENSITIVE 5) inhibited the expression of MaJOINTLESS. Finally, the differentially expressed genes (DEGs) were analyzed by transcriptome sequencing to investigate the expression and synergistic relationship of endogenous genes in mulberry during abscission. GO classification and KEGG pathway enrichment analysis showed that most of the DEGs were concentrated in MAPK signaling pathway, flavonoid biosynthesis, citric acid cycle, phytohormone signaling, amino acid biosynthesis, and glycolysis. These results provide a theoretical basis for subsequent in-depth study of physiological fruit abscission in mulberry.

Light-Induced TaHY5-7A and TaBBX-3B Physically Interact to Promote PURPLE PERICARP-MYB 1 Expression in Purple-Grained Wheat

Purple-grained wheat (Triticum aestivum L.) is an important germplasm source in crop breeding. Anthocyanin biosynthesis in the pericarps of purple-grained wheat is largely light-dependent; however, the regulatory mechanisms underlying light-induced anthocyanin accumulation in the wheat pericarp remain unknown. Here we determined that anthocyanins rapidly accumulate in the pericarps of the purple-grained wheat cultivar Heixiaomai 76 (H76) at 16 days after pollination under light treatment. Using transcriptome sequencing, differential gene expression analysis, and phylogenetic analysis, we identified two key genes involved in light signaling in wheat: ELONGATED HYPOCOTYL 5-7A (TaHY5-7A) and B-BOX-3B (TaBBX-3B). TaHY5-7A and TaBBX-3B were highly expressed in purple-grained wheat pericarps. The heterologous expression of TaHY5-7A partially restored the phenotype of the Arabidopsis (Arabidopsis thaliana) hy5 mutant, resulting in increased anthocyanin accumulation and a shortened hypocotyl. The heterologous expression of TaBBX-3B in wild-type Arabidopsis had similar effects. TaHY5-7A and TaBBX-3B were nucleus-localized, consistent with a function in transcription regulation. However, TaHY5-7A, which lacks a transactivation domain, was not sufficient to activate the expression of PURPLE PERICARP-MYB 1 (TaPpm1), the key anthocyanin biosynthesis regulator in purple pericarps of wheat. TaHY5-7A physically interacted with TaBBX-3B in yeast two-hybrid and bimolecular fluorescence complementation assays. Additionally, TaHY5-7A, together with TaBBX-3B, greatly enhanced the promoter activity of TaPpm1 in a dual luciferase assay. Overall, our results suggest that TaHY5-7A and TaBBX-3B collaboratively activate TaPpm1 expression to promote light-induced anthocyanin biosynthesis in purple-pericarp wheat.

Quality analysis and metabolomic profiling of the effects of exogenous abscisic acid on rabbiteye blueberry

Blueberry is a characteristic berry fruit shrub of the genus Vaccinium in the Rhododendron family. The fruit is rich in anthocyanins and has a variety of nutritional and health functions. This study aimed to systematically study the effect of exogenous abscisic acid (ABA) application on ripening and metabolites in blueberry fruits. Blueberry fruit ripening was divided into six stages for further analysis. In this study, nontarget metabolomics was performed to demonstrate the effect on metabolite levels. The results showed that 1000 mg/L ABA significantly promoted fruit ripening and increased anthocyanin content. Moreover, exogenous ABA treatment can affect endogenous ABA levels and improve its antioxidant capacity. Important metabolites of the flavonoid pathway were detected, and the results showed that anthocyanin synthesis increased, and some other bioactive metabolite levels decreased. After comprehensive assessments, we believe that 1000 mg/L exogenous ABA application will have positive impacts on blueberry fruit quality and economic benefits.

Transcription factor LcNAC002 coregulates chlorophyll degradation and anthocyanin biosynthesis in litchi

Chlorophyll degradation and anthocyanin biosynthesis, which often occur almost synchronously during fruit ripening, are crucial for vibrant coloration of fruits. However, the interlink point between their regulatory pathways remains largely unknown. Here, 2 litchi (Litchi chinensis Sonn.) cultivars with distinctively different coloration patterns during ripening, i.e. slow-reddening/stay-green "Feizixiao" (FZX) vs rapid-reddening/degreening "Nuomici" (NMC), were selected as the materials to study the key factors determining coloration. Litchi chinensis STAY-GREEN (LcSGR) was confirmed as the critical gene in pericarp chlorophyll loss and chloroplast breakdown during fruit ripening, as LcSGR directly interacted with pheophorbide a oxygenase (PAO), a key enzyme in chlorophyll degradation via the PAO pathway. Litchi chinensis no apical meristem (NAM), Arabidopsis transcription activation factor 1/2, and cup-shaped cotyledon 2 (LcNAC002) was identified as a positive regulator in the coloration of litchi pericarp. The expression of LcNAC002 was significantly higher in NMC than in FZX. Virus-induced gene silencing of LcNAC002 significantly decreased the expression of LcSGR as well as L. chinensis MYELOBLASTOSIS1 (LcMYB1), and inhibited chlorophyll loss and anthocyanin accumulation. A dual-luciferase reporter assay revealed that LcNAC002 significantly activates the expression of both LcSGR and LcMYB1. Furthermore, yeast-one-hybrid and electrophoretic mobility shift assay results showed that LcNAC002 directly binds to the promoters of LcSGR and LcMYB1. These findings suggest that LcNAC002 is an important ripening-related transcription factor that interlinks chlorophyll degradation and anthocyanin biosynthesis by coactivating the expression of both LcSGR and LcMYB1.

ABA Biosynthesis- and Signaling-Related Gene Expression Differences between Sweet Cherry Fruits Suggest Attenuation of ABA Pathway in Bicolored Cultivars

Fruit development involves exocarp color evolution. However, signals that control this process are still elusive. Differences between dark-red and bicolored sweet cherry cultivars rely on MYB factor gene mutations. Color evolution in bicolored fruits only occurs on the face receiving sunlight, suggesting the perception or response to color-inducing signals is affected. These color differences may be related to synthesis, perception or response to abscisic acid (ABA), a phytohormone responsible for non-climacteric fruit coloring. This work aimed to determine the involvement of ABA in the coloring process of color-contrasting varieties. Several phenolic accumulation patterns differed between bicolored 'Royal Rainier' and dark-red 'Lapins'. Transcript abundance of ABA biosynthetic genes (PavPSY, PavZEP and PavNCED1) decreased dramatically from the Pink to Red stage in 'Royal Rainier' but increased in 'Lapins', which correlated with a higher ABA content in this dark-red cultivar. Transcripts coding for ABA signaling (PavPP2Cs, PavSnRKs and PavMYB44.1) were almost undetectable at the Red stage in 'Royal Rainier'. Field trials revealed that 'Royal Rainier' color development was insensitive to exogenous ABA, whereas it increased in 'Lapins'. Furthermore, ABA treatment only increased transcript levels of signaling genes in 'Lapins'. Further studies may address if the ABA pathway is attenuated in bicolor cultivars.

BSA-Seq and Transcriptomic Analysis Provide Candidate Genes Associated with Inflorescence Architecture and Kernel Orientation by Phytohormone Homeostasis in Maize

The developmental plasticity of the maize inflorescence depends on meristems, which directly affect reproductive potential and yield. However, the molecular roles of upper floral meristem (UFM) and lower floral meristem (LFM) in inflorescence and kernel development have not been fully elucidated. In this study, we characterized the reversed kernel1 (rk1) novel mutant, which contains kernels with giant embryos but shows normal vegetative growth like the wild type (WT). Total RNA was extracted from the inflorescence at three stages for transcriptomic analysis. A total of 250.16-Gb clean reads were generated, and 26,248 unigenes were assembled and annotated. Gene ontology analyses of differentially expressed genes (DEGs) detected in the sexual organ formation stage revealed that cell differentiation, organ development, phytohormonal responses and carbohydrate metabolism were enriched. The DEGs associated with the regulation of phytohormone levels and signaling were mainly expressed, including auxin (IAA), jasmonic acid (JA), gibberellins (GA), and abscisic acid (ABA). The transcriptome, hormone evaluation and immunohistochemistry observation revealed that phytohormone homeostasis were affected in rk1. BSA-Seq and transcriptomic analysis also provide candidate genes to regulate UFM and LFM development. These results provide novel insights for understanding the regulatory mechanism of UFM and LFM development in maize and other plants.

Physiological response of anthocyanin synthesis to different light intensities in blueberry

Fruit color is an important economic character of blueberry, determined by the amount of anthocyanin content. Anthocyanin synthesis within the blueberry fruits is significantly affected by light. To reveal the physiological response mechanism of anthocyanin synthesis in blueberry fruits in different light intensities, four light intensities (100% (CK), 75%, 50% and 25%) were set for the 'O'Neal' southern highbush blueberry as the experimental material in our study. The relationship between endogenous hormones content, associated enzyme activities, and variations with the anthocyanin content in blueberry fruits under various light intensities during the white fruit stage (S1), purple fruit stage (S2), and blue fruit stage (S3) were studied. The results showed that adequate light could significantly promote anthocyanin synthesis in blueberry fruits (P < 0.05). Blueberry fruits had an anthocyanin content that was 1.76~24.13 times higher under 100% light intensity than it was under non-full light intensity. Different light intensities significantly affected the content of endogenous hormones and the activity of associated enzymes in anthocyanin synthesis pathway (P < 0.05). Among them, the JA (jasmonic acid) content and PAL (phenylalanine ammonia lyase) activity of fruits under 100% light intensity were 2.49%~41.83% and 2.47%~48.48% higher than those under other light intensity, respectively. And a significant correlation was found between the variations in anthocyanin content in fruits and the content or activities of JA, ABA (abscisic acid), ETH (ethylene), GA3 (gibberellin 3), IAA (indoleacetic acid), PAL, CHI (chalcone isomerase), DFR (dihydroflavonol reductase) and UFGT (UDP-glucose: flavonoid 3-glucosyltransferase) (P < 0.05). It indicated that 100% light intensity significantly promoted anthocyanin synthesis in blueberry fruits by affecting endogenous hormones content and associated enzyme activities in the anthocyanin synthesis pathway. This study will lay a foundation for further research on the molecular mechanism of light intensity regulating anthocyanin synthesis in blueberry.

Domestication has altered the ABA and gibberellin profiles in developing pea seeds

MAIN CONCLUSION

We showed that wild pea seeds contained a more diverse combination of bioactive GAs and had higher ABA content than domesticated peas. Although the role of abscisic acid (ABA) and gibberellins (GAs) interplay has been extensively studied in Arabidopsis and cereals models, comparatively little is known about the effect of domestication on the level of phytohormones in legume seeds. In legumes, as in other crops, seed dormancy has been largely or entirely removed during domestication. In this study, we have measured the endogenous levels of ABA and GAs comparatively between wild and domesticated pea seeds during their development. We have shown that wild seeds contained more ABA than domesticated ones, which could be important for preparing the seeds for the period of dormancy. ABA was catabolised particularly by an 8´-hydroxylation pathway, and dihydrophaseic acid was the main catabolite in seed coats as well as embryos. Besides, the seed coats of wild and pigmented cultivated genotypes were characterised by a broader spectrum of bioactive GAs compared to non-pigmented domesticated seeds. GAs in both seed coat and embryo were synthesized mainly by a 13-hydroxylation pathway, with GA29 being the most abundant in the seed coat and GA20 in the embryos. Measuring seed water content and water loss indicated domesticated pea seeds´ desiccation was slower than that of wild pea seeds. Altogether, we showed that pea domestication led to a change in bioactive GA composition and a lower ABA content during seed development.

Storage of halved strawberry fruits affects aroma, phytochemical content and gene expression, and is affected by pre-harvest factors

Introduction

Strawberry fruit are highly valued for their aroma which develops during ripening. However, they have a short shelf-life. Low temperature storage is routinely used to extend shelf-life for transport and storage in the supply chain, however cold storage can also affect fruit aroma. Some fruit continue to ripen during chilled storage; however, strawberries are a non-climacteric fruit and hence ripening postharvest is limited. Although most strawberry fruit is sold whole, halved fruit is also used in ready to eat fresh fruit salads which are of increasing consumer demand and pose additional challenges to fresh fruit storage.

Methods

To better understand the effects of cold storage, volatilomic and transcriptomic analyses were applied to halved Fragaria x ananassa cv. Elsanta fruit stored at 4 or 8°C for up to 12 days over two growing seasons.

Results and discussion

The volatile organic compound (VOC) profile differed between 4 or 8°C on most days of storage. Major differences were detected between the two different years of harvest indicating that aroma change at harvest and during storage is highly dependent on environmental factors during growth. The major component of the aroma profile in both years was esters. Over 3000 genes changed in expression over 5 days of storage at 8°C in transcriptome analysis. Overall, phenylpropanoid metabolism, which may also affect VOCs, and starch metabolism were the most significantly affected pathways. Genes involved in autophagy were also differentially expressed. Expression of genes from 43 different transcription factor (TF) families changed in expression: mostly they were down-regulated but NAC and WRKY family genes were mainly up-regulated. Given the high ester representation amongst VOCs, the down-regulation of an alcohol acyl transferase (AAT) during storage is significant. A total of 113 differentially expressed genes were co-regulated with the AAT gene, including seven TFs. These may be potential AAT regulators.

Genome-Wide Identification and Comparative Transcriptome Methods Reveal FaMDHAR50 Regulating Ascorbic Acid Regeneration and Quality Formation of Strawberry Fruits

Ascorbic acid (AsA) is a crucial water-soluble antioxidant in strawberry fruit, but limited research is currently available on the identification and functional validation of key genes involved in AsA metabolism in strawberries. This study analyzed the FaMDHAR gene family identification, which includes 168 genes. Most of the products of these genes are predicted to exist in the chloroplast and cytoplasm. The promoter region is rich in cis-acting elements related to plant growth and development, stress and light response. Meanwhile, the key gene FaMDHAR50 that positively regulates AsA regeneration was identified through comparative transcriptome analysis of 'Benihoppe' strawberry (WT) and its natural mutant (MT) with high AsA content (83 mg/100 g FW). The transient overexpression experiment further showed that overexpression of FaMDHAR50 significantly enhanced the AsA content by 38% in strawberry fruit, with the upregulated expression of structural genes involved in AsA biosynthesis (FaGalUR and FaGalLDH) and recycling and degradation (FaAPX, FaAO and FaDHAR) compared with that of the control. Moreover, increased sugar (sucrose, glucose and fructose) contents and decreased firmness and citric acid contents were observed in the overexpressed fruit, which were accompanied by the upregulation of FaSNS, FaSPS, FaCEL1 and FaACL, as well as the downregulation of FaCS. Additionally, the content of pelargonidin 3-glucoside markedly decreased, while cyanidin chloride increased significantly. In summary, FaMDHAR50 is a key positive regulatory gene involved in AsA regeneration in strawberry fruit, which also plays an important role in the formation of fruit flavor, apperance and texture during strawberry fruit ripening.

Virus-Induced Gene Silencing (VIGS) in Chinese Jujube

Virus-induced gene silencing (VIGS) is a fast and efficient method for assaying gene function in plants. At present, the VIGS system mediated by Tobacco rattle virus (TRV) has been successfully practiced in some species such as cotton and tomato. However, little research of VIGS systems has been reported in woody plants, nor in Chinese jujube. In this study, the TRV-VIGS system of jujube was firstly investigated. The jujube seedlings were grown in a greenhouse with a 16 h light/8 h dark cycle at 23 °C. After the cotyledon was fully unfolded, Agrobacterium mixture containing pTRV1 and pTRV2-ZjCLA with OD₆₀₀ = 1.5 was injected into cotyledon. After 15 days, the new leaves of jujube seedlings showed obvious photo-bleaching symptoms and significantly decreased expression of ZjCLA, indicating that the TRV-VIGS system had successfully functioned on jujube. Moreover, it found that two injections on jujube cotyledon could induce higher silencing efficiency than once injection. A similar silencing effect was then also verified in another gene, ZjPDS. These results indicate that the TRV-VIGS system in Chinese jujube has been successfully established and can be applied to evaluate gene function, providing a breakthrough in gene function verification methods.

Insights into the Genes Involved in ABA Biosynthesis and Perception during Development and Ripening of the Chilean Strawberry Fruit

Hormones act as master ripening regulators. In non-climacteric fruit, ABA plays a key role in ripening. Recently, we confirmed in Fragaria chiloensis fruit that in response to ABA treatment the fruit induces ripening-associated changes such as softening and color development. In consequence of these phenotypic changes, transcriptional variations associated with cell wall disassembly and anthocyanins biosynthesis were reported. As ABA stimulates the ripening of F. chiloensis fruit, the molecular network involved in ABA metabolism was analyzed. Therefore, the expression level of genes involved in ABA biosynthesis and ABA perception was quantified during the development of the fruit. Four NCED/CCDs and six PYR/PYLs family members were identified in F. chiloensis. Bioinformatics analyses confirmed the existence of key domains related to functional properties. Through RT-qPCR analyses, the level of transcripts was quantified. FcNCED1 codifies a protein that displays crucial functional domains, and the level of transcripts increases as the fruit develops and ripens, in parallel with the increment in ABA. In addition, FcPYL4 codifies for a functional ABA receptor, and its expression follows an incremental pattern during ripening. The study concludes that FcNCED1 is involved in ABA biosynthesis; meanwhile, FcPYL4 participates in ABA perception during the ripening of F. chiloensis fruit.

Abscisic Acid Synthesis and Signaling during the Ripening of Raspberry (Rubus idaeus 'Heritage') Fruit

The raspberry (Rubus idaeus L.) fruit is characterized by its richness in functional molecules and high nutritional value, but the high rate of fruit softening limits its quality during postharvest. Raspberry drupelets have a particular ripening regulation, depending partially on the effect of ethylene produced from the receptacle. However, the possible role of abscisic acid (ABA) in the modulation of quality parameters during the ripening of raspberry is unclear. This study characterized the fruit quality-associated parameters and hormonal contents during fruit development in two seasons. The quality parameters showed typical changes during ripening: a drastic loss of firmness, increase in soluble solids content, loss of acidity, and turning to a red color from the large green stage to fully ripe fruit in both seasons. A significant increase in the ABA content was observed during the ripening of drupelets and receptacles, with the higher content in the receptacle of ripe and overripe stages compared to the large green stage. Moreover, identification of ABA biosynthesis-(9-cis-epoxycarotenoid dioxygenase/NCED) and ABA receptor-related genes (PYRs-like receptors) showed three genes encoding RiNCEDs and nine genes for RiPYLs. The expression level of these genes increased from the large green stage to the full-ripe stage, specifically characterized by a higher expression of RiNCED1 in the receptacle tissue. This study reports a consistent concomitant increase in the ABA content and the expression of RiNCED1, RiPYL1, and RiPYL8 during the ripening of the raspberry fruit, thus supporting the role for ABA signaling in drupelets.

A metabolic perspective of selection for fruit quality related to apple domestication and improvement

BACKGROUND

Apple is an economically important fruit crop. Changes in metabolism accompanying human-guided evolution can be revealed using a multiomics approach. We perform genome-wide metabolic analysis of apple fruits collected from 292 wild and cultivated accessions representing various consumption types.

RESULTS

We find decreased amounts of certain metabolites, including tannins, organic acids, phenolic acids, and flavonoids as the wild accessions transition to cultivated apples, while lysolipids increase in the "Golden Delicious" to "Ralls Janet" pedigree, suggesting better storage. We identify a total of 222,877 significant single-nucleotide polymorphisms that are associated with 2205 apple metabolites. Investigation of a region from 2.84 to 5.01 Mb on chromosome 16 containing co-mapping regions for tannins, organic acids, phenolic acids, and flavonoids indicates the importance of these metabolites for fruit quality and nutrition during breeding. The tannin and acidity-related genes Myb9-like and PH4 are mapped closely to fruit weight locus fw1 from 3.41 to 3.76 Mb on chromosome 15, a region under selection during domestication. Lysophosphatidylethanolamine (LPE) 18:1, which is suppressed by fatty acid desaturase-2 (FAD2), is positively correlated to fruit firmness. We find the fruit weight is negatively correlated with salicylic acid and abscisic acid levels. Further functional assays demonstrate regulation of these hormone levels by NAC-like activated by Apetala3/Pistillata (NAP) and ATP binding cassette G25 (ABCG25), respectively.

CONCLUSIONS

This study provides a metabolic perspective for selection on fruit quality during domestication and improvement, which is a valuable resource for investigating mechanisms controlling apple metabolite content and quality.

Participation of FaTRAB1 Transcription Factor in the Regulation of FaMADS1 Involved in ABA-Dependent Ripening of Strawberry Fruit

Abscisic acid (ABA) plays a crucial role in regulating the ripening of non-climacteric strawberry fruit. In the present study, ABA was confirmed to promote strawberry ripening and induce the down-regulation of FaMADS1. The transient silence of FaMADS1 in strawberries promoted fruit ripening and induced the content of anthocyanin and soluble pectin but reduced firmness and protopectin through a tobacco rattle virus-induced gene silencing technique. In parallel with the accelerated ripening, the genes were significantly induced in the transiently modified fruit, including anthocyanin-related PAL6, C4H, 4CL, DFR, and UFGT, softening-related PL and XTH, and aroma-related QR and AAT2. In addition, the interaction between FaMADS1 and ABA-related transcription factors was researched. Yeast one-hybrid analysis indicated that the FaMADS1 promoter could interact with FaABI5-5, FaTRAB1, and FaABI5. Furthermore, dual-luciferase assay suggested that FaTRAB1 could actively bind with the FaMADS1 promoter, resulting in the decreased expression of FaMADS1. In brief, these results suggest that the ABA-dependent ripening of strawberry fruit was probably inhibited through inhibiting FaMADS1 expression by the active binding of transcript FaTRAB1 with the FaMADS1 promoter.

Genome-Wide Identification and Expression Analysis of NCED Gene Family in Pear and Its Response to Exogenous Gibberellin and Paclobutrazol

The 9-cis-epoxycarotenoid dioxygenase (NCED) is a key enzyme for the process of ABA synthesis that plays key roles in a variety of biological processes. In the current investigation, genome-wide identification and comprehensive analysis of the NCED gene family in 'Kuerle Xiangli' (Pyrus sinkiangensis Yu) were conducted using the pear genomic sequence. In total, nineteen members of PbNCED genes were identified from the whole genome of pear, which are not evenly distributed over the scaffolds, and most of which were focussed in the chloroplasts. Sequence analysis of promoters showed many cis-regulatory elements, which presumably responded to phytohormones such as abscisic acid, auxin, etc. Synteny block indicated that the PbNCED genes have experienced strong purifying selection. Multiple sequence alignment demonstrated that these members are highly similar and conserved. In addition, we found that PbNCED genes were differentially expressed in various tissues, and three PbNCED genes (PbNCED1, PbNCED2, and PbNCED13) were differentially expressed in response to exogenous Gibberellin (GA₃) and Paclobutrazol (PP₃₃₃). PbNCED1 and PbNCED13 positively promote ABA synthesis in sepals after GA₃ and PP₃₃₃ treatment, whereas PbNCED2 positively regulated ABA synthesis in ovaries after GA₃ treatment, and PbNCED13 positively regulated ABA synthesis in the ovaries after PP₃₃₃ treatment. This study was the first genome-wide report of the pear NCED gene family, which could improve our understanding of pear NCED proteins and provide a solid foundation for future cloning and functional analyses of this gene family. Meanwhile, our results also give a better understanding of the important genes and regulation pathways related to calyx abscission in 'Kuerle Xiangli'.