Cucumber abscisic acid 8'-hydroxylase Csyf2 regulates yellow flesh by modulating carotenoid biosynthesis

An intronic SNP in the Carotenoid Cleavage Dioxygenase 1 (CsCCD1) controls yellow flesh formation in cucumber fruit (Cucumis sativus L.)

Vitamin A is a crucial yet scarce vitamin essential for maintaining normal metabolism and bodily functions in humans and can only be obtained from food. Carotenoids represent a diverse group of functional pigments that act as precursors for vitamins, hormones, aroma volatiles and antioxidants. As a vital vegetable in the world, elevated carotenoid levels in cucumber fruit produce yellow flesh, enhancing both visual appeal and nutritional value. However, the genetic mechanisms and regulatory networks governing yellow flesh in cucumbers remain inadequately characterized. In this study, we employed map-based cloning to identify a Carotenoid Cleavage Dioxygenase 1 (CsCCD1) as a key genetic factor influencing yellow flesh in cucumbers. A causal single nucleotide polymorphism (SNP) in the eighth intron of CsCCD1 led to aberrant splicing, resulting in a truncated transcript. The truncated protein has significantly decreased enzyme activity and increased carotenoid accumulation in the fruit. CRISPR/Cas9-generated CsCCD1 knockout mutants exhibited yellow flesh and significantly higher carotenoid content compared to wild-type cucumbers. Metabolic profiling indicated a marked accumulation of β-cryptoxanthin in the flesh of these knockout mutants. The intronic SNP was shown to perfectly segregate with yellow flesh in 159 diverse cucumber germplasms, particularly within the semi-wild ecotype Xishuangbanna, known for its substantial carotenoid accumulation. Furthermore, transient overexpression of CsCCD1 in yellow-fleshed Xishuangbanna cucumbers restored a white flesh phenotype, underscoring the critical role of CsCCD1 in determining flesh colour in both cultivated and semi-wild cucumbers. These findings lay a theoretical foundation for breeding high-nutrient yellow-fleshed cucumber varieties.

The regulatory landscape of β-caryophyllene biosynthesis in pak choi

β-Caryophyllene is a key volatile sesquiterpene involved in plant defense and contributes to the characteristic aroma of pak choi (Brassica campestris). This study aimed to elucidate the regulatory landscape of β-caryophyllene biosynthesis in pak choi to understand the genetic and molecular mechanisms controlling the production of this volatile sesquiterpene. Among 61 germplasm accessions of pak choi, β-caryophyllene was detected in only 11 accessions. Genetic analysis revealed that β-caryophyllene production is controlled by a single dominant gene. Fine mapping and gene sequencing identified the candidate gene B. campestris terpene synthases 21 (BcTPSa21), which encodes a β-caryophyllene synthase. Functional validation of BcTPSa21 through transient expression of BcTPSa21 in Nicotiana benthamiana leaves and enzyme activity assays in vitro confirmed its role in β-caryophyllene biosynthesis. A single nucleotide polymorphism (SNP) (C-T) in the promoter region of BcTPSa21 was found to affect the binding of the transcription factor BcMYC2, thereby influencing gene expression. Additionally, BcDIVARICATA (an R-R-type MYB TF BcDIV) was identified as a negative regulator of β-caryophyllene synthesis. The molecular experiments showed that abscisic acid participates in the biosynthesis of β-caryophyllene via the B. campestris pyrabactin resistance 1-like (BcPYL6)-BcDIVARICATA-BcMYC2 module. RNA-seq analysis suggested that under temperature stress, the transcription of BcTPSa21 and the biosynthesis of β-caryophyllene were the collective result of multilevel regulation. These findings provide comprehensive insights into the regulatory mechanisms governing β-caryophyllene biosynthesis in pak choi, identifying key factors and regulatory modules involved and offering a foundation for enhancing the flavor quality of pak choi through targeted genetic interventions.

Boosting Antioxidant Quality in Cucumber Beverages with Encapsulated Tomato Carotenoids

Tomato by-products are widely generated during processing, which deserve revalorization due to being rich in bioactive compounds that can be incorporated into novel formulas. This study explores the use of tomato by-products as a source of pigments and antioxidant compounds to develop a seasoned cucumber beverage enriched with encapsulated carotenoids. Extracts from industrial tomato pomace were obtained using ultrasound-assisted extraction (USAE) and accelerated solvent extraction (ASE), and then encapsulated by spray-drying with inulin (I), maltodextrin (M), or a maltodextrin-inulin blend (MI). The powders were added to a cucumber beverage treated with high hydrostatic pressure (HHP) and stored for 28 days at 4 °C. Physicochemical properties, microbial load, carotenoid content (U-HPLC), free phenolic content (FPC), and total antioxidant capacity (TAC) were monitored. Beverage samples with maltodextrin (ASE-M, USAE-M) and the maltodextrin-inulin blend (ASE-MI, USAE-MI) showed superior color stability and pH maintenance. USAE-MI achieved the highest TAC at the end of storage and ensured microbial safety by reducing mesophilic bacteria, molds, and yeast. During storage, FPC declined (to ~3.5-5 mg 100 mL-1), TAC increased (to ~16-20 mg 100 mL-1), and carotenoid was kept stable (~9-13 mg L-1). These results highlight the potential of combining HHP with tomato by-product encapsulates to improve the shelf life, quality, pigment stability, and antioxidant properties of vegetable-based beverages.

Identifying candidate genes for sugar accumulation in sugarcane: an integrative approach

BACKGROUND

Elucidating the intricacies of the sugarcane genome is essential for breeding superior cultivars. This economically important crop originates from hybridizations of highly polyploid Saccharum species. However, the large size (10 Gb), high degree of polyploidy, and aneuploidy of the sugarcane genome pose significant challenges to complete genome sequencing, assembly, and annotation. One successful strategy for identifying candidate genes linked to agronomic traits, particularly those associated with sugar accumulation, leverages synteny and potential collinearity with related species.

RESULTS

In this study, we explored synteny between sorghum and sugarcane. Genes from a sorghum Brix QTL were used to screen bacterial artificial chromosome (BAC) libraries from two Brazilian sugarcane varieties (IACSP93-3046 and SP80-3280). The entire region was successfully recovered, confirming synteny and collinearity between the species. Manual annotation identified 51 genes in the hybrid varieties that were subsequently confirmed to be present in Saccharum spontaneum. This study employed a multifaceted approach to identify candidate genes for sugar accumulation, including retrieving the genomic region of interest, performing a gene-by-gene analysis, analyzing RNA-seq data for internodes from Saccharum officinarum and S. spontaneum accessions, constructing a coexpression network to examine the expression patterns of genes within the studied region and their neighbors, and finally identifying differentially expressed genes (DEGs).

CONCLUSIONS

This comprehensive approach led to the discovery of three candidate genes potentially involved in sugar accumulation: an ethylene-responsive transcription factor (ERF), an ABA 8'-hydroxylase, and a prolyl oligopeptidase (POP). These findings could be valuable for identifying additional candidate genes for other important agricultural traits and directly targeting candidate genes for further work in molecular breeding.

Preharvest Application of Exogenous 2,4-Epibrassinolide and Melatonin Enhances the Maturity and Flue-Cured Quality of Tobacco Leaves

Tobacco (Nicotiana tabacum) is a globally cultivated crop, with its quality closely associated with the color and chemical composition of cured tobacco leaves. In this experiment, the effects of spraying exogenous 2, 4-epibrassinolide (EBR) and melatonin (MT) on the development of tobacco leaves at maturity stage and the quality after curing were investigated. Both EBR and MT treatments significantly enhanced the appearance quality of tobacco leaves at the stem-drying stage. Following preharvest applications, the sugar-to-alkali ratio and potassium content increased, while the contents of starch, total alkaloids, and proteins decreased. The levels of conventional chemical components were improved, enhancing the overall coordination of the tobacco. Transcriptome analysis revealed that EBR treatment down-regulated the chlorophyll biosynthetic genes hemA, MgPEC, and ChlD, while up-regulating the chlorophyll degradation genes CHL2, SGR, and PAOs. Similarly, MT treatment down-regulated the chlorophyll biosynthetic genes FC2 and MgPEC and up-regulated the degradation genes CHL2 and SGR, thus promoting chlorophyll degradation. Furthermore, in the downstream carotenoid biosynthetic pathway, both EBR and MT treatments regulated abscisic acid-related genes, with NCEDs being up-regulated and CYP707A1s down-regulated, thereby promoting the leaf ripening. Metabolomics analysis indicated that EBR treatment primarily regulated alkaloids, terpenoids, and flavonoids, while MT treatment mainly affected flavonoids. Both treatments also reduced the accumulation of the harmful substance aristolochic acid B. Comprehensive evaluations of appearance quality, physiological parameters, transcriptome, and metabolomics analyses demonstrated that exogenous spraying of EBR and MT treatments improved the maturity and quality of cured tobacco leaves, with EBR treatment exhibiting a greater effect than MT treatment.

From Regulation to Application: The Role of Abscisic Acid in Seed and Fruit Development and Agronomic Production Strategies

Abscisic acid (ABA) is a crucial plant hormone that plays a decisive role in regulating seed and fruit development and is becoming increasingly important in agricultural applications. This article delves into ABA's regulatory functions in plant growth, particularly during the stages of seed and fruit development. In the seed phase, elevated ABA levels help maintain seed dormancy, aiding seed survival under unfavorable conditions. During fruit development, ABA regulates pigment synthesis and sugar accumulation, influencing the nutritional value and market quality of the fruit. This article highlights three main strategies for applying ABA in agricultural production: the use of ABA analogs, the development of ABA signal modulators, and breeding techniques based on ABA signaling. ABA analogs can mimic the natural functions of ABA, while ABA signal modulators, including enhancers and inhibitors, are used to finely tune plant responses to ABA, optimizing crop performance under specific growth conditions. Furthermore, breeding strategies based on ABA signaling aim to select crop varieties that effectively utilize ABA pathways through genetic engineering and other technologies. ABA is not only a key regulator of plant growth and development but also holds great potential for modern agricultural practices.

The AGAMOUS-LIKE 16-GENERAL REGULATORY FACTOR 1 module regulates axillary bud outgrowth via catabolism of abscisic acid in cucumber

Lateral branches are important components of shoot architecture and directly affect crop yield and production cost. Although sporadic studies have implicated abscisic acid (ABA) biosynthesis in axillary bud outgrowth, the function of ABA catabolism and its upstream regulators in shoot branching remain elusive. Here, we showed that the MADS-box transcription factor AGAMOUS-LIKE 16 (CsAGL16) is a positive regulator of axillary bud outgrowth in cucumber (Cucumis sativus). Functional disruption of CsAGL16 led to reduced bud outgrowth, whereas overexpression of CsAGL16 resulted in enhanced branching. CsAGL16 directly binds to the promoter of the ABA 8'-hydroxylase gene CsCYP707A4 and promotes its expression. Loss of CsCYP707A4 function inhibited axillary bud outgrowth and increased ABA levels. Elevated expression of CsCYP707A4 or treatment with an ABA biosynthesis inhibitor largely rescued the Csagl16 mutant phenotype. Moreover, cucumber General Regulatory Factor 1 (CsGRF1) interacts with CsAGL16 and antagonizes CsAGL16-mediated CsCYP707A4 activation. Disruption of CsGRF1 resulted in elongated branches and decreased ABA levels in the axillary buds. The Csagl16 Csgrf1 double mutant exhibited a branching phenotype resembling that of the Csagl16 single mutant. Therefore, our data suggest that the CsAGL16-CsGRF1 module regulates axillary bud outgrowth via CsCYP707A4-mediated ABA catabolism in cucumber. Our findings provide a strategy to manipulate ABA levels in axillary buds during crop breeding to produce desirable branching phenotypes.