A novel R2R3-MYB transcription factor FaMYB5 positively regulates anthocyanin and proanthocyanidin biosynthesis in cultivated strawberries (Fragaria × ananassa)

Genetic factors explaining anthocyanin pigmentation differences

BACKGROUND

Anthocyanins are important contributors to coloration across a wide phylogenetic range of plants. Biological functions of anthocyanins span from reproduction to protection against biotic and abiotic stressors. Owing to a clearly visible phenotype of mutants, the anthocyanin biosynthesis and its sophisticated regulation have been studied in numerous plant species. Genes encoding the anthocyanin biosynthesis enzymes are regulated by a transcription factor complex comprising MYB, bHLH and WD40 proteins.

RESULTS

A systematic comparison of anthocyanin-pigmented vs. non-pigmented varieties was performed within numerous plant species covering the taxonomic diversity of flowering plants. The literature was screened for cases in which genetic factors causing anthocyanin loss were reported. Additionally, transcriptomic data sets from four previous studies were reanalyzed to determine the genes possibly responsible for color variation based on their expression pattern. The contribution of different structural and regulatory genes to the intraspecific pigmentation differences was quantified. Differences concerning transcription factors are by far the most frequent explanation for pigmentation differences observed between two varieties of the same species. Among the transcription factors in the analyzed cases, MYB genes are significantly more prone to account for pigmentation differences compared to bHLH or WD40 genes. Among the structural genes, DFR genes are most often associated with anthocyanin loss.

CONCLUSIONS

These findings support previous assumptions about the susceptibility of transcriptional regulation to evolutionary changes and its importance for the evolution of novel coloration phenotypes. Our findings underline the particular significance of MYBs and their apparent prevalent role in the specificity of the MBW complex.

The R2R3 MYB Ruby1 is activated by two cold responsive ethylene response factors, via the retrotransposon in its promoter, to positively regulate anthocyanin biosynthesis in citrus

Anthocyanins are natural pigments and dietary antioxidants that play multiple biological roles in plants and are important in animal and human nutrition. Low temperature (LT) promotes anthocyanin biosynthesis in many species including blood orange. A retrotransposon in the promoter of Ruby1, which encodes an R2R3 MYB transcription factor, controls cold-induced anthocyanin accumulation in blood orange flesh. However, the specific mechanism remains unclear. In this study, we characterized two LT-induced ETHYLENE RESPONSE FACTORS (CsERF054 and CsERF061). Both CsERF054 and CsERF061 can activate the expression of CsRuby1 by directly binding to a DRE/CRT cis-element within the retrotransposon in the promoter of CsRuby1, thereby positively regulating anthocyanin biosynthesis. Further investigation indicated that CsERF061 also forms a protein complex with CsRuby1 to co-activate the expression of anthocyanin biosynthetic genes, providing a dual mechanism for the upregulation of the anthocyanin pathway. These results provide insights into how LT mediates anthocyanin biosynthesis and increase the understanding of the regulatory network of anthocyanin biosynthesis in blood orange.

A novel three-layer module BoMYB1R1-BoMYB4b/BoMIEL1-BoDFR1 regulates anthocyanin accumulation in kale

Anthocyanin is an important pigment responsible for plant coloration and beneficial to human health. Kale (Brassica oleracea var. acephala), a primary cool-season flowers and vegetables, is an ideal material to study anthocyanin biosynthesis and regulation mechanisms due to its anthocyanin-rich leaves. However, the underlying molecular mechanism of anthocyanin accumulation in kale remains poorly understood. Previously, we demonstrated that BoDFR1 is a key gene controlling anthocyanin biosynthesis in kale. Here, we discovered a 369-bp InDel variation in the BoDFR1 promoter between the two kale inbred lines with different pink coloration, which resulted in reduced transcriptional activity of the BoDFR1 gene in the light-pink line. With the 369-bp insertion as a bait, an R2R3-MYB repressor BoMYB4b was identified using the yeast one-hybrid screening. Knockdown of the BoMYB4b gene led to increased BoDFR1 expression and anthocyanin accumulation. An E3 ubiquitin ligase, BoMIEL1, was found to mediate the degradation of BoMYB4b, thereby promoting anthocyanin biosynthesis. Furthermore, the expression level of BoMYB4b was significantly reduced by light signals, which was attributed to the direct repression of the light-signaling factor BoMYB1R1 on the BoMYB4b promoter. Our study revealed that a novel regulatory module comprising BoMYB1R1, BoMIEL1, BoMYB4b, and BoDFR1 finely regulates anthocyanin accumulation in kale. The findings aim to establish a scientific foundation for genetic improvement of leaf color traits in kale, meanwhile, providing a reference for plant coloration studies.

Genome-wide investigation and analysis of NAC transcription factor family in Populus tomentosa and expression analysis under salt stress

The NAC transcription factor family is one of the largest families of TFs in plants, and members of NAC gene family play important roles in plant growth and stress response. Recent release of the haplotype-resolved genome assembly of P. tomentosa provide a platform for NAC protein genome-wide analysis. A total of 270 NAC genes were identified and a comprehensive overview of the PtoNAC gene family is presented, including gene promoter, structure and conserved motif analyses, chromosome localization and collinearity analysis, protein phylogeny, expression pattern, and interaction analysis. The results indicate that protein length, molecular weight, and theoretical isoelectric points of the NAC TF family vary, while gene structure and motif are relatively conserved. Chromosome mapping analysis showed that the P. tomentosa NAC genes are unevenly distributed on 19 chromosomes. The interchromosomal evolutionary results indicate 12 pairs of tandem and 280 segmental duplications. Segmental duplication is possibly related to amplification of P. tomentosa NAC gene family. Expression patterns of 35 PtoNAC genes from P. tomentosa subgroup were analysed under high salinity, and seven NAC genes were induced by this treatment. Promoter and protein interaction network analyses showed that PtoNAC genes are closely associated with growth, development, and abiotic and biotic stress, especially salt stress. These results provide a meaningful reference for follow-up studies of the functional characteristics of NAC genes in the mechanism of stress response and their potential roles in development of P. tomentosa.

Transcriptomic Analysis Reveals the Flavonoid Biosynthesis Pathway Involved in Rhizome Development in Polygonatum cyrtonema Hua

Polygonatum cyrtonema Hua (P. cyrtonema) rhizomes are rich in flavonoids and other secondary metabolites, exhibiting remarkable antioxidant, anti-tumor, and immunomodulatory effects. Polygonatum flavonoid-biosynthesis-related genes have been characterized already. However, a comprehensive overview of Polygonatum flavonoid biosynthesis pathways is still absent. To articulate the accumulation of the flavonoid biosynthesis pathways, we examined transcriptome changes using Illumina HiSeq from five different tissues and the RNA-seq of 15 samples had over 105 Gb of a clean base, generating a total of 277,955 unigenes. The cDNA libraries of the fruits (F), leaves (L), roots (R), stems (S), and rhizomes (T) of three-year-old P. cyrtonema plants generated 57,591, 53,578, 60,321, 51,530, and 54,935 unigenes. Comparative transcriptome analysis revealed that 379 differentially expressed genes (DEGs) were in the group of F _vs_ T, L _vs_ T, R _vs_ T, and S _vs_ T, and the transcripts of flavonoid-biosynthesis-related DEGs were principally enriched in rhizomes. In addition, combined with WGCNA and the FPKM of five tissues' transcription, nine differentially expressed transcription factor families (MYB, WRKY, AP2/ERF, etc.) were characterized in the red module, the red module positively correlated with rhizome flavonoid accumulation. Quantitative real-time PCR (qRT-PCR) further indicated that BZIP1, C3H31, ERF114, and DREB21 are differentially expressed in rhizomes, accompanied in rhizome development in P. cyrtonema. Therefore, this study provides a foundation for further research into uncovering the accumulation of flavonoid biosynthesis in the rhizomes of P. cyrtonema.

Update on functional analysis of long non-coding RNAs in common crops

With the rapid advances in next-generation sequencing technology, numerous non-protein-coding transcripts have been identified, including long noncoding RNAs (lncRNAs), which are functional RNAs comprising more than 200 nucleotides. Although lncRNA-mediated regulatory processes have been extensively investigated in animals, there has been considerably less research on plant lncRNAs. Nevertheless, multiple studies on major crops showed lncRNAs are involved in crucial processes, including growth and development, reproduction, and stress responses. This review summarizes the progress in the research on lncRNA roles in several major crops, presents key strategies for exploring lncRNAs in crops, and discusses current challenges and future prospects. The insights provided in this review will enhance our comprehension of lncRNA functions in crops, with potential implications for improving crop genetics and breeding.

A 224-bp Indel in the Promoter of PeMYB114 Accounts for Anthocyanin Accumulation of Skin in Passion Fruit (Passiflora spp.)

Passion fruit (Passiflora spp.) is an important fruit tree in the family Passifloraceae. The color of the fruit skin, a significant agricultural trait, is determined by the content of anthocyanin in passion fruit. However, the regulatory mechanisms behind the accumulation of anthocyanin in different passion fruit skin colors remain unclear. In the study, we identified and characterized a R2R3-MYB transcription factor, PeMYB114, which functions as a transcriptional activator in anthocyanin biosynthesis. Yeast one-hybrid system and dual-luciferase analysis showed that PeMYB114 could directly activate the expression of anthocyanin structural genes (PeCHS and PeDFR). Furthermore, a natural variation in the promoter region of PeMYB114 alters its expression. PeMYB114purple accessions with the 224-bp insertion have a higher anthocyanin level than PeMYB114yellow accessions with the 224-bp deletion. The findings enhance our understanding of anthocyanin accumulation in fruits and provide genetic resources for genome design for improving passion fruit quality.

Comparative metabolomics profiling highlights unique color variation and bitter taste formation of Chinese cherry fruits

Chinese cherry [Cerasus pseudocerasus (Lindl.) G.Don], native to China, is an economically important fruit crop with attractive colors and delicious flavors. However, the specific metabolites present in cherry fruits have remained unknown. Here, we firstly characterized 1439 metabolite components of Chinese cherry fruits, predominantly including amino acids, flavonoids, and phenolic acids. Moreover, we screened ten biomarkers of Chinese cherry accessions by ROC curve analysis. Among 250 flavonoids, 26 structurally unique anthocyanins collectively determined fruit color, with cyanidins playing a dominant role. Differences in accumulated metabolites between anthocyanin and proanthocyanidin pathways were likely responsible for the variation in fruit color, ranging from yellow to black purple. Meanwhile, we found limocitrin-7-O-glucoside, along with eight other compounds, as underlying contributors to bitter off-taste experienced in fruits. This study provides insights into the regulatory network of metabolites involved in color variation and bitterness formation and genetic improvement of Chinese cherry fruits.

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

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

Identification and Expression Analysis of R2R3-MYB Transcription Factors Associated with Flavonoid Biosynthesis in Panax quinquefolius

Panax quinquefolius L. is an important medicinal plant, and flavonoids are among its main secondary metabolites. The R2R3-MYB transcription factor plays an irreplaceable role in plant growth, development, and secondary metabolism. In our study, we identified 159 R2R3-MYBs and analyzed their physical and chemical properties in P. quinquefolius. The protein length of 159 PqMYBs varied from 107 to 1050 amino acids. The molecular weight ranged from 12.21 to 116.44 kDa. The isoelectric point was between 4.57 and 10.34. We constructed a phylogenetic tree of P. quinquefolius and Arabidopsis thaliana R2R3-MYB family members, and PqMYB members were divided into 33 subgroups. Transcriptome data analysis showed that the expression patterns of PqMYBs in root, leaf, and flower were significantly different. Following the MeJA treatment of seedlings, five candidate PqMYB genes demonstrated a response. A correlation analysis of PqMYBs and candidate flavonoid pathway genes showed that PqMYB2, PqMYB46, and PqMYB72 had correlation coefficients that were higher than 0.8 with PqCHS, PqANS4, and PqCCoAMT10, respectively. Furthermore, a transient expression assay confirmed that the three PqMYBs were localized in the nucleus. We speculated that these three PqMYBs were related to flavonoid biosynthesis in P. quinquefolius. These results provided a theoretical basis and a new perspective for further understanding the R2R3-MYB gene family and the biosynthesis mechanism of secondary metabolites in P. quinquefolius.

Potential Regulatory Networks and Heterosis for Flavonoid and Terpenoid Contents in Pak Choi: Metabolomic and Transcriptome Analyses

Pak choi exhibits a diverse color range and serves as a rich source of flavonoids and terpenoids. However, the mechanisms underlying the heterosis and coordinated regulation of these compounds-particularly isorhamnetin-remain unclear. This study involved three hybrid combinations and the detection of 528 metabolites from all combinations, including 26 flavonoids and 88 terpenoids, through untargeted metabolomics. Analysis of differential metabolites indicated that the heterosis for the flavonoid and terpenoid contents was parent-dependent, and positive heterosis was observed for isorhamnetin in the two hybrid combinations (SZQ, 002 and HMG, ZMG). Moreover, there was a high transcription level of flavone 3'-O-methyltransferase, which is involved in isorhamnetin biosynthesis. The third group was considered the ideal hybrid combination for investigating the heterosis of flavonoid and terpenoid contents. Transcriptome analysis identified a total of 12,652 DEGs (TPM > 1) in various groups that were used for comparison, and DEGs encoding enzymes involved in various categories, including "carotenoid bio-synthesis" and "anthocyanin biosynthesis", were enriched in the hybrid combination (SZQ, 002). Moreover, the category of anthocyanin biosynthesis also was enriched in the hybrid combination (HMG, ZMG). The flavonoid pathway demonstrated more differential metabolites than the terpenoid pathway did. The WGCNA demonstrated notable positive correlations between the dark-green modules and many flavonoids and terpenoids. Moreover, there were 23 ERF genes in the co-expression network (r ≥ 0.90 and p < 0.05). Thus, ERF genes may play a significant role in regulating flavonoid and terpenoid biosynthesis. These findings enhance our understanding of the heterosis and coordinated regulation of flavonoid and terpenoid biosynthesis in pak choi, offering insights for genomics-based breeding improvements.

Genome-wide analysis and functional validation reveal the role of late embryogenesis abundant genes in strawberry (Fragaria × ananassa) fruit ripening

BACKGROUND

Late embryogenesis abundant (LEA) proteins play important roles in plant growth and development, as well as stresses responsiveness. Nowadays, it has been found that LEAs also have function in fruit ripening. However, the comprehensive analysis on a genome-wide basis of LEA family remains limited, and the role of LEA in fruit ripening has not been fully explored yet, especially in strawberry, an economic important plant and ideal material for studying fruit ripening.

RESULTS

In this study, a total of 266 putative LEA proteins were identified and characterized in strawberry genome. Subcellular localization prediction indicated that they were mostly localized in chloroplast, cytoplasm and nucleus. Duplication events detection revealed that whole genome duplication or segmental was the main driver for the expansion of LEA family in strawberry. The phylogenetic analysis suggested that FaLEAs were classified into eight groups, among which, LEA2 was the largest subgroup with 179 members, followed by LEA3, dehydrin (DHN), LEA4 and SMP (seed maturation protein). The LEA1 and DHN groups were speculated to play dominant roles in strawberry fruit development and ripening, according to their larger proportion of members detected as differentially expressed genes during such process. Notably, the expression of FaLEA167 belonging to LEA1 group was altered by strawberry maturation, and inhibited by overexpression of negative regulators of ripening (a cytosolic/plastid glyceraldehyde-3-phosphate dehydrogenase, FaGAPC2 and a cytosolic pyruvate kinase, FaPKc2.2). Subsequently, overexpression of FaLEA167 significantly increased the percentage of fruit at green stage, while reduced the full red fruit proportion. In consistent, the anthocyanins content and the fruit skin color variable reflecting a range from greenness to redness (a* value) were significantly reduced. Whereas, FaLEA167 overexpression apparently up-regulated citric acid, soluble protein and malondialdehyde content, but had no obvious effects on total soluble solids, sugar, flavonoids, phenolics content and antioxidant capacity.

CONCLUSIONS

These findings not only provided basic information of FaLEA family for further functional research, but also revealed the involvement of FaLEA167 in negatively regulating strawberry fruit ripening, giving new insights into understanding of FaLEA functions.

IbMYC2 Contributes to Salt and Drought Stress Tolerance via Modulating Anthocyanin Accumulation and ROS-Scavenging System in Sweet Potato

Basic helix-loop-helix (bHLH) transcription factors extensively affect various physiological processes in plant metabolism, growth, and abiotic stress. However, the regulation mechanism of bHLH transcription factors in balancing anthocyanin biosynthesis and abiotic stress in sweet potato (Ipomoea batata (L.) Lam.) remains unclear. Previously, transcriptome analysis revealed the genes that were differentially expressed among the purple-fleshed sweet potato cultivar 'Jingshu 6' and its anthocyanin-rich mutant 'JS6-5'. Here, we selected one of these potential genes, IbMYC2, which belongs to the bHLH transcription factor family, for subsequent analyses. The expression of IbMYC2 in the JS6-5 storage roots is almost four-fold higher than Jingshu 6 and significantly induced by hydrogen peroxide (H2O2), methyl jasmonate (MeJA), NaCl, and polyethylene glycol (PEG)6000. Overexpression of IbMYC2 significantly enhances anthocyanin production and exhibits a certain antioxidant capacity, thereby improving salt and drought tolerance. In contrast, reducing IbMYC2 expression increases its susceptibility. Our data showed that IbMYC2 could elevate the expression of anthocyanin synthesis pathway genes by binding to IbCHI and IbDFR promoters. Additionally, overexpressing IbMYC2 activates genes encoding reactive oxygen species (ROS)-scavenging and proline synthesis enzymes under salt and drought conditions. Taken together, these results demonstrate that the IbMYC2 gene exercises a significant impact on crop quality and stress resistance.

Integrated transcriptomics and metabolomics analysis provides insights into aromatic volatiles formation in Cinnamomum cassia bark at different harvesting times

BACKGROUND

Cinnamomum cassia Presl, classified in the Lauraceae family, is widely used as a spice, but also in medicine, cosmetics, and food. Aroma is an important factor affecting the medicinal and flavoring properties of C. cassia, and is mainly determined by volatile organic compounds (VOCs); however, little is known about the composition of aromatic VOCs in C. cassia and their potential molecular regulatory mechanisms. Here, integrated transcriptomic and volatile metabolomic analyses were employed to provide insights into the formation regularity of aromatic VOCs in C. cassia bark at five different harvesting times.

RESULTS

The bark thickness and volatile oil content were significantly increased along with the development of the bark. A total of 724 differentially accumulated volatiles (DAVs) were identified in the bark samples, most of which were terpenoids. Venn analysis of the top 100 VOCs in each period showed that twenty-eight aromatic VOCs were significantly accumulated in different harvesting times. The most abundant VOC, cinnamaldehyde, peaked at 120 months after planting (MAP) and dominated the aroma qualities. Five terpenoids, α-copaene, β-bourbonene, α-cubebene, α-funebrene, and δ-cadinene, that peaked at 240 MAP could also be important in creating C. cassia's characteristic aroma. A list of 43,412 differentially expressed genes (DEGs) involved in the biosynthetic pathways of aromatic VOCs were identified, including phenylpropanoids, mevalonic acid (MVA) and methylerythritol phosphate (MEP). A gene-metabolite regulatory network for terpenoid and phenylpropanoid metabolism was constructed to show the key candidate structural genes and transcription factors involved in the biosynthesis of terpenoids and phenylpropanoids.

CONCLUSIONS

The results of our research revealed the composition and changes of aromatic VOCs in C. cassia bark at different harvesting stages, differentiated the characteristic aroma components of cinnamon, and illuminated the molecular mechanism of aroma formation. These foundational results will provide technical guidance for the quality breeding of C. cassia.

Eggplant transcription factor SmMYB5 integrates jasmonate and light signaling during anthocyanin biosynthesis

Low light conditions severely suppress anthocyanin synthesis in fruit skins, leading to compromised fruit quality in eggplant (Solanum melongena L.) production. In this study, we found that exogenous methyl-jasmonate (MeJA) application can effectively rescue the poor coloration of the eggplant pericarp under low light conditions. However, the regulatory relationship between jasmonate and light signaling for regulating anthocyanin synthesis remains unclear. Here, we identified a JA response factor, SmMYB5, as an anthocyanin positive regulator by applying RNA-sequencing and characterization of transgenic plants. Firstly, we resolved that SmMYB5 can interact with TRANSPARENT TESTA8 (SmTT8), an anthocyanin-promoted BASIC HELIX-LOOP-HELIX (bHLH) transcription factor, to form the SmMYB5-SmTT8 complex and activate CHALCONE SYNTHASE (SmCHS), FLAVANONE-3-HYDROXYLASE (SmF3H), and ANTHOCYANIN SYNTHASE (SmANS) promoters by direct binding. Secondly, we revealed that JA signaling repressors JASMONATE ZIM DOMAIN5 (SmJAZ5) and SmJAZ10 can interfere with the stability and transcriptional activity of SmMYB5-SmTT8 by interacting with SmMYB5. JA can partially rescue the transcriptional activation of SmF3H and SmANS promoters by inducing SmJAZ5/10 degradation. Thirdly, we demonstrated that the protein abundance of SmMYB5 is regulated by light. CONSTITUTIVELY PHOTOMORPHOGENIC1 (SmCOP1) interacts with SmMYB5 to trigger SmMYB5 degradation via the 26S proteasome pathway. Finally, we delineated a light-dependent JA-SmMYB5 signaling pathway that promotes anthocyanin synthesis in eggplant fruit skins. These results provide insights into the mechanism of the integration of JA and light signals in regulating secondary metabolite synthesis in plants.

Genome-Wide Identification and Expression Analysis of the MYB Transcription Factor Family in Salvia nemorosa

The MYB transcription factor gene family is among the most extensive superfamilies of transcription factors in plants and is involved in various essential functions, such as plant growth, defense, and pigment formation. Salvia nemorosa is a perennial herb belonging to the Lamiaceae family, and S. nemorosa has various colors and high ornamental value. However, there is little known about its genome-wide MYB gene family and response to flower color formation. In this study, 142 SnMYB genes (MYB genes of S. nemorosa) were totally identified, and phylogenetic relationships, conserved motifs, gene structures, and expression profiles during flower development stages were analyzed. A phylogenetic analysis indicated that MYB proteins in S. nemorosa could be categorized into 24 subgroups, as supported by the conserved motif compositions and gene structures. Furthermore, according to their similarity with AtMYB genes associated with the control of anthocyanin production, ten SnMYB genes related to anthocyanin biosynthesis were speculated and chosen for further qRT-PCR analyses. The results indicated that five SnMYB genes (SnMYB75, SnMYB90, SnMYB6, SnMYB82, and SnMYB12) were expressed significantly differently in flower development stages. In conclusion, our study establishes the groundwork for understanding the anthocyanin biosynthesis of the SnMYB gene family and has the potential to enhance the breeding of S. nemorosa.

Genome-wide identification, classification and expression analysis of MYB gene family in coconut (Cocos nucifera L.)

MYB transcription factors regulate the growth, development, and secondary metabolism of plant species. To investigate the origin of color variations in coconut pericarp, we identified and analyzed the MYB gene family present in coconut. According to the sequence of MYB genes in Arabidopsis thaliana, homologous MYB gene sequences were found in the whole genome database of coconut, the conserved sequence motifs within MYB proteins were analyzed by Motif Elicitation (MEME) tool, and the sequences without conservative structure were eliminated. Additionally, we employed RNA-seq technology to generate gene expression signatures of the R2R3-MYB genes across distinctive coconut parts exhibiting diverse colors. To validate these profiles, we conducted quantitative PCR (qPCR). Through comprehensive genome-wide screening, we successfully identified a collection of 179 MYB genes in coconut. Subsequent phylogenetic analysis categorized these 179 coconut MYB genes into 4-subfamilies: 124 R2R3-MYB, 4 3R-MYB types, 4 4R-MYB type, and 47 unknown types. Furthermore, these genes were further divided into 34 subgroups, with 28 of these subgroups successfully classified into known subfamilies found in Arabidopsis thaliana. By mapping the CnMYB genes onto the 16 chromosomes of the coconut genome, we unveiled a collinearity association between them. Moreover, a preservation of gene structure and motif distribution was observed across the CnMYB genes. Our research encompassed a thorough investigation of the R2R3-MYB genes present in the coconut genome, including the chromosomal localization, gene assembly, conserved regions, phylogenetic associations, and promoter cis-acting elements of the studied genes. Our findings revealed a collection of 12 R2R3-MYB candidate genes, namely CnMYB8, CnMYB15, CnMYB27, CnMYB28, CnMYB61, CnMYB63, CnMYB68, CnMYB94, CnMYB101, CnMYB150, CnMYB153, and CnMYB164. These genes showed differential expressions in diverse tissues and developmental stages of four coconut species, such as CnMYB68, CnMYB101, and CnMYB28 exhibited high expression in majority of tissues and coconut species, while CnMYB94 and CnMYB164 showed lower expression. These findings shed light on the crucial functional divergence of CnMYB genes across various coconut tissues, suggesting these genes as promising candidate genes for facilitating color development in this important crop.

MiMYB10 transcription factor regulates biosynthesis and accumulation of carotenoid involved genes in mango fruit

Carotenoids are essential and beneficial substances for both plant and human health. Identifying the regulatory network of these pigments is necessary for improving fruit quality and commodity value. In this study, we performed integrative analyses of transcriptome data from two different type fruits, ripening peel color at green ('Neelum' mango) and red ('Irwin' mango). Specifically, we found that MiMYB10 transcription level was highly associated with mango peel color. Further, silencing MiMYB10 homologous gene in tomato fruits resulted in lower carotenoid and anthocyanin content. Electrophoretic mobility shift assays and dual-luciferase clarified that MiMYB10 regulates the carotenoid biosynthesis gene MiPDS (phytoene desaturase gene) in a direct manner. On the other hand, MiMYB10 activates the expression of carotenoid biosynthesis genes (PSY, Z-ISO, CRTISO, LCYE) and chlorophyll degradation gene (SGR1), promoting the accumulation of carotenoid, accelerating chlorophyll degradation, and controlling peel color. In summary, this study identified important roles of MiMYB10 in pigment regulatory and provided new options for breeding strategies aiming to improve fruit quality.

SlMYB7, an AtMYB4-Like R2R3-MYB Transcription Factor, Inhibits Anthocyanin Accumulation in Solanum lycopersicum Fruits

Tomato is a horticultural crop with an incomplete flavonoid metabolic pathway that does not typically accumulate anthocyanins in the fruit. In recent years, intensive studies of the loci Anthocyanin fruit (Aft) and atroviolacium (atv) have clarified the functions of positive regulators (R2R3-MYBs) and a negative regulator (CPC-MYB) in anthocyanin biosynthesis in the fruits. However, little is known about the R2R3-MYB repressors. Here, we used transient overexpression analysis to show that SlMYB7, a subgroup 4 AtMYB4-like R2R3-MYB, inhibited anthocyanin accumulation and reduced expression of anthocyanin synthase genes in the 'black pearl' tomato fruits, which usually accumulate high concentrations of anthocyanins. These findings revealed that SlMYB7 served as a repressor of anthocyanin production. Furthermore, SlMYB7 actively repressed SlANS expression by binding its promoter and passively inhibited anthocyanin synthesis by interacting with the basic helix-loop-helix (bHLH) proteins SlJAF13 and SlAN1, which are involved in the formation of MBW complexes. Thus, SlMYB7 and the MBW complex may coregulate the anthocyanin content of 'black pearl' tomato fruits via a negative feedback loop. These findings provide a theoretical basis for the future enhancement of tomato anthocyanin contents through genetic manipulation of the biosynthetic regulatory network.

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

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

Deciphering the genetic architecture of fruit color in strawberry

Fruits of Fragaria species usually have an appealing bright red color due to the accumulation of anthocyanins, water-soluble flavonoid pigments. Octoploid cultivated strawberry (Fragaria × ananassa) is a major horticultural crop for which fruit color and associated nutritional value are main breeding targets. Great diversity in fruit color intensity and pattern is observed not only in cultivated strawberry but also in wild relatives such as its octoploid progenitor F. chiloensis or the diploid woodland strawberry F. vesca, a model for fruit species in the Rosaceae. This review examines our understanding of fruit color formation in strawberry and how ongoing developments will advance it. Natural variations of fruit color as well as color changes during fruit development or in response to several cues have been used to explore the anthocyanin biosynthetic pathway and its regulation. So far, the successful identification of causal genetic variants has been largely driven by the availability of high-throughput genotyping tools and high-quality reference genomes of F. vesca and F. × ananassa. The current completion of haplotype-resolved genomes of F. × ananassa combined with QTL mapping will accelerate the exploitation of the untapped genetic diversity of fruit color and help translate the findings into strawberry improvement.

The R2R3-MYB transcription factor OfMYB21 positively regulates linalool biosynthesis in Osmanthus fragrans flowers

Osmanthus fragrans is a well-known landscape ornamental tree species for its pleasing floral fragrance and abundance of flowers. Linalool, the core floral volatiles of O. fragrans, has tremendous economic value in the pharmaceuticals, cleaning products and cosmetics industries. However, the transcriptional regulatory network for the biosynthesis of linalool in O. fragrans remains unclear. Here, OfMYB21, a potential transcription factor regulating the linalool synthetase OfTPS2, was identified using RNA-seq data and qRT-PCR analysis. Yeast one-hybrid, dual-luciferase and EMSA showed that OfMYB21 directly binds to the promoter of OfTPS2 and activates its expression. Overexpression of OfMYB21 in the petals of O. fragrans led to up-regulation of OfTPS2 and increased accumulation of linalool, while silencing of OfMYB21 led to down-regulation of OfTPS2 and decreased biosynthesis of linalool. Subsequently, yeast two-hybrid, pull-down and BiFC experiments showed that OfMYB21 interacts with JA signaling factors OfJAZ2/3 and OfMYC2. Interestingly, the interaction between OfMYC2 and OfMYB21 further enhanced the transcription of OfTPS2, whereas OfJAZ3 attenuated this effect. Overall, our studies provided novel finding on the regulatory mechanisms responsible for the biosynthesis of the volatile monoterpenoid linalool in O. fragrans.

Comprehensive Analysis of the Pectate Lyase Gene Family and the Role of FaPL1 in Strawberry Softening

Fruit softening is a crucial factor that controls shelf life and commercial value. Pectate lyase (PL) has a major role in strawberry fruit softening. However, the PL gene family in strawberry has not been comprehensively analyzed. In this study, 65 FaPL genes were identified in the octoploid strawberry genome. Subcellular localization prediction indicated that FaPLs are mostly localized to the extracellular and cytoplasmic spaces. Duplication event analysis suggested that FaPL gene family expansion is mainly driven by whole genome or segmental duplication. The FaPL family members were classified into six groups according to the phylogenetic analysis. Among them, FaPL1, 3, 5, 20, 25, 42, and 57 had gradually increased expressions during strawberry fruit development and ripening and higher expression levels in the fruits with less firmness than that in firmer fruit. This result suggested that these members are involved in strawberry softening. Furthermore, overexpression of FaPL1 significantly reduced the fruit firmness, ascorbic acid (AsA), and malondialdehyde (MDA) content but obviously increased the anthocyanins, soluble proteins, and titratable acidity (TA), while it had no apparent effects on flavonoids, phenolics, and soluble sugar content. These findings provide basic information on the FaPL gene family for further functional research and indicate that FaPL1 plays a vital role in strawberry fruit softening.

FaMYB5 Interacts with FaBBX24 to Regulate Anthocyanin and Proanthocyanidin Biosynthesis in Strawberry (Fragaria × ananassa)

MYB and BBX transcription factors play important roles in flavonoid biosynthesis. Here, we obtained transgenic woodland strawberry with stable overexpression of FaMYB5, demonstrating that FaMYB5 can increase anthocyanin and proanthocyanidin content in roots, stems and leaves of woodland strawberry. In addition, bimolecular fluorescence complementation assays and yeast two-hybridization demonstrated that the N-terminal (1-99aa) of FaBBX24 interacts with FaMYB5. Transient co-expression of FaBBX24 and FaMYB5 in cultivated strawberry 'Xiaobai' showed that co-expression strongly promoted the expression of F3'H, 4CL-2, TT12, AHA10 and ANR and then increased the content of anthocyanin and proanthocyanidin in strawberry fruits. We also determined that FaBBX24 is also a positive regulator of anthocyanin and proanthocyanidin biosynthesis in strawberry. The results reveal a novel mechanism by which the FaMYB5-FaBBX24 module collaboratively regulates anthocyanin and proanthocyanidin in strawberry fruit.

Hetero-grafting affects flavonoid biosynthesis in sweet orange 'Newhall' (Citrus sinensis) peels: a metabolomics and transcriptomics analysis

Citrus cultivation involves the widespread practice of grafting, which has a significant impact on citrus development and fruit quality and yield. However, understanding the effect of flavonoid compounds after different rootstock grafting have been limited. Flavonoid compounds, found at the highest levels in citrus peels, contribute to improving fruit quality and nutritional value. In this study, scion-rootstock interaction was investigated at various developmental stages when sweet orange 'Newhall' was hetero-grafted with two commonly used rootstocks (Poncirus trifoliate population, C. junos Siebold ex Tanaka). Physiological index detection showed a higher concentration of total flavonoid content in peels of sweet orange 'Newhall' grafted on Poncirus trifoliate population (ct) than C. junos Siebold ex Tanaka (cj). Further metabolomic analysis identified 703 flavonoid compounds, including flavones, flavonols, and flavanones. Out of the 25 flavonoids affected by different rootstock grafting and developmental stages, most were flavones. Transcriptomic analysis identified 8,562 differentially expressed genes (DEGs). Co-expression and Pearson's correlation analysis discovered six hub structure genes and 19 transcription factors (TFs) that affected flavonoid biosynthesis. In addition to increasing the transcript levels of genes that synthesize flavones, flavonols, and flavanones, the scion-rootstock interaction also affected the expression of many TFs. Taken together, our findings suggested that hetero-grafting could promote the accumulation of flavonoid compounds in citrus peels during the development stages. These results offered fresh perspectives on grafting's application usefulness and the enhancement of the accumulation of nutritive flavonoid components by grafting in citrus.

Involvement of a MYB Transcription Factor in Anthocyanin Biosynthesis during Chinese Bayberry (Morella rubra) Fruit Ripening

Anthocyanin is a class of water-soluble flavonoids found in Chinese bayberry (Morella rubra) that is not only responsible for the variety of colors visible in nature but also has numerous health-promoting benefits in humans. Through comparative transcriptomics, we isolated and identified a transcription factor (TF) of the R2R3-MYB type, MrMYB9, in order to explore the anthocyanin biosynthesis pathway in red and white Chinese bayberries. MrMYB9 transcript was positively correlated with anthocyanin level and anthocyanin biosynthetic gene expression during Chinese bayberry fruit maturation (R-values in the range 0.54-0.84, p < 0.05). Sequence analysis revealed that MrMYB9 shared a similar R2R3 domain with MYB activators of anthocyanin biosynthesis in other plants. MrMYB9 substantially transactivated promoters of anthocyanin biosynthesis-related EBGs (MrCHI, MrF3'H, and MrANS) and LBGs (MrUFGT) upon co-expression of the AtEGL3 gene. Our findings indicated that MrMYB9 may positively modulate anthocyanin accumulation in Chinese bayberry.

Regulation of flavonoids in strawberry fruits by FaMYB5/FaMYB10 dominated MYB-bHLH-WD40 ternary complexes

Anthocyanins endowing strawberry fruit red color are regulated by the MYB-bHLH-WD40 complex. By analyzing the MYBs involved in the flavonoid biosynthesis in strawberry, we found that R2R3-FaMYB5 promoted the content of anthocyanin and proanthocyanidins in strawberry fruits. Yeast two-hybrid and BiFC assays confirmed that MBW complexes connected with flavonoid metabolism were FaMYB5/FaMYB10-FaEGL3 (bHLH)-FaLWD1/FaLWD1-like (WD40). Transient overexpression and qRT-PCR analysis revealed that disparate MBW models hold different patterns in the regulation of flavonoid biosynthesis in strawberry fruits. Compared with FaMYB10, FaMYB5 and its dominant complexes showed a more specific regulatory range on strawberry flavonoid biosynthetic pathway, while FaMYB10 was more extensive. In addition, the complexes involved in FaMYB5 facilitated PAs accumulation primarily through the LAR tributary while FaMYB10 mainly by the ANR branch. FaMYB9 and FaMYB11 tremendously elicited the accumulation of proanthocyanidins by up-regulating the expression levels of both LAR and ANR, and also affected anthocyanin metabolism by changing the ratio of Cy3G and Pg3G which were constituted as two major anthocyanin monomers in strawberries. Our study also illustrated that FaMYB5-FaEGL3-FaLWD1-like directly targeted the promoters of F3'H, LAR, and AHA10 thus committing to flavonoid accumulation. These results allow the specific members involved in the MBW complex to be deciphered and provide new insights into the regulatory mechanisms of anthocyanins and proanthocyanidins regulated by the MBW complex.