The R2R3-MYB transcription factor MdMYB24-like is involved in methyl jasmonate-induced anthocyanin biosynthesis in apple

Fungal invasion-induced accumulation of salicylic acid promotes anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module in apple fruits

In the field, necrosis area induced by pathogens is usually surrounded by a red circle in apple fruits. However, the underlying molecular mechanism of this phenomenon remains unclear. In this study, we demonstrated that accumulated salicylic acid (SA) induced by fungal infection promoted anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module in apple (Malus domestica). Inoculating apple fruits with Valsa mali or Botryosphaeria dothidea induced a red circle surrounding the necrosis area, which mimicked the phenotype observed in the field. The red circle accumulated a high level of anthocyanins, which was positively correlated with SA accumulation stimulated by fungal invasion. Further analysis showed that SA promoted anthocyanin biosynthesis in a dose-dependent manner in both apple calli and fruits. We next demonstrated that MdNPR1, a master regulator of SA signaling, positively regulated anthocyanin biosynthesis in both apple and Arabidopsis. Moreover, MdNPR1 functioned as a co-activator to interact with and enhance the transactivation activity of MdTGA2.2, which could directly bind to the promoters of anthocyanin biosynthetic and regulatory genes to promote their transcription. Suppressing expression of either MdNPR1 or MdTGA2.2 inhibited coloration of apple fruits, while overexpressing either of them significantly promoted fruit coloration. Finally, we revealed that silencing either MdNPR1 or MdTGA2.2 in apple fruits repressed SA-induced fruit coloration. Therefore, our data determined that fungal-induced SA promoted anthocyanin biosynthesis through MdNPR1-MdTGA2.2 module, resulting in a red circle surrounding the necrosis area in apple fruits.

MdWER interacts with MdERF109 and MdJAZ2 to mediate methyl jasmonate- and light-induced anthocyanin biosynthesis in apple fruit

Anthocyanin generation in apples (Malus domestica) and the pigmentation that results from it may be caused by irradiation and through administration of methyl jasmonate (MeJA). However, their regulatory interrelationships associated with fruit coloration are not well defined. To determine whether MdERF109, a transcription factor (TF) involved in light-mediated coloration and anthocyanin biosynthesis, has synergistic effects with other proteins, we performed a yeast two-hybrid assessment and identified another TF, MdWER. MdWER was induced by MeJA treatment, and although overexpression of MdWER alone did not promote anthocyanin accumulation co-overexpression with MdERF109 resulted in significantly increase in anthocyanin biosynthesis. MdWER may form a protein complex with MdERF109 to promote anthocyanin accumulation by enhancing combinations between the proteins and their corresponding genes. In addition, MdWER, as a MeJA responsive protein, interacts with the anthocyanin repressor MdJAZ2. Transient co-expression in apple fruit and protein interaction assays allowed us to conclude that MdERF109 and MdJAZ2 interact with MdWER and take part in the production of anthocyanins upon MeJA treatment and irradiation. Our findings validate a role for the MdERF109-MdWER-MdJAZ2 module in anthocyanin biosynthesis and uncover a novel mechanism for how light and MeJA signals are coordinated anthocyanin biosynthesis in apple fruit.

Alcohol dehydrogenases regulated by a MYB44 transcription factor underlie Lauraceae citral biosynthesis

Lineage-specific terpenoids have arisen throughout the evolution of land plants and are believed to play a role in interactions between plants and the environment. Species-specific gene clusters in plants have provided insight on the evolution of secondary metabolism. Lauraceae is an ecologically important plant family whose members are also of considerable economic value given their monoterpene contents. However, the gene cluster responsible for the biosynthesis of monoterpenes remains yet to be elucidated. Here, a Lauraceae-specific citral biosynthetic gene cluster (CGC) was identified and investigated using a multifaceted approach that combined phylogenetic, collinearity, and biochemical analyses. The CGC comprises MYB44 as a regulator and 2 alcohol dehydrogenases (ADHs) as modifying enzymes, which derived from species-specific tandem and proximal duplication events. Activity and substrate divergence of the ADHs has resulted in the fruit of mountain pepper (Litsea cubeba), a core Lauraceae species, consisting of more than 80% citral. In addition, MYB44 negatively regulates citral biosynthesis by directly binding to the promoters of the ADH-encoding genes. The aggregation of citral biosynthetic pathways suggests that they may form the basis of important characteristics that enhance adaptability. The findings of this study provide insights into the evolution of and the regulatory mechanisms involved in plant terpene biosynthesis.

Transcriptome Analysis of White- and Red-Fleshed Apple Fruits Uncovered Novel Genes Related to the Regulation of Anthocyanin Biosynthesis

The red flesh coloration of apples is a result of a biochemical pathway involved in the biosynthesis of anthocyanins and anthocyanidins. Based on apple genome analysis, a high number of regulatory genes, mainly transcription factors such as MYB, which are components of regulatory complex MYB-bHLH-WD40, and several structural genes (PAL, 4CL, CHS, CHI, F3H, DFR, ANS, UFGT) involved in anthocyanin biosynthesis, have been identified. In this study, we investigated novel genes related to the red-flesh apple phenotype. These genes could be deemed molecular markers for the early selection of new apple cultivars. Based on a comparative transcriptome analysis of apples with different fruit-flesh coloration, we successfully identified and characterized ten potential genes from the plant hormone transduction pathway of auxin (GH3); cytokinins (B-ARR); gibberellins (DELLA); abscisic acid (SnRK2 and ABF); brassinosteroids (BRI1, BZR1 and TCH4); jasmonic acid (MYC2); and salicylic acid (NPR1). An analysis of expression profiles was performed in immature and ripe fruits of red-fleshed cultivars. We have uncovered genes mediating the regulation of abscisic acid, salicylic acid, cytokinin, and jasmonic acid signaling and described their role in anthocyanin biosynthesis, accumulation, and degradation. The presented results underline the relationship between genes from the hormone signal transduction pathway and UFGT genes, which are directly responsible for anthocyanin color transformation as well as anthocyanin accumulation during apple-fruit ripening.

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.

Anthocyanin Production from Plant Cell and Organ Cultures In Vitro

Anthocyanins are water-soluble pigments found in plants. They exist in various colors, including red, purple, and blue, and are utilized as natural colorants in the food and cosmetics industries. The pharmaceutical industry uses anthocyanins as therapeutic compounds because they have several medicinal qualities, including anti-obesity, anti-cancer, antidiabetic, neuroprotective, and cardioprotective effects. Anthocyanins are conventionally procured from colored fruits and vegetables and are utilized in the food, pharmaceutical, and cosmetic industries. However, the composition and concentration of anthocyanins from natural sources vary quantitively and qualitatively; therefore, plant cell and organ cultures have been explored for many decades to understand the production of these valuable compounds. A great deal of research has been carried out on plant cell cultures using varied methods, such as the selection of suitable cell lines, medium optimization, optimization culture conditions, precursor feeding, and elicitation for the production of anthocyanin pigments. In addition, metabolic engineering technologies have been applied for the hyperaccumulation of these compounds in varied plants, including tobacco and arabidopsis. In this review, we describe various strategies applied in plant cell and organ cultures for the production of anthocyanins.

LcMYB106 suppresses monoterpene biosynthesis by negatively regulating LcTPS32 expression in Litsea cubeba

Litsea cubeba, the core species of the Lauraceae family, is valuable for the production of essential oils due to its high concentration of monoterpenes (90%). The key monoterpene synthase and metabolic regulatory network of monoterpene biosynthesis have provided new insights for improving essential oil content. However, there are few studies on the regulation mechanism of monoterpenes in L. cubeba. In this study, we investigated LcTPS32, a member of the TPS-b subfamily, and identified its function as an enzyme for the synthesis of monoterpenes, including geraniol, α-pinene, β-pinene, β-myrcene, linalool and eucalyptol. The quantitative real-time PCR analysis showed that LcTPS32 was highly expressed in the fruits of L. cubeba and contributed to the characteristic flavor of its essential oil. Overexpression of LcTPS32 resulted in a significant increase in the production of monoterpenes in L. cubeba by activating both the MVA and MEP pathways. Additionally, the study revealed that LcMYB106 played a negative regulatory role in monoterpenes biosynthesis by directly binding to the promoter of LcTPS32. Our study indicates that LcMYB106 could serve as a crucial target for metabolic engineering endeavors, aiming at enhancing the monoterpene biosynthesis in L. cubeba.

Molecular insights into the VIRESCENS amino acid sequence and its implication in anthocyanin production in red- and yellow-fruited cultivars of date palm

This study examined the amino acid sequence of the VIRESCENS gene (VIR), which regulates the production of anthocyanin in 12 cultivars of the date palm (Phoenix dactylifera L.), grown in Al-Madinah Al-Munawarah of the Kingdom of Saudi Arabia. The gene products were amplified via polymerase chain reactions, amplifying both exons and introns. The products were sequenced for the reconstruction of a phylogenetic tree, which used the associated amino acid sequences. The ripening stages of Khalal, Rutab, and Tamar varied among the cultivars. Regarding VIR genotype, the red date had the wild-type gene (VIR+), while the yellow date carried a dominant mutation (VIRIM), i.e., long terminal repeat retrotransposons (LTR-RTs). The DNA sequence of VIRIM revealed that the insertion length of the LTR-RTs ranged between 386 and 476 bp. The R2 and R3 motifs in both VIR+ and VIRIM were conserved. The C-terminus motifs S6A, S6B, and S6C were found in the VIR+ protein sequence. However, the amino acids at positions 123, 161, 166, and 168 differed between VIR+ and VIRIM, and were not included in the C-terminus motifs. Within the VIR+ allele, the lysine at position 187 in the C-terminus was located immediately after S6B, with a protein binding score of 0.3, which was unique to the dark, red-fruited cultivars Ajwah, Anbarah, and Safawi. In the lighter, red-fruited cultivars, the presence of glutamic acid at the same position suggested that the anthocyanin regulation of date palm might be outside the R2 and R3 domains in the N-terminus.

Transcription factors MdMYC2 and MdMYB85 interact with ester aroma synthesis gene MdAAT1 in apple

Volatile esters in apple (Malus domestica) fruit are the critical aroma components determining apple flavor quality. While the exact molecular regulatory mechanism remains unknown, jasmonic acid (JA) plays a crucial role in stimulating the synthesis of ester aromas in apples. In our study, we investigated the effects of methyl jasmonate (MeJA) on the production of ester aroma in apples. MeJA treatment significantly increased ester aroma synthesis, accompanied by the upregulation of several genes involved in the jasmonate pathway transduction. Specifically, expression of the gene MdMYC2, which encodes a transcription factor associated with the jasmonate pathway, and the R2R3-MYB transcription factor gene MdMYB85 increased upon MeJA treatment. Furthermore, the essential gene ALCOHOL ACYLTRANSFERASE 1 (MdAAT1), encoding an enzyme responsible for ester aroma synthesis, showed increased expression levels as well. Our investigation revealed that MdMYC2 and MdMYB85 directly interacted with the promoter region of MdAAT1, thereby enhancing its transcriptional activity. In addition, MdMYC2 and MdMYB85 directly bind their promoters and activate transcription. Notably, the interaction between MdMYC2 and MdMYB85 proteins further amplified the regulatory effect of MdMYB85 on MdMYC2 and MdAAT1, as well as that of MdMYC2 on MdMYB85 and MdAAT1. Collectively, our findings elucidate the role of the gene module consisting of MdMYC2, MdMYB85, and MdAAT1 in mediating the effects of JA and promoting ester aroma synthesis in apples.

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.

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.

The pivotal role of MYB transcription factors in plant disease resistance

MAIN CONCLUSION

MYB transcription factors are essential for diverse biology processes in plants. This review has focused on the potential molecular actions of MYB transcription factors in plant immunity. Plants possess a variety of molecules to defend against disease. Transcription factors (TFs) serve as gene connections in the regulatory networks controlling plant growth and defense against various stressors. As one of the largest TF families in plants, MYB TFs coordinate molecular players that modulate plant defense resistance. However, the molecular action of MYB TFs in plant disease resistance lacks a systematic analysis and summary. Here, we describe the structure and function of the MYB family in the plant immune response. Functional characterization revealed that MYB TFs often function either as positive or negative modulators towards different biotic stressors. Moreover, the MYB TF resistance mechanisms are diverse. The potential molecular actions of MYB TFs are being analyzed to uncover functions by controlling the expression of resistance genes, lignin/flavonoids/cuticular wax biosynthesis, polysaccharide signaling, hormone defense signaling, and the hypersensitivity response. MYB TFs have a variety of regulatory modes that fulfill pivotal roles in plant immunity. MYB TFs regulate the expression of multiple defense genes and are, therefore, important for increasing plant disease resistance and promoting agricultural production.

Unraveling the functional characterization of a jasmonate-induced flavonoid biosynthetic CYP45082G24 gene in Carthamus tinctorius

The cytochrome P450 superfamily of monooxygenases plays a major role in the evolution and diversification of plant natural products. The function of cytochrome P450s in physiological adaptability, secondary metabolism, and xenobiotic detoxification has been studied extensively in numerous plant species. However, their underlying regulatory mechanism in safflower still remained unclear. In this study, we aimed to elucidate the functional role of a putative CtCYP82G24-encoding gene in safflower, which suggests crucial insights into the regulation of methyl jasmonate-induced flavonoid accumulation in transgenic plants. The results showed that methyl jasmonate (MeJA) was associated with a progressive upregulation of CtCYP82G24 expression in safflower among other treatment conditions including light, dark, and polyethylene glycol (PEG). In addition, transgenic plants overexpressing CtCYP82G24 demonstrated increased expression level of other key flavonoid biosynthetic genes, such as AtDFR, AtANS, and AtFLS, and higher content of flavonoid and anthocyanin accumulation when compared with wild-type and mutant plants. Under exogenous MeJA treatment, the CtCYP82G24 transgenic overexpressed lines showed a significant spike in flavonoid and anthocyanin content compared with wild-type and mutant plants. Moreover, the virus-induced gene silencing (VIGS) assay of CtCYP82G24 in safflower leaves exhibited decreased flavonoid and anthocyanin accumulation and reduced expression of key flavonoid biosynthetic genes, suggesting a possible coordination between transcriptional regulation of CtCYP82G24 and flavonoid accumulation. Together, our findings confirmed the likely role of CtCYP82G24 during MeJA-induced flavonoid accumulation in safflower.

The CsHSFA-CsJAZ6 module-mediated high temperature regulates flavonoid metabolism in Camellia sinensis

High temperatures (HTs) seriously affect the yield and quality of tea. Catechins, derived from the flavonoid pathway, are characteristic compounds that contribute to the flavour of tea leaves. In this study, we first showed that the flavonoid content of tea leaves was significantly reduced under HT conditions via metabolic profiles; and then demonstrated that two transcription factors, CsHSFA1b and CsHSFA2 were activated by HT and negatively regulate flavonoid biosynthesis during HT treatment. Jasmonate (JA), a defensive hormone, plays a key role in plant adaption to environmental stress. However, little has been reported on its involvement in HT response in tea. Herein, we demonstrated that CsHSFA1b and CsHSFA2 activate CsJAZ6 expression through directly binding to heat shock elements in its promoter, and thereby repress the JA pathway. Most secondary metabolites are regulated by JA, including catechin in tea. Our study reported that CsJAZ6 directly interacts with CsEGL3 and CsTTG1 and thereby reduces catechin accumulation. From this, we proposed a CsHSFA-CsJAZ6-mediated HT regulation model of catechin biosynthesis. We also determined that negative regulation of the JA pathway by CsHSFAs and its homologues is conserved in Arabidopsis. These findings broaden the applicability of the regulation of JAZ by HSF transcription factors and further suggest the JA pathway as a valuable candidate for HT-resistant breeding and cultivation.

Safflower Flavonoid 3′5′Hydroxylase Promotes Methyl Jasmonate-induced Anthocyanin Accumulation in Transgenic Plants

Flavonoids are the most abundant class of secondary metabolites that are ubiquitously involved in plant development and resistance to biotic and abiotic stresses. Flavonoid biosynthesis involves multiple channels of orchestrated molecular regulatory factors. Methyl jasmonate (MeJA) has been demonstrated to enhance flavonoid accumulation in numerous plant species; however, the underlying molecular mechanism of MeJA-induced flavonoid biosynthesis in safflower is still not evident. In the present study, we revealed the underlying molecular basis of a putative F3′5′H gene from safflower imparting MeJA-induced flavonoid accumulation in transgenic plants. The constitutive expression of the CtF3′5′H1 gene was validated at different flowering stages, indicating their diverse transcriptional regulation through flower development in safflower. Similarly, the CtF3′5′H1-overexpressed Arabidopsis plants exhibit a higher expression level, with significantly increased anthocyanins and flavonoid content, but less proanthocyanidins than wild-type plants. In addition, transgenic plants treated with exogenous MeJA revealed the up-regulation of CtF3′5′H1 expression over different time points with significantly enhanced anthocyanin and flavonoid content as confirmed by HPLC analysis. Moreover, CtF3′5′H1- overexpressed Arabidopsis plants under methyl violet and UV-B irradiation also indicated significant increase in the expression level of CtF3′5′H1 with improved anthocyanin and flavonoid content, respectively. Noticeably, the virus-induced gene silencing (VIGS) assay of CtF3′5′H1 in safflower leaves also confirmed reduced anthocyanin accumulation. However, the CtF3′5′H1 suppression in safflower leaves under MeJA elicitation demonstrated significant increase in total flavonoid content. Together, our findings confirmed that CtF3′5′H1 is likely mediating methyl jasmonate-induced flavonoid biosynthesis in transgenic plants via enhanced anthocyanin accumulation.

MYB24 Negatively Regulates the Biosynthesis of Lignin and Capsaicin by Affecting the Expression of Key Genes in the Phenylpropanoid Metabolism Pathway in Capsicum chinense

The wide application of pepper is mostly related to the content of capsaicin, and phenylpropanoid metabolism and its branch pathways may play an important role in the biosynthesis of capsaicin. The expression level of MYB24, a transcription factor screened from the transcriptome data of the pepper fruit development stage, was closely related to the spicy taste. In this experiment, CcMYB24 was cloned from Hainan Huangdenglong pepper, a hot aromatic pepper variety popular in the world for processing, and its function was confirmed by tissue expression characteristics, heterologous transformation in Arabidopsis thaliana, and VIGS technology. The results showed that the relative expression level of CcMYB24 was stable in the early stage of pepper fruit development, and increased significantly from 30 to 50 days after flowering. Heterologous expression led to a significant increase in the expression of CcMYB24 and decrease in lignin content in transgenic Arabidopsis thaliana plants. CcMYB24 silencing led to a significant increase in the expression of phenylpropanoid metabolism pathway genes PAL, 4CL, and pAMT; lignin branch CCR1 and CAD; and capsaicin pathway CS, AT3, and COMT genes in the placenta of pepper, with capsaicin content increased by more than 31.72% and lignin content increased by 20.78%. However, the expression of PAL, pAMT, AT3, COMT, etc., in the corresponding pericarps did not change significantly. Although CS, CCR1, and CAD increased significantly, the relative expression amount was smaller than that in placental tissue, and the lignin content did not change significantly. As indicated above, CcMYB24 may negatively regulate the formation of capsaicin and lignin by regulating the expression of genes from phenylpropanoid metabolism and its branch pathways.

Jasmonic acid regulates the biosynthesis of medicinal metabolites via the JAZ9-MYB76 complex in Salvia miltiorrhiza

Jasmonic acid (JA) signaling pathway plays an important role in tanshinone and phenolic acid biosynthesis in Salvia miltiorrhiza. However, the specific regulatory mechanism remains largely unclear. Previous work showed that a JASMONATE ZIM-domain (JAZ) protein, SmJAZ9, acted as a repressor of tanshinone production in S. miltiorrhiza. In this study, we revealed that SmJAZ9 reduced both phenolic acid accumulation and related biosynthetic gene expression, confirming that SmJAZ9 also negatively affected phenolic acid biosynthesis. Then, we identified a novel MYB transcription factor, SmMYB76, which interacted with SmJAZ9. SmMYB76 repressed phenolic acid biosynthesis by directly downregulating SmPAL1, Sm4CL2, and SmRAS1. Further investigation demonstrated that JA mediated phenolic acids biosynthesis via SmJAZ9-SmMYB76 complex. Taken together, these findings state the molecular mechanism that SmJAZ9-SmMYB76 regulated phenolic acid biosynthesis at the transcriptional and protein levels, which provided new insights into JA signaling pathway regulating plant metabolism.

MPK6-mediated HY5 phosphorylation regulates light-induced anthocyanin accumulation in apple fruit

Light is known to regulate anthocyanin pigment biosynthesis in plants on several levels, but the significance of protein phosphorylation in light-induced anthocyanin accumulation needs further investigation. In this study, we investigated the dynamics of the apple fruit phosphoproteome in response to light, using high-performance liquid chromatography-tandem mass spectrometry analysis. Among the differentially phosphorylated proteins, the bZIP (basic leucine zipper) transcription factor, HY5, which has been identified as an anthocyanin regulator, was rapidly activated by light treatment of the fruit. We hypothesized that phosphorylated MdHY5 may play a role in light-induced anthocyanin accumulation of apple fruit. Protein interaction and phosphorylation assays showed that mitogen-activated protein kinase MdMPK6 directly interacted with, and activated, MdHY5 via phosphorylation under light conditions, thereby increasing its stability. Consistent with this finding, the suppression of the mitogen-activated protein kinase genes MdMPK6 or MdHY5 resulted in an inhibition of anthocyanin accumulation, and further showed that light-induced anthocyanin accumulation is dependent on MdMPK6 kinase activity, and is required for maximum MdHY5 activity. Under light conditions, active MdMPK6 phosphorylated MdHY5 leading to accumulation of phospho-MdHY5, which enhanced the binding of MdHY5 to its target anthocyanin related genes in fruit. Our findings reveal an MdMPK6-MdHY5 phosphorylation pathway in light-induced anthocyanin accumulation, providing new insights into the regulation of light-induced anthocyanin biosynthesis in apple fruit at both the transcriptional and post-translational levels.

Betalain biosynthesis in red pulp pitaya is regulated via HuMYB132: a R-R type MYB transcription factor

BACKGROUND

Multiple MYB transcription factors (TFs) are involved in the regulation of plant coloring. Betalain is a kind of natural plant pigment and its biosynthesis is regulated by a number of enzymes. Despite this, little is known about the molecular properties and roles of MYB TFs in pitaya betalain biosynthesis.

RESULTS

In the present study, we identified a 1R-MYB gene, HuMYB132, which is preferentially expressed in red-pulp pitaya at the mature stage. It was clustered with Arabidopsis R-R-type genes and had two DNA-binding domains and a histidine-rich region. The expression assays in N. benthamiana and yeast indicated that HuMYB132 is a nucleus-localized protein with transcriptional activation activity. Dual luciferase reporter assay and electrophoretic mobility shift assays (EMSA) demonstrated that HuMYB132 could promote the transcriptional activities of HuADH1, HuCYP76AD1-1, and HuDODA1 by binding to their promoters. Silencing HuMYB132 reduced betalain accumulation and the expression levels of betalain biosynthetic genes in pitaya pulps.

CONCLUSIONS

According to our findings, HuMYB132, a R-R type member of 1R-MYB TF subfamily, positively regulates pitaya betalain biosynthesis by regulating the expression of HuADH1, HuCYP76AD1-1, and HuDODA1. The present study provides a new theoretical reference for the management of pitaya betalain biosynthesis and also provides an essential basis for future regulation of betalain biosynthesis in Hylocereus.

Characterization of Highbush Blueberry (Vaccinium corymbosum L.) Anthocyanin Biosynthesis Related MYBs and Functional Analysis of VcMYB Gene

As one of the most important transcription factors regulating plant anthocyanin biosynthesis, MYB has attracted great attentions. In this study, we identified fifteen candidate anthocyanin biosynthesis related MYB (ABRM) proteins, including twelve R2R3-MYBs and three 1R-MYBs, from highbush blueberry. The subcellular localization prediction results showed that, with the exception of VcRVE8 (localized in chloroplast and nucleus), all of the blueberry ABRMs were nucleus-localized. The gene structure analysis revealed that the exon numbers of the blueberry ABRM genes varied greatly, ranging between one and eight. There are many light-responsive, phytohormone-responsive, abiotic stress-responsive and plant growth and development related cis-acting elements in the promoters of the blueberry ABRM genes. It is noteworthy that almost all of their promoters contain light-, ABA- and MeJA-responsive elements, which is consistent with the well-established results that anthocyanin accumulation and the expression of MYBs are influenced significantly by many factors, such as light, ABA and JA. The gene expression analysis revealed that VcMYB, VcMYB6, VcMYB23, VcMYBL2 and VcPH4 are expressed abundantly in blueberry fruits, and VcMYB is expressed the highest in the red, purple and blue fruits among all blueberry ABRMs. VcMYB shared high similarity with functionally proven ABRMs from many other plant species. The gene cloning results showed that VcMYB had three variable transcripts, but only the transient overexpression of VcMYB-1 promoted anthocyanin accumulation in the green fruits. Our study can provide a basis for future research on the anthocyanin biosynthesis related MYBs in blueberry.

Spatiotemporal dynamics of the tomato fruit transcriptome under prolonged water stress

Water availability influences all aspects of plant growth and development; however, most studies of plant responses to drought have focused on vegetative organs, notably roots and leaves. Far less is known about the molecular bases of drought acclimation responses in fruits, which are complex organs with distinct tissue types. To obtain a more comprehensive picture of the molecular mechanisms governing fruit development under drought, we profiled the transcriptomes of a spectrum of fruit tissues from tomato (Solanum lycopersicum), spanning early growth through ripening and collected from plants grown under varying intensities of water stress. In addition, we compared transcriptional changes in fruit with those in leaves to highlight different and conserved transcriptome signatures in vegetative and reproductive organs. We observed extensive and diverse genetic reprogramming in different fruit tissues and leaves, each associated with a unique response to drought acclimation. These included major transcriptional shifts in the placenta of growing fruit and in the seeds of ripe fruit related to cell growth and epigenetic regulation, respectively. Changes in metabolic and hormonal pathways, such as those related to starch, carotenoids, jasmonic acid, and ethylene metabolism, were associated with distinct fruit tissues and developmental stages. Gene coexpression network analysis provided further insights into the tissue-specific regulation of distinct responses to water stress. Our data highlight the spatiotemporal specificity of drought responses in tomato fruit and indicate known and unrevealed molecular regulatory mechanisms involved in drought acclimation, during both vegetative and reproductive stages of development.

CsMYB Transcription Factors Participate in Jasmonic Acid Signal Transduction in Response to Cold Stress in Tea Plant (Camellia sinensis)

Low-temperature stress is an increasing problem for the cultivation of tea (Camellia sinensis), with adverse effects on plant growth and development and subsequent negative impacts on the tea industry. Methyl jasmonate (MeJA), as a plant inducer, can improve the cold-stress tolerance in tea plants. R2R3-MYB transcription factors (TFs) are considered potentially important regulators in the resistance to cold stress in plants. However, the molecular mechanisms, by which MYB TFs via the jasmonic acid pathway respond to cold stress in the tea plant, remain unknown. In this study, physiological and biochemical assays showed that exogenous MeJA application could effectively promote ROS scavenging in the tea plant under cold stress, maintaining the stability of the cell membrane. Sixteen R2R3-MYB TFs genes were identified from the tea plant genome database. Quantitative RT-PCR analysis showed that three CsMYB genes were strongly induced under a combination of MeJA and cold-stress treatment. Subcellular localization assays suggest CsMYB45, CsMYB46, and CsMYB105 localized in the nucleus. Exogenous MeJA treatment enhanced the overexpression of CsMYB45, CsMYB46, and CsMYB105 in E. coli and improved the growth and survival rates of recombinant cells compared to an empty vector under cold stress. Yeast two-hybrid and bimolecular fluorescence complementation experiments confirmed that CsMYB46 and CsMYB105 interacted with CsJAZ3, CsJAZ10, and CsJAZ11 in the nucleus. Taken together, these results highlight that CsMYB45, CsMYB46, and CsMYB105 are not only key components in the cold-stress signal response pathway but also may serve as points of confluence for cold stress and JA signaling pathways. Furthermore, our findings provide new insight into how MYB TFs influence cold tolerance via the jasmonic acid pathway in tea and provide candidate genes for future functional studies and breeding.

Anthocyanin Biosynthesis Induced by MYB Transcription Factors in Plants

Anthocyanins act as polyphenolic pigment that is ubiquitously found in plants. Anthocyanins play a role not only in health-promoting as an antioxidant, but also in protection against all kinds of abiotic and biotic stresses. Most recent studies have found that MYB transcription factors (MYB TFs) could positively or negatively regulate anthocyanin biosynthesis. Understanding the roles of MYB TFs is essential in elucidating how MYB TFs regulate the accumulation of anthocyanin. In the review, we summarized the signaling pathways medicated by MYB TFs during anthocyanin biosynthesis including jasmonic acid (JA) signaling pathway, cytokinins (CKs) signaling pathway, temperature-induced, light signal, 26S proteasome pathway, NAC TFs, and bHLH TFs. Moreover, structural and regulator genes induced by MYB TFs, target genes bound and activated or suppressed by MYB TFs, and crosstalk between MYB TFs and other proteins, were found to be vitally important in the regulation of anthocyanin biosynthesis. In this study, we focus on the recent knowledge concerning the regulator signaling and mechanism of MYB TFs on anthocyanin biosynthesis, covering the signaling pathway, genes expression, and target genes and protein expression.

Integrated metabolic, transcriptomic and chromatin accessibility analyses provide novel insights into the competition for anthocyanins and flavonols biosynthesis during fruit ripening in red apple

Fruit ripening is accompanied by a wide range of metabolites and global changes in gene expression that are regulated by various factors. In this study, we investigated the molecular differences in red apple 'Hongmantang' fruits at three ripening stages (PS1, PS5 and PS9) through a comprehensive analysis of metabolome, transcriptome and chromatin accessibility. Totally, we identified 341 and 195 differentially accumulated metabolites (DAMs) in comparison I (PS5_vs_PS1) and comparison II (PS9_vs_PS5), including 57 and 23 differentially accumulated flavonoids (DAFs), respectively. Intriguingly, among these DAFs, anthocyanins and flavonols showed opposite patterns of variation, suggesting a possible competition between their biosynthesis. To unveil the underlying mechanisms, RNA-Seq and ATAC-Seq analyses were performed. A total of 852 DEGs significantly enriched in anthocyanin metabolism and 128 differential accessible regions (DARs) significantly enriched by MYB-related motifs were identified as up-regulated in Comparison I but down-regulated in Comparison II. Meanwhile, the 843 DEGs significantly enriched in phenylalanine metabolism and the 364 DARs significantly enriched by bZIP-related motifs showed opposite trends. In addition, four bZIPs and 14 MYBs were identified as possible hub genes regulating the biosynthesis of flavonols and anthocyanins. Our study will contribute to the understanding of anthocyanins and flavonols biosynthesis competition in red apple fruits during ripening.

Genome-wide analysis of the apple family 1 glycosyltransferases identified a flavonoid-modifying UGT, MdUGT83L3, which is targeted by MdMYB88 and contributes to stress adaptation

The plant family 1 UDP-glycosyltransferases (UGTs) are increasingly being investigated because of their contribution to plant secondary metabolism and other diverse biological roles. The apple (Malus domestica) is one of the most widely cultivated fruit trees with great economic importance. However, little is known regarding the apple UGTs. In this study, we identified 229 members of family 1 through a genome-wide analysis of the apple UGTs, which were clustered into 18 groups, from A to R. We also performed detailed analysis of 34 apple UGTs by quantitative RT-PCR, and discovered a number of stress-regulated UGTs. Among them, we characterized the role of MD09G1064900, also named MdUGT83L3, which was significantly induced by salt and cold. In vivo analysis showed that it has high activity towards cyanidin, and moderate activity towards quercetin and keampferol. Transgenic callus and regenerated apple plants overexpressing MdUGT83L3 showed enhanced tolerance to salt and cold treatments. Overexpression of MdUGT83L3 also increased anthocyanin accumulation in the callus tissues and enhanced ROS clearing upon exposure to salt and cold stresses. Furthermore, via yeast-one-hybrid assay, EMSA and CHIP analyses, we also found that MdUGT83L3 could be directly regulated by MdMYB88. Our study indicated that MdUGT83L3, under the regulation of MdMYB88, plays important roles in salt and cold stress adaptation via modulating flavonoid metabolism in apple.

MdERF1B-MdMYC2 module integrates ethylene and jasmonic acid to regulate the biosynthesis of anthocyanin in apple

Ethylene and jasmonic acid (JA) are crucial hormones that promote anthocyanin synthesis in apple (Malus × domestica). However, the mechanism by which these hormones cooperate to modulate anthocyanin production in apple is unclear. According to our results, MdERF1B expression was strongly induced by ethylene and JA. Physiological phenotypes and the results of molecular biological analyses indicated that MdERF1B encodes a positive regulator of anthocyanin synthesis. Specifically, MdERF1B was capable of combining directly with the MdMYC2 promoter to promote gene expression. Additionally, MdERF1B interacted with two JA signaling pathway inhibitors, namely MdJAZ5 and MdJAZ10. The MdERF1B-MdJAZ5/10 protein complex decreased the ability of MdERF1B to activate the MdMYC2 promoter. Furthermore, MdEIL1, which is a crucial protein for ethylene signal transduction, was observed to bind directly to the MdERF1B promoter, thereby upregulating gene expression. These results suggest that MdERF1B is a core gene responsive to JA and ethylene signals. The encoded protein, together with MdMYC2, MdJAZ5/10, and MdEIL1, modulates anthocyanin synthesis in apple. This study clarifies the synergistic mechanism by which JA and ethylene regulate anthocyanin production in apple.

New red-fleshed apple cultivars: a comprehensive review of processing effects, (poly)phenol bioavailability and biological effects

Red-fleshed apple cultivars with an enhanced content of anthocyanins have recently attracted the interest of apple producers and consumers due to their attractive color and promising added health benefits. In this paper, we provide the first comprehensive overview of new hybrid red-fleshed apples, mainly focusing on their (poly)phenolic composition, the effect of processing, the (poly)phenolic bioavailability and the biological effects. Evidence so far from in vitro and in vivo studies supports their added beneficial effects compared to common apples on health outcomes such as cancer, cardiovascular disease, inflammation and immune function, which are mainly related to their specific (poly)phenol composition.

Post-harvest Application of Methyl Jasmonate or Prohydrojasmon Affects Color Development and Anthocyanins Biosynthesis in Peach by Regulation of Sucrose Metabolism

The roles of methyl jasmonate (MeJA) and prohydrojasmon (PDJ) in postharvest color development and anthocyanins biosynthesis in the skin of peach fruit remain unclear. In this study, peach fruit were infiltrated with MeJA (200 μM) or PDJ (40 μM) and stored at 22°C for 7 days. The results showed that treatment with MeJA or PDJ had a positive effect on red color formation in peach fruits due to anthocyanins accumulation (∼120% increase). This was attributed to increased enzyme activities, and enhanced transcript abundance of the genes associated with anthocyanins biosynthesis, induced by MeJA or PDJ. Both MeJA and PDJ promoted sucrose biosynthesis, and the subsequently elevated levels of the sucrose during storage were positively correlated with anthocyanins accumulation (0.49) and the activities of key biosynthesis enzymes (0.42-0.79). Based on these findings, we proposed that MeJA or PDJ treatments promote anthocyanins biosynthesis by regulating sucrose metabolism during the postharvest storage of peach fruit.

Evolution and functional diversification of R2R3-MYB transcription factors in plants

R2R3-MYB genes (R2R3-MYBs) form one of the largest transcription factor gene families in the plant kingdom, with substantial structural and functional diversity. However, the evolutionary processes leading to this amazing functional diversity have not yet been clearly established. Recently developed genomic and classical molecular technologies have provided detailed insights into the evolutionary relationships and functions of plant R2R3-MYBs. Here, we review recent genome-level and functional analyses of plant R2R3-MYBs, with an emphasis on their evolution and functional diversification. In land plants, this gene family underwent a large expansion by whole genome duplications and small-scale duplications. Along with this population explosion, a series of functionally conserved or lineage-specific subfamilies/groups arose with roles in three major plant-specific biological processes: development and cell differentiation, specialized metabolism, and biotic and abiotic stresses. The rapid expansion and functional diversification of plant R2R3-MYBs are highly consistent with the increasing complexity of angiosperms. In particular, recently derived R2R3-MYBs with three highly homologous intron patterns (a, b, and c) are disproportionately related to specialized metabolism and have become the predominant subfamilies in land plant genomes. The evolution of plant R2R3-MYBs is an active area of research, and further studies are expected to improve our understanding of the evolution and functional diversification of this gene family.

SmbHLH60 and SmMYC2 antagonistically regulate phenolic acids and anthocyanins biosynthesis in Salvia miltiorrhiza

INTRODUCTION

Salvia miltiorrhiza is a renowned traditional Chinese medicinal plant with extremely high medicinal value, especially for cardiovascular and cerebrovascular diseases. The jasmonic acid (JA) signaling pathway plays an important role in the improved biosynthesis of secondary metabolites, which is mediated by a major transcriptional regulator, MYC2. However, the JA regulatory mechanism of secondary metabolites biosynthesis in S. miltiorrhiza is still largely unknown.

OBJECTIVES

Our work focuses on the dissection of the molecular mechanism of transcriptional regulation in MeJA-mediated biosynthesis of medicinal components of S. miltiorrhiza. We examined the role of MeJA-responsive bHLH transcription factors (TFs) in improving bioactive secondary metabolites accumulation in S. miltiorrhiza.

METHODS

Hairy root transformation based on CRISPR/Cas9 technique was used to decipher gene function(s). Changes in the content of phenolic acids were evaluated by HPLC. Y1H, EMSA and dual-LUC assays were employed to analyze the molecular mechanism of SmbHLH60 in the regulation on the biosynthesis of phenolic acids and anthocyanins. Y2H, BiFC and pull-down affinity assays were used to corroborate the interaction between SmbHLH60 and SmMYC2.

RESULTS

Being one of the most significantly negatively regulated bHLH genes by MeJA, a new transcription factor SmbHLH60 was discovered and characterized. Over-expression of SmbHLH60 resulted in significant inhibition of phenolic acid and anthocyanin biosynthesis in S. miltiorrhiza by transcriptionally repressing of target genes such as SmTAT1 and SmDFR, whereas CRISPR/Cas9-generated knockout of SmbHLH60 resulted in the opposite effect. In addition, SmbHLH60 and SmMYC2 formed a heterodimer to antagonistically regulate phenolic acid and anthocyanin biosynthesis.

CONCLUSION

Our results clarified that SmbHLH60 is a negativeregulator on the biosynthesis of phenolic acids and anthocyanins. SmbHLH60 competed with SmMYC2 in an antagonistic manner, providing new insights for the molecular mechanism of MeJA-mediated regulation on the biosynthesis of secondary metabolites in S. miltiorrhiza.

Pigmentation and Flavonoid Metabolite Diversity in Immature 'Fuji' Apple Fruits in Response to Lights and Methyl Jasmonate

Artificial pigmentation of apple fruits has been intensely evaluated to generate less pigmented red apples, which are profitable because of the changes in fruit quality. In this study, we analyzed the diversity of flavonoids and the patterns of flavonoid metabolic gene expression under light irradiation with or without methyl jasmonate (MeJA) treatment in immature (S1) and color-turning (S2) staged ‘Fuji’ apples. Further, we assessed the metabolic regulation at the gene level between anthocyanin and flavonol in light-responsive apple skins. UV-B exposure within 3 days was found to significantly stimulate anthocyanin accumulation in apple skin compared to other light exposure. S1 skin was more sensitive to UV-B and MeJA treatment, in the aspect of indaein accumulation. The enhancement of apple pigmentation following treatment with adequate levels of UV-B and MeJA was maximized at approximately 72 h. Red (range from 4.25 to 17.96 µg·g⁻¹ DW), blue (range from 4.59 to 9.17 µg·g⁻¹ DW) and UV-A (range from 3.98 to 19.12 µg·g⁻¹ DW) lights contributed to the induction of idaein content. Most genes related to the flavonoid pathways increased their expression under UV-B exposure, including the gene expression of the transcription factor, MdMYB10, a well-known upstream factor of flavonoid biosynthesis in apples. The boosted upregulation of MdMYB10, MdCHS, MdF3H MdLDOX, and MdUFGT genes due to MeJA in UV-B was found and may contribute the increase of idaein. UV-A and UV-B caused higher quercetin glycoside content in both S1 and S2 apple skins than longer wavelengths, resulting in significant increases in quercetin-3-O-galactoside and quercetin-3-O-glucoside. These results suggest that the application of adequate UV-B with MeJA in less-pigmented postharvest apples will improve apple color quality within a short period.

Transcriptome Analysis Reveals Roles of Anthocyanin- and Jasmonic Acid-Biosynthetic Pathways in Rapeseed in Response to High Light Stress

Rapeseed (Brassica napus) is one of the major important oil crops worldwide and is largely cultivated in the Qinghai-Tibetan plateau (QTP), where long and strong solar-radiation is well-known. However, the molecular mechanisms underlying rapeseed's response to light stress are largely unknown. In the present study, the color of rapeseed seedlings changed from green to purple under high light (HL) stress conditions. Therefore, changes in anthocyanin metabolism and the transcriptome of rapeseed seedlings cultured under normal light (NL) and HL conditions were analyzed to dissect how rapeseed responds to HL at the molecular level. Results indicated that the contents of anthocyanins, especially glucosides of cyanidin, delphinidin, and petunidin, which were determined by liquid chromatography-mass spectrometry (LC-MS), increased by 9.6-, 4.2-, and 59.7-fold in rapeseed seedlings exposed to HL conditions, respectively. Next, RNA-sequencing analysis identified 7390 differentially expressed genes (DEGs), which included 4393 up-regulated and 2997 down-regulated genes. Among the up-regulated genes, many genes related to the anthocyanin-biosynthetic pathway were enriched. For example, genes encoding dihydroflavonol reductase (BnDFR) and anthocyanin synthase (BnANS) were especially induced by HL conditions, which was also confirmed by RT-qPCR analysis. In addition, two PRODUCTION OF ANTHOCYANIN PIGMENTATION 2 (BnPAP2) and GLABRA3 (BnGL3) genes encoding MYB-type and bHLH-type transcription factors, respectively, whose expression was also up-regulated by HL stress, were found to be associated with the changes in anthocyanin biosynthesis. Many genes involved in the jasmonic acid (JA)-biosynthetic pathway were also up-regulated under HL conditions. This finding, which is in agreement with the well-known positive regulatory role of JA in anthocyanin biosynthesis, suggests that the JA may also play a key role in the responses of rapeseed seedlings to HL. Collectively, these data indicate that anthocyanin biosynthesis-related and JA biosynthesis-related pathways mediate HL responses in rapeseed. These findings collectively provide mechanistic insights into the mechanisms involved in the response of rapeseed to HL stress, and the identified key genes may potentially be used to improve HL tolerance of rapeseed cultivars through genetic engineering or breeding strategies.

Review: The effects of hormones and environmental factors on anthocyanin biosynthesis in apple

Fruit coloration is an appearance trait that directly affects the commercial value and market competitiveness of apples. The red color of apple fruit is mainly affected by anthocyanin accumulation, and the synthesis of anthocyanin is affected by various factors. The critical roles of hormones and environmental factors during apple anthocyanin biosynthesis are described. This review also elaborates the specific mechanisms of the responses of internal genes to stress and changes in anthocyanin when apples are exposed to different environmental stressors. This study provides direction for future research on apple anthocyanin and is a reference for anthocyanin studies in other species.

Integrative Analyses of Metabolomes and Transcriptomes Provide Insights into Flavonoid Variation in Grape Berries

Flavonoids in grapes contribute the quality of the berry, but the flavonoid diversity and the regulatory networks underlying the variation require a further investigation. In this study, we integrated multi-omics data to systematically explore the global metabolic and transcriptional profiles in the skins and pulps of three grape cultivars. The results revealed large-scale differences involved in the flavonoid metabolic pathway. A total of 133 flavonoids, including flavone and flavone C-glycosides, were identified. Beyond the visible differences of anthocyanins, there was large variation in other sub-branched flavonoids, most of which were positively correlated with anthocyanins in grapes. The expressions of most flavonoid biosynthetic genes and the major regulators MYBA1 were strongly consistent with the changes in flavonoids. Integrative analysis identified two novel transcription factors (MYB24 and MADS5) and two ubiquitin proteins (RHA2) as promising regulatory candidates for flavonoid biosynthesis in grapes. Further verification in various grape accessions indicated that five major genes including flavonol 3'5'-hydroxylase (F3'5'H), UDP-glucose:flavonoid 3-O-glycosyl-transferase, anthocyanin O-methyltransferase, acyltransferase (3AT), and glutathione S-transferase (GST4) controlled flavonoid variation in grape berries. These findings provide valuable information for understanding the mechanism of flavonoid biosynthesis in grape berries and the further development of grape health products.

The beauty of biocatalysis: sustainable synthesis of ingredients in cosmetics

Covering: 2015 up to July 2021The market for cosmetics is consumer driven and the desire for green, sustainable and natural ingredients is increasing. The use of isolated enzymes and whole-cell organisms to synthesise these products is congruent with these values, especially when combined with the use of renewable, recyclable or waste feedstocks. The literature of biocatalysis for the synthesis of ingredients in cosmetics in the past five years is herein reviewed.

Comparative transcriptome analysis reveals key genes associated with pigmentation in radish (Raphanus sativus L.) skin and flesh

Radish (Raphanus sativus) is an important vegetable worldwide that exhibits different flesh and skin colors. The anthocyanins responsible for the red and purple coloring in radishes possess nutritional value and pharmaceutical potential. To explore the structural and regulatory networks related to anthocyanin biosynthesis and identify key genes, we performed comparative transcriptome analyses of the skin and flesh of six colored radish accessions. The transcript profiles showed that each accession had a species-specific transcript profile. For radish pigmentation accumulation, the expression levels of anthocyanin biosynthetic genes (RsTT4, RsC4H, RsTT7, RsCCOAMT, RsDFR, and RsLDOX) were significantly upregulated in the red- and purple-colored accessions, but were downregulated or absent in the white and black accessions. The correlation test, combined with metabolome (PCC > 0.95), revealed five structural genes (RsTT4, RsDFR, RsCCOAMT, RsF3H, and RsBG8L) and three transcription factors (RsTT8-1, RsTT8-2, and RsPAR1) to be significantly correlated with flavonoids in the skin of the taproot. Four structural genes (RsBG8L, RsDFR, RsCCOAMT, and RsLDOX) and nine transcription factors (RsTT8-1, RsTT8-2, RsMYB24L, RsbHLH57, RsPAR2L, RsbHLH113L, RsOGR3L, RsMYB24, and RsMYB34L) were found to be significantly correlated with metabolites in the flesh of the taproot. This study provides a foundation for future studies on the gene functions and genetic diversity of radish pigmentation and should aid in the cultivation of new valuable radish varieties.

Jasmonate induces biosynthesis of anthocyanin and proanthocyanidin in apple by mediating the JAZ1-TRB1-MYB9 complex

Jasmonate (JA) induces the biosynthesis of anthocyanin and proanthocyanidin. MdMYB9 is essential for modulating the accumulation of both anthocyanin and proanthocyanidin in apple, but the molecular mechanism for induction of anthocyanin and proanthocyanidin biosynthesis by JA is unclear. In this study, we discovered an apple telomere-binding protein (MdTRB1) to be the interacting protein of MdMYB9. A series of biological assays showed that MdTRB1 acted as a positive modulator of anthocyanin and proanthocyanidin accumulation, and is dependent on MdMYB9. MdTRB1 interacted with MdMYB9 and enhanced the activation activity of MdMYB9 to its downstream genes. In addition, we found that the JA signaling repressor MdJAZ1 interacted with MdTRB1 and interfered with the interaction between MdTRB1 and MdMYB9, therefore negatively modulating MdTRB1-promoted biosynthesis of anthocyanin and proanthocyanidin. These results show that the JAZ1-TRB1-MYB9 module dynamically modulates JA-mediated accumulation of anthocyanin and proanthocyanidin. Taken together, our data further expand the functional study of TRB1 and provide insights for further studies of the modulation of anthocyanin and proanthocyanidin biosynthesis by JA.

Research progress of fruit color development in apple (Malus domestica Borkh.)

Apple (Malus domestica Borkh.) is one of the most widely produced and economically important fruits in temperate regions. Fruit color development in apple is a major focus for both breeders and researchers as consumers associate brightly colored red apples with ripeness and a good flavor. In recent years, great progress has been made in the research of apple fruit color development, but its development mechanism has not been systematic dissected from the aspects of genetics, transcription or environmental factors. Here, we summarize research on the coloration of apple fruit, including the development of important genomic databases to identify important genomic regions and genes, genetic and transcriptional factors that regulate pigment accumulation, environmental factors that affect anthocyanin synthesis, and the current breeding progress of red-skinned and red-fleshed apples. We describe key transcription factors, such as MYB, bHLH, and WD40, which are involved in the regulation of anthocyanin synthesis and fruit color development in apple. We also discuss the regulation of apple color by external environmental factors such as light, temperature, and water. The aim of this review is to provide insights into the molecular mechanisms underlying anthocyanin biosynthesis in apple. This information will provide significant guidance for the breeding of high-quality red-skinned and red-fleshed apple varieties.

Identification of candidate genes influencing anthocyanin biosynthesis during the development and ripening of red and white strawberry fruits via comparative transcriptome analysis

Strawberries are one of the most economically important berry fruits worldwide and exhibit colours ranging from white to dark red, providing a rich genetic resource for strawberry quality improvement. In the present study, we conducted transcriptome analyses of three strawberry cultivars, namely, 'Benihoppe', 'Xiaobai', and 'Snow White', and compared their gene expression profiles. Among the high-quality sequences, 5,049 and 53,200 differentially expressed genes (DEGs) were obtained when comparing the diploid and octoploid strawberry genomes and analysed to identify anthocyanin-related candidate genes. Sixty-five DEGs in the diploid genome (transcriptome data compared to the diploid strawberry genome) and 317 DEGs in the octoploid genome (transcriptome data compared to the octoploid strawberry genome) were identified among the three cultivars. Among these DEGs, 19 and 70 anthocyanin pathway genes, six and 42 sugar pathway genes, 23 and 101 hormone pathway genes, and 17 and 104 transcription factors in the diploid and octoploid genomes, respectively, correlated positively or negatively with the anthocyanin accumulation observed among the three cultivars. Real-time qPCR analysis of nine candidate genes showed a good correlation with the transcriptome data. For example, the expression of PAL was higher in 'Benihoppe' and 'Xiaobai' than in 'Snow White', consistent with the RNA-seq data. Thus, the RNA-seq data and candidate DEGs identified in the present study provide a sound basis for further studies of strawberry fruit colour formation.

Overexpression of SlMYB75 enhances resistance to Botrytis cinerea and prolongs fruit storage life in tomato

SlMYB75 increased the accumulation of JA and improved the scavenging of excess H₂O₂ to resist B. cinerea. Overexpression of SlMYB75 greatly prolongs tomato fruit storage life. Botrytis cinerea (B. cinerea) is a major threat to the production and storage life of tomato (Solanum lycopersicum) fruit around the world. SlMYB75 is an R2R3MYB transcription factor associated with the biosynthesis of anthocyanidin, but little is known about its function in the resistance of tomato to B. cinerea. In this study, we found that the overexpression of SlMYB75 regulated the accumulation of jasmonic acid (JA) and promoted the JA-mediated signaling pathway to resist B. cinerea infection. Moreover, the activities of peroxidase and superoxide dismutase, which were activated to scavenge hydrogen peroxide produced as a result of the B. cinerea infection, were enhanced in the transgenic tomato plants. Scanning electron microscopy images showed that the wax on the fruit skin surface was significantly decreased in the transgenic tomatoes compared with the wild type. However, SlMYB75 prolonged fruit storage life by both enhancing resistance to B. cinerea and directly downregulating the fruit shelf life-related gene SlFSR. Collectively, this study provides a good candidate gene for breeding high-quality tomatoes with a long storage life and high disease resistance.

High-Quality Genome of the Medicinal Plant Strobilanthes cusia Provides Insights Into the Biosynthesis of Indole Alkaloids

Strobilanthes cusia (Nees) Kuntze is an important plant used to process the traditional Chinese herbal medicines "Qingdai" and "Nanbanlangen". The key active ingredients are indole alkaloids (IAs) that exert antibacterial, antiviral, and antitumor pharmacological activities and serve as natural dyes. We assembled the S. cusia genome at the chromosome level through combined PacBio circular consensus sequencing (CCS) and Hi-C sequencing data. Hi-C data revealed a draft genome size of 913.74 Mb, with 904.18 Mb contigs anchored into 16 pseudo-chromosomes. Contig N50 and scaffold N50 were 35.59 and 68.44 Mb, respectively. Of the 32,974 predicted protein-coding genes, 96.52% were functionally annotated in public databases. We predicted 675.66 Mb repetitive sequences, 47.08% of sequences were long terminal repeat (LTR) retrotransposons. Moreover, 983 Strobilanthes-specific genes (SSGs) were identified for the first time, accounting for ~2.98% of all protein-coding genes. Further, 245 putative centromeric and 29 putative telomeric fragments were identified. The transcriptome analysis identified 2,975 differentially expressed genes (DEGs) enriched in phenylpropanoid, flavonoid, and triterpenoid biosynthesis. This systematic characterization of key enzyme-coding genes associated with the IA pathway and basic helix-loop-helix (bHLH) transcription factor family formed a network from the shikimate pathway to the indole alkaloid synthesis pathway in S. cusia. The high-quality S. cusia genome presented herein is an essential resource for the traditional Chinese medicine genomics studies and understanding the genetic underpinning of IA biosynthesis.

Transcriptome analysis provides new insights into the transcriptional regulation of methyl jasmonate-induced flavonoid biosynthesis in pear calli

BACKGROUND

Flavonoid biosynthesis is strongly influenced by phytohormones. For example, methyl jasmonate (MeJA) enhances the flavonoid accumulation in pear. However, the molecular mechanism underlying the MeJA-induced flavonoid biosynthesis in pear is largely uncharacterized. Therefore, the transcriptome of pear calli treated with MeJA was analyzed to elucidate the mechanism regulating MeJA-mediated flavonoid biosynthesis.

RESULTS

The application of exogenous MeJA significantly enhanced flavonoid accumulation, especially anthocyanin, in pear calli. A weighted gene co-expression network analysis identified the differentially expressed genes associated with MeJA-induced flavonoid biosynthesis. The MeJA treatment upregulated the expression of the flavonoid biosynthesis pathway structural genes (PcCHS, PcCHI, PcF3H, PcDFR, PcANS, PcANR2a, and PcLAR1). The MYB family members were the main transcription factors regulating the MeJA-induced flavonoid biosynthesis, but the bHLH, AP2-EREBP, NAC, WRKY, and TIFY families were also involved. In addition to PcMYB10, which is a known positive regulator of anthocyanin biosynthesis in pear, several novel MYB candidates that may regulate flavonol and proanthocyanidin biosynthesis were revealed. Yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated that PcMYB10 and PcMYC2 can directly interact with each other and bind to JAZ repressors (PcJAZ1 and PcJAZ2).

CONCLUSIONS

The PcMYB10-PcMYC2 molecular complex is likely involved in the regulation of jasmonate-mediated flavonoid biosynthesis at the transcript level. The data generated in this study may clarify the transcriptional regulatory network associated with the MeJA-induced flavonoid accumulation in pear calli and provide a solid foundation for future studies.

Two responses to MeJA induction of R2R3-MYB transcription factors regulate flavonoid accumulation in Glycyrrhiza uralensis Fisch

Flavonoids are key components of licorice plant that directly affect its medicinal quality. Importantly, the MYB family of transcription factors serves to regulate the synthesis of flavonoids in plants. The MYB transcription factors represent one of the largest families of transcription factors in plants and play important roles in the process of plant growth and development. MYB gene expression is induced by a number of plant hormones, including the lipid-based hormone jasmonate (JA). Methyl jasmonate (MeJA) is an endogenous plant growth regulator that can induce the JA signaling pathway, which functions to regulate the synthesis of secondary metabolites, including flavonoids. In this study, MeJA was added to licorice cell suspensions, and RNA-seq analysis was performed to identify the differentially expressed genes. As a result, the MYB transcription factors GlMYB4 and GlMYB88 were demonstrated to respond significantly to MeJA induction. Subsequently, the GlMYB4 and GlMYB88 protein were shown to localize to the cell nucleus, and it was verified that GlMYB4 and GlMYB88 could positively regulate the synthesis of flavonoids in licorice cells. Overall, this research helps illustrate the molecular regulation of licorice flavonoid biosynthesis induced by MeJA.

Anthocyanins, multi-functional natural products of industrial relevance: Recent biotechnological advances

Anthocyanins, the color compounds of plants, are known for their wide applications in food, nutraceuticals and cosmetic industry. The biosynthetic pathway of anthocyanins is well established with the identification of potential key regulatory genes, which makes it possible to modulate its production by biotechnological means. Various biotechnological systems, including use of in vitro plant cell or tissue cultures as well as microorganisms have been used for the production of anthocyanins under controlled conditions, however, a wide range of factors affects their production. In addition, metabolic engineering technologies have also used the heterologous production of anthocyanins in recombinant plants and microorganisms. However, these approaches have mostly been tested at the lab- and pilot-scales, while very few up-scaling studies have been undertaken. Various challenges and ways of investigation are proposed here to improve anthocyanin production by using the in vitro plant cell or tissue culture and metabolic engineering of plants and microbial culture systems. All these methods are capable of modulating the production of anthocyanins , which can be further utilized for pharmaceutical, cosmetics and food applications.

Transcriptome and metabolome reveal redirection of flavonoids in a white testa peanut mutant

BACKGROUND

Coat color determines both appearance and nutrient quality of peanut. White seed coat in peanut can enhance the processing efficiency and quality of peanut oil. An integrative analysis of transcriptomes, metabolomes and histocytology was performed on wsc mutant and its wild type to investigate the regulatory mechanisms underlying color pigmentation.

RESULT

Metabolomes revealed flavonoids were redirected in wsc, while multi-omics analyses of wsc mutant seeds and testae uncovered WSC influenced the flavonoids biosynthesis in testa as well as suberin formation, glycolysis, the TCA cycle and amino acid metabolism. The mutation also enhanced plant hormones synthesis and signaling. Further, co-expression analysis showed that FLS genes co-expressed with MBW complex member genes. Combining tissue expression patterns, genetic analyses, and the annotation of common DEGs for these three stages revealed that three testa specific expressed candidate genes, Araip.M7RY3, Aradu.R8PMF and Araip.MHR6K were likely responsible for the white testa phenotype. WSC might be regulated expression competition between FLS and DFR by controlling hormone synthesis and signaling as well as the MBW complex.

CONCLUSIONS

The results of this study therefore provide both candidate genes and novel approaches that can be applied to improve peanut with desirable seed coat color and flavonoid quality.