Light- and Temperature-Induced Expression of an R2R3-MYB Gene Regulates Anthocyanin Biosynthesis in Red-Fleshed Kiwifruit

Screening and identification of photoresponse factors in kiwifruit (Actinidia arguta) development

BACKGROUND

Light is essential for kiwifruit development, in which photoresponse factors contributes greatly to the quality formation. 'Light sensitive hypocotyls, also known as light-dependent short hypocotyls' (LSH) gene family can participate in fruit development as photoresponse factor. However, the key LSH gene that determine kiwifruit development remains unclear. This study aim to screen and identify the key gene AaLSH9 in A. arguta.

MATERIALS AND METHODS

Genome-wide identification of the LSH gene family was used to analyse LSH genes in kiwifruit. Homologous cloning was used to confirm the sequence of candidate LSH genes. qRT-PCR and cluster analysis of expression pattern were used to screen the key AaLSH9 gene. Subcellular localization of AaLSH9 in tobacco leaves and overexpression of AaLSH9 in Arabidopsis thaliana hy5 mutant plants were used to define the acting place in cell and identify molecular function, respectively.

RESULTS

We identified 15 LSH genes, which were divided into two sub-families namely A and B. Domain analysis of A and B showed that they contained different domain organizations, which possibly played key roles in the evolution process. Three LSH genes, AaLSH2, AaLSH9, and AaLSH11, were successfully isolated from Actinidia arguta. The expression pattern and cluster analysis of these three AaLSH genes suggested AaLSH9 might be a key photoresponse gene participating in fruit development in A. arguta. Subcellular localization showed AaLSH9 protein was located in the nucleus. The overexpression of AaLSH9 gene in Arabidopsis thaliana hy5 mutant plants partially complemented the long hypocotyls of hy5 mutant, implying AaLSH9 played a key role as photoresponse factor in cells. In addition, the seed coat color of A. thaliana over-expressing AaLSH9 became lighter than the wide type A.thaliana. Finally, AaCOP1 was confirmed as photoresponse factor to participate in developmental process by stable transgenic A. thaliana.

CONCLUSIONS

AaLSH9 can be involved in kiwifruit (A. arguta) development as key photoresponse factor. Our results not only identified the photoresponse factors AaLSH9 and AaCOP1 but also provided insights into their key role in fruit quality improvement in the process of light response.

AcMYB10 Involved in Anthocyanin Regulation of 'Hongyang' Kiwifruit Induced via Fruit Bagging and High-Postharvest-Temperature Treatments

Light and temperature are key factors influencing the accumulation of anthocyanin in fruit crops. To assess the effects of fruit bagging during development and high post-ripening temperature on 'Hongyang' kiwifruit, we compared the pigmentation phenotypes and expression levels of anthocyanin-related genes between bagged and unbagged treatments, and between 25 °C and 37 °C postharvest storage temperatures. Both the bagging and 25 °C treatments showed better pigmentation phenotypes with higher anthocyanin concentrations. The results of the qRT-PCR analysis revealed that the gene expression levels of LDOX (leucoanthocyanidin dioxygenase), F3GT (UDP-flavonoid 3-O-glycosyltransferase ), AcMYB10, and AcbHLH42 were strongly correlated and upregulated by both the bagging treatment and 25 °C storage. The results of bimolecular fluorescence complementation and luciferase complementation imaging assays indicated an interaction between AcMYB10 and AcbHLH42 in plant cells, whereas the results of a yeast one-hybrid assay further demonstrated that AcMYB10 activated the promoters of AcLODX and AcF3GT. These results strongly suggest that enhanced anthocyanin synthesis is caused by the promoted expression of AcLODX and AcF3GT, regulated by the complex formed by AcMYB10-AcbHLH42.

Methylation of AcGST1 Is Associated with Anthocyanin Accumulation in the Kiwifruit Outer Pericarp

Most red-fleshed kiwifruit cultivars, such as Hongyang, only accumulate anthocyanins in the inner pericarp; the trait of full red flesh becomes the goal pursued by breeders. In this study, we identified a mutant "H-16" showing a red color in both the inner and outer pericarps, and the underlying mechanism was explored. Through transcriptome analysis, a key differentially expressed gene AcGST1 was screened out, which was positively correlated with anthocyanin accumulation in the outer pericarp. The result of McrBC-PCR and bisulfite sequencing revealed that the SG3 region (-292 to -597 bp) of AcGST1 promoter in "H-16" had a significantly lower CHH cytosine methylation level than that in Hongyang, accompanied by low expression of methyltransferase genes (MET1 and CMT2) and high expression of demethylase genes (ROS1 and DML1). Transient calli transformation confirmed that demethylase gene DML1 can activate transcription of AcGST1 to enhance its expression. Overexpression of AcGST1 enhanced the anthocyanin accumulation in the fruit flesh and leaves of the transgenic lines. These results suggested that a decrease in the methylation level of the AcGST1 promoter may contribute to accumulation of anthocyanin in the outer pericarp of "H-16".

The CsMYB123 and CsbHLH111 are involved in drought stress-induced anthocyanin biosynthesis in Chaenomeles speciosa

Drought stress has been demonstrated to enhance the biosynthesis of anthocyanins in the leaves, resulting in an increased aesthetic appeal. However, the molecular mechanisms underlying drought-induced anthocyanin biosynthesis in Chaenomeles speciosa remain unclear. In this study, the metabolites of C. speciosa leaves were analyzed, and it was found that the content of cyanidin-3-O-rutinoside increased significantly under drought stress. The differentially expressed genes CsMYB123 and CsbHLH111 were isolated by transcriptomics data analysis and gene cloning, and gene overexpression and VIGS experiments verified that both play important roles in anthocyanin biosynthesis. Subsequently, Y1H and Dual-luciferase reporter assay showed that CsMYB123 binds to the promoters of anthocyanin biosynthesis-related structural genes (such as CsCHI, CsF3H, and CsANS), while CsbHLH111 was shown to bind to the promoter of CsCHI, positively regulating its activity. Furthermore, BIFC and Y2H assays unveiled potential protein-protein interactions between CsMYB123 and CsbHLH111 at the cell nucleus. Collectively, these results shed light on the critical roles played by CsMYB123 and CsbHLH111 in anthocyanin biosynthesis, thus providing a valuable insight into understanding the molecular mechanisms of how the MYB and bHLH genes regulate anthocyanin biosynthesis in the process of leaf coloration in C. speciosa.

Increased ascorbic acid synthesis by overexpression of AcGGP3 ameliorates copper toxicity in kiwifruit

The widespread application of copper (Cu) -based fertilizers and pesticides could increase the accumulation of Cu in kiwifruit. According to a global survey, red- and yellow-fleshed kiwifruit contained more elevated amounts of Cu than green-fleshed kiwifruit due to weaker disease resistance and higher use of Cu pesticides. Intriguingly, our research revealed that external and endogenous ascorbic acid (AsA) reduced the phenotypic and physiological injury of Cu toxicity in kiwifruit. Cu stress assays and transcriptional analysis have shown that Cu treatment for 12 h significantly increased the AsA content in kiwifruit leaves and up-regulated key genes involved in AsA biosynthesis, such as GDP-L-galactose phosphorylase3 (GGP3) and GDP-mannose-3',5'-epimerase (GME). Overexpressing GGP3 in transgenic kiwifruit significantly increased the endogenous AsA content of kiwifruit, which was beneficial in mitigating Cu toxicity by decreasing levels of reactive oxygen species, malondialdehyde, and electrolyte leakage, as well as reducing damage to the chloroplast structure and photosystem II. This study presented a novel strategy to ameliorate plant Cu stress by increasing the endogenous antioxidant (AsA) content through transgenesis.

The Synergistic Effects of Environmental and Genetic Factors on the Regulation of Anthocyanin Accumulation in Plant Tissues

Anthocyanin accumulation is responsible for the coloration of apple fruit, and their accumulation depends on the expression of anthocyanin biosynthesis-related genes. Light is an environmental stimulus that induces fruit color by regulating genes involved in the anthocyanin biosynthesis pathway. In this study, the roles of light and genetic factors on fruit coloration and anthocyanin accumulation in apple fruit were investigated. Three genes in the anthocyanin biosynthesis pathway, MdCHS, MdANS, and MdUFGT1, were synthesized and cloned into a viral-based expression vector system for transient expression in 'Ruby S' apple fruits. Apple fruits were agroinfiltrated with expression vectors harboring MdCHS, MdANS, and MdUFGT1. Agroinfiltrated apple fruits were then either kept in the dark (bagged fruits) or exposed to light (exposed fruits). The agroinfiltrated fruits showed significantly different coloration patterns, transcript expression levels, and anthocyanin accumulation compared to the control fruits. Moreover, these parameters were higher in exposed fruits than in bagged fruits. For stable expression, MdCHS was introduced into a binary vector under the control of the rice α-amylase 3D (RAmy3D) promoter. The ectopic overexpression of MdCHS in transgenic rice calli showed a high accumulation of anthocyanin content. Taken together, our findings suggest that light, together with the overexpression of anthocyanin biosynthesis genes, induced the coloration and accumulation of anthocyanin content in apple fruits by upregulating the expression of the genes involved in the anthocyanin biosynthesis pathway.

Kiwifruit bZIP transcription factor AcePosF21 elicits ascorbic acid biosynthesis during cold stress

Cold stress seriously affects plant development, resulting in heavy agricultural losses. L-ascorbic acid (AsA, vitamin C) is an antioxidant implicated in abiotic stress tolerance and metabolism of reactive oxygen species (ROS). Understanding whether and how cold stress elicits AsA biosynthesis to reduce oxidative damage is important for developing cold-resistant plants. Here, we show that the accumulation of AsA in response to cold stress is a common mechanism conserved across the plant kingdom, from single-cell algae to angiosperms. We identified a basic leucine zipper domain (bZIP) transcription factor (TF) of kiwifruit (Actinidia eriantha Benth.), AcePosF21, which was triggered by cold and is involved in the regulation of kiwifruit AsA biosynthesis and defense responses against cold stress. AcePosF21 interacted with the R2R3-MYB TF AceMYB102 and directly bound to the promoter of the gene encoding GDP-L-galactose phosphorylase 3 (AceGGP3), a key conduit for regulating AsA biosynthesis, to up-regulate AceGGP3 expression and produce more AsA, which neutralized the excess ROS induced by cold stress. On the contrary, VIGS or CRISPR-Cas9-mediated editing of AcePosF21 decreased AsA content and increased the generation of ROS in kiwifruit under cold stress. Taken together, we illustrated a model for the regulatory mechanism of AcePosF21-mediated regulation of AceGGP3 expression and AsA biosynthesis to reduce oxidative damage by cold stress, which provides valuable clues for manipulating the cold resistance of kiwifruit.

Genome-Wide Analysis of MYB Transcription Factors and Screening of MYBs Involved in the Red Color Formation in Rhododendron delavayi

Flower color is one of the crucial traits of ornamental plants. Rhododendron delavayi Franch. is a famous ornamental plant species distributed in the mountain areas of Southwest China. This plant has red inflorescence and young branchlets. However, the molecular basis of the color formation of R. delavayi is unclear. In this study, 184 MYB genes were identified based on the released genome of R. delavayi. These genes included 78 1R-MYB, 101 R2R3-MYB, 4 3R-MYB, and 1 4R-MYB. The MYBs were divided into 35 subgroups using phylogenetic analysis of the MYBs of Arabidopsis thaliana. The members of the same subgroup in R. delavayi had similar conserved domains and motifs, gene structures, and promoter cis-acting elements, which indicate their relatively conserved function. In addition, transcriptome based on unique molecular identifier strategy and color difference of the spotted petals, unspotted petals, spotted throat, unspotted throat, and branchlet cortex were detected. Results showed significant differences in the expression levels of R2R3-MYB genes. Weighted co-expression network analysis between transcriptome and chromatic aberration values of five types of red samples showed that the MYBs were the most important TFs involved in the color formation, of which seven were R2R3-MYB, and three were 1R-MYB. Two R2R3-MYB (DUH019226.1 and DUH019400.1) had the highest connectivity in the whole regulation network, and they were identified as hub genes for red color formation. These two MYB hub genes provide references for the study of transcriptional regulation of the red color formation of R. delavayi.

Genome-Wide Identification and Characterization of R2R3-MYB Provide Insight into Anthocyanin Biosynthesis Regulation Mechanism of Ananas comosus var. bracteatus

The R2R3-MYB proteins comprise the largest class of MYB transcription factors, which play an essential role in regulating anthocyanin synthesis in various plant species. Ananas comosus var. bracteatus is an important colorful anthocyanins-rich garden plant. The spatio-temporal accumulation of anthocyanins in chimeric leaves, bracts, flowers, and peels makes it an important plant with a long ornamental period and highly improves its commercial value. We conducted a comprehensive bioinformatic analysis of the R2R3-MYB gene family based on genome data from A. comosus var. bracteatus. Phylogenetic analysis, gene structure and motif analysis, gene duplication, collinearity, and promoter analysis were used to analyze the characteristics of this gene family. In this work, a total of 99 R2R3-MYB genes were identified and classified into 33 subfamilies according to phylogenetic analysis, and most of them were localized in the nucleus. We found these genes were mapped to 25 chromosomes. Gene structure and protein motifs were conserved among AbR2R3-MYB genes, especially within the same subfamily. Collinearity analysis revealed four pairs of tandem duplicated genes and 32 segmental duplicates in AbR2R3-MYB genes, indicating that segmental duplication contributed to the amplification of the AbR2R3-MYB gene family. A total of 273 ABRE responsiveness, 66 TCA elements, 97 CGTCA motifs, and TGACG motifs were the main cis elements in the promoter region under response to ABA, SA, and MEJA. These results revealed the potential function of AbR2R3-MYB genes in response to hormone stress. Ten R2R3-MYBs were found to have high homology to MYB proteins reported to be involved in anthocyanin biosynthesis from other plants. RT-qPCR results revealed the 10 AbR2R3-MYB genes showed tissue-specific expression patterns, six of them expressed the highest in the flower, two genes in the bract, and two genes in the leaf. These results suggested that these genes may be the candidates that regulate anthocyanin biosynthesis of A. comosus var. bracteatus in the flower, leaf, and bract, respectively. In addition, the expressions of these 10 AbR2R3-MYB genes were differentially induced by ABA, MEJA, and SA, implying that these genes may play crucial roles in hormone-induced anthocyanin biosynthesis. Our study provided a comprehensive and systematic analysis of AbR2R3-MYB genes and identified the AbR2R3-MYB genes regulating the spatial-temporal anthocyanin biosynthesis in A. comosus var. bracteatus, which would be valuable for further study on the anthocyanin regulation mechanism of A. comosus var. bracteatus.

Transcription and Metabolism Pathways of Anthocyanin in Purple Shamrock (Oxalis triangularis A.St.-Hil.)

Anthocyanins are water-soluble pigments that can impart various colors to plants. Purple shamrock (Oxalis triangularis) possesses unique ornamental value due to its purple leaves. In this study, three anthocyanins, including malvidin 3-O-(4-O-(6-O-malonyl-glucopyranoside)-rhamnopyranosyl)-5-O-(6-O-malonyl-glucopyranoside), delphinidin-3-O-rutinoside and malvidin-3,5-di-O-glucoside, were characterized with ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) in purple shamrock. To investigate the molecular mechanism of anthocyanin biosynthesis in green shamrock (Oxalis corymbosa) and purple shamrock, RNA-seq and qRT-PCR were performed, and the results showed that most of the anthocyanin biosynthetic and regulatory genes were up-regulated in purple shamrock. Then, dark treatment and low temperature treatment experiments in purple shamrock showed that both light and low temperature can induce the biosynthesis of anthocyanins.

The red flesh of kiwifruit is differentially controlled by specific activation-repression systems

Anthocyanins are visual cues for pollination and seed dispersal. Fruit containing anthocyanins also appeals to consumers due to its appearance and health benefits. In kiwifruit (Actinidia spp.) studies have identified at least two MYB activators of anthocyanin, but their functions in fruit and the mechanisms by which they act are not fully understood. Here, transcriptome and small RNA high-throughput sequencing were used to comprehensively identify contributors to anthocyanin accumulation in kiwifruit. Stable overexpression in vines showed that both 35S::MYB10 and MYB110 can upregulate anthocyanin biosynthesis in Actinidia chinensis fruit, and that MYB10 overexpression resulted in anthocyanin accumulation which was limited to the inner pericarp, suggesting that repressive mechanisms underlie anthocyanin biosynthesis in this species. Furthermore, motifs in the C-terminal region of MYB10/110 were shown to be responsible for the strength of activation of the anthocyanic response. Transient assays showed that both MYB10 and MYB110 were not directly cleaved by miRNAs, but that miR828 and its phased small RNA AcTAS4-D4(-) efficiently targeted MYB110. Other miRNAs were identified, which were differentially expressed between the inner and outer pericarp, and cleavage of SPL13, ARF16, SCL6 and F-box1, all of which are repressors of MYB10, was observed. We conclude that it is the differential expression and subsequent repression of MYB activators that is responsible for variation in anthocyanin accumulation in kiwifruit species.

Kiwifruit MYBS1-like and GBF3 transcription factors influence l-ascorbic acid biosynthesis by activating transcription of GDP-L-galactose phosphorylase 3

Plant-derived Vitamin C (l-ascorbic acid (AsA)) is crucial for human health and wellbeing and thus increasing AsA content is of interest to plant breeders. In plants GDP-l-galactose phosphorylase (GGP) is a key biosynthetic control step and here evidence is presented for two new transcriptional activators of GGP. AsA measurement, transcriptomics, transient expression, hormone application, gene editing, yeast 1/2-hybrid, and electromobility shift assay (EMSA) methods were used to identify two positively regulating transcription factors. AceGGP3 was identified as the most highly expressed GGP in Actinidia eriantha fruit, which has high fruit AsA. A gene encoding a 1R-subtype myeloblastosis (MYB) protein, AceMYBS1, was found to bind the AceGGP3 promoter and activate its expression. Overexpression and gene-editing show AceMYBS1 effectively increases AsA accumulation. The bZIP transcription factor AceGBF3 (a G-box binding factor), also was shown to increase AsA content, and was confirmed to interact with AceMYBS1. Co-expression experiments showed that AceMYBS1 and AceGBF3 additively promoted AceGGP3 expression. Furthermore, AceMYBS1, but not GBF3, was repressed by abscisic acid, resulting in reduced AceGGP3 expression and accumulation of AsA. This study sheds new light on the roles of MYBS1 homologues and ABA in modulating AsA synthesis, and adds to the understanding of mechanisms underlying AsA accumulation.

Weighted gene coexpression correlation network analysis reveals a potential molecular regulatory mechanism of anthocyanin accumulation under different storage temperatures in 'Friar' plum

BACKGROUND

Flesh is prone to accumulate more anthocyanin in postharvest 'Friar' plum (Prunus salicina Lindl.) fruit stored at an intermediate temperature. However, little is known about the molecular mechanism of anthocyanin accumulation regulated by storage temperature in postharvest plum fruit.

RESULTS

To reveal the potential molecular regulation mechanism of anthocyanin accumulation in postharvest 'Friar' plum fruit stored at different temperatures (0 °C, 10 °C and 25 °C), the fruit quality, metabolite profile and transcriptome of its flesh were investigated. Compared to the plum fruit stored at 0 °C and 25 °C, the fruit stored at 10 °C showed lower fruit firmness after 14 days and reduced the soluble solids content after 21 days of storage. The metabolite analysis indicated that the fruit stored at 10 °C had higher contents of anthocyanins (pelargonidin-3-O-glucoside, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside and quercetin-3-O-rutinose), quercetin and sucrose in the flesh. According to the results of weighted gene coexpression correlation network analysis (WGCNA), the turquoise module was positively correlated with the content of anthocyanin components, and flavanone 3-hydroxylase (F3H) and chalcone synthase (CHS) were considered hub genes. Moreover, MYB family transcription factor APL (APL), MYB10 transcription factor (MYB10), ethylene-responsive transcription factor WIN1 (WIN1), basic leucine zipper 43-like (bZIP43) and transcription factor bHLH111-like isoform X2 (bHLH111) were closely related to these hub genes. Further qRT-PCR analysis verified that these transcription factors were specifically more highly expressed in plum flesh stored at 10 °C, and their expression profiles were significantly positively correlated with the structural genes of anthocyanin synthesis as well as the content of anthocyanin components. In addition, the sucrose biosynthesis-associated gene sucrose synthase (SS) was upregulated at 10 °C, which was also closely related to the anthocyanin content of plum fruit stored at 10 °C.

CONCLUSIONS

The present results suggest that the transcription factors APL, MYB10, WIN1, bZIP43 and bHLH111 may participate in the accumulation of anthocyanin in 'Friar' plum flesh during intermediate storage temperatures by regulating the expression of anthocyanin biosynthetic structural genes. In addition, the SS gene may play a role in anthocyanin accumulation in plum flesh by regulating sucrose biosynthesis.

Comparative Transcriptome Analysis Revealed the Key Genes Regulating Ascorbic Acid Synthesis in Actinidia

Actinidia (kiwifruit) is known as ‘the king of vitamin C’ due to its rich ascorbic acid (AsA) concentration, which makes it an important model for studying the regulation of AsA metabolism. Herein, transcriptomic analysis was employed to identify candidate genes that regulate AsA synthesis in Actinidia species with 100-fold variations in fruit AsA content (A. latifolia and A. rufa). Approximately 1.16 billion high-quality reads were generated, and an average of 66.68% of the data was uniquely aligned against the reference genome. AsA-associated DEGs that predominately respond to abiotic signals, and secondary metabolic pathways were identified. The key candidate genes, for instance, GDP-L-galactose phosphorylase-3 (GGP3), were explored according to integrated analysis of the weighted gene co-expression network and L-galactose pathway. Transgenic kiwifruit plants were generated, and the leaves of GGP3 (OE-GGP3) overexpressing lines had AsA contents 2.0- to 6.4-fold higher than those of the wild type. Transcriptomic analysis of transgenic kiwifruit lines was further implemented to identify 20 potential downstream target genes and understand GGP3-regulated cellular processes. As a result, two transcription factors (AcESE3 and AcMYBR) were selected to carry out yeast two-hybrid and BiFC assays, which verified that there were obvious AcESE3–AcMYBR and AcESE3–AcGGP3 protein–protein interactions. This study provides insight into the mechanism of AsA synthesis and provides candidate factors and genes involved in AsA accumulation in kiwifruit.

Emerging roles of brassinosteroids and light in anthocyanin biosynthesis and ripeness of climacteric and non-climacteric fruits

Anthocyanins are important pigments that contribute to fruit quality. The regulation of anthocyanin biosynthesis by several transcription factors via sophisticated regulatory networks has been studied in various plants. Brassinosteroids (BRs), a new class of plant hormone, are involved in regulating anthocyanin biosynthesis in fruits. Furthermore, light directly affects the synthesis and distribution of anthocyanins. Here, we summarize the recent progress toward understanding the impact of BR and light on anthocyanin biosynthesis in climacteric and non-climacteric fruits. We review the BR and light signaling pathways and highlight the important transcription factors that are associated with the synthesis of anthocyanins, such as BZR1 (brassinazole-resistant 1, BR signaling pathway), HY5 (elongated hypocotyl 5) and COP1 (constitutively photomorphogenic 1, light signal transduction pathway), which bind with the target genes involved in anthocyanin synthesis. In addition, we review the mechanism by which light signals interact with hormonal signals to regulate anthocyanin biosynthesis.

Transcriptomic and Proteomic Profiling Reveal the Key Role of AcMYB16 in the Response of Pseudomonas syringae pv. actinidiae in Kiwifruit

Kiwifruit bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa), is an important disease of kiwifruit (Actinidia Lind.). Plant hormones may induce various secondary metabolites to resist pathogens via modulation of hormone-responsive transcription factors (TFs), as reported in past studies. In this study, we showed that JA accumulated in the susceptible cultivar Actinidia chinensis 'Hongyang' but decreased in the resistant cultivar of A. chinensis var. deliciosa 'Jinkui' in response to Psa. Integrated transcriptomic and proteomic analyses were carried out using the resistant cultivar 'Jinkui'. A total of 5,045 differentially expressed genes (DEGs) and 1,681 differentially expressed proteins (DEPs) were identified after Psa infection. Two pathways, 'plant hormone signal transduction' and 'phenylpropanoid biosynthesis,' were activated at the protein and transcript levels. In addition, a total of 27 R2R3-MYB transcription factors (TFs) were involved in the response to Psa of 'Jinkui,' including the R2R3-MYB TF subgroup 4 gene AcMYB16, which was downregulated in 'Jinkui' but upregulated in 'Hongyang.' The promoter region of AcMYB16 has a MeJA responsiveness cis-acting regulatory element (CRE). Transient expression of the AcMYB16 gene in the leaves of 'Jinkui' induced Psa infection. Together, these data suggest that AcMYB16 acts as a repressor to regulate the response of kiwifruit to Psa infection. Our work will help to unravel the processes of kiwifruit resistance to pathogens and will facilitate the development of varieties with resistance against bacterial pathogens.

Recent Advanced Metabolic and Genetic Engineering of Phenylpropanoid Biosynthetic Pathways

The MYB transcription factors (TFs) are evolving as critical role in the regulation of the phenylpropanoid and tanshinones biosynthetic pathway. MYB TFs relate to a very important gene family, which are involved in the regulation of primary and secondary metabolisms, terpenoids, bioactive compounds, plant defense against various stresses and cell morphology. R2R3 MYB TFs contained a conserved N-terminal domain, but the domain at C-terminal sorts them different regarding their structures and functions. MYB TFs suppressors generally possess particular repressive motifs, such as pdLNLD/ELxiG/S and TLLLFR, which contribute to their suppression role through a diversity of complex regulatory mechanisms. A novel flower specific "NF/YWSV/MEDF/LW" conserved motif has a great potential to understand the mechanisms of flower development. In the current review, we summarize recent advanced progress of MYB TFs on transcription regulation, posttranscriptional, microRNA, conserved motif and propose directions to future prospective research. We further suggest there should be more focus on the investigation for the role of MYB TFs in microalgae, which has great potential for heterologous protein expression system for future perspectives.

Applications of virus-induced gene silencing for identification of gene function in fruit

With the development of bioinformatics, it is easy to obtain information and data about thousands of genes, but the determination of the functions of these genes depends on methods for rapid and effective functional identification. Virus-induced gene silencing (VIGS) is a mature method of gene functional identification developed over the last 20 years, which has been widely used in many research fields involving many species. Fruit quality formation is a complex biological process, which is closely related to ripening. Here, we review the progress and contribution of VIGS to our understanding of fruit biology and its advantages and disadvantages in determining gene function.

Genomic analysis uncovers functional variation in the C-terminus of anthocyanin-activating MYB transcription factors

MYB transcription factors regulate diverse aspects of plant development and secondary metabolism, often by partnering in transcriptional regulatory complexes. Here, we harness genomic resources to identify novel MYBs, thereby producing an updated eudicot MYB phylogeny with revised relationships among subgroups as well as new information on sequence variation in the disordered C-terminus of anthocyanin-activating MYBs. BLAST® and hidden Markov model scans of gene annotations identified a total of 714 MYB transcription factors across the genomes of four crops that span the eudicots: apple, grape, kiwifruit and tomato. Codon model-based phylogenetic inference identified novel members of previously defined subgroups, and the function of specific anthocyanin-activating subgroup 6 members was assayed transiently in tobacco leaves. Sequence conservation within subgroup 6 highlighted one previously described and two novel short linear motifs in the disordered C-terminal region. The novel motifs have a mix of hydrophobic and acidic residues and are predicted to be relatively ordered compared with flanking protein sequences. Comparison of motifs with the Eukaryotic Linear Motif database suggests roles in protein-protein interaction. Engineering of motifs and their flanking regions from strong anthocyanin activators into weak activators, and vice versa, affected function. We conclude that, although the MYB C-terminal sequence diverges greatly even within MYB clades, variation within the C-terminus at and near relatively ordered regions offers opportunities for exploring MYB function and developing superior alleles for plant breeding.

Regulation of MYB Transcription Factors of Anthocyanin Synthesis in Lily Flowers

Flower color is the decisive factor that affects the commercial value of ornamental flowers. Therefore, it is important to study the regulation of flower color formation in lily to discover the positive and negative factors that regulate this important trait. In this study, MYB transcription factors (TFs) were characterized to understand the regulatory mechanism of anthocyanin biosynthesis in lily. Two R2R3-MYB TFs, LvMYB5, and LvMYB1, were found to regulate anthocyanin biosynthesis in lily flowers. LvMYB5, which has an activation motif, belongs to the SG6 MYB protein subgroup of Arabidopsis thaliana. Transient expression of LvMYB5 indicated that LvMYB5 can promote coloration in Nicotiana benthamiana leaves, and that expression of LvMYB5 increases the expression levels of NbCHS, NbDFR, and NbANS. VIGS experiments in lily petals showed that the accumulation of anthocyanins was reduced when LvMYB5 was silenced. Luciferase assays showed that LvMYB5 can promote anthocyanin synthesis by activating the ANS gene promoter. Therefore, LvMYB5 plays an important role in flower coloration in lily. In addition, the transient expression experiment provided preliminary evidence that LvMYB1 (an R2R3-MYB TF) inhibits anthocyanin synthesis in lily flowers. The discovery of activating and inhibitory factors related to anthocyanin biosynthesis in lily provides a theoretical basis for improving flower color through genetic engineering. The results of our study provide a new direction for the further study of the mechanisms of flower color formation in lilies.

Red Chinese Cabbage Transcriptome Analysis Reveals Structural Genes and Multiple Transcription Factors Regulating Reddish Purple Color

Reddish purple Chinese cabbage (RPCC) is a popular variety of Brassica rapa (AA = 20). It is rich in anthocyanins, which have many health benefits. We detected novel anthocyanins including cyanidin 3-(feruloyl) diglucoside-5-(malonoyl) glucoside and pelargonidin 3-(caffeoyl) diglucoside-5-(malonoyl) glucoside in RPCC. Analyses of transcriptome data revealed 32,395 genes including 3345 differentially expressed genes (DEGs) between 3-week-old RPCC and green Chinese cabbage (GCC). The DEGs included 218 transcription factor (TF) genes and some functionally uncharacterized genes. Sixty DEGs identified from the transcriptome data were analyzed in 3-, 6- and 9-week old seedlings by RT-qPCR, and 35 of them had higher transcript levels in RPCC than in GCC. We detected cis-regulatory motifs of MYB, bHLH, WRKY, bZIP and AP2/ERF TFs in anthocyanin biosynthetic gene promoters. A network analysis revealed that MYB75, MYB90, and MYBL2 strongly interact with anthocyanin biosynthetic genes. Our results show that the late biosynthesis genes BrDFR, BrLDOX, BrUF3GT, BrUGT75c1-1, Br5MAT, BrAT-1,BrAT-2, BrTT19-1, and BrTT19-2 and the regulatory MYB genes BrMYB90, BrMYB75, and BrMYBL2-1 are highly expressed in RPCC, indicative of their important roles in anthocyanin biosynthesis, modification, and accumulation. Finally, we propose a model anthocyanin biosynthesis pathway that includes the unique anthocyanin pigments and genes specific to RPCC.