Isolation and molecular characterization of NtMYB4a, a putative transcription activation factor involved in anthocyanin synthesis in tobacco

Analysis of the Spatholobus suberectus full-length transcriptome identified an R2R3-MYB transcription factor-encoding gene SsMYB158 that regulates flavonoid biosynthesis

Spatholobus suberectus Dunn (Leguminosae) has been used for medicinal purposes for a long period. Flavonoids are the major bioactive components of S. suberectus. However, there is still limited knowledge of the exact method via which transcription factors (TFs) regulate flavonoid biosynthesis. The full-length transcriptome of S. suberectus was analyzed using SMRT sequencing; 61,548 transcripts were identified, including 12,311 new gene loci, 53,336 novel transcripts, 44,636 simple sequence repeats, 36,414 complete coding sequences, 871 long non-coding RNAs and 6781 TFs. The SsMYB158 TF, which is associated with flavonoid biosynthesis, belongs to the R2R3-MYB class and is localized subcellularly to the nucleus. The overexpression of SsMYB158 in Nicotiana benthamiana and the transient overexpression of SsMYB158 in S. suberectus resulted in a substantial enhancement in both flavonoids and catechin levels. In addition, there was a remarkable upregulation in the expression of essential enzyme-coding genes associated with the flavonoid biosynthesis pathways. Our study revealed SsMYB158 as a critical regulator of flavonoid biosynthesis in S. suberectus and laying the foundation for its molecular breeding.

Integrated Transcriptome and Proteome Analysis Reveals the Regulatory Mechanism of Root Growth by Protein Disulfide Isomerase in Arabidopsis

Protein disulfide isomerase (PDI, EC 5.3.4.1) is a thiol-disulfide oxidoreductase that plays a crucial role in catalyzing the oxidation and rearrangement of disulfides in substrate proteins. In plants, PDI is primarily involved in regulating seed germination and development, facilitating the oxidative folding of storage proteins in the endosperm, and also contributing to the formation of pollen. However, the role of PDI in root growth has not been previously studied. This research investigated the impact of PDI gene deficiency in plants by using 16F16 [2-(2-Chloroacetyl)-2,3,4,9-tetrahydro-1-methyl-1H-pyrido[3,4-b]indole-1-carboxylic acid methyl ester], a small-molecule inhibitor of PDI, to remove functional redundancy. The results showed that the growth of Arabidopsis roots was significantly inhibited when treated with 16F16. To further investigate the effects of 16F16 treatment, we conducted expression profiling of treated roots using RNA sequencing and a Tandem Mass Tag (TMT)-based quantitative proteomics approach at both the transcriptomic and proteomic levels. Our analysis revealed 994 differentially expressed genes (DEGs) at the transcript level, which were predominantly enriched in pathways associated with "phenylpropane biosynthesis", "plant hormone signal transduction", "plant-pathogen interaction" and "starch and sucrose metabolism" pathways. Additionally, we identified 120 differentially expressed proteins (DEPs) at the protein level. These proteins were mainly enriched in pathways such as "phenylpropanoid biosynthesis", "photosynthesis", "biosynthesis of various plant secondary metabolites", and "biosynthesis of secondary metabolites" pathways. The comprehensive transcriptome and proteome analyses revealed a regulatory network for root shortening in Arabidopsis seedlings under 16F16 treatment, mainly involving phenylpropane biosynthesis and plant hormone signal transduction pathways. This study enhances our understanding of the significant role of PDIs in Arabidopsis root growth and provides insights into the regulatory mechanisms of root shortening following 16F16 treatment.

Metabolic GWAS-based dissection of genetic basis underlying nutrient quality variation and domestication of cassava storage root

BACKGROUND

Metabolites play critical roles in regulating nutritional qualities of plants, thereby influencing their consumption and human health. However, the genetic basis underlying the metabolite-based nutrient quality and domestication of root and tuber crops remain largely unknown.

RESULTS

We report a comprehensive study combining metabolic and phenotypic genome-wide association studies to dissect the genetic basis of metabolites in the storage root (SR) of cassava. We quantify 2,980 metabolic features in 299 cultivated cassava accessions. We detect 18,218 significant marker-metabolite associations via metabolic genome-wide association mapping and identify 12 candidate genes responsible for the levels of metabolites that are of potential nutritional importance. Me3GT, MeMYB4, and UGT85K4/UGT85K5, which are involved in flavone, anthocyanin, and cyanogenic glucoside metabolism, respectively, are functionally validated through in vitro enzyme assays and in vivo gene silencing analyses. We identify a cluster of cyanogenic glucoside biosynthesis genes, among which CYP79D1, CYP71E7b, and UGT85K5 are highly co-expressed and their allelic combination contributes to low linamarin content. We find MeMYB4 is responsible for variations in cyanidin 3-O-glucoside and delphinidin 3-O-rutinoside contents, thus controlling SR endothelium color. We find human selection affects quercetin 3-O-glucoside content and SR weight per plant. The candidate gene MeFLS1 is subject to selection during cassava domestication, leading to decreased quercetin 3-O-glucoside content and thus increased SR weight per plant.

CONCLUSIONS

These findings reveal the genetic basis of cassava SR metabolome variation, establish a linkage between metabolites and agronomic traits, and offer useful resources for genetically improving the nutrition of cassava and other root crops.

Genome-Wide Identification and Analysis of MYB Transcription Factors in Pyropia yezoensis

MYB transcription factors are one of the largest transcription factor families in plants, and they regulate numerous biological processes. Red algae are an important taxonomic group and have important roles in economics and research. However, no comprehensive analysis of the MYB gene family in any red algae, including Pyropia yezoensis, has been conducted. To identify the MYB gene members of Py. yezoensis, and to investigate their family structural features and expression profile characteristics, a study was conducted. In this study, 3 R2R3-MYBs and 13 MYB-related members were identified in Py. yezoensis. Phylogenetic analysis indicated that most red algae MYB genes could be clustered with green plants or Glaucophyta MYB genes, inferring their ancient origins. Synteny analysis indicated that 13 and 5 PyMYB genes were orthologous to Pyropia haitanensis and Porphyra umbilicalis, respectively. Most Bangiaceae MYB genes contain several Gly-rich motifs, which may be the result of an adaptation to carbon limitations and maintenance of important regulatory functions. An expression profile analysis showed that PyMYB genes exhibited diverse expression profiles. However, the expression patterns of different members appeared to be diverse, and PyMYB5 was upregulated in response to dehydration, low temperature, and Pythium porphyrae infection. This is the first comprehensive study of the MYB gene family in Py. Yezoensis and it provides vital insights into the functional divergence of MYB genes.

Transcriptomic analysis reveals the mechanism underlying the anthocyanin changes in Fragaria nilgerrensis Schlecht. and its interspecific hybrids

BACKGROUND

Fragaria nilgerrensis (FN) provides a rich source of genetic variations for strawberry germplasm innovation. The color of strawberry fruits is a key factor affecting consumer preferences. However, the genetic basis of the fruit color formation in F. nilgerrensis and its interspecific hybrids has rarely been researched.

RESULTS

In this study, the fruit transcriptomes and flavonoid contents of FN (white skin; control) and its interspecific hybrids BF1 and BF2 (pale red skin) were compared. A total of 31 flavonoids were identified. Notably, two pelargonidin derivatives (pelargonidin-3-O-glucoside and pelargonidin-3-O-rutinoside) were revealed as potential key pigments for the coloration of BF1 and BF2 fruits. Additionally, dihydroflavonol 4-reductase (DFR) (LOC101293459 and LOC101293749) and anthocyanidin 3-O-glucosyltransferase (BZ1) (LOC101300000), which are crucial structural genes in the anthocyanidin biosynthetic pathway, had significantly up-regulated expression levels in the two FN interspecific hybrids. Moreover, most of the genes encoding transcription factors (e.g., MYB, WRKY, TCP, bHLH, AP2, and WD40) related to anthocyanin accumulation were differentially expressed. We also identified two DFR genes (LOC101293749 and LOC101293459) that were significantly correlated with members in bHLH, MYB, WD40, AP2, and bZIP families. Two chalcone synthase (CHS) (LOC101298162 and LOC101298456) and a BZ1 gene (LOC101300000) were highly correlated with members in bHLH, WD40 and AP2 families.

CONCLUSIONS

Pelargonidin-3-O-glucoside and pelargonidin-3-O-rutinoside may be the key pigments contributing to the formation of pale red fruit skin. DFR and BZ1 structural genes and some bHLH, MYB, WD40, AP2, and bZIP TF family members enhance the accumulation of two pelargonidin derivatives. This study provides important insights into the regulation of anthocyanidin biosynthesis in FN and its interspecific hybrids. The presented data may be relevant for improving strawberry fruit coloration via genetic engineering.

Identification of F-box gene family in Brassica oleracea and expression analysis in response to low-temperature stress

Unfavorable climatic conditions, such as low temperatures, often hinder the growth and production of crops worldwide. The F-box protein-encoding gene family performs an essential role in plant stress resistance. However, a comprehensive analysis of the F-box gene family in cabbage (Brassica oleracea var capitata L.) has not been reported yet. In this study, genome-wide characterization of F-box proteins in cabbage yielded 303 BoFBX genes and 224 BoFBX genes unevenly distributed on 9 chromosomes of cabbage. Phylogenetic analysis of 303 BoFBX genes was classified into nine distinct subfamily groups (GI-GIX). Analysis of the gene structure of BoFBX genes indicated that most genes within the same clade are highly conserved. In addition, tissue-specific expression analysis revealed that six F-box genes in cabbage showed the highest expression in rosette leaves, followed by roots and stems and the lowest expression was observed in the BoFBX156 gene. In contrast, the expression of the other five genes, BoFBX100, BoFBX117, BoFBX136, BoFBX137 and BoFBX213 was observed to be upregulated in response to low-temperature stress. Moreover, we found that the expression level of the BoFBX gene in the cold-tolerant cultivar "ZG" was higher than that in cold-sensitive "YC" with the extension of stress duration, while expression levels of each gene in "ZG" were higher than "YC" at 24 h. Knowledge of the various functions provided by BoFBXs genes and their expression patterns provides a firm theoretical foundation for explaining the functions of BoFBXs, thereby contributing to the molecular breeding process of cabbage.

Comprehensive analysis of metabolome and transcriptome reveals the mechanism of color formation in different leave of Loropetalum Chinense var. Rubrum

BACKGROUND

Loropetalum chinense var. rubrum (L. chinense var. rubrum) is a precious, coloured-leaf native ornamental plant in the Hunan Province. We found an L. chinense var. rubrum tree with three different leaf colours: GL (green leaf), ML (mosaic leaf), and PL (purple leaf). The mechanism of leaf coloration in this plant is still unclear. Therefore, this study aimed to identify the metabolites and genes involved in determining the colour composition of L. chinense var. rubrum leaves, using phenotypic/anatomic observations, pigment content detection, and comparative metabolomics and transcriptomics.

RESULTS

We observed that the mesophyll cells in PL were purple, while those in GL were green and those in ML were a mix of purple-green. The contents of chlorophyll a, b, carotenoids, and total chlorophyll in PL and ML were significantly lower than those in GL. While the anthocyanin content in PL and ML was significantly higher than that in GL. The metabolomics results showed the differences in the content of cyanidin 3-O-glucoside, delphinidin 3-O-glucoside, cyanidin 3,5-O-diglucoside, pelargonidin, and petunidin 3,5-diglucoside in ML, GL, and PL were significant. Considering that the change trend of anthocyanin content change was consistent with the leaf colour difference, we speculated that these compounds might influence the colour of L. chinense var. rubrum leaves. Using transcriptomics, we finally identified nine differentially expressed structural genes (one ANR (ANR1217); four CYP75As (CYP75A1815, CYP75A2846, CYP75A2909, and CYP75A1716); four UFGTs (UFGT1876, UFGT1649, UFGT1839, and UFGT3273) and nine transcription factors (two MYBs (MYB1057 and MYB1211), one MADS-box (MADS1235), two AP2-likes (AP2-like1779 and AP2-like2234), one bZIP (bZIP3720), two WD40s (WD2173 and WD1867) and one bHLH (bHLH1631) that might be related to flavonoid biosynthesis and then impacted the appearance of colour in L. chinense var. rubrum leaves.

CONCLUSION

This study revealed potential molecular mechanisms associated with leaf coloration in L. chinense var. rubrum by analyzing differential metabolites and genes related to the anthocyanin biosynthesis pathway. It also provided a reference for research on leaf colour variation in other ornamental plants.

Full-Length Transcriptome Sequencing Provides Insights into Flavonoid Biosynthesis in Camellia nitidissima Petals

Flavonoids are the main medicinal ingredients in Camellia nitidissima, but the regulatory mechanism of flavonoid biosynthesis in flowers is unclear; therefore, the flavonoids in C. nitidissima have not been effectively used. The present study performed full-length transcriptome sequencing of C. nitidissima flower. Furthermore, the reported RNA-sequencing data of C. nitidissima petals were reanalyzed using the full-length transcriptome as a reference, and the regulatory mechanism of flavonoid synthesis in petals was elucidated. The analysis identified 43,350 isoforms annotated in non-redundant protein (Nr), Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG), and Swiss-Prot databases, among which 34,602 aligned to Camellia sinensis genes. A total of 11,857 differentially expressed genes (DEGs), including 112 related to flavonoid synthesis, were identified by pairwise comparison. Subsequently, analysis of the phylogeny and the conserved motifs of R2R3-MYB using the proteins sequences identified three R2R3-MYB transcription factors that regulated flavonoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified phenylalanine ammonia-lyase (PAL) and 4-coumarate: CoA ligase(4CL) as the hub genes and showed that bHLH79 interacted with PAL. Finally, validated the expression of seven DEGs involved in flavonoid biosynthesis using real-time quantitative PCR (qRT-PCR). Thus, the present study generated and used the full-length transcriptome as the reference to analyze the transcriptome of petals and proposed a possible regulatory mechanism of flavonoid synthesis in C. nitidissima. The study's findings unravel the genetic mechanisms underlying flavonoid synthesis and suggest candidate genes for the genetic improvement of C. nitidissima.

Genome-wide identification and expression analysis of the R2R3-MYB gene family in tobacco (Nicotiana tabacum L.)

BACKGROUND

The R2R3-MYB transcription factor is one of the largest gene families in plants and involved in the regulation of plant development, hormone signal transduction, biotic and abiotic stresses. Tobacco is one of the most important model plants. Therefore, it will be of great significance to investigate the R2R3-MYB gene family and their expression patterns under abiotic stress and senescence in tobacco.

RESULTS

A total of 174 R2R3-MYB genes were identified from tobacco (Nicotiana tabacum L.) genome and were divided into 24 subgroups based on phylogenetic analysis. Gene structure (exon/intron) and protein motifs were especially conserved among the NtR2R3-MYB genes, especially members within the same subgroup. The NtR2R3-MYB genes were distributed on 24 tobacco chromosomes. Analysis of gene duplication events obtained 3 pairs of tandem duplication genes and 62 pairs of segmental duplication genes, suggesting that segmental duplications is the major pattern for R2R3-MYB gene family expansion in tobacco. Cis-regulatory elements of the NtR2R3-MYB promoters were involved in cellular development, phytohormones, environmental stress and photoresponsive. Expression profile analysis showed that NtR2R3-MYB genes were widely expressed in different maturity tobacco leaves, and however, the expression patterns of different members appeared to be diverse. The qRT-PCR analysis of 15 NtR2R3-MYBs confirmed their differential expression under different abiotic stresses (cold, salt and drought), and notably, NtMYB46 was significantly up-regulated under three treatments.

CONCLUSIONS

In summary, a genome-wide identification, evolutionary and expression analysis of R2R3-MYB gene family in tobacco were conducted. Our results provided a solid foundation for further biological functional study of NtR2R3-MYB genes in tobacco.

Genome-wide identification and characterization of bZIP gene family and cloning of candidate genes for anthocyanin biosynthesis in pomegranate (Punica granatum)

BACKGROUND

The basic leucine zipper (bZIP) transcription factor is one of the most abundant and conserved gene families in eukaryotes. In addition to participating in plant development and growth, bZIP transcription factors play crucial roles in various abiotic stress responses and anthocyanin accumulation. Up to now, analysis of bZIP gene family members in pomegranate (Punica granatum) has not been reported. Three published pomegranate genome sequences provide valuable resources for further gene function analysis.

RESULTS

Using bioinformatics analysis, 65 PgbZIPs were identified and analyzed from the 'Taishanhong' pomegranate genome. We divided them into 13 groups (A, B, C, D, E, F, G, H, I, J, K, M, and S) according to the phylogenetic relationship with those of Arabidopsis, each containing a different number of genes. The regularity of exon/intron number and distribution was consistent with the classification of groups in the evolutionary tree. Transcriptome analysis of different tissues showed that members of the PgbZIP gene family were differentially expressed in different developmental stages and tissues of pomegranate. Among them, we selected PgbZIP16 and PgbZIP34 as candidate genes which affect anthocyanin accumulation. The full-length CDS region of PgbZIP16 and PgbZIP34 were cloned from pomegranate petals by homologous cloning technique, encoding 170 and 174 amino acids, which were 510 bp and 522 bp, respectively. Subcellular localization assays suggested that both PgbZIP16 and PgbZIP34 were nucleus-localized. Real-time quantitative PCR (qPCR) was used to explore the expression of PgbZIP16 and PgbZIP34 in the petals of three kinds of ornamental pomegranates at the full flowering stage. The results demonstrated that the expression of PgbZIP16 in red petals was 5.83 times of that in white petals, while PgbZIP34 was 3.9 times. The results of transient expression in tobacco showed that consistent trends were observed in anthocyanin concentration and expression levels of related genes, which both increased and then decreased. Both PgbZIP16 and PgbZIP34 could promote anthocyanin accumulation in tobacco leaves. We obtained transgenic strains overexpressing PgbZIP16, and the histochemical staining for GUS activity showed that overexpressed PgbZIP16 seedlings were expressed in the stem. Transgenic experiments indicated that overexpression of PgbZIP16 significantly upregulated UF3GT, ANS and DFR genes in Arabidopsis and enhanced anthocyanin accumulation.

CONCLUSIONS

The whole genome identification, gene structure, phylogeny, gene cloning, subcellular location and functional verification of the pomegranate bZIP gene family provide a theoretical foundation for the functional study of the PgbZIP gene family and candidate genes for anthocyanin biosynthesis.

Transcriptome profiling unveils the mechanism of phenylpropane biosynthesis in rhizome development of Caucasian clover

Caucasian clover is the only perennial herb of the genus Leguminous clover with underground rhizomes. However, we know very little about its development process and mechanism. Transcriptome studies were conducted on the roots of Caucasian clover without a rhizome (NR) at the young seedling stage and the fully developed rhizome, including the root neck (R1), main root (R2), horizontal root (R3), and rhizome bud (R4), of the tissues in the mature phase. Compared with the rhizome in the mature phase, NR had 893 upregulated differentially expressed genes (DEGs), most of which were enriched in 'phenylpropanoid biosynthesis', 'phenylalanine metabolism', 'DNA replication' and 'biosynthesis of amino acids'. A higher number of transcription factors (AP2/ERF, C2H2 and FAR1) were found in NR. There were highly expressed genes for R4, such as auxin response factor SAUR, galacturonosyltransferase (GAUT), and sucrose synthase (SUS). Phenylpropanoids are very important for the entire process of rhizome development. We drew a cluster heat map of genes related to the phenylpropanoid biosynthesis pathway, in which the largest number of genes belonged to COMT, and most of them were upregulated in R4.