Identification of CaAN3 as a fruit-specific regulator of anthocyanin biosynthesis in pepper (Capsicum annuum)

Phenotypic, genetic, variation, and molecular function of CaMYB113 in pepper (Capsicum annuum L.)

Pepper (Capsicum annuum L.) is widely consumed vegetables worldwide, and F1 hybrids are highly sought after in the pepper seed industry. However, studies on gene mutations affecting the color of cotyledon are rare, and the same is true for peppers. In this study, a segregating population was developed by crossing the pepper accession 21C1344 with purple cotyledon and accession 21C912 with green cotyledon. Initially, a target genomic region was identified by screening polymorphic SSR markers distributed across 12 chromosomes. Subsequently, polymorphic markers were developed based on resequencing data from the two parental lines, and genetic linkage analysis was performed. This approach ultimately identified Capana10g001433 (CaMYB113) as the candidate gene responsible for the purple cotyledons. The gene mutation type in 21C912 represents a new mutation type distinct from the reported missense mutation types, and this mutation affects the biosynthesis of anthocyanins. Virus-induced gene silencing (VIGS) of CaMYB113 substantially decreased anthocyanin accumulation in the cotyledons. Subsequent overexpression of CaMYB113 resulted in purple callus and leaves of pepper, and changed the expression levels of downstream genes involved in anthocyanin synthesis. Yeast one-hybrid and dual-luciferase transient expression assays demonstrated the binding of CaMYB113 to anthocyanin biosynthesis-related genes, thereby regulating anthocyanin accumulation in pepper cotyledons.

Global transcription and metabolic profiles of five tissues in pepper fruits

Studying the regulatory mechanisms in different tissues of pepper is crucial for understanding organ formation, growth, and development. However, relevant studies are far from sufficient. In the current study, the stipe, calyx, pericarp, placenta, and seed of ripe pepper were sampled, and metabolites were determined by the untargeted metabolomics method. Transcriptome sequencing was performed by Illumina NovaSeq 6000, and then a high-throughput data set was built. The results showed that a total of 4879 annotated metabolites were detected in 15 samples of the five tissues under positive and negative ion mode. A total of 110.66 Gb of clean data was obtained by transcriptome sequencing, the clean data of each sample reached 6.21 Gb, and a total of 35 336 annotated expression genes were obtained. Furthermore, validate the accuracy of the data by combining principal component analysis and other methods. In summary, this study provides valuable information for the genetic improvement and breeding of peppers, and it holds potential application value, particularly in enhancing the quality and nutritional value of pepper fruits.

Research advances of coloring mechanism regulated by MicroRNAs in plants

In plants, microRNAs (miRNAs) are a class of important small RNAs involved in their growth and development, and play a very significant role in regulating their tissue coloring. In this paper, the mechanisms on miRNA regulation of plant coloring are mainly reviewed from three aspects: macroscopic physiological and molecular foundations related to tissue coloring, miRNA biosynthesis and function, and specific analysis of miRNA regulation studies on leaf color, flower color, fruit color, and other tissue color formation in plants. Furthermore, we also systematically summarize the miRNA regulatory mechanisms identified on pigments biosynthesis and color formation in plants, and the regulatory mechanisms of these miRNAs mentioned on the existing researches can be divided into four main categories: directly targeting the related transcription factors, directly targeting the related structural genes, directly targeting the related long noncoding RNAs (LncRNAs) and miRNA-mediated production of trans-acting small interfering RNAs (ta-siRNAs). Together, these research results aim to provide a theoretical reference for the in-depth study of plant coloring mechanism and molecular breeding study of related plants in the future.

Genome-wide identification of CaWD40 proteins reveals the involvement of a novel complex (CaAN1-CaDYT1-CaWD40-91) in anthocyanin biosynthesis and genic male sterility in Capsicum annuum

BACKGROUND

The WD40 domain, one of the most abundant in eukaryotic genomes, is widely involved in plant growth and development, secondary metabolic biosynthesis, and mediating responses to biotic and abiotic stresses. WD40 repeat (WD40) protein has been systematically studied in several model plants but has not been reported in the Capsicum annuum (pepper) genome.

RESULTS

Herein, 269, 237, and 257 CaWD40 genes were identified in the Zunla, CM334, and Zhangshugang genomes, respectively. CaWD40 sequences from the Zunla genome were selected for subsequent analysis, including chromosomal localization, phylogenetic relationships, sequence characteristics, motif compositions, and expression profiling. CaWD40 proteins were unevenly distributed on 12 chromosomes, encompassing 19 tandem duplicate gene pairs. The 269 CaWD40s were divided into six main branches (A to F) with 17 different types of domain distribution. The CaWD40 gene family exhibited diverse expression patterns, and several genes were specifically expressed in flowers and seeds. Yeast two-hybrid (Y2H) and dual-luciferase assay indicated that CaWD40-91 could interact with CaAN1 and CaDYT1, suggesting its involvement in anthocyanin biosynthesis and male sterility in pepper.

CONCLUSIONS

In summary, we systematically characterized the phylogeny, classification, structure, and expression of the CaWD40 gene family in pepper. Our findings provide a valuable foundation for further functional investigations on WD40 genes in pepper.

Genetic characterization of a locus responsible for low pungency using EMS-induced mutants in Capsicum annuum L

KEY MESSAGE

The pepper mutants ('221-2-1a' and '1559-1-2h') with very low pungency were genetically characterized. The Pun4 locus, responsible for the reduced pungency of the mutant fruits, was localized to a 208 Mb region on chromosome 6. DEMF06G16460, encoding 3-ketoacyl-CoA synthase, was proposed as a strong candidate gene based on the genetic analyses of bulked segregants, DEG, and expression analyses. Capsaicinoids are unique alkaloids present in pepper (Capsicum spp.), synthesized through the condensation of by-products from the phenylpropanoid and branched-chain fatty acid pathways, and accumulating in the placenta. In this study, we characterized two allelic ethyl methanesulfonate-induced mutant lines with extremely low pungency ('221-2-1a' and '1559-1-2h'). These mutants, derived from the pungent Korean landrace 'Yuwolcho,' exhibited lower capsaicinoid content than Yuwolcho but still contained a small amount of capsaicinoid with functional capsaicinoid biosynthetic genes. Genetic crosses between the mutants and Yuwolcho or pungent lines indicated that a single recessive mutation was responsible for the low-pungency phenotype of mutant 221-2-1a; we named the causal locus Pungency 4 (Pun4). To identify Pun4, we combined genome-wide polymorphism analysis and transcriptome analysis with bulked-segregant analysis. We narrowed down the location of Pun4 to a 208-Mb region on chromosome 6 containing five candidate genes, of which DEMF06G16460, encoding a 3-ketoacyl-CoA synthase associated with branched-chain fatty acid biosynthesis, is the most likely candidate for Pun4. The expression of capsaicinoid biosynthetic genes in placental tissues in Yuwolcho and the mutant was consistent with the branched-chain fatty acid pathway playing a pivotal role in the lower pungency observed in the mutant. We also obtained a list of differentially expressed genes in placental tissues between the mutant and Yuwolcho, from which we selected candidate genes using gene co-expression analysis. In summary, we characterized the capsaicinoid biosynthesis-related locus Pun4 through integrated of genetic, genomic, and transcriptome analyses. These findings will contribute to our understanding of capsaicinoid biosynthesis in pepper.

Molecular mapping of the broad bean wilt virus 2 resistance locus bwvr in Capsicum annuum using BSR-seq

KEY MESSAGE

Bulked segregant RNA seq of pools of pepper accessions that are susceptible or resistant to Broad bean wilt virus 2 identifies a gene that might confer resistance to this devastating pathogen. The single-stranded positive-sense RNA virus Broad bean wilt virus 2 (BBWV2) causes substantial damage to pepper (Capsicum annuum) cultivation. Here, we describe mapping the BBWV2 resistance locus bwvr using a F7:8 recombinant inbred line (RIL) population constructed by crossing the BBWV2-resistant pepper accession 'SNU-C' with the susceptible pepper accession 'ECW30R.' All F1 plants infected with the BBWV2 strain PAP1 were susceptible to the virus, and the RIL population showed a 1:1 ratio of resistance to susceptibility, indicating that this trait is controlled by a single recessive gene. To map bwvr, we performed bulked segregant RNA-seq (BSR-seq). We sequenced pools of resistant and susceptible lines from the RILs and aligned the reads to the high-quality 'Dempsey' reference genome to identify variants between the pools. This analysis identified 519,887 variants and selected the region from 245.9-250.8 Mb of the Dempsey reference genome as the quantitative trait locus region for bwvr. To finely map bwvr, we used newly designed high-resolution melting (HRM) and Kompetitive allele specific PCR (KASP) markers based on variants obtained from the BSR-seq reads and the PepperSNP16K array. Comparative analysis identified 11 SNU-C-specific SNPs within the bwvr locus. Using markers derived from these variants, we mapped the candidate bwvr locus to the region from 246.833-246.949 kb. SNU-C-specific variants clustered near DEM.v1.00035533 within the bwvr locus. DEM.v1.00035533 encodes the nitrate transporter NPF1.2 and contains a SNP within its 5' untranslated region. The bwvr locus, which contains four genes including DEM.v1.00035533, could represent a valuable resource for global pepper breeding programs.

Construction of a high-density genetic map for yardlong bean and identification of ANT1 as a regulator of anthocyanin biosynthesis

Because its long, tender pods supply essential proteins, vitamins, and fibers to humans, yardlong bean (Vigna unguiculata ssp. sesquipedalis) is a commonly consumed vegetable, especially in Southeast Asia. To provide insights into the genetic bases of key agricultural traits in yardlong bean, we here created a high-density bin-map with 2084 bin markers using 514 227 SNPs from a recombinant-inbred line (RIL) population. Quantitative trait loci (QTL) mapping was carried out to identify loci associated with anthocyanin content (ANT), vitamin E content (VE), total soluble protein content (TSP), pod length (PL), hundred-seed weight (HSW), seed length and width (SL and SW, respectively), and seed coat color (SCC). In total, 20 related QTLs were isolated, explaining 7.58-56.03% of the phenotypic variation. Of these, five major QTLs (qANT5, qTSP11, qVE7, qPL3, and qSCC9) were detected in 2020, 2021, and the combined environment, explaining 11.96-56.03% of the phenotypic variation. VuANT1 was identified as a causal gene for the QTL qANT5, which regulated anthocyanin content; VuANT1 was highly expressed in immature purple pods but barely detectable in white pods. VuANT1 overexpression in tobacco leaves and yardlong bean hairy roots resulted in purple coloration as a result of anthocyanin accumulation. These findings suggested that VuANT1 was a key regulator of anthocyanin accumulation in yardlong bean. Our results lay a firm foundation for target agricultural trait improvement and clarification of the genetic mechanisms underlying agricultural traits in yardlong bean.

Genetic Regulation, Environmental Cues, and Extraction Methods for Higher Yield of Secondary Metabolites in Capsicum

Capsicum (chili pepper) is a widely popular and highly consumed fruit crop with beneficial secondary metabolites such as capsaicinoids, carotenoids, flavonoids, and polyphenols, among others. Interestingly, the secondary metabolite profile is a dynamic function of biosynthetic enzymes, regulatory transcription factors, developmental stage, abiotic and biotic environment, and extraction methods. We propose active manipulable genetic, environmental, and extraction controls for the modulation of quality and quantity of desired secondary metabolites in Capsicum species. Specific biosynthetic genes such as Pun (AT3) and AMT in the capsaicinoids pathway and PSY, LCY, and CCS in the carotenoid pathway can be genetically engineered for enhanced production of capsaicinoids and carotenoids, respectively. Generally, secondary metabolites increase with the ripening of the fruit; however, transcriptional regulators such as MYB, bHLH, and ERF control the extent of accumulation in specific tissues. The precise tuning of biotic and abiotic factors such as light, temperature, and chemical elicitors can maximize the accumulation and retention of secondary metabolites in pre- and postharvest settings. Finally, optimized extraction methods such as ultrasonication and supercritical fluid method can lead to a higher yield of secondary metabolites. Together, the integrated understanding of the genetic regulation of biosynthesis, elicitation treatments, and optimization of extraction methods can maximize the industrial production of secondary metabolites in Capsicum.

Identification of CaPs locus involving in purple stripe formation on unripe fruit, reveals allelic variation and alternative splicing of R2R3-MYB transcription factor in pepper (Capsicum annuum L.)

The purple color of unripe pepper fruit is attributed to the accumulation of anthocyanins. Only a few genes controlling the biosynthesis and regulation of anthocyanins have been cloned in Capsicum. In this study, we performed a bulked segregant analysis of the purple striped trait using an F² population derived from a cross between the immature purple striped fruit line Chen12-4-1-1-1-1 and the normal green fruit line Zhongxian101-M-F⁹. We mapped the CaPs locus to an 841.39 kb region between markers M-CA690-Xba and MCA710-03 on chromosome 10. CA10g11690 encodes an R2R3-MYB transcription factor that is involved in the biosynthesis of anthocyanins as the best candidate gene. Overexpression and silencing in transformed tobacco (Nicotiana tabacum) lines indicated that CA10g11690 is involved in the formation of purple stripes in the exocarp. A comparison of parental sequences identified an insertion fragment of 1,926 bp in the second intron region of Chen12-4, and eight SNPs were detected between the two parents. Additionally, there were 49 single nucleotide polymorphic variations, two sequence deletions, and four sequence insertions in the promoter region. We found that CA10g11690 undergoes alternative splicing and generates different transcripts. Thus, the functional transcript of CA10g11690 appeared to be primarily involved in the development of purple phenotype in the exocarp. Our data provide new insight into the mechanism of anthocyanin biosynthesis and a theoretical basis for the future breeding of purple striped pepper varieties.