The pungent-variable sweet chili pepper 'Shishito' (Capsicum annuum) provides insights regarding the relationship between pungency, the number of seeds, and gene expression involving capsaicinoid biosynthesis

An Analysis of Capsaicin, Dihydrocapsaicin, Vitamin C and Flavones in Different Tissues during the Development of Ornamental Pepper

As a fruit and vegetable crop, the ornamental pepper is not just highly ornamental but also rich in nutritional value. The quality of ornamental pepper fruits is given in their contents of capsaicin, vitamin C (VC), flavonoids and total phenols. The study concentrated on the accumulation of capsaicin and dihydrocapsaicin in different tissues of 18 peppers during fruit growth and development. The results showed that the pericarp and placenta contained significantly higher levels of capsaicin than dihydrocapsaicin. Additionally, the placenta contained significantly higher levels of both capsaicin and dihydrocapsaicin compared to the pericarp. The content of capsaicin was in the range of 0-6.7915 mg·g-1, the range of dihydrocapsaicin content was 0-5.329 mg·g-1. Interestingly, we found that the pericarp is rich in VC (5.4506 mg·g-1) and the placenta is high in flavonoids (4.8203 mg·g-1) and total phenols (119.63 mg·g-1). The capsaicin is the most important component using the correlation analysis and principal component analysis. The qPCR results substantiated that the expression of genes in the placenta was significantly higher than that in the pericarp and that the expression of genes in green ripening stage was higher than that in red ripening stage. This study could be utilized to select the best ripening stages and tissues to harvest peppers according to the use of the pepper and to the needs of producers. It not only provides a reference for quality improvement and processing for consumers and market but also provides a theoretical basis for high-quality pepper breeding.

Genetic analysis of pungency deficiency in Japanese chili pepper 'Shishito' (Capsicum annuum) revealed its unique heredity and brought the discovery of two genetic loci involved with the reduction of pungency

The sensation of pungency generated by capsaicinoids is a characteristic trait of chili peppers (Capsicum spp.), and the presence or absence of pungency is central in determining its usage as a spice or a vegetable. In the present study, we aimed to clarify the heredity and genetic factors involved in the deficiency of pungency (quite low pungency) that is uniquely observed in the Japanese chili pepper 'Shishito' (Capsicum annuum). First, the F₂ population ('Shishito' × pungent variety 'Takanotsume') was used for segregation analysis, and pungency level was investigated using capsaicinoid quantification with high-performance liquid chromatography. Also, restriction site associated DNA sequencing of the F₂ population was performed, and genetic map construction and quantitative trait locus (QTL) mapping were implemented. The results indicated that the F₂ population showed varying capsaicinoid content and two major QTLs were detected, Shql3 and Shql7, which explained 39.8 and 19.7% of the genetic variance, respectively. According to these results, the quite low pungency of 'Shishito' was a quantitative trait that involved at least the two loci. Further, this trait was completely separate from general non-pungent traits controlled by individual recessive genes, as described in previous studies. The present study is the first report to investigate the genetic mechanism of pungency deficiency in Japanese chili peppers, and our results provide new insights into the genetic regulation of pungency in chili pepper.

Putative Transcription Factor Genes Associated with Regulation of Carotenoid Biosynthesis in Chili Pepper Fruits Revealed by RNA-Seq Coexpression Analysis

During the ripening process, the pericarp of chili pepper (Capsicum spp.) fruits accumulates large amounts of carotenoids. Although the carotenoid biosynthesis pathway in the Capsicum genus has been widely studied from different perspectives, the transcriptional regulation of genes encoding carotenoid biosynthetic enzymes has not been elucidated in this fruit. We analyzed RNA-Seq transcriptomic data from the fruits of 12 accessions of Capsicum annuum during the growth, development, and ripening processes using the R package named Salsa. We performed coexpression analyses between the standardized expression of genes encoding carotenoid biosynthetic enzymes (target genes (TGs)) and the genes of all expressed transcription factors (TFs). Additionally, we analyzed the promoter region of each biosynthetic gene to identify putative binding sequences for each selected TF candidate. We selected 83 TFs as putative regulators of the carotenogenic structural genes. From them, putative binding sites in the promoters of the carotenoid-biosynthesis-related structural genes were found for only 54 TFs. These results could guide the search for transcription factors involved in the regulation of the carotenogenic pathway in chili pepper fruits and might facilitate the collection of corresponding experimental evidence to corroborate their participation in the regulation of this biosynthetic pathway in Capsicum spp.

Transcriptional Regulation of Ripening in Chili Pepper Fruits (Capsicum spp.)

Chili peppers represent a very important horticultural crop that is cultivated and commercialized worldwide. The ripening process makes the fruit palatable, desirable, and attractive, thus increasing its quality and nutritional value. This process includes visual changes, such as fruit coloration, flavor, aroma, and texture. Fruit ripening involves a sequence of physiological, biochemical, and molecular changes that must be finely regulated at the transcriptional level. In this review, we integrate current knowledge about the transcription factors involved in the regulation of different stages of the chili pepper ripening process.