Transcriptome analysis of green and purple fruited pepper provides insight into novel regulatory genes in anthocyanin biosynthesis.

Background: Pepper (Capsicum annuum L.) is a valuable horticultural crop with economic significance, and its purple fruit color is attributed to anthocyanin, a phytonutrient known for its health-promoting benefits. However, the mechanisms regulating anthocyanin biosynthesis in pepper have yet to be fully elucidated. Methods: RNA sequencing (RNA-seq) was utilized to analyze the transcriptome of fruits from three purple-fruited varieties (HN191, HN192, and HN005) and one green-fruited variety (EJT) at various developmental stages. To determine the relationships between samples, Pearson correlation coefficients (PCC) and principal component analysis (PCA) were calculated. Differential expression analysis was performed using the DESeq2 package to identify genes that were expressed differently between two samples. Transcription factors (TF) were predicted using the iTAK program. Heatmaps of selected genes were generated using Tbtools software. Results: The unripe fruits of HN191, HN192, and HN005, at the stages of 10, 20, and 30 days after anthesis (DAA), display a purple color, whereas the unripe fruits of variety EJT remain green. To understand the molecular basis of this color difference, five transcriptome comparisons between green and purple fruits were conducted: HN191-10 vs EJT-10, HN191-20 vs EJT-20, HN191-30 vs EJT-30, HN192-30 vs EJT-30, and HN005-30 vs EJT-30. Through this analysis, 503 common differentially expressed genes (DEGs) were identified. Among these DEGs, eight structural genes related to the anthocyanin biosynthesis pathway and 24 transcription factors (TFs) were detected. Notably, one structural gene (MSTRG.12525) and three TFs (T459_25295, T459_06113, T459_26036) exhibited expression patterns that suggest they may be novel candidate genes involved in anthocyanin biosynthesis. These results provide new insights into the regulation of anthocyanin biosynthesis in purple pepper fruit and suggest potential candidate genes for future genetic improvement of pepper germplasm with enhanced anthocyanin accumulation.

High-density genetic map construction and comparative genome analysis in asparagus bean.

Genetic maps are a prerequisite for quantitative trait locus (QTL) analysis, marker-assisted selection (MAS), fine gene mapping, and assembly of genome sequences. So far, several asparagus bean linkage maps have been established using various kinds of molecular markers. However, these maps were all constructed by gel- or array-based markers. No maps based on sequencing method have been reported. In this study, an NGS-based strategy, SLAF-seq, was applied to create a high-density genetic map for asparagus bean. Through SLAF library construction and Illumina sequencing of two parents and 100 F2 individuals, a total of 55,437 polymorphic SLAF markers were developed and mined for SNP markers. The map consisted of 5,225 SNP markers in 11 LGs, spanning a total distance of 1,850.81 cM, with an average distance between markers of 0.35 cM. Comparative genome analysis with four other legume species, soybean, common bean, mung bean and adzuki bean showed that asparagus bean is genetically more related to adzuki bean. The results will provide a foundation for future genomic research, such as QTL fine mapping, comparative mapping in pulses, and offer support for assembling asparagus bean genome sequence.

Transcriptome Profiling of Two Asparagus Bean (Vigna unguiculata subsp. sesquipedalis) Cultivars Differing in Chilling Tolerance under Cold Stress.

Cowpea (V. unguiculata L. Walp.) is an important tropical grain legume. Asparagus bean (V. unguiculata ssp. sesquipedialis) is a distinctive subspecies of cowpea, which is considered one of the top ten Asian vegetables. It can be adapted to a wide range of environmental stimuli such as drought and heat. Nevertheless, it is an extremely cold-sensitive tropical species. Improvement of chilling tolerance in asparagus bean may significantly increase its production and prolong its supply. However, gene regulation and signaling pathways related to cold response in this crop remain unknown. Using Illumina sequencing technology, modification of global gene expression in response to chilling stress in two asparagus bean cultivars-"Dubai bean" and "Ningjiang-3", which are tolerant and sensitive to chilling, respectively-were investigated. More than 1.8 million clean reads were obtained from each sample. After de novo assembly, 88,869 unigenes were finally generated with a mean length of 635 bp. Of these unigenes, 41,925 (47.18%) had functional annotations when aligned to public protein databases. Further, we identified 3,510 differentially expressed genes (DEGs) in Dubai bean, including 2,103 up-regulated genes and 1,407 down-regulated genes. While in Ningjiang-3, we found 2,868 DEGs, 1,786 of which were increasing and the others were decreasing. 1,744 DEGs were commonly regulated in two cultivars, suggesting that some genes play fundamental roles in asparagus bean during cold stress. Functional classification of the DEGs in two cultivars using Mercator pipeline indicated that RNA, protein, signaling, stress and hormone metabolism were five major groups. In RNA group, analysis of TFs in DREB subfamily showed that ICE1-CBF3-COR cold responsive cascade may also exist in asparagus bean. Our study is the first to provide the transcriptome sequence resource for asparagus bean, which will accelerate breeding cold resistant asparagus bean varieties through genetic engineering, and advance our knowledge of the genes involved in the complex regulatory networks of this plant under cold stress.