Integrated analysis of multi-omics and fine-mapping reveals a candidate gene regulating pericarp color and flavonoids accumulation in wax gourd (Benincasa hispida)

Map-based cloning revealed BhAPRR2 gene regulating the black peel formation of mature fruit in wax gourd (Benincasa hispida)

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Map-based cloning revealed BhAPRR2, encoding a two-component response-regulating protein that regulates the black peel formation of mature fruit in wax gourd. Wax gourd is an economically significant vegetable crop, and peel color is a crucial agronomic trait that influences its commercial value. Although genes controlling light green or white peel have been cloned in wax gourd, the genetic basis and molecular mechanism underlying black peel remain unclear. Here, we confirmed that the peel color of wax gourd is a qualitative trait governed by single gene, with black being dominant over green. Through bulked segregant analysis sequencing (BSA-seq) and map-based cloning, we identified Bh.pf3chr5g483 as the candidate gene. This gene encodes a two-component response-regulating protein and is homologous to APRR2, referred to as BhAPRR2. Compared to P170, the BhAPRR2 in YD1 exhibits multiple mutations in both its coding and promoter regions. Notably, the mutations in the coding region do not affect its nuclear localization or transcriptional activation activity. However, the mutations in the promoter region substantially increase its expression in the peel of YD1, potentially contributing to the black peel phenotype observed in this variety. Furthermore, we developed an insertion/deletion (InDel) marker based on a 93-base pair (bp) insertion/deletion mutation in the promoter region of BhAPRR2, which achieved up to 95.8% phenotypic accuracy in a natural population comprising 165 wax gourd germplasms. In summary, our findings suggest that mutations in the promoter region of BhAPRR2 may contribute to the development of black peel in wax gourd. This discovery provides new insights into the molecular and genetic mechanisms underlying peel color diversity and offers a valuable molecular marker for wax gourd breeding efforts.

Comparative transcriptomic and metabolomic analyses reveal differences in flavonoid biosynthesis between PCNA and PCA persimmon fruit

The fruit of the persimmon (Diospyros kaki.) has high economic and nutritional value and is rich in flavonoids. Flavonoids are essential secondary metabolisms in plants. The association between persimmon astringency and changes in the proanthocyanidins (a flavonoid subclass) content is well-known. However, information on the relationships between different astringency types and other flavonoid subclasses and biosynthetic genes is more limited. In this study, an initial correlation analysis between total flavonoids and fruit astringency type, and KEGG analysis of metabolites showed that flavonoid-related pathways were linked to differences between mature pollination-constant non-astringent (PCNA) varieties ('Jiro' and 'Yohou') and pollination-constant astringent (PCA) fruit varieties ('Zhongshi5' and 'Huojing'). Based on these findings, variations in the expression of genes and metabolites associated with flavonoid biosynthesis were investigated between typical PCNA ('Jiro') and PCA ('Huojing') persimmons during fruit development. The flavonoid concentration in 'Huojing' fruit was significantly higher than that of 'Jiro' fruit, especially, in levels of proanthocyanin precursor epicatechin and anthocyanin cyanidin derivatives. Combined WGCNA and KEGG analyses showed that genes such as PAL, C4H, CHI, CHS, F3H, F3'5'H, FLS, DFR, ANR, ANS, and UF3GT in the phenylpropanoid and flavonoid biosynthesis pathways may be significant factors impacting the proanthocyanin precursor and anthocyanin contents. Moreover, interactions between the R2R3MYB (evm.TU.contig7272.598) and WD40 (evm.TU.contig3208.5) transcription factors were found to be associated with the above structural genes. These findings provide essential information on flavonoid biosynthesis and its regulation in the persimmon and lay a foundation for further investigation into how astringency types affect flavor components in PCNA and PCA persimmons.