McAPRR2: The Key Regulator of Domesticated Pericarp Color in Bitter Gourd

Pericarp color is a crucial commercial trait influencing consumer preferences for bitter gourds. However, until now, the gene responsible for this trait has remained unidentified. In this study, we identified a gene (McAPRR2) controlling pericarp color via a genome-wide association study (GWAS) utilizing the resequencing data of 106 bitter gourd accessions. McAPRR2 exhibits three primary haplotypes: Hap1 is a wild type with a green pericarp, Hap2 is a SA (South Asian) and SEA (Southeast Asia) type with a green pericarp, and Hap3 is primarily a SEA type with a light green pericarp. The McAPRR2 haplotype is significantly correlated with both pericarp color and ecological type. Importantly, McAPRR2 with the light green pericarp demonstrated premature termination due to a 15 bp sequence insertion. The phylogenetic tree clustered according to pericarp color and ecological type, using SNPs located in the McAPRR2 gene and its promoter. High πwild/SEA and πSA/SEA values indicate high nucleotide diversity between wild and SEA types and between SA and SEA types in the McAPRR2 gene. The haplotypes, phylogenetic tree, and nucleotide diversity of McAPRR2 suggest that McAPRR2 has undergone domestication selection. This study identifies McAPRR2 as the key gene determining pericarp color in bitter gourds and introduces a novel insight that McAPRR2 is subject to domestication selection.

Map-based cloning of the APRR2 gene controlling green stigma in bitter gourd (Momordica charantia)

Bitter gourd is an economically important vegetable and medicinal crop distinguished by its bitter fruits. Its stigma color is widely used to assess the distinctiveness, uniformity, and stability of bitter gourd varieties. However, limited researches have been dedicated to genetic basis of its stigma color. In this study, we employed bulked segregant analysis (BSA) sequencing to identify a single dominant locus McSTC1 located on pseudochromosome 6 through genetic mapping of an F₂ population (n =241) derived from the cross between green and yellow stigma parental lines. An F₂-derived F₃ segregation population (n = 847) was further adopted for fine mapping, which delimited the McSTC1 locus to a 13.87 kb region containing one predicted gene McAPRR2 (Mc06g1638), a homolog of the Arabidopsis two-component response regulator-like gene AtAPRR2. Sequence alignment analysis of McAPRR2 revealed that a 15 bp insertion at exon 9 results in a truncated GLK domain of its encoded protein, which existed in 19 bitter gourd varieties with yellow stigma. A genome-wide synteny search of the bitter gourd McAPRR2 genes in Cucurbitaceae family revealed its close relationship with other cucurbits APRR2 genes that are corresponding to white or light green fruit skin. Our findings provide insights into the molecular marker-assisted breeding of bitter gourd stigma color and the mechanism of gene regulation for stigma color.