Analysis of BhAPRR2 allele variation, chlorophyll content, and chloroplast structure of different peel colour varieties of wax gourd ( Benincasa hispida ) and development of molecular marker s

In this study, four non-synonymous mutations and one 3-base insertion were found in the BhAPRR2 sequences of four wax gourds with different peel colour. The analysis of pigment content and chloroplast structure showed that the total chlorophyll content of the black peel was significantly higher than that of the green peel at 20 days after pollination, that of the green peel was significantly higher than that of the light-green peel and white peel lines, and there was no significant difference between the light-green peel and white peel lines. No significant differences were found in the number of chloroplasts in the peel cells of the four peel colours; however, there were differences in the thylakoid structure. The results of gene expression analysis performed 20 days after pollination showed that the expression level of BhAPRR2 in the black peel line was significantly higher than that in the green peel, light-green peel, and white peel lines. Therefore, we can conclude that the colour difference between green-, black-, light-green-, and white-peeled wax gourds is caused by its allelic variation, while the colour difference between black and light-green peels is caused by the difference in BhAPRR2 expression. We also developed two specific InDel molecular markers, and the identification accuracies for wax gourd peel colour were 98.61% and 97.91%, respectively.