The 3AT gene determines fruit color of Myrica rubra (Myricaceae)
Myrica rubra has been cultivated for more than 2000 years it is one of most popular fruits in south China. We compared three M. rubra cultivars, "Muye" (MY), "DongKui" (DK), and "Zao Jia" (ZJ) to determine the causes of the differences in fruit color. We found changes in the anthocyanin and carotenoid contents during the fruit coloring and maturity phases. The anthocyanin contents of the three cultivars increased from the initial fruit coloring phase to the maturity phase. During this period, the total contents of anthocyanin and cyanidin in MY were higher than those in ZJ by 8.57 and 26.45% and higher than those in DK by 80.16 and 129.37%, respectively. RNA-Seq based transcriptome analysis of veraison and mature berries of the three M. rubra cultivars was conducted. The total numbers of genes and N50 lengths were 33,033 and 1,426 for MY, 35,166 and 1,145 for DK, and 31,374 and 476 for ZJ, respectively From the initial color-turning phase to the maturity phase, there were three up-regulated and three down-regulated genes in MY, while there were 3,058 up-regulated and 65 down-regulated genes in DK and 1,484 up-regulated and 1,169 down-regulated genes in ZJ. Based on functional insight of the differentially expressed genes, 3-Amino-1,2,4-triazole (3AT) would be the key gene responsible for color variation in these three cultivars. We concluded that the 3AT gene controls M. rubra berry color. Based on qRT-PCR, we found that expression of 3AT was much higher in MY and ZJ. This result was consistent with our RNA-Seq analysis. In conclusion, cy-3glu and peonidin are pigments that have a significant effect on the color of M. rubra fruit, and 3AT is a functional gene that regulates these pigments. These results could have practical significance for M. rubra selection strategies.