HmGST9, an anthocyanin-related glutathione S-transferase gene, is essential for sepals coloration in Hydrangea macrophylla

Flower color is an important ornamental trait of Hydrangea macrophylla. The transport of anthocyanin from endoplasmic reticulum to vacuole for storage is the basis of flower color formation. Glutathione S-transferase (GST) plays an important role in this transport process. However, little is known about the GST genes involved in anthocyanin transport and their functions in H. macrophylla. In this study, the sepals of H. macrophylla 'Blue Mom' was used as the experimental material. The gene HmGST9 that may be involved in anthocyanin accumulation was identified from the genome, and it was found to be located in the endoplasmic reticulum and tonoplast. Through Arabidopsis tt19 mutant molecular complementation experiment, it was proved that HmGST9 could restore anthocyanin accumulation in vegetative tissues of Arabidopsis tt19 mutant, but could not restore the color of seed coat. In the sepals of H. macrophylla, virus-induced HmGST9 gene silencing resulted in a significant decrease in anthocyanin content, and the structural genes and transcription factors in the anthocyanin biosynthesis pathway were also significantly down-regulated. In contrast, transient overexpression of HmGST9 in sepals resulted in a significant increase in anthocyanin content and promoted the up-regulation of related structural genes and transport genes. These results indicate that HmGST9 plays an important role in regulating the transport and accumulation of anthocyanins in H. macrophylla, and is of great significance for analyzing the molecular mechanism of flower color formation in H. macrophylla.