Differential gene expression in leaves and roots of Hydrangea serrata treated with aluminium chloride

Hydrangea serrata, also knowen as the Japanese tea hortensia, is known for its sweet taste and health properties of bevarages produced from this plant. The H. serrata 3,4-dihydroisocoumarins, hydrangenol and phyllodulcin harbour a variety of biological activities and pharmacological properties. Therefore, a detailed understanding of dihydroisocoumarin biosynthesis in H. serrata is of major interest. Their biosynthesis is assumed to be enhanced by elicitors and mediated by polyketide synthases like in cases of phenylpropanoid derived phytoalexins. A de-novo transcriptome assembly of leaves and roots from the aluminium chloride treatment group versus the control group alongside with annotation was generated. Secondary plant metabolites were analysed by LC-MS. It revealed that a terpene synthase and a triterpenoid synthase gene as well as lignin biosynthesis encoding genes were upregulated in roots. Many genes for transporters, glycosyl, and other transferases as well as glycosylases were found to be differentially expressed in both organs. As no differentially expressed polyketide synthase gene homolog was found, the relative leaf and root 3,4-dihydroisocoumarin content was analysed by LC-MS measurement. Although Hydrangea species are known for their aluminium detoxification using phenylpropanoid-derived compounds, the levels of 3,4- dihydroisocoumarins were not enhanced. In this metabolite analysis, an organ- specific accumulation profile of hydrangenol, phyllodulcin, hydrangeic acid and their mono- and di-glycosides was figured out.