A dihydrochalcone-specific O-methyltransferase from leaf buds of Populus trichocarpa implicated in bud resin formation

We used transcriptomics and differential gene expression analyses of P. trichocarpa and P. balsamifera leaf buds to identify a gene encoding a P. trichocarpa dihydrochalcone-specific O-methyltransferase, which we named PtDOMT1. Detailed enzymatic analyses demonstrated PtDOMT1 to be a highly selective and regiospecific O-methyltransferase which methylates 4 and 4' positions of dihydrochalcones using S-adenosyl-L-methionine as a methyl donor. Dormant cuttings of P. balsamifera and P. trichocarpa, harvested in February, were induced to flush in a growth chamber. The cutting were ~30 cm long and were stored at 4 °C in the dark until the controlled experiment. The twigs were placed in water in a growth chamber at 22 °C under 16 h of light and sampled at 2 d intervals. For each time point, leaf buds were collected from one individual cutting as a replicate to prevent wound-induced effects during the time course. Samples were collected from three replicates of P. balsamifera and two replicates of P. trichocarpa. Each sampling consisted of 10 leaf buds, and samples were collected over 12 d. Samples collected at day 0 (D0), day 4 (D4), and day 10 (D10) were selected to represent dormant, pre-bud break, and bud break phases of the lateral leaf buds, respectively. Three biological replicates of P. balsamifera and two biological replicates of P. trichocarpa were used to prepare RNA-seq libraries as previously described using the NEBNext® Ultra™ RNA Library Prep Kit for Illumina® (New England Biolabs)