Overexpression of the AbSAUR1 gene enhanced biomass production and alkaloid yield in Atropa belladonna

•A root-expressed SAUR gene (AbSAUR1) was cloned from Atropa belladonna.•Overexpression of AbSAUR1 significantly increased the biomass of Atropa belladonna.•Overexpression of AbSAUR1 did not reduce biosynthesis of tropane alkaloids.•The yield of TAs was significantly improved in AbSAUR1-overexpressing plants. Tropane alkaloids (TAs), including hyoscyamine, anisodamine and scopolamine, are widely used as anticholinergic drugs in the clinic. At present, the production of TAs is completely dependent on extraction from medicinal plants of Solanaceae. Atropa belladonna, commonly known as deadly nightshade, is a major commercial source of TAs. Previous studies have focused on increasing TA content by overexpressing TA biosynthesis genes. However, research on increasing TA yield by increasing the biomass of A. belladonna has not been reported. In this study, a Small Auxin Up-regulated RNA (SAUR) gene from A. belladonna (AbSAUR1) had been cloned for the first time. Based on heat map and tissue expression analysis, it was demonstrated that AbSAUR1 was specifically expressed in roots. Compared to control plants, transgenic lines of A. belladonna overexpressing AbSAUR1 showed a number of phenotypic changes, including increased plant height, thickened stems, increased number of branches, leaves and roots. Meanwhile, the biomass of AbSAUR1-overexpressing plants also increased significantly, with fresh weight and dry weight being 3.79- and 3.20-fold higher than control plants, respectively. On average, there was no significant change in TA content, but the production of hyoscyamine, anisodamine and scopolamine was slightly enhanced. The overall yield of TAs was significantly improved, reaching 3.55 times that of the control. In summary, the AbSAUR1 gene can be employed as an effective molecular tool to increase the yield of TAs by increasing the biomass of A. belladonna.