An auxin-responsive transcription factor AbLBD1 promotes the development of lateral roots and reduces the biosynthesis of tropane alkaloids in Atropa belladonna

Atropa belladonna produces anticholinergic tropane alkaloids (TAs), such as hyoscyamine and scopolamine, which are synthesized in its lateral roots. Yet, the regulation of lateral root growth and TA biosynthesis remain poorly understood. In this study, an auxin-responsive transcription factor (AbLBD1), encoding a lateral organ boundaries domain protein (LBD), was functionally characterized from A. belladonna. Overexpression of AbLBD1 effectively promoted the initiation of lateral roots and adventitious roots of A. belladonna. The root biomass of AbLBD1-overexpressing lines was 1.48 to 2.45 fold higher that of the control. However, the contents of hyoscyamine and scopolamine were markedly reduced in AbLBD1-overexpressing lines. Gene expression analysis showed that the expression levels of TAs biosynthesis genes, namely AbPMT, AbPYKS, AbCYP82M3, and AbH6H, were greatly decreased in AbLBD1-overpressing lines. In conclusion, AbLBD1 plays a positive role in regulating lateral root development but a negative one in regulating TAs biosynthesis in A. belladonna. This study proved for the first time that AbLBD1 was a key auxin response regulator in root, which promotes initiation of lateral root and inhibits the biosynthesis of tropane alkaloids.