| Summary: | Stinging nettle (<i>Urtica dioica</i> L.) has been used as herbal medicine to treat various ailments since ancient times. The biological activity of nettle is chiefly attributed to a large group of phenylpropanoid dimers, namely lignans. Despite the pharmacological importance of nettle lignans, there are no studies addressing lignan biosynthesis in this plant. We herein identified 14 genes encoding dirigent proteins (<i>UdDIR</i>s) and 3 pinoresinol-lariciresinol reductase genes (<i>UdPLR</i>s) in nettle, which are two gene families known to be associated with lignan biosynthesis. Expression profiling of these genes on different organs/tissues revealed a specific expression pattern. Particularly, <i>UdDIR7</i>, <i>12</i> and <i>13</i> displayed a remarkable high expression in the top internode, fibre tissues of bottom internodes and roots, respectively. The relatively high expression of <i>UdPLR1</i> and <i>UdPLR2</i> in the young internodes, core tissue of bottom internode and roots is consistent with the high accumulation of lariciresinol and secoisolariciresinol in these tissues. Lignan quantification showed a high abundance of pinoresinol in roots and pinoresinol diglucosides in young internodes and leaves. This study sheds light on lignan composition and biosynthesis in nettle, providing a good basis for further functional analysis of <i>DIR</i>s and <i>PLR</i>s and, ultimately, engineering lignan metabolism <i>in planta</i> and in cell cultures.
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