Data_Sheet_1_The MicroRNA397a-LACCASE17 module regulates lignin biosynthesis in Medicago ruthenica (L.).PDF

Mechanical strength is essential for the upright growth habit, which is one of the most important characteristics of terrestrial plants. Lignin, a phenylpropanoid-derived polymer mainly present in secondary cell walls plays critical role in providing mechanical support. Here, we report that the prostrate-stem cultivar of the legume forage Medicago ruthenica cultivar ‘Mengnong No. 1’ shows compromised mechanical strength compared with the erect-stem cultivar ‘Zhilixing’. The erect-stem cultivar, ‘Zhilixing’ has significantly higher lignin content, leading to higher mechanical strength than the prostrate-stem cultivar. The low abundance of miRNA397a in the Zhiixing cultivar causes reduced cleavage of MrLAC17 transcript, which results in enhanced expression level of MrLAC17 compared to that in the prostrate-stem cultivar Mengnong No. 1. Complementation of the Arabidopsis lac4 lac17 double mutants with MrLAC17 restored the lignin content to wild-type levels, confirming that MrLAC17 perform an exchangeable role with Arabidopsis laccases. LAC17-mediated lignin polymerization is therefore increased in the ‘Zhilixing’, causing the erect stem phenotype. Our data reveal the importance of the miR397a in the lignin biosynthesis and suggest a strategy for molecular breeding targeting plant architecture in legume forage.

机械强度对于陆生植物最重要的特征之一——直立生长习性而言至关重要。木质素（Lignin）是一类主要存在于次生细胞壁的苯丙烷类衍生聚合物，在为植物提供机械支撑方面发挥关键作用。本研究发现，豆科饲草扁蓿豆（Medicago ruthenica）的匍匐茎品种‘Mengnong No. 1’（蒙农1号），其机械强度相较于直立茎品种‘Zhilixing’显著受损。‘Zhilixing’的木质素含量显著更高，因此其机械强度优于‘Mengnong No. 1’（蒙农1号）。‘Zhilixing’品种中低丰度的miRNA397a会减弱对MrLAC17转录本的切割作用，使得MrLAC17的表达水平相较于匍匐茎品种‘Mengnong No. 1’（蒙农1号）显著上调。将MrLAC17互补转化拟南芥（Arabidopsis）lac4 lac17双突变体后，该突变体的木质素含量恢复至野生型（wild-type）水平，证实MrLAC17与拟南芥漆酶（laccases）具有功能替代性。因此，‘Zhilixing’品种中LAC17介导的木质素聚合过程得以增强，最终造就了直立茎表型。本研究数据揭示了miRNA397a在木质素生物合成中的重要性，并为豆科饲草的株型分子育种提供了可行策略。