AUTHOR=Zhang Yutong , Shan Xiaotong , Zhao Qiao , Shi Fengling 

TITLE=The MicroRNA397a-LACCASE17 module regulates lignin biosynthesis in Medicago ruthenica (L.)

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.978515

DOI=10.3389/fpls.2022.978515

ISSN=1664-462X

ABSTRACT=<p>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 <italic>Medicago ruthenica</italic> 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 <italic>MrLAC17</italic> transcript, which results in enhanced expression level of <italic>MrLAC17</italic> compared to that in the prostrate-stem cultivar Mengnong No. 1. Complementation of the <italic>Arabidopsis lac4 lac17</italic> double mutants with <italic>MrLAC17</italic> restored the lignin content to wild-type levels, confirming that MrLAC17 perform an exchangeable role with <italic>Arabidopsis</italic> laccases. <italic>LAC17-</italic>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.</p>