Silencing of the MP Gene via dsRNA Affects Root Development and Growth in the Invasive Weed Mikania micrantha

<i>Mikania micrantha</i> ("mile-a-minute" weed) is a global invasive alien weed that can cause severe damage to agroforestry ecosystems and significant agricultural losses worldwide. Although chemical, manual, or mechanical control methods are widely used to control <i>M. micrantha</i>, RNA interference (RNAi)-based biocontrol methods have rarely been reported for this species. The <i>MONOPTEROS</i> (<i>MP</i>) gene, encoding an auxin response factor, plays an essential role in embryonic root initiation in <i>Arabidopsis thaliana</i>. In this study, we identified the <i>MP</i> gene from <i>M. micrantha</i> via orthologous gene analysis. A total of 37 <i>MP</i> orthologous genes was identified in 4 plants, including 9 <i>MP</i> candidate genes in <i>M. micrantha</i>, 13 in <i>Helianthus annuus</i>, 6 in <i>Chrysanthemum nankingense</i>, and 9 in <i>Lactuca sativa</i>. Phylogenetic analysis revealed that an <i>MP</i> candidate gene in <i>M. micrantha (Mm01G000655,</i> named <i>MmMP</i>) was clustered into one clade with the <i>MP</i> gene in <i>A. thaliana</i> (<i>AtMP</i>). In addition, both <i>MmMP</i> and <i>AtMP</i> contain a B3-DNA binding domain that is shared by transcription factors that regulate plant embryogenesis. To study gene function, dsRNA against <i>MmMP</i> (<i>dsMmMP</i>) was applied to the roots of <i>M. micrantha</i>. Compared with those of the controls, the expression of <i>MmMP</i> was reduced by 43.3%, 22.1%, and 26.2% on the first, third, and fifth days after <i>dsMmMP</i> treatment, respectively. The <i>dsMmMP</i>-treated plants presented several morphological defects, mostly in the roots. Compared with water-treated plants, the <i>dsMmMP</i>-treated plants presented reduced developmental parameters, including root length, number of adventitious roots, root fresh and dry weights, plant height, and aboveground biomass. Additionally, safety assessment suggested that this <i>dsMmMP</i> treatment did not silence <i>MP</i> genes from non-target plants, including rice and tomato; nor did it inhibit root growth in those species. Collectively, these results suggest that <i>MmMP</i> plays an important role in root development in <i>M. micrantha</i> and provides a potential target for the development of species-specific RNAi-based herbicides.