Negative regulation of conserved RSL class I bHLH transcription factors evolved independently among land plants

• Main Authors: Suvi Honkanen, Anna Thamm, Mario A Arteaga-Vazquez, Liam Dolan
• Format: Article
• Language: English
• Published: eLife Sciences Publications Ltd 2018-08-01
• Series: eLife
• Subjects: Marchantia polymorpha; transcription factors; plant development
• Online Access: https://elifesciences.org/articles/38529

Basic helix-loop-helix transcription factors encoded by RSL class I genes control a gene regulatory network that positively regulates the development of filamentous rooting cells – root hairs and rhizoids – in land plants. The GLABRA2 transcription factor negatively regulates these genes in the angiosperm Arabidopsis thaliana. To find negative regulators of RSL class I genes in early diverging land plants we conducted a mutant screen in the liverwort Marchantia polymorpha. This identified FEW RHIZOIDS1 (MpFRH1) microRNA (miRNA) that negatively regulates the RSL class I gene MpRSL1. The miRNA and its mRNA target constitute a feedback mechanism that controls epidermal cell differentiation. MpFRH1 miRNA target sites are conserved among liverwort RSL class I mRNAs but are not present in RSL class I mRNAs of other land plants. These findings indicate that while RSL class I genes are ancient and conserved, independent negative regulatory mechanisms evolved in different lineages during land plant evolution.