The bHLH transcription factor MpHYPNOS regulates gemma dormancy in the liverwort Marchantia polymorpha

Abstract

SummaryDormancy is a key process for land plants to adapt drastically changing terrestrial environment. The liverwort Marchantia polymorpha produce dormant propagules called gemmae for asexual reproduction. The plant hormone abscisic acid (ABA) plays significant roles in the regulation of dormancy in both seed of flowering plants and gemma of M. polymorpha.Based on the previous transcriptome analysis, here we identified the basic helix-loop-helix transcription factor MpHYPNOS (MpHYP), as a key regulator of gemma dormancy.The knock-out mutants showed much higher germination rate of gemmae in gemma cup than ABA-related mutants did, while the growth and development were the same as wild type. Transient induction of MpHYP caused irreversible growth arrest in gemma and thallus. Transcriptome and qRT-PCR analyses revealed that MpHYP repressed cell-cycle related genes and induced the ABA biosynthesis and responsive genes. Indeed, ABA amounts were increased or decreased by overexpression or knock-out of MpHYP, respectively. However, the growth arrest caused by MpHYP overexpression was not suppressed by the mutation in the ABA receptor gene.These data suggest that MpHYP regulates gemma dormancy and thallus growth partially through the ABA pathway. Our findings would provide the clues to understand ABA-dependent and independent regulation of dormancy in land plants.