Making Sense of Antisense Transcriptional Control during Sexual Differentiation of the Liverwort, Marchantia polymorpha

Sexual differentiation is a critical step to produce dimorphic gametes and hence fundamental for successful sexual reproduction.Although a large body of work has revealed the developmental and molecular mechanisms of gametogenesis and fertilization (Larose et al., 2019), the evolutionary origins of sexual development is poorly understood.In land plants, gametes are produced by sexual organs that differentiated from the multicellular haploid body and are termed gametophytes.While flowering plants evolved extremely reduced gametophytes (embryo sac and pollen), extant bryophytes retain a gametophyte-dominant life cycle, where each step of sexual reproduction is spatially and temporally separated.Recently, using the model bryophyte Marchantia polymorpha (Bowman et al., 2022),researchers have discovered the molecular mechanisms regulating sexual differentiation in gametophytes (Hisanaga et al., 2019).M. polymorpha is a dioicous liverwort whose sex is determined by the 2 sex chromosomes U (female) and V (male) (Bowman et al., 2017;Iwasaki et al., 2021).Under specific light conditions, M. polymorpha develops dimorphic sexual branches, termed archegoniophores for females and antheridiophores for males, in the notch region at the tip of vegetative thalli (Ishizaki et al., 2016).In females, archegoniophore development is regulated by FEMALE GAMETOPHYTE MYB (FGMYB) which encodes a transcription factor with a MYB domain (Hisanaga et al., 2019).Although FGMYB is an autosomal gene, its expression is specific to female archegoniophores.Consistent with this expression