Fig. 1

Illustration of the life cycle of M. polymorpha. Land plants have a more complex life cycle than animals, alternating between two multicellular, heteromorphic generations: the sporophyte and the gametophyte. In bryophytes (mosses, hornworts, and liverworts), the gametophytes constitute the dominant generation while the sporophyte is a small and simple structure, whose development depends on the female gametophyte. The male gametophyte forms antheridiophores, the reproductive structures that harbor the antheridia with the antherozoids (sperm). The female gametophyte forms archegoniophores, the reproductive structures that harbor the archegonia, each of which contains a single egg cell. During sexual reproduction, the antherozoids are released from the antheridia and swim towards the archegonia on the female gametophyte. The sporophyte is formed upon fertilization and remains attached to the archegoniophore during its entire development. Spores are formed in the sporophyte through meiosis and are finally released. The spores germinate and develop into either male (with Y chromosome) or female (with X chromosome) gametophytes, thereby concluding the life cycle. Both, male and female gametophytes are capable of asexual reproduction through the formation of gemmae in the gemma cups [57]. Numbers in magenta mark the tissues isolated for this study: (1/2) thallus of the female/male gametophyte, respectively, (3/4) apical notch of the female/male gametophyte, respectively, (5) archegonia, (6) antherozoids, (7) early sporophyte, and (8) late sporophyte