This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Liverworts reproduce through a life cycle involving two distinct stages. First, sperm fertilize eggs in the presence of water, producing embryos that develop into spore-producing structures called sporophytes.
These structures then produce spores that can disperse and grow into new liverwort plants. Liverworts, hornworts, and mosses—known collectively as bryophytes—must all accommodate two contrasting reproductive demands: water-dependent fertilization and effective spore dispersal, with the latter process benefiting from exposure to drier conditions. Understanding how bryophytes balance these competing requirements may offer key insights into the structural innovations that enabled plants to reproduce successfully on land.
Now, a new study reveals how the female reproductive structures of the liverwort Marchantia polymorpha evolved step by step to balance the demands of water-dependent fertilization and efficient spore dispersal. The study, published in Nature Plants, was led by professor Xu Bo of the Institute of Botany of the Chinese Academy of Sciences. The findings uncover how lineage-specific adaptations of female reproductive structures in the liverwort M. polymorpha facilitate successful fertilization on land.
In this study, the researchers identified a previously unknown water-transport system in M. polymorpha that moves water upward against gravity. This helps deliver water to elevated female reproductive organs, facilitating fertilization. This system relies on an integrated network of specialized surface structures on the female reproductive stalk and receptacle.
The coordinated development of these structures is regulated by a single GRAS-family transcription factor called MpLAS. This finding suggests that evolutionary pressures favoring successful reproduction may have driven the development of multiple structures that work together to facilitate fertilization and spore dispersal. A second regulator, a GRAS-family protein called MpGRAS10, was also shown to play a key role in forming the stalk of female reproductive structures.
By promoting the expression of the gibberellin biosynthesis genes MpKAOL1 and MpKAOL2, MpGRAS10 contributes to the development of elevated reproductive structures that can enhance spore dispersal. Comparative evolutionary analyses revealed that the stalk evolved before the specialized surface structures associated with efficient fertilization. This supports a stepwise model for the evolution of the female reproductive structure: an initial innovation enhanced spore dispersal, while subsequent adaptations addressed its limitations in water delivery and fertilization.
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