ReviewTracking the evolutionary innovations of plant terrestrialization
Introduction
Our diverse plant world might have originated from a subaerial/terrestrial unicellular alga. Today's >380,000 of land plant species (Embryophyta) with morphological and functional diversities are mainly attributed to two major evolutionary events (Bowles et al., 2020). The first is the evolution of life from single-cell to multi-cells; the second is the gradual transition to land from the aquatic and survive in the more variable terrestrial environment. Compared with the aquatic environment, the terrestrial environment is characterized by reduced moisture, enhanced ultraviolet radiation, sudden changes in temperature, and increased damage by herbivores/pathogens (de Vries and Archibald, 2018). For centuries, the gradual transition of the algal ancestor from the freshwater to the terrestrial environment has always attracted biologists, ecologists, and geneticists (Bowles et al., 2020, Zhang, 1998).
Plant genome contains the most critical information of plant evolution, physiological functions and genetic variations. With the advancement of sequencing technology and the sharp drop in sequencing costs, more and more plant genomes have been sequenced and released during these years. By comparing plant genomes of different lineages, the derived conclusions could help us explore the evolutionary route of multicellularity in algae (Hanschen et al., 2016), the evolutionary innovations of plant terrestrialization (Bowles et al., 2020, de Vries et al., 2018, Delaux et al., 2015, Radhakrishnan et al., 2020), the development of stomata, and the genetic basis for angiosperms to become the most successful plant lineage on Earth (Chen et al., 2020, Twyford, 2018). For example, the gradual transition of the algal ancestor and the underlying mechanisms from the freshwater to land is an old question in evolutionary biology.
Section snippets
Horizontal gene transfer
For centuries, people are curious about which plant species (or lineage) might be the common ancestor of extant land plants and how did the first land plants evolve step by step from aquatic to terrestrial successfully. Recently, Cheng et al. (2019) found that Zygnematophyceae algae (Spirogloea muscicola and Mesotaenium endlicherianum) had a large number of core gene families previously thought to be unique to land plants, such as genes involved in plant hormones, symbiosis with bacteria and
Pre-adaptation of terrestrialization
The transition from freshwater to land is a big leap in plant evolution and lots of morphological and molecular changes are needed for this adaption. Wang et al. (2020) sequenced the genomes of two Charophyta Mesostigma viride, a unicellular green algae in freshwater (Liang et al., 2020) and Chlorokybus atmophyticus, a multicellular algae living in subaerial/terrestrial, both are members of the earliest lineages of Streptophyta. These ancient Charophyta algae are ideal model to study earliest
Jigsaw of the bryophytes’ genomes
The bryophytes originated ~500 Mya and have been an intriguing plant lineage to study the evolution of land plants (Lang et al., 2018). While the Embryophyta (land plants) could be dated back to ~580 Mya (Morris et al., 2018), the divergences between bryophytes and other tracheophytes (vascular plants) probably dated back to ~470 Mya, suggesting bryophytes might be listed as monophyletic and a sister group to tracheophytes (Puttick et al., 2018). Bryophytes are relatively primitive land plants
Conclusions and future perspectives
These studies on early diverging plants are encouraging and have extraordinary significance, especially the single-celled S. muscicola (or P. margaritaceum) that dated back to Precambrian terrestrial that might be the candidate common ancestor of land plants (Cheng et al., 2019, Jiao et al., 2020), which probably can be used to explain the “Cambrian Explosion” that perplexed Charles Darwin. The “Cambrian Explosion” was an event ~540 Mya in the Cambrian period when almost all present (including
Declaration of Competing Interest
The author declares that there are no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
I am grateful to five anonymous reviewers for constructive suggestions on this manuscript. I would like to acknowledge Professor Shu-Nong Bai (Peking University) and Zhong-Jian Liu (Fujian Agriculture and Forestry University) for their critical comments on this manuscript. I would also like to thank Professor Pamela Diggle (University of Connecticut) for critical reading of this article.
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2022, Computational and Structural Biotechnology JournalCitation Excerpt :Collaborative research projects and global efforts remain required to fill current gaps in phylogenetic sampling, in inferring and positioning ancient WGDs across plant phylogeny and in deeply resolving the consequences of WGDs in plant adaptation and rapid expansion. Terrestrialization is a landmark of plant evolution and radiation, which had a profound influence on Earth’s ecosystems [41–47]. The genome sequencing of streptophyte algae–the sister lineage to land plants (Embryophyta)–has reinforced our understanding of genome and gene changes of early plants during the evolutionary transition from water to land [48–53].