Green planet - from small beginnings 550 million years ago.
One of the prerequisites for irreducible complexity to emerge naturally without needing a designer is for the components to be there either as part of a pre-existing structure, or as the result of neutral mutations that have been retained because there is no selection pressure to get rid of them.
This was the situation the first land plants found themselves in about 550 million years ago when gene and genome duplication had created redundant genes that could mutate, diversify, and eventually provide the complex metabolic machinery to enable the marine algae to colonize the land and so beginning the greening of the planet. The result was the appearance of a sudden, one-off event that created the ancestor of land plants.
This is the conclusion of a large international team led by scientists from the Universities of Göttingen and Nebraska–Lincoln, who have published their findings, open access, in the journal Nature Genetics and explained it in a University of Göttingen news release:
International research team generates first genomes of complex closest relatives of land plants
Land plants cover the surface of our planet and often tower over us. They form complex bodies with multiple organs that consist of a broad range of cell types. Developing this morphological complexity is underpinned by intricate networks of genes, whose coordinated action shapes plant bodies through various molecular mechanisms. All of these magnificent forms burst forth from a one-off evolutionary event: when plants conquered Earth’s surface, known as plant terrestrialization. Among those algae most closely related to land plants, diverse body types are found – ranging from single-celled algae to more complex cell filaments. From this group of relatives, an international group of researchers led by the Universities of Göttingen and Nebraska–Lincoln has now generated the first genome data of such complex specimens, on four filamentous “star algae” of the genus Zygnema. Their results were published in Nature Genetics.
The researchers worked with four algal strains in total, two from a culture collection in the USA and two that have been kept safe in the Algal Culture Collection at Göttingen University (SAG). The research involved more than 50 scientists from nine countries who combined a range of cutting-edge sequencing techniques to elucidate the entire DNA sequence of these algae. The advanced methods enabled them to generate complete genomes for these organisms at the level of whole chromosomes – something that had never been done before on this group of algae. Comparing the genes on the genomes with those of other plants and algae led to the discovery of specific overabundances of signalling genes and environmental response factors.
Land plants cover the surface of our planet and often tower over us. They form complex bodies with multiple organs that consist of a broad range of cell types. Developing this morphological complexity is underpinned by intricate networks of genes, whose coordinated action shapes plant bodies through various molecular mechanisms. All of these magnificent forms burst forth from a one-off evolutionary event: when plants conquered Earth’s surface, known as plant terrestrialization. Among those algae most closely related to land plants, diverse body types are found – ranging from single-celled algae to more complex cell filaments. From this group of relatives, an international group of researchers led by the Universities of Göttingen and Nebraska–Lincoln has now generated the first genome data of such complex specimens, on four filamentous “star algae” of the genus Zygnema. Their results were published in Nature Genetics.
The researchers worked with four algal strains in total, two from a culture collection in the USA and two that have been kept safe in the Algal Culture Collection at Göttingen University (SAG). The research involved more than 50 scientists from nine countries who combined a range of cutting-edge sequencing techniques to elucidate the entire DNA sequence of these algae. The advanced methods enabled them to generate complete genomes for these organisms at the level of whole chromosomes – something that had never been done before on this group of algae. Comparing the genes on the genomes with those of other plants and algae led to the discovery of specific overabundances of signalling genes and environmental response factors.
Many of these genes underpin molecular functions that were important for the emergence of the first multicellular terrestrial plants. It is fascinating that the genetic building blocks, whose origins predate land plants by millions of years, duplicated and diversified in the ancestors of plants and algae and, in doing so, enabled the evolution of more specialized molecular machinery.
Dr Iker Irisarri, co-lead author
Institute of Microbiology and Genetics,
Department of Applied Bioinformatics
University of Goettingen, Goettingen, Germany.
Institute of Microbiology and Genetics,
Department of Applied Bioinformatics
University of Goettingen, Goettingen, Germany.
Not only do we present a valuable, high-quality resource for the entire plant scientific community, who can now explore these genome data, our analyses uncovered intricate connections between environmental responses. This sheds light on one of land plants’ most important features: their ability to adjust their growth and development so that it aligns with the environment in which they dwell – a process known as developmental plasticity.
Professor Jan de Vries, corresponding author
Institute of Microbiology and Genetics
Department of Applied Bioinformatics
University of Goettingen, Goettingen, Germany.
Institute of Microbiology and Genetics
Department of Applied Bioinformatics
University of Goettingen, Goettingen, Germany.
AbstractHere we have an evolutionary event happening 550 million years before they believe the Universe was created; we have examples of new genetic information arising by gene doubling and new functions evolving by mutations in those duplicated genes; then we have irreducible complexity arising naturally by exaptation of redundant processes and structures, and lastly we have zero evidence of scientists about to abandon the TOE in favour of creationism.
Zygnematophyceae are the algal sisters of land plants. Here we sequenced four genomes of filamentous Zygnematophyceae, including chromosome-scale assemblies for three strains of Zygnema circumcarinatum. We inferred traits in the ancestor of Zygnematophyceae and land plants that might have ushered in the conquest of land by plants: expanded genes for signaling cascades, environmental response, and multicellular growth. Zygnematophyceae and land plants share all the major enzymes for cell wall synthesis and remodifications, and gene gains shaped this toolkit. Co-expression network analyses uncover gene cohorts that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution.
Main
Plant terrestrialization changed the surface of the Earth. The first land plants (Embryophyta) emerged from within the clade of Streptophyta about 550 million years ago1. Among six classes of streptophyte algae, the closest relatives of land plants are the Zygnematophyceae2,3,4, algae with more than 4,000 described species5 arranged into five orders6. So far, genome sequences are available only for unicellular Zygnematophyceae7,8,9.
Zygnematophyceae possess adaptations to withstand terrestrial stressors, such as desiccation, ultraviolet light, freezing and other abiotic stresses10. The nature of these stress responses is of deep biological importance: various orthologous groups of proteins once considered specific to land plants have recently been inferred to predate the origin of Embryophyta11,12. The accuracy of inferring the developmental and physiological programs of the first land plant ancestors depends on our ability to predict them in its sister group.
In this Article, we report on the first four genomes of filamentous Zygnematophyceae, including the first chromosome-scale assemblies for any streptophyte algae. By using comparative genomics, we pinpoint genetic innovations of the earliest land plants. Our network analyses reveal co-expression of genes that were expanded and gained in the last common ancestor (LCA) of land plants and Zygnematophyceae. We shed light on the deep evolutionary roots of the mechanism for balancing environmental responses and multicellular growth.
Feng, X., Zheng, J., Irisarri, I. et al.
Genomes of multicellular algal sisters to land plants illuminate signaling network evolution. Nat Genet (2024). https://doi.org/10.1038/s41588-024-01737-3
Copyright: © 2024 The authors.
Published by Springer Nature Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
All in all, enough to send any dedicated creationists into deep denial and start wondering about the best way to bear false witness against the scientists or the science, or both.
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