Friday, 6 October 2017

Tracing Plant Evolution Back To Its Roots

Common liverwort, Marchantia polymorpha
Liverwort Genes and Land Plant Evolution - DOE Joint Genome Institute.

Today we have a lovely example of how the Theory of Evolution forms the foundation of biology, enabling biologists to make predictions and make sense of what we can see today in the diversity and similarities of organisms; in this case, plants.

Contrary to what creationist frauds would have their willing dupes believe, not only is there no sign that the Theory of Evolution is a 'theory in crisis' but there is every sign that it is never even seriously doubted. No-one tries to validate it these days; it is simply accepted as the very basis of biology as surely as atomic theory is the basis of chemistry.

As reported yesterday in Cell, an international team, including researchers from the U.S. Department of Energy Joint Genome Institute (DOE JGI) have analysed the genome of the common liverwort, Marchantia polymorpha to identify those genes which evolved early in the evolution of plants as they adapted for a terrestrial existence and which have been conserved across lineages as plants diversified into the different plant orders we have today.

The DOE JGI press release explains the reason for this choice in the context of this study:

"Early plants like the liverwort are what set the world up for land plants. Without them, we wouldn’t have plants more than two feet from the ocean and freshwater," said DOE JGI Plant Program head Jeremy Schmutz. "In going back to liverworts, we find genes shared with grasses that are candidate genes for crops for biofuel generation. Land plants began with same parts present in Marchantia today so the changes are all due to factors such as evolution, polyploidy, gene exchange and rounds of selection. We want to know what genes do and we do this by translating function across genomes using conserved sequences. Smaller genomes with less complexity – such as those in a basal or early plant model like liverwort – give us the ability to identify ancestral genes for a gene or gene family. We identify gene function in a plant and determine how this gene works, and then we identify other genes by understanding the evolutionary history of gene or gene family across the history of plants."

Of course, this is possible because all modern plants evolved from a common ancestor by modification of ancestral genes. Those which were essential for basic life processes were highly conserved because most mutations would have been detrimental - as predicted by natural selection.

By comparing their findings with the know genomes of the spikemoss Selaginella moellendorffi and the moss Physcomitrella patens. What the team found was interesting.

  • Although relatively small and undifferentiated, Marchantia polymorpha had a minimal metabolic pathway for producing the plant hormone, auxin, which regulated growth and development.
  • Genes encoding for enzymes which protect plants against the harmful effects of UV radiation may have been acquired by horizontal gene transfer from soil bacteria.
  • Early lignin biosynthesis genes similar to those in Physcomitrella patens were present in Marchantia polymorpha. Lignin is an essential component of the plant cell wall, which was essential for the transition to land plants.
  • Marchantia polymorpha has genes for plasmodesmata formation. Plasmodesmata form cell membrane channels involved in intra-cellular nutrient and signal molecule transfers. These form part of the pathway for cell division in land plants
  • The liverwort also has vestigial remnants of cell-division pathways that predate land plants, showing their transitional status.
  • The stress hormone, abscisic acid, which regulates when a plant goes dormant in response to drought, has homologues genes for its biosynthesis in the liverwort. This is essential for a terrestrial existence that enables plants to colonise areas prone to periodic desiccation.

The press release continues:

Schmutz pointed out that through the Community Science Program, the DOE JGI’s exploration of plant evolutionary history is expanding, leading to the development of a comparative genomics framework, including those from early plant lineages like the liverwort, that benefits the plant research community at large. “The more we accumulate this information in early plant lineages, the easier it is to transfer plant function across plant phylogeny and compare plant families to see the radiation of these genes. We’ll be focusing quite a bit more on the basal lineages of plants to get at the evolutionary history and position of genes. If we can understand the origin of these genes then we can understand historical function. Having multiple species allows us to do more and show more than what we can with just one genome.”

By learning the original functions of genes, elucidated from the genomes of earlier, simpler, plants and cells, scientists can more easily solve for the functions of related genes seen in more complex plants that may help address DOE missions in bioenergy and environmental processes.

This should not only tell any objective person that the Theory of Evolution is not only emphatically not a scientific theory in crisis, but that the genomes of modern plants only make any sense as the product of evolution over time. As I've noted before, every instance of this sort of research quite incidentally, and unintentionally refutes creationism and confirms evolution.

Only someone completely disinterested in the truth could ignore evidence such as this and continue to dispute the Theory of Evolution or even consider for a moment that there might be some doubt about its validity. Profound ignorance of the facts and a complete disregard for truth is an essential requirement for being a creationist.

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