All terrestrial plants evolved roughly 470 million years ago from algae. Since then, these organisms have reshaped the planet. Throughout the plant's evolution, ferns have undergone various changes that allowed them to adapt and survive on land. Today, for the first time, researchers were able to characterize the genome arrangements of tree ferns shedding light on their evolution.
Evolution of Tree Fern
The invention of the plant's vascular system was a major evolutionary event for land plants which helped them conduct water, food, and nutrients. Two tissues, the xylem and phloem compose the system. The xylem enables water transportation to the plant's stems and leaves, while the phloem helps transport sugars made via photosynthesis to the rest of the plant.
Also, only xylem cells are lined with a supportive structure material called lignin that provides the rigidity of wood and bark.
Researchers aimed to understand how the v vascular systems evolved in the tree fern and how lignin is made.
Ray Ming, a co-author of the study and a professor of plant biology at the University of Illinois, says that the ferns are among the first vascular plants, and lignified cell walls were vital innovations during the plant's evolution. He adds that the study improved understanding of how vascular tissues developed in firms and various other land plant species.
In the study published in the journal Nature Plants, titled "The flying spider-monkey tree fern genome provides insights into fern evolution and arborescence." researchers sequenced the genomic sequence of the flying spider-monkey tree fern, Alsophila spinulosa, and analyzed the construction of its vascular tissues.
The team found that two vascular-related MAC-domain genes were expressed highly in xylem compared to other plant tissues. This indicates that these cells may be vital regulators in forming xylem-specific cells.
Using biochemical methods and microscopy, the team measured lignin levels and secondary metabolites - compounds that aren't detrimental to the growth or reproduction of the plant but confer benefits - in the tree ferns.
Reconstructing Tree Fern Evolutionary Timeline
Researchers found that lignin comprised 40% of the plant's stem cell wall. In comparison, wood typically contains 25% lignin. The team also discovered a new secondary metabolite made primarily in the xylem, named alsophilin, reports PhysOrg.
Ming explains that the new compound was observed to be abundant in the xylem, likely as one of the compounds filling up the cavities of non-functional tracheid cells. Also, the team identified genes involved in the biosynthesis of alsophilin in the plant's genome.
To understand how the tree fern evolved, experts compared genomic sequences of the plant to other members of the same species across various locations in China. Surprisingly, researchers discovered six distinct populations of tree ferns with differing genomic sequences.
Based on the results of sequencing, experts reconstructed the history of the fern population and saw that there were two times that the plant species underwent a drastic decrease in population numbers. The first occurred 35.6 to 34.5 million years ago, and the second event occurred 2.5 to 0.7 million years ago.
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