Selaginella genome adds piece to plant evolutionary puzzle

Jody Banks, a professor of botany and plant pathology, led a team of about 100 scientists from 11 countries to sequence the genome of Selaginella, a lycophyte. Lycophytes, which are the oldest living vascular plants, shed spores to reproduce and have a single vascular vein through their leaves, as opposed to more complex vascular plants.

“There are only three families and about 1,000 species of lycophytes remaining. Selaginella has been on Earth about 200 million years,” said Banks, whose findings were published Thursday (May 5) in the journal Science. “This plant is a survivor. It has a really long history and it hasn't really changed much over time. When you burn coal, you're burning the Carboniferous relatives of these plants.”

Banks said the Selaginella genome, with about 22,300 genes, is relatively small. Scientists also discovered that Selaginella is the only known plant not to have experienced a polyploidy event, in which it creates one or more extra sets of chromosomes.

Selaginella also is missing genes known in other plants to control flowering, phase changes from juvenile plants to adults and other functions.

“It does these in a totally unknown way,” Banks said.

Banks said Selaginella's genome would help scientists understand how its genes give the plant some of its unique characteristics. The genome also will help them understand how Selaginella and other plants are evolutionarily connected.

In comparing this genome sequence with others, researchers were able to identify genes that are present only in vascular plants and genes present only in flowering plants. These genes likely played important roles in the early evolution of vascular and flowering plants, respectively. Many of these genes have unknown functions, but it is likely that those genes that are present only in flowering plants may function in the development of fruits and seeds, which are important to agriculture.

“For many plant genes, we have no idea what their function is,” Banks said. “Knowing this gives us ideas. It's an important piece of the puzzle in understanding how plants evolved.”

Banks also noted that Selaginella and Arabidopsis thaliana, a plant widely used in research, use significantly different genes to control creation of secondary metabolites, molecules that are responsible for creating scents, seed dispersal functions, defense and other tasks. Those secondary metabolites also are used to create pharmaceuticals.

“These metabolic genes evolved independently in Selaginella and flowering plants, so the metabolites they make are likely to be very different,” Banks said. “This means Selaginella could be a huge resource for new pharmaceuticals.”

Banks said the genome sequence would now be mined for more information as scientists learn more about plant evolution and applications for Selaginella's genes.

The National Science Foundation, the National Institutes of Health and several international organizations funded the research. The Joint Genome Institute of the U.S. Department of Energy sequenced the genome.

Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu
Source: Jody Banks, 765-494-5895, banksj@purdue.edu
Ag Communications: (765) 494-2722;
Keith Robinson, robins89@purdue.edu