Why is your Christmas tree so big? Let science explain.

Christmas-Tree-Branch-In-The-Light_blogIt’s that time of year again as families begin heading out to a Christmas tree farm in search of the perfect tree for this year’s celebrations. What many people probably don’t think about, however, is how, when left to grow in the wild, these types of trees are among the tallest, hardiest plants in the world.

In fact, it was recently discovered by Michael Barker and other researchers from the University of Arizona in Tucson that spruces, pines, firs, and their relatives, underwent a genomic “hiccup” in their deep past, creating a complete second set of genes.

A recent article explains that this genome-wide duplication likely helped shape these species into the massive plants they are today. This discovery is also causing biologists to rewrite the history of gymnosperms, the group of plants that includes conifers and other nonflowering, seed-producing plants.

“This is really exciting work,” Douglas Soltis, a botanist at the University of Florida in Gainesville, said in the article. “It has long been known that [genome duplication] was important in flowering plants and ferns,” he said. “This work shows that genome doubling has played an important role in conifers as well.”

As more and more plant and animal genomes have been deciphered and compared, researchers have developed a growing appreciation that the distant ancestors of various groups underwent genome duplications. But as the article explains, when the first pass of the genome of the Norway spruce, a common Christmas tree, came out in 2013, Stefan Jansson, a geneticist in Sweden concluded that although some genes had been copied elsewhere in the genome — the genome itself had not duplicated.

Barker, however, wasn’t so sure. So many other plants had undergone such duplications that “it didn’t make sense that [gymnosperms] didn’t have any,” he said in the article. He and his colleagues therefore sequenced just the genes—which are just a small fraction of the total DNA—for 24 gymnosperms and three other plants. They also developed a sophisticated computer program that could ferret out possible genome duplications by analyzing similarities among genes within and between those plant species.

What they discovered was that two duplications actually occurred in conifers and one happened at the base of the spruce, pine, and fir trees. The genome of the ancestor of box shrubs, junipers, and cedars, another group of conifers, also underwent a doubling. But no duplications have taken place in the third branch of conifers, which includes the monkey puzzle tree, they noted. As more tree genomes are deciphered, other rounds of duplication may become evident, Barker mentioned in the article. But what is clear is “the mechanisms in which the genomes have evolved in gymnosperms and [flowering plants] are not as different as previously portrayed,” he said.

There’s growing evidence an extra copy of a genome provides fodder for the evolution of new traits, and new species. Duplicated genes provide freedom for one copy to change what it does without affecting the organism’s survival. Some of those changes may underlie the redwood’s height, or the ponderosa pine’s longevity, for example.

Next, Jansson hopes researchers will take a close look at different genes that have survived long after the duplication event, as they likely played important roles in plant evolution. James Leebens-Mack, a plant geneticist at the University of Georgia in Athens, agrees: “We now need to determine whether certain types of genes tended to be retained in duplicate and investigate how functional evolution of these genes contributed to major innovations such as the origin of the seed.”

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