New information about early Native Americans' horticultural（园艺的） practices comes not from hieroglyphs（象形文字，图画文字） or other artifacts（史前古器物，人工产品） , but from a suite of four gene duplicates（副本，复制品） found in wild and domesticated（家养的） sunflowers. In an upcoming issue of Current Biology, Indiana University Bloomington biologists present the first concrete evidence（证据确凿） for how gene duplications can lead to functional diversity in organisms. In this case, the scientists learned how duplications of a gene called FLOWERING LOCUS T, or FT, could have evolved and interacted to prolong（拖延，延长） a flower's time to grow. A longer flower growth period means a bigger sunflower -- presumably an attribute of great value to the plant's first breeders.

"Our paper shows how gene duplication creates potential for evolutionary innovation not just through creating new gene content but also through new interactions among duplicates," said Ben Blackman, the report's lead author.

Blackman conducted the research as an IU Bloomington Ph.D. student. He is now a postdoctoral fellow at Duke University.

Biologists have long thought the accidental duplication of genetic material provides important fodder（饲料，素材） for evolution. Less risky than modifying an existing, possibly important gene, duplicates offer an out -- one copy can continue its normal activities while the other copy acquires new functions. That's a hypothesis（假设） , anyway. The Current Biology paper suggests reality may be a little more complex.

FT genes play a role in sensitizing flowering plants to seasons, and their expression is usually triggered by changes in day length. Some flowering plants express FT genes early in the growing season as days get longer. Sunflower FT genes are expressed toward the end of the growing season when days are getting shorter. As far as biologists know, all flowering plants have at least one FT gene.

Blackman and his colleagues identified four FT genes in sunflower, Helianthus annuus, which are known as HaFT paralogs. Each of the paralogs, HaFT1 through HaFT4, has a unique genetic sequence, but is similar enough to the others to conclude three of them were the result of DNA duplication events in sunflower's distant past.

"Based on the level of divergence（分歧） between the various HaFTs and the presence of a single FT copy in lettuce（莴苣，生菜） , we inferred（推测，推论） that one copy became two during a whole genome doubling event that occurred roughly 30 million years ago," Blackman said. "One of those copies proliferated（增殖，扩散） further through two small-scale duplications that we infer occurred much more recently."

The scientists examined each paralog（横向同源物） 's expression patterns within sunflower, and by strategically cloning variants of the HaFT genes into the model plant Arabidopsis thaliana, discerned（看清楚，识别） the paralogs' physiological properties in one another's presence.