Fuzzy history of the first flower

U. FLORIDA (US) — Since the first bloom, flowering plants have evolved at a booming rate, yet their origin remains a mystery. A 10-year effort to trace the genetic trail back to the first flower reveals new details about how those genes have changed over time.

“Our survival depends on products we get from the flower—grains, fruits, and many other materials,” says Doug Soltis, a biology professor at the University of Florida and a co-investigator on a study reported in PNAS. “Crop improvement is so important, but you don’t understand how a flower is put together unless you have a reference point—you can’t modify what you can’t understand.”

“There are 350,000 species of flowering plants (or angiosperms), and they serve as the foundation of nearly all of Earth’s ecosystems, yet we don’t know how the flower originated,” says Pam Soltis, University of Florida professor, Florida Museum of Natural History curator, and project co-investigator. “We now know the origin of many of the genes responsible for making a flower and how those genes have changed during the history of angiosperms.”

A 2009 University of Florida study traced the origin of flowers using genetic data for the avocado (a representative of one of the early lineages of flowering plants) and a well-known plant in genetics research, Arabidopsis thaliana. The new study includes additional comparisons with a water lily, California poppy, and cycad (a gymnosperm or non-flowering seed plant) and shows how the first flowers evolved from pre-existing genetic programs in gymnosperm cones.

“We have a much better understanding of the flower than we did 10 years ago and it’s a huge improvement,” says Doug Soltis. “We don’t know every pathway, but we have a much better handle on what makes those parts tick.”

Typical angiosperms have flowers with four organs: sepals (typically green), petals (typically colorful), stamens (male organs, which produce pollen) and carpels (female organs, which produce eggs). But in the earliest flowers, the distinct borders between their floral organs fade to a blur.

The flowers of early angiosperms have organs that merge into each other—for example, a stamen of a water lily produces pollen but it may also be petal-like and colorful.

“Our study found that the floral organs of basal angiosperms merge not only in appearance, but also in their underlying genetic pathways,” Pam Soltis says. “During evolution, the timing and location of where these genes act have become restricted, ultimately producing flowers with separate and distinguishable flower parts.”

“These missing links are incredibly important,” Doug Soltis adds. “They are our key to the past.”

“Flowers are the defining feature of angiosperms, the dominant vegetation of our world,” says Stanford University biology professor Virginia Walbot. “[The new study] represents a breakthrough in understanding the origin and evolutionary trajectories of the separate male and female floral parts.”

Researchers from Pennsylvania State University, the University of Georgia, and the University at Buffalo collaborate don the project, which was funded by the National Science Foundation.

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