The footprints of plant evolution left for us by flowers - School of Science, the University of Tokyo
Dec 7, 2015

The footprints of plant evolution left for us by flowers

Department of Biology — Hirano Laboratory

Professor Hiroyuki Hirano
Department of Biology
Graduate School of Science


Professor Hirano graduated from Tohoku University’s biology program in 1978. In 1983 he completed the graduate course of biochemical regulation at Nagoya University. He then became a fellow at the Japan Society for the Promotion of Science (Tokyo University), and became an assistant professor at the National Institute of Genetics in 1988. In 1996 he became an associate professor in the University of Tokyo Graduate School of Agricultural and Life Sciences, and obtained his current position in 2004.

Did you know that the great writer Goethe was also a botanist?

In his 1790 book Metamorphosis of Plants, he states, “flowers are a metamorphosis of leaves.” Goethe had carefully observed flowers by employing sensibilities honed through his creation of poetry and novels, and this was the conclusion he was led to. It was not until two hundred years later, in 1991, that Goethe’s words were confirmed experimentally by modern biological research. That was the year in which the four floral organs—sepals, petals, stamens, and carpels—were found to be determined by three classes of floral homeotic genes (A, B, and C genes).

“If all ABC genes are defective, the result is floral organs that look like leaves,” says Professor Hiroyuki Hirano. “This mechanism, which has been named the ‘ABC model,’ is both simple and beautiful, truly a glorious and monumental work in botany.”

It is primarily angiosperms that create beautiful flowers, which evolved as reproductive organs for the production of offspring. In contrast, the ancient ancestors of angiosperms, ferns, produce offspring through the release of spores that develop on the underside of their fronds. Sperm and eggs are produced from germinated spores, and then fertilized. However, water in the form of rain or dew is required for sperm to reach the eggs, leaving part of the reproductive process up to chance. This is the reason why some plants developed flowers, Professor Hirano explains. “Plants developed flowers as reproductive organs so that they can better procreate in areas where there is little water. The flowers attract insects, which are used as a mediator for transferring pollen from the stamen to the pistil. We believe that the evolution of flowering plants was therefore a way of making reproduction safer and more efficient.”

It is typical in plant research to use Arabidopsis thaliana (thale cress) as a model organism, but Professor Hirano has focused on Oryza sativa, better known as rice. Professor Hirano says, “Taxonomically speaking, Arabidopsis and rice are distantly related species — the former is a eudicot, while the latter is a monocot. The ABC model explaines the developmental mechanism of eudicot flowers well, so my first question was whether the model could be simply applied to flowers in other plants. To address this question, we started rice developmental research.”

Through his rice studies, Professor Hirano has been revealing mechanisms unique to monocots. Although the ABC model serves as a foundation, Professor Hirano has revealed that a new gene, which was not involved in the model, plays a key role in pistil development.

The research theme of the Hirano Laboratory is evolutionary genetics. Genetics research starts with the discovery of mutations. Collecting a sufficient number of mutations requires examining a large number of samples, so working in rice paddies is a big part of the research process.

Planting rice and searching for mutants is too large a task to perform alone, so the entire lab pitches in. To improve feelings of solidarity, the lab has created T-shirts for its members, and Professor Hirano takes charge in creating a positive atmosphere in the lab. This is quite evident to students there; as Shigehiro Sugiyama (B4) says, “We have lunch with Professor Hirano every week after our seminar. That lets us speak with him on friendly terms, bringing us closer.” Takuya Ikeda (M1) says, “When students come to rice plantings for the first time, he shows them how to do it himself.” Chie Suzuki (B4) reports that “He gives us all ice cream when we’re working in the summer. Afterward we all go out drinking. He probably out-drinks us all!”

Another characteristic feature of the Hirano Laboratory is teamwork that spans generations. “Rice only produces one generation per year. If one were to make a solo attempt at finding mutations, isolating the target genes, and figuring out their function, that would easily take three to five years,” explains Professor Hirano.

Current students pick up from where their predecessors left off, and leave the seeds of their own research to be carried on by subsequent students they may never meet. Sometimes these are literal seeds, those of mutants they found in the field. Just as seeds connect generations of plants, so too do they connect generations of research at the Hirano Laboratory.


 A question mark formed by a mutated rice stamen, inspired by the fact that research begins with simple questions. This image entitled “The Spirit of Science” won second place in a 2011 University of Tokyo scientific imagery contest, and, since then, the image has been used in promotional posters as a symbol of the contest.



The entire laboratory team, planting rice.


Student evaluations
“He’s easy to speak with, which creates a positive, stress-free environment.” (Takuya Ikeda, M1)
“He loves hot and spicy Chinese and Korean food.” (Chie Suzuki, B4)
“He’s quite passionate about his research, and has a keen eye.” (Shigehiro Sugiyama, B4)

― Office of Communication ―

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