42nd International Prize for Biology awarded to Dr. Sharon Rugel Long

The Japan Society for the Promotion of Science (JSPS) convened the International Prize for Biology Committee (Chair: Yoshinori Fujiyoshi, Specially Appointed Professor, Institute of Science Tokyo) and decided to award the 42nd International Prize for Biology to Dr. Sharon Rugel Long, Steere-Pfizer Professor of Biological Sciences at Stanford University. This year's prize is awarded in the field of "Biology of Symbiosis (interspecific interactions)."

Long elucidated the mechanism by which rhizobia and leguminous plants recognize one another as appropriate symbiotic partners through chemical signaling and establish root nodule symbiosis. Through this work, she established a theoretical foundation for chemical communication between different species and its role in the formation of symbiotic relationships.

The International Prize for Biology was established in 1985 to commemorate the 60th year of the reign of Emperor Showa, honor his lifelong interest in biological research, and promote the advancement of biological sciences. The prize is awarded to researchers who have achieved internationally outstanding accomplishments and made significant contributions to the progress of biological science. In conjunction with the 25th award, the prize's purpose was expanded to commemorate the long-standing research on fish taxonomy conducted by the Emperor Emeritus and to further promote the development of biological sciences. Recipients receive a certificate, a medal, and a prize of ¥10 million, along with a commemorative gift from Crown Prince Akishino. The award ceremony is traditionally held in December at the Japan Academy in Ueno, Tokyo.

To commemorate Long's award, a symposium will be held in Nara on December 19 and 20. Researchers from Japan and abroad, including Long, will present the latest findings in the field of symbiosis research.

Long elucidated how rhizobia, bacteria that live symbiotically in the roots of leguminous plants, and their host plants recognize one another as appropriate partners and establish a relationship known as root nodule symbiosis. Leguminous plants can utilize atmospheric nitrogen gas as a nutrient source, even though most organisms cannot use it directly. This capability is made possible by their symbiotic association with rhizobia, which inhabit root nodules on the host plant's roots, fix atmospheric nitrogen, and supply it to the plant as a source of nutrition. This symbiotic relationship is highly host specific. Although alfalfa and pea are both legumes, rhizobial strains that form symbiosis with alfalfa are unable to establish the same relationship with pea.

When Long began her research, little was known about the molecular mechanisms by which rhizobia and leguminous plants recognize one another and establish root nodule symbiosis. Through molecular genetic, biochemical, and cell biological studies of both rhizobia and their host plants, she elucidated the mechanisms underlying host specificity.

Specifically, Long demonstrated that flavonoids secreted by host plant roots induce the expression of rhizobial nod genes required for symbiosis. She also made major contributions to the discovery and functional characterization of Nod factors, signaling molecules synthesized by enzymes encoded by the nod genes. For example, luteolin, a flavonoid secreted by alfalfa roots, induces nod gene expression in alfalfa rhizobia, whereas flavonoids secreted by other plants do not possess this activity. These findings demonstrated that flavonoids released by host plants trigger the synthesis of Nod factors in their compatible rhizobial partners.

Long also made major contributions to elucidating the effects of Nod factors on host plants. The structure of Nod factors differs among rhizobial species. She discovered that Nod factors produced by alfalfa rhizobia trigger periodic fluctuations in intracellular calcium ion concentrations, known as calcium spiking, in alfalfa root cells. By contrast, Nod factors produced by other rhizobial species fail to elicit the same response in alfalfa.

These findings demonstrated that the structural specificity of Nod factors governs host specificity by inducing calcium spiking, thereby initiating root nodule symbiosis only with compatible host plants. Long's work showed that the "molecular dialogue" between host plants and rhizobia, mediated by flavonoids and Nod factors, is translated into calcium spiking within host cells, thereby initiating root nodule symbiosis. This achievement represents an exceptionally significant contribution to biological science.

Long has published 158 scientific papers, which have been cited more than 17,000 times. In addition to being an outstanding researcher, she is also highly regarded as an educator.