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Raymond C. Valentine
In Memoriam

Raymond C. Valentine

Professor of Plant Science, Emeritus

UC Davis

Raymond Carlyle Valentine, the discoverer of the genes for biological nitrogen fixation, an out-of-the box thinker who believed that “simplicity equals elegance” and a plant biotechnology pioneer, passed away peacefully on March 9, 2023. He was 86. Born in a log cabin on September 20, 1936 to a poor but innovative farming family from rural Illinois, he started helping on the farm at 5 years of age. He was charged with weeding the rows of corn, hard work that left him bloodied due to the sharp edges of the corn leaves, an experience he credited with fueling his drive to improve agricultural practices through biotechnology. Working at his uncle’s apple farm exposed him to plant breeding, and he developed an appreciation for the vigor of hybrids, which also shaped his research philosophy.

Valentine’s scientific journey began in 1954 with his undergraduate studies at the University of Illinois, where he commuted daily from his family home nearly an hour away. He was recruited by Ralph S. Wolfe to conduct undergraduate research, reportedly after proving himself to be inept as a laboratory dishwasher. As an undergraduate he developed a biochemical assay to test for electron transfer reactions. The assay caught the notice of I.C. Gunsalus, who arranged for Valentine to visit DuPont de Nemours, Inc., and test his assay against the chemical company’s collection of enzyme preparations. Just days into his internship at DuPont, Valentine applied his assay to a preparation and discovered a key proteinaceous electron carrier that DuPont subsequently named ferredoxin.

Valentine was encouraged to continue with graduate work in microbiology at the University of Illinois with Wolfe, earning his Ph.D. in 1962. He focused on the biochemical reactions of ferredoxin, recreating his discovery in Micrococcus after DuPont blocked his attempts to work on ferredoxin in Clostridium. The study of ferredoxin function unraveled the critical role it plays in multiple fundamental cellular processes from animals to plants to bacteria to archaea. His postdoctoral training in Norton Zinder’s laboratory at what was then the Rockefeller Institute from 1962 to 1964 introduced him to molecular biology, genetics, and bacterial viruses. After he joined the Department of Biochemistry at the University of California, Berkeley, in 1964, Valentine combined the power of genetic analysis with his understanding of biochemistry, reaching across scientific disciplines with his version of “hybrid vigor.” His philosophical approach to science was reinforced and inspired by his friend and hiking partner, the renowned physicist and geneticist Max Delbrück. He regarded Delbrück as a mentor from whom he absorbed his reductionist philosophy, which he summed up as: “simplicity equals elegance.”

His most significant breakthrough came while studying biological nitrogen fixation, beginning at UC Berkeley and continuing in the Chemistry Department at UC San Diego from 1972 to 1975. Previously, bacterial nitrogen fixation was described only as a biochemical process. Valentine recognized the need for a genetic characterization and a tractable system, which he identified in Klebsiella pneumoniae. He isolated multiple mutants that could not fix nitrogen. He discovered that bacteriophage P1 could transfer genetic information from one strain of Klebsiella to another, and he used this genetic tool to map the nitrogen fixation genes. The nif genes, which he named, were located at a chromosomal site next to the genes for histidine biosynthesis. The demonstration that a critical biosphere process was genetically tractable opened the door to its extensive characterization.

In 1975, he moved to the UC Davis where he continued his work on nitrogen fixation in bacteria that formed associations with legumes. In the 1980s, he became interested in drought and salt stress, recognizing the importance of osmoregulation. His lab identified compounds that, during drought, protect and maintain macromolecular cellular structure and function.

His research activity continued well beyond his 1992 retirement as his interest turned to lipid membrane function and the role of semiconductor hydrogels in biologically encoded memory. His lab was a furnace of activities and reductionist ideas, where American and international students and scientists worked to identify key genes that could be used to make new products, divert biochemical pathways, or confer new traits.

Valentine’s visionary ideas extended far beyond the confines of the UC Davis campus, most notably as the scientific founder of Calgene Inc. in Davis, one of the very first agricultural biotechnology companies. Calgene played a pivotal role in the development of herbicide-tolerant plants and marketed the first genetically engineered food product, the FLAVRSAVR tomato in 1994. He embraced the importance of herbicide resistance, derived from his boyhood experiences weeding corn back in Illinois, and his interactions with the UC Davis weed science program and with chemical companies, with which he interacted as a consequence of his research on nitrogen fixation. By demonstrating the power of genetic engineering, Calgene paved the way for the development of crops capable of withstanding herbicides, while minimizing environmental impact and maximizing yields. This ground-breaking technology, born out of a hybrid vigor combining biochemistry and genetics that Valentine understood as being vital, became a turning point for the application of biotechnology to address agricultural challenges and the creation of novel agricultural products.

While his scientific contributions and entrepreneurial endeavors were remarkable, Valentine’s impact extended beyond his achievements. As a mentor and guiding force, he nurtured the minds of countless students and colleagues, instilling in them a passion for scientific exploration and a commitment to making a difference in the world. He was a science ambassador and champion, frequently presenting his work to visiting dignitaries and occasional royalty. He also was deeply engaged in the societal discussion of genetic engineering technologies and was a presenter at the famed 1975 Asilomar Conference on the potential applications of recombinant DNA technologies.

He will be remembered for his unwavering dedication to dissecting complex ideas, reducing them to manipulable components, and pushing the boundaries of knowledge to develop innovative solutions that could impact global challenges. He had a great sense of humor, a warm and charming personality and a willingness to help others and unselfishly respond to their needs, personally as well as scientifically. He loved the wild and would go on long hikes: The Desolation Wilderness in the Sierra Nevada was one of his favorite places, as were the wilds of Alaska. He loved to fish, hunt and explore, and many scientific discussions with his students, coworkers and colleagues would take place far from the laboratory.

He is survived by Cindy Anders, his partner of 30 years; his former wife Annalisa Valentine; loving daughters Rebecca Valentine and Lori Valentine; son David Valentine and daughter-in-law Carla Valentine; beloved grandchildren Isabella Valentine, Sawyer Crandall, Sienna Valentine, and Stella Valentine; Anders’ sons Ben (Shari) Anders, David (Julie) Anders and Elliot (Tessa) Anders, and grandchildren, Eva, Sarah, Eli, Jude and Elsa Anders; and his sisters Barbara Hinton, Marilynn Scott and Paula Valentine.

Abhaya M. Dandekar
David L. Valentine
Luca Comai
Tom Gradziel

Photo credit: Archives and Special Collections, UC Davis Library