Tomonori Shiraishi was born in 1948 in Onomichi-city, Japan. He received a B.S. degree in 1970 from the College of Agriculture, Okayama University, and was hired directly as assistant professor of plant pathology at that university. In 1980, he received a Ph.D. degree from Nagoya University, under the direction of Professor K. Tomiyama, and published his dissertation “The role of phytoalexin in determining host–parasite specificity”. He was promoted to associate professor at Okayama University in 1985 and to professor in 1992.
Shiraishi’s ground-breaking research contributed enormously to our understanding of the physiological and molecular mechanisms of specificity between plants and fungal parasites. He made seminal contributions in two major areas: in pathogen suppression of plant defenses and in defining physiological functions for plant cell walls. He spent almost seven years isolating suppressors from fungal exudates and determining the molecular structures of these supprescins. Until the early 1970s, plant cell walls were considered as a mere frame to protect the cell contents, with no other physiological function. However, Shiraishi discovered that a significant number of enzymes are present in the cell walls and that these enzymes play key roles in a cascade to transduce external stimuli to the underlying plant membrane system, enabling rapid plant responses to these stimuli.
Shiraishi is recognized internationally as an authority on molecular mechanisms of defense suppression by plant-pathogenic fungi. Focusing his research on how the immune response of pea plants is suppressed by “suppressors of defense” produced by Mycosphaerella pinodes, Shiraishi established the “suppressor hypothesis” based on his finding that a low-molecular-weight substance in spore germination fluids from M. pinodes blocks pea phytoalexin production and induces accessibility only in the host plant. The suppressors block the signal transmission pathway and consequently interfere with active defense responses induced by elicitors, such as accumulation of pathogenesis-related proteins, phytoalexin production, superoxide generation, and the synthesis of elicitor-induced infection inhibitors. Inversely, the suppressors elicit these active defenses in nonhosts. In 1992, Shiraishi determined the molecular structures of the suppressors GalNAc-o-Ser-Ser-Gly (supprescin A) and Gal-GalNAc-o-Ser-Ser-Gly-Asp-Glu-Thr (supprescin B). His report was the first on the molecular basis of suppressors; the careful and thorough approach he used to link response phenotype with chemical structure are characteristic of his science. He demonstrated that one of the sites of supprescin action was the NTPase associated with a superoxide generator located in the plant cell wall. His careful work revealed that the pea cell wall-bound NTPase (PsAPY1) was a receptor for both supprescins and elicitors and that the affinity coefficient of specific supprescins was much higher than nonspecific elicitors, indicating that supprescins impede activation of defense responses. The regulated activation and suppression of cell wall NTPase by elicitors and supprescins, respectively, were demonstrated by lead-phosphate deposition in the wall structure by TEM/EDX, a novel technique at the time. Further, he determined that inorganic phosphate generated by NTPase, participated, in part, in the immune reaction by activating several peroxidase genes. His patent on the use of the NTPase gene for engineering disease-resistant plants illustrates the potential application of his basic research to disease control strategies.
Shiraishi first demonstrated the indispensable role of the plant cell wall in the cross-talk involved in determination of host-parasite specificity by showing that tobacco plants transformed with the PsAPY1 gene, a pea ATPase gene, were resistant to bacterial and fungal pathogens. Thus, he discovered novel and invaluable phenomena that advanced our understanding of the basic mechanisms of pathogenesis.
Shiraishi established the concept that obligate parasitic fungi were not only capable of inducing systemic acquired resistance (SAR), but also of blocking plant defenses in a limited area where a compatible interaction had been pre-established. He demonstrated that SAR was induced in barley within a few hours after wounding or inoculation with avirulent or virulent fungal pathogens and that the immune response induced by these stimuli was accompanied by a rapid increase of gramine, a naturally occurring indole alkaloid that inhibits the powdery mildew fungus. He demonstrated that the virulent pathogen blocked gramine accumulation at the inoculated sites.
His group isolated and characterized species-specific, endogenous suppressors from various plant species that were most likely involved in the mechanism of the induced susceptibility. All these studies on suppression of defense by his group are milestones for understanding basic principles of plant infection. During the course of his studies, he authored or coauthored 180 refereed papers, 43 book chapters, and three books. In recognition of his contributions, in particular, the determination of the molecular structure of supprescins, he was selected for the first Award for Excellent Papers in Plant Cell Physiology in 1994.
Since 1988, Shiraishi has supervised and been an excellent role model and advisor for 26 Ph.D. and 43 M.S. plant pathology students who have respected his insight and humility and appreciated his cheerfulness. He has taught the courses Regulation of Plant Infection and Molecular Mechanisms in Plant–Microbe Interactions and presented invited lectures on physiological and molecular plant pathology at numerous universities and at national and international meetings. His research has led to collaborations with many scientists in Japan as well as in the United States, Germany, and the United Kingdom.
Shiraishi has been and an excellent citizen of the plant pathology community and a long-standing member of The American Phytopathological Society. He has served as editor for Annals of the Phytopathological Society of Japan and Journal of Phytopathology. He served on numerous peer-review panels for competitive research grants, including panels for the USDA-NRI and the Japan Society for the Promotion of Science and New Energy. Examples of Shiraishi’s tireless services in promoting plant pathology include his membership on the Japan Science Council, which is an advisory organization for the national Cabinet, and service as vice president and president of the Phytopathological Society of Japan (PSJ). He was a co-organizer of the 5th International Congress of Plant Pathology in Kyoto, Japan, and an organizer/co-organizer of the 9th and 10th U.S.-Japan Cooperative Science Seminars. In recognition of these accomplishments, he received the Promising Young Plant Pathologist Award from the PSJ in 1980 and was designated a PSJ fellow in 1995.
