From 1954 through 1958 Dr. Zaitlin was a Research Officer at the Microbiology Section, Division of Plant Industry, CSIRO, Canberra. At this time, plant virology was concerned mostly with the identification of new viruses and the characterization of the virus particles. However, Dr. Zaitlin directed his attention to virus replication and the investigation of virus mutants. His moved as a postdoctoral researcher to the Department of Horticulture, University of Missouri, Columbia, in 1958. In 1960 he accepted a position in the Department of Agricultural Biochemistry at the University of Arizona, Tucson, where he rose to the rank of full professor. He moved to the Cornell University, Ithaca, Department of Plant Pathology in 1973 and became Professor Emeritus in 1997.
Professor Zaitlin was both a Fulbright Scholar and a Guggenheim Fellow during his sabbatical leave in 1966-1967 with Paul Whitfeld at the Division of Plant Industry, CSIRO, Canberra. He was Visiting Scientist at the John Innes Institute, Norwich in 1986 and Visiting Research Scientist, Department of Biochemistry and Biophysics, UC Davis, 1979-1980. Professor Zaitlin was elected a Fellow of the AAAS in 1969 and a Fellow of the APS in 1978. His refereed research publications are dated over a 50 year span, 1951-2000.
Although Professor Zaitlin emphasized virus replication, he nonetheless made important contributions to the detection, purification and analysis of virions and viroids and to understanding virion function. He often employed simple and direct approaches to test hypotheses. He demonstrated that TMV uncoating and gene expression occurred in animal cells, thereby providing a strong argument against hypotheses for uncoating that would require the plant cell wall. Similarly, he isolated and incubated protoplasts from inoculated leaves to show that certain “subliminal” infections are in fact infections entirely restricted to the few cells infected at the time of inoculation, a conclusion that could not be drawn from direct examination of the leaves. He was among the first to realize the importance of cell-to-cell movement as a point of vulnerability exploited by natural resistance, and made significant contributions to our understanding of long-distance movement.
Professor Zaitlin is well known for his studies on virus strains and mutants, mixtures thereof, defective viruses and their phenotypes. His work revealed that functional coat protein was not essential for infection or induction of symptoms.
He devoted considerable effort to devising plant single-cell systems as virus hosts. After developing tools for evaluating the accumulation of specific virus proteins and RNA in virus-infected cells, Professor Zaitlin published an extensive series of papers on virus RNA replication and others on TMV genome organization and gene expression. Before Professor Zaitlin’s 1972 paper, no TMV protein other than coat protein had been demonstrated. Later, careful peptide mapping revealed that a high molecular weight protein observed by him was indeed, as he had postulated, a TMV-specified replicase protein. Using a variety of clever hybridization and other techniques, Professor Zaitlin was able to elucidate the genetic map of TMV six years before the nucleotide sequence of the TMV genome was available.
Professor Zaitlin has a long-standing interest in plant resistance to viruses. When plant transformation technology became available, he and his colleagues transformed tobacco with various wildtype and mutant versions of virus replicase genes, creating strong resistance that in at least some instances affected both replication and virus movement and likely did not rely on gene silencing.
Other interests include the relationship between virus infection of chloroplasts and chloroplast function. Professor Zaitlin also contributed substantially to our understanding of the nature of viroids and of the induction of symptoms by satellite RNAs. A barely noticed minor band on a gel stimulated Professor Zaitlin to discover the phenomenon of ubiquination of virus coat proteins.
Professor Zaitlin is the author of more than 30 review articles, many of which influenced directly or indirectly the development of plant virology. Prof. David Baulcombe of the Sainsbury Laboratory stated “his Annual Review with Roger Hull was a key text for me when I was entering the virology field.”
Professor Zaitlin was committed to good teaching based on careful preparation and organization. His classroom and other lectures were characterized by clarity and precise expression in a pleasant and friendly atmosphere that never neglected critical thinking. He was an outstanding mentor to the many graduate students and postdoctoral associates. Roger Beachy, President of the Danforth Plant Science Center, states that "Milt was perhaps the most influential mentor in my career in science in general, and in plant virology in particular. His willingness to encourage, critique, and advise was part of a collegial relationship that fostered confidence and innovation while demanding critical thinking…”
Professor Zaitlin advanced his profession by serving two terms as Associate Editor of Virology (1966-1971; 1982-1984) and as the Editor of Virology for all plant virus submissions (1972-1981). He was Senior Editor for Virology of Molecular Plant-Microbe Interactions 1987-1990. He was a member of the group that formed the American Society for Virology in 1982. Professor Zaitlin was the Associate Director of the Cornell biotechnology program (New York State Center for Advanced Technology), 1983-1990, and was Director in 1990-1991. He is widely recognized for his success in obtaining support for biotechnology research, facilitating communication among biotechnology researchers, and informing the public on biotechnology issues.
Professor Emeritus Milton Zaitlin is recognized as a very influential pioneer of plant virology who also is a valued mentor and a master of university instruction in the plant sciences.