Professor Guido Sessa, plant-microbe biologist, educator, mentor, and former head of the School of Plant Sciences and Food Security at Tel Aviv University, died unexpectedly on July 4, 2023, in Tel Aviv. He was 59. Guido was known for his research on the molecular basis of bacterial pathogenesis and plant immunity using multiple experimental systems, including the interaction of Xanthomonas euvesicatoria with tomato and Arabidopsis. He was a respected colleague and a cherished friend.

Born April 26, 1964, in Rome, Guido immigrated to Israel in 1983. After military service, he earned a bachelor's degree at the Faculty of Agriculture, Food and Environment in Rehovot. His interest in plant-microbe biology began as a graduate student with Prof. Robert Fluhr at the Weizmann Institute of Science, where he investigated transcriptional control of pathogenesis-related genes and earned master's and Ph.D. degrees in plant biology. In 1997, Guido was awarded a fellowship from the Israel-US Binational Agricultural Research and Development Fund (BARD) and moved to the United States for postdoctoral research with Greg Martin, first at Purdue University and then at Cornell University.

In 2000, Guido returned to Israel and established a research laboratory at Tel Aviv University in the Department of Plant Sciences, which is now the School of Plant Sciences and Food Security. He progressed through the academic ranks to full professor and was a senior and esteemed member of the faculty's academic staff and research team. Between 2018 and 2022, while serving as the head of the School of Plant Sciences and Food Security, Guido led the restoration and reopening to visitors of the Yehuda Naftali Botanical Garden. In 2023, he was appointed head of the Institute of Cereal Crops Research at Tel Aviv University and led projects to improve wheat, in particular wheat resistance to rust disease.

Guido guided a dynamic research program focused on understanding molecular mechanisms in bacterial pathogenesis of plants and in plant stress responses and immunity. Early in his career he established the tomato–X. euvesicatoria interaction as a model system, and this became the foundation of many of his important discoveries over the years. His lab was an early adopter of genome-wide gene expression profiling methods, and this work revealed the importance of certain transcription factors and MAP kinases in the tomato immune response. From his postdoctoral work onward Guido's skill in applying protein biochemistry techniques to understand signaling events drove numerous pioneering advances. One example is his finding that a MAP kinase in tomato, MPK3, autophosphorylates on a specific tyrosine residue that is critical for its role in both the wound response and defense. His lab also made important discoveries in how type III effectors from Xanthomonas suppress host defenses. One study, a collaboration with Mary Beth Mudgett, showed how a widely conserved effector XopQ interacts with a host 14-3-3 protein to compromise MAPK signaling and immunity to X. euvesicatoria. In recent years, the Sessa lab published a series of studies on the roles of type III and VI secretion in the pathogenicity of a Pantoea agglomerans pathovar that causes a serious disease of beets. He was also the editor of a comprehensive overview of the field in 2012, titled Molecular Plant Immunity. These and many other contributions over the years from Guido and his lab enriched our molecular understanding of bacterial interactions with plants and plant defense and laid the foundation for more effective disease control.

A hallmark of Guido's research was the many collaborations he developed with scientists in Israel and around the world. A particularly fruitful collaboration was with Greg Martin, which began during Guido's postdoctoral period and continued for 25 years. Their joint work spanned a range of fundamental topics, including early work on gene expression profiling of the tomato defense response to bacterial pathogens, the role of GRAS family transcription factors in immunity, the discovery and characterization of MAPKKKe and MAPKKKa, which play key roles in activating immunity-associated MAPK cascades, and, most recently, a broad investigation of the negative regulation of immune signaling by PP2C protein phosphatases in tomato. Their collaboration was supported by seven successive BARD research grants, one of which is still active, and resulted in more than 30 publications, dozens of presentations at scientific meetings and the training of many students and postdoctoral associates. Guido was also a PI on four other BARD-funded research projects, and co-organized with Mary Beth Mudgett and Avi Avni a BARD- and NSF-supported workshop at Tel Aviv University on Microbial Virulence Determinants and Plant Innate Immunity, which aimed to assemble junior and senior colleagues in the field to share their insights and forge new collaborations.

Guido was a strong supporter of basic and applied plant sciences in Israel, most notably through his service to the BARD Program. He served for seven years on grant evaluation committees, where he played an important role in setting and maintaining BARD's high scientific standards. In addition, Guido frequently reviewed proposals on an ad hoc basis, even on short notice, provided advice on technical issues, and helped identify scientists to serve on BARD committees. He also provided scientists who wished to pursue BARD funding assistance in finding an Israeli or U.S. partner.

As a long-time member of the Association of Italian Scholars and Scientists, Guido avidly and effectively promoted research relationships between researchers from Italy and Israel in the field of plant-microbe biology, with support from the Italian Embassy in Tel Aviv. Most recently, he organized a joint conference in Israel with the participation of researchers from both countries. Unfortunately, he did not get to participate in the conference, as it was held the day before his death.

Guido was an exemplary mentor to young researchers throughout Israel and to his students and postdocs in particular. He excelled at identifying important and appropriate research projects for his lab members and allowed them great independence in pursuing their research, while at the same time always being available with advice and challenging questions. Many of his students went on to careers in academia or the biotech industry in Israel and around the world. Guido's genuine interest in others and his collegiality sparked many collaborations and connections in Israel, and these often led to invitations to serve on graduate student committees at universities within Israel in addition to his own. Guido, thus, had a major impact on both established and upcoming scientists in the plant-microbe biology field.

In addition to being an exceptional scientist and insightful, supportive colleague, Guido was a great friend to many. He had a warm smile, a subtle sense of humor, and a quiet laugh. He was kind and generous. He loved traveling, playing soccer, and skiing in the Italian Alps, and he had a lifelong interest in opera. Ying-Tsu Loh, a graduate student who overlapped with Guido at Purdue University writes, "I will always remember Guido for our 'opera Saturdays' at the lab, really loud opera, that you could hear walking down the hall. You knew then that Guido was in and that Saturday at the lab would be fun." Greg Martin remembers many good times with Guido, including during visits to Israel, where "we once spontaneously met his parents who happened to be out for a walk as we drove into Jerusalem, visited Masada, which was close to where Guido had done his military service, floated in the Dead Sea, and, memorably, in March of this year enjoyed a long lunch at Guido's favorite Italian restaurant in northern Tel Aviv. Those are great memories to have of a great friend." Adam Bogdanove, who was a postdoc with Martin at the same time as Guido, says of his lab mate and longtime friend, "I learned a lot from Guido. To this day, my lab uses Guido's western blot protocol. And, I'll always remember coffee breaks with Guido outside the Martin lab. We'd talk about science, and other topics, and laugh often. Those kinds of conversations continued throughout our careers and are what I will miss most." Mary Beth Mudgett shares, "Some of my best days as a scientist were brainstorming with Guido and drafting project ideas on napkins in cafes around the world. He was a critical thinker, thought provoking, down-to-earth and always warmhearted. I am missing Guido deeply."

Guido is survived by his mother, a brother, and by the light of his life, his daughter Shira, whom many of his colleagues were privileged to know as he often invited her to join him at scientific conferences and visits with collaborators. He will be greatly missed.

Gregory B. Martin,^1,2 Adam J. Bogdanove,¹ and Mary Beth Mudgett³

¹ Plant Pathology and Plant-Microbe Biology, School of Integrative Plant Science, Cornell University, Ithaca, NY, USA
² Boyce Thompson Institute for Plant Research, Ithaca, NY, USA
³ Department of Biology, Stanford University, Stanford, CA, USA

Acknowledgments

We thank Guy Sobol, Dor Salomon, Saul Burdman, and Haim Katz for helpful information.

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