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Daniel F. Klessig, who was born on February 24, 1949, in Fond du Lac, WI, grew up on a dairy farm. He graduated from the University of Wisconsin-Madison in 1971 with a B.S. degree in biochemistry, followed by two years as a Marshall scholar at the University of Edinburgh, which culminated with a first-class honors degree in molecular biology. Klessig worked with J. D. Watson and R. Gesteland at Harvard University and Cold Spring Harbor Laboratories (CSHL) and was awarded a Ph.D. degree in 1978. After a brief post-doctoral fellowship with J. Sambrook at CSHL, he was promoted to staff scientist in 1978. Klessig joined the University of Utah as an assistant professor in its Medical School in 1980 and was promoted to associate professor in 1983. In 1985, he joined Rutgers University as a full professor and associate director of Waksman Institute. In 2000, Klessig moved to Cornell University to become president and CEO of the Boyce Thompson Institute for Plant Research (BTI). Due to health problems, he stepped down as president and CEO and presently continues to work as a senior scientist at BTI and as an adjunct professor of plant pathology and plant-microbe biology at Cornell University.

Klessig’s work over the past 36 years includes more than 215 publications, which encompass both animal and plant fields. As a student studying gene regulation in human adenovirus, he helped uncover split genes in 1977 (providing some of the strongest biochemical evidence for RNA splicing at that time), and he proposed the model of RNA splicing to explain this phenomenon, as well as the existence of hnRNA. This pioneering work also established that gene expression can be regulated by alternative splicing. In addition, his work in the early 1980s on RuBISCO provided the first rigorous demonstration of translational regulation and its importance in plants.

Since the mid-1980s, Klessig has made major contributions to our understanding of how plants protect themselves against microbial pathogens, and he is internationally recognized for his pioneering work in this area. In landmark 1990 papers, Klessig’s group, along with that of Jean-Pierre Métraux and John Ryals, demonstrated that salicylic acid (SA) is a critical endogenous signaling molecule for the activation of plant defenses following pathogen attack. Using biochemical, as well as genetic and molecular approaches, Klessig’s laboratory has worked to decipher the SA signal transduction network and underlying mechanism(s). These studies have revealed that plants can trigger defense responses using both SA-dependent and -independent defense signaling pathways. In addition, his group has isolated several components of the defense signal transduction network, including resistance genes belonging to the TIR-NBS-LRR and CC-NBS-LRR classes, a nucleotide-gated ion channel protein, and a fatty acid desaturase. The latter provided some of the first evidence for the involvement of lipids in plant immunity. Another important contribution from his group was the discovery that several MAP kinases, including the SA-induced protein kinase (SIPK), are involved in disease resistance.

In 1998, Daniel Klessig’s group, as well as that of Chris Lamb and Richard Dixon, published landmark papers demonstrating that nitric oxide (NO) is a key defense-signaling molecule in plants. Klessig’s group further established that NO modulates the activity of several enzymes that are induced during defense responses; these enzymes may specifically participate in plant defense signaling and/or have housekeeping functions. Additionally, his group demonstrated that several critical players in NO signaling in animals are also operative in plants. Klessig’s and Nigel Crawford’s groups identified two putative nitric oxide synthase (NOS) proteins in plants. However, subsequent work by Klessig’s group showed that neither of these proteins functions as a true NOS; instead, Crawford’s AtNOS/A was found to be a GTPase.

Using a biochemical approach, Klessig’s group has attempted to identify a receptor for SA. Although this effort has been unsuccessful to date, several important SA effector proteins have been identified, such as the two major hydrogen peroxide-metabolizing enzymes catalase and ascorbate peroxidase, and a methyl salicylate (MeSA) esterase (SABP2). SA binding inhibits the activity of these enzymes, thereby helping to mediate SA’s many physiological (and perhaps in humans, pharmacological) effects. Through detailed molecular, biochemical, and biophysical characterization of SABP2, the Klessig lab also has identified the first mobile long-distance signal for systemic acquired resistance, namely MeSA. Current studies in Klessig’s laboratory aim at uncovering additional SA effector proteins that will help reveal the breadth of the SA signaling network. Recent studies also have identified a critical factor that is unique to plants and participates in four levels of immunity, from resistance gene-mediated to nonhost resistance. Together his group’s pioneering work in defense signaling has helped establish that plants and animals share many aspects of immunity, a finding that is likely to have significant impact on human, as well as plant, health.

Klessig’s work has had a major impact not only on the field of plant immunity but also on the plant scientific community as a whole. As part of a highly successful and demanding scientific career, he has mentored a large number of post-doctoral (70), graduate (12), and undergraduate students, many of whom have also made a name for themselves in their respective fields. He has participated as a member of several peer-review committees and acted as an editorial member of several leading scientific journals. His leadership roles in directing research and education, not only as an associate director at the Waksman Institute, president and CEO of the prestigious BTI, and presently as a senior scientist of BTI, have led to many positive and inspiring changes at these research institutes. His contributions to the field of plant science, both in terms of scientific advancement and service to the scientific community, are commendable and deserving of appropriate recognition.