Leland (Sandy) Pierson III was born in Norwalk, Connecticut. He received a B.A. degree in microbiology in 1979 from the University of California (UC), Davis, and a Ph.D. degree in 1986 from Washington State University, where he genetically characterized site-specific recombination in bacteriophage P4 under the direction of M. L. Kahn. He held a post-doctoral appointment in the laboratory of L. S. Thomashow at the USDA-ARS Root Disease and Biological Control Research Unit in Pullman from 1986 to 1990 and then joined the Department of Plant Pathology & Microbiology at the University of Arizona, where he rose to the rank of professor and associate director of the School of Plant Sciences. In 2009, he assumed the position of professor and head in the Department of Plant Pathology & Microbiology at Texas A&M University.
Pierson’s research program has defined principles important to the success of rhizosphere bacteria as biocontrol agents in suppressing soilborne fungal pathogens. A major goal of Pierson’s research is focused on the regulation and function of phenazines produced by Pseudomonas chlororaphis 30-84. His studies have revealed that phenazine production leads to surprisingly complex influences on the lifestyle of the producing bacterium and the rhizosphere microbial community to the benefit of the host plant. Pierson’s laboratory was the first to demonstrate that biofilm development by P. chlororaphis depends on phenazine production and that altering the ratio of phenazines produced strongly influences cell adhesion, biofilm architecture, and bacterial dispersal. Furthermore, he determined that different phenazine structural derivatives affect cellular responses, including adhesion, biofilm architecture, and root colonization. Transcriptomic analysis demonstrated that phenazines themselves alter patterns of gene expression in P. chlororaphis, and he is currently investigating whether phenazines are also involved in cell–cell communication via novel mechanisms. These and other studies of phenazine production by root-colonizing Pseudomonas species signify important milestones in understanding how antibiotic production can shift microbial communities to benefit plant health.
Pierson is also recognized as a pioneer in studies of quorum sensing mediated by N-acyl-homoserine lactones that regulate gene networks in response to environmental stimuli. He was the first to delve into the inconsistency of biocontrol from the viewpoint of how the bacterium senses its environment and determines when to express behaviors beneficial to biocontrol. He made the groundbreaking observation that phenazine production is regulated by a quorum-sensing system reliant on diffusible microbial pheromones. Mutants defective in the production of these signals were rescued for phenazine production in vitro and in situ by signals produced by another component of the wheat rhizosphere microbial community. Additionally, a second subpopulation was identified that inhibited phenazine production by producing signals that interfere with quorum-sensing activation of the phenazine biosynthetic operon. This landmark observation demonstrates that both positive and negative cross-communication occurs within the rhizosphere community to directly influence phenazine production.
Pierson has the distinct advantage of working with Elizabeth Pierson, who complements his genetic expertise with her ecological expertise. Other research contributions include the first cloning and sequencing of a large portion of the phenazine biosynthesis operon; description of beneficial roles for spontaneous gac mutants in survival in wheat rhizospheres; contribution to the sequencing of P. fluorescens Pf-5 genome; and participation in a landmark study on comparative genomics of eight strains of plant-associated Pseudomonas species that yielded novel insights into diversity and inheritance of traits relevant to biocontrol. Pierson also is a member of a NSF-funded Microbial Observatories project to analyze microbial communities and their metabolic contributions to speleothem formation in Kartchner Caverns in southern Arizona.
At the University of Arizona, Pierson was recognized as a dedicated and innovative instructor with the goal of exposing students to how microbial genetics influences all aspects of society. He is committed to training the next generation of scientists. In the classroom, students were exposed to thought-provoking discussions of scientific concepts and literature and gained a strong perspective on their future role in scientific discovery. Accordingly, he was honored with the Outstanding Faculty Teaching Award for the college in 2007–2008, the Student’s Choice Teaching Award in 1999, and the College’s Creative Teaching Award in 1995. Finally, Pierson is an inspiring mentor for graduate students and post-doctoral associates.
Currently, Pierson serves as department head at Texas A&M University, where he provides a strong foundation for establishing research priorities in plant pathology. He actively promotes research throughout Texas and works closely with a broad spectrum of agricultural industries. For example, he serves on a USDA-NIFA committee established to prioritize and fund research on the huanglongbing disease that threatens citrus production in Texas and elsewhere nationally. Pierson is active in service to APS and IS-MPMI, having served as an associate editor for Molecular Plant-Microbe Interactions from 1998 to 2002 and organizer/coorganizer of several APS-sponsored colloquia. He has served as chair of the Department Head Committee for APS and promoted its recognition as the Academic Unit Leaders Forum by APS. He served as an associate editor for Applied and Environmental Microbiology from 1997 to 2003. Pierson serves on competitive grants panels, including USDA programs for microbial communities in soils and in plant pathology research. He participated in the ESCOP/ACOP Leadership Development Program in 2002. He served on academic program review committees at UC-Riverside and Iowa State University. In addition to service on numerous committees at the University of Arizona, he was chair of the university-wide Institutional Biosafety Committee from 2002 to 2009. He is a gifted and popular speaker at scientific venues that comprise nearly 50 invited presentations since 1990 related to rhizosphere bacterial ecology, genomics, and phenazine production by Pseudomonas.
In conclusion, Pierson is a pioneer in defining the role of phenazines in rhizosphere microbial communities and biocontrol. He has provided new awareness of the mechanisms responsible for the success of root-colonizing Pseudomonas species in a complex root environment that has culminated in a body of research characterized by scientific depth. Consequently, he is recognized worldwide as an innovative scientist who is an authority on quorum sensing, secondary metabolite production, and other attributes beneficial to the success of microbial populations in the plant rhizosphere.
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