James R. Alfano was born June 2, 1963, in Burbank, CA. He received his B.S. degree in 1986 in microbiology from San Diego State University and his Ph.D. degree in 1993 in microbiology from Washington State University, where he pursued his thesis research at the Institute of Biological Chemistry. From 1993 to 1997, he was a post-doctoral research associate in the Department of Plant Pathology of Cornell University (CU) in Ithaca, NY. From 1997 to 2000, he was an assistant professor in the Department of Biological Sciences at the University of Nevada-Las Vegas. In 2000, he moved to the University of Nebraska-Lincoln, where he is now a professor in the Plant Science Initiative and the Department of Plant Pathology.
Alfano’s research focuses on the type III secretion system (T3SS) of Pseudomonas syringae pv. tomato DC3000 and the effector proteins injected via the T3SS into plant cells by this model pathogen. The T3SS is central to the virulence of DC3000 and many other Gram-negative plant pathogens, and Alfano has made major contributions to several aspects of our current understanding of this system, including the genomic context of the T3SS, the control of substrate traffic, the role of chaperones in effector delivery, the ability of various type III effectors in the DC3000 repertoire to suppress plant defenses, and the biochemical activity of two effectors, HopAO1 and HopU1.
Alfano was a major player in elucidating the genomic context for the T3SS in P. syringae pv. tomato DC3000. This effort began with a sequence-based analysis of the 50-kb region of the DC3000 chromosome that contains the tripartite Hrp pathogenicity island, which was initiated by Alfano when he was at CU and was brought to completion when he was an assistant professor at the University of Nevada through collaboration with Amy Charkowski at the University of Wisconsin and Alan Collmer at CU. Alfano subsequently was a co-principal investigator on the NSF Plant Genome Research Program project that sequenced the complete DC3000 genome and characterized the type III effector repertoire. His lab led the genome-wide identification of type III effector genes in the draft genome of DC3000 using targeting-associated amino acid patterns and translocation tests to find and validate candidates, which was published in Proceeding of the National Academy of Sciences of the United States of America in 2002. Alfano and his lab members at the University of Nebraska contributed as either lead authors or coauthors to 15 research publications associated with the P. syringae pv. tomato DC3000 functional genomics project and thus played a major role in the community-wide development of DC3000 as a reference strain for molecular plant pathology research in the genomics era.
Alfano has made seminal contributions to our understanding of how the T3SS operates. These include the discovery in 1999 that the secretion of effectors in culture is dependent on temperature and pH levels that are associated with conditions in planta known to promote infection, that HrpK is secreted by the T3SS and appears to function as a translocator of effectors across the host plasma membrane (2005), and that HrpJ functions like homologs in animal pathogens in controlling T3SS substrate traffic (2006). In addition, the Alfano group has published a series of reports demonstrating that chaperones are important for the translocation of a significant subset of the DC3000 type III effectors. These findings have highlighted similarities between the T3SS of plant and animal pathogens.
In an effort that also began with the P. syringae pv. tomato DC3000 functional genomics project, Alfano and his collaborators in 2004 identified several of the DC3000 type III effectors that were capable of suppressing the hypersensitive response elicited by the nonpathogen Pseudomonas fluorescens expressing a cloned P. syringae T3SS and an effector conferring avriulence. The Alfano lab extended this type of analysis in 2009 to the entire repertoire of DC3000 type III effectors and discovered that a majority of the effectors is capable of suppressing at least one level of plant defense. This comprehensive analysis highlights the importance of host defense suppression in the virulence of P. syringae.
The Alfano group also has made major advances in elucidating the mechanisms by which individual effectors can suppress plant defenses. First, they reported in 2003 in Molecular Microbiology that HopAO1 (formerly HopPtoD2) is a protein tyrosine phosphatase and that a catalytic cysteine residue is required for phosphatase activity in vitro and for defense suppression activity in planta. Second, they reported in a 2007 article in Nature that HopU1 is a mono-ADP-ribosyltransferase that ADP-ribosylates several Arabidopsis thaliana RNA-binding proteins, including the glycine-rich protein GRP7. Furthermore, evidence based on both HopU1 and GRP7 mutants indicates that this activity is important for the ability of HopU1 to suppress plant defense. There is precedence for ADP-ribosyltransferase activity in some effectors produced by animal pathogens, but this was the first report of such an activity in a plant pathogen and the first report for an effector from any pathogen targeting RNA-binding proteins. Importantly, this finding indicates that type III effectors can manipulate post-transcriptional control of host RNA as a means to suppress defense. Finally, in 2010, the Alfano group reported the first plant pathogen effector, HopG1, to be targeted to the plant mitochondria.
Alfano has served the plant pathology community in other ways in addition to his research. He has written several insightful review articles. He teaches a variety of courses at the University of Nebraska, including undergraduate General Microbiology and graduate courses in the Genetics of Host-Microbe Interactions and Topics in Molecular Plant-Microbe Interactions. He has served on numerous NSF, USDA-NRI, and NIH grant panels and study sections. He has been an associate editor for Microbiology (2004–2006), a senior editor for Molecular Plant Pathology (2002–2007), and he has been serving as a senior editor for Molecular Plant-Microbe Interactions since 2007. His research has been funded by NSF, USDA-NRI, and NIH NIAID. Alfano received the 2005 Syngenta Award from The American Phytopathological Society and a 2010 Charles Bessey Distinguished Faculty Award from the University of Nebraska at Lincoln.
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