The society grants this honor to a current APS member in recognition of distinguished contributions to plant pathology or to The American Phytopathological Society. Fellow recognition is based on significant contributions in one or more of the following areas: original research, teaching, administration, professional and public service, and/or extension and outreach.
Jin-Rong Xu was born in Zhejiang Province, China, received BS (1984) and MS (1987) degrees from Beijing Agricultural University and a PhD (1994) from Kansas State University. Following postdoctoral work at Purdue University and fungicide target research at Novartis, he joined Purdue University in 1999 and currently is a professor of botany and plant pathology.
Xu pioneered research on the molecular genetics and cell biology of fungal pathogens. During infection, pathogens recognize signals from both the environment and the host plant to overcome defense responses and invade. Xu has made important contributions in three major areas: characterization of conserved signaling pathways that are critical for infection and developmental processes in fungi; genomics approaches to study fungal pathogens; and the recent discovery of A-to-I RNA editing in Fusarium graminearum and other ascomycetes.
Xu characterized MAP kinase (MAPK) signaling pathways in the rice blast fungus Magnaporthe oryzae and the wheat scab fungus F. graminearum. He was the first to demonstrate that PMK1 (a MAPK) regulates appressorium formation and invasive growth in M. oryzae. The regulatory role of this pathway during appressorium formation in diverse fungi has been shown subsequently by others. This MAPK pathway is conserved in non-appressorium-forming fungi, where it regulates invasive growth and pathogenesis. Xu's group identified and characterized additional components of the PMK1 pathway in M. oryzae, including the upstream receptor, adaptor protein, and downstream transcription factors, making it one of the best-characterized MAP kinase pathways in plant-pathogenic fungi. Results from his studies also led to a better understanding of cAMP-PKA signaling in hyphal growth and its relationship with the PMK1 cascade during appressorium formation and plant infection. Contrary to popular belief, loss of PKA activities by deletion of both catalytic subunits is not lethal but causes severe growth defects due to the requirement of PKA phosphorylation of SFL1 to relieve its repressor function. In F. graminearum, besides being essential for plant infection, both the cAMP signaling and FMK1 MAP kinase pathways play critical roles in regulating synthesis of the trichothecene mycotoxin deoxynivalenol (DON) and sexual reproduction.
Xu's pioneering studies of MAP kinase signaling have helped make M. oryzae the best-characterized system for studying the cAMP signaling and MAP kinase pathways among plant-pathogenic fungi. One of the MAP-kinase pathways centered on MPS1 was first characterized by Xu and plays an essential role in regulating plant penetration and infectious growth. MPS1 is important for cell wall integrity and responses to nutrients and stresses. In M. oryzae it regulates conidiation during vegetative growth and expression of effector genes during invasive growth in planta. Expression of the HopAI-1 MAPK inhibitor blocks cell-to-cell movement of invasive hyphae. Although the third MAP kinase gene is dispensable for pathogenesis in M. oryzae, its ortholog FgOS-2 is essential for plant infection and sexual reproduction in F. graminearum, demonstrating species-specific functions of this highly conserved MAP kinase pathway. Xu showed that phenylpyrrole fungicides such as fludioxonil and fenpiclonil function by over-stimulating the OS-2 MAP kinase in Neurospora crassa. Mutations in this pathway confer resistance to phenylpyrrole and vinclozoline fungicides, showing the feasibility to develop fungicides targeting this MAP kinase pathway.
Xu has been actively involved in genomics and functional genomics studies of plant-pathogenic fungi. He was a co-author on genome sequence publications for M. oryzae, F. graminearum, F. oxysporum, F. verticillioides, Puccinia striiformis f. sp. tritici, Peltaster fructicola, Valsa mali, and Ustilaginoidea virens. The systematic characterization of all protein kinase genes in F. graminearum by his lab was the first kinome-wide study in plant-pathogenic fungi. Deletion mutants were identified for many kinase genes that were assumed to be essential for hyphal growth because of the essential roles of their yeast orthologs in the cell cycle, indicating that cell cycle regulation and cytokinesis differ between Saccharomyces cerevisiae and filamentous fungi. Xu's group also demonstrated that cell cycle regulation differs between vegetative and infectious hyphae in F. graminearum. Recently, Xu's group generated mutants for all of the hypothetical proteins unique to F. graminearum and characterized all the predicted GPCR genes.
A recent major discovery by Xu is the identification of A-to-I RNA editing in F. graminearum. A-to-I RNA editing was considered unique to animals because fungi and plants lack genes encoding ADAR (adenosine deaminase acting on RNA). Xu's group identified genome-wide A-to-I RNA editing events that occur during sexual reproduction in F. graminearum, F. verticillioides, and N. crassa. Unlike RNA editing in animals, the majority of A-to-I editing events in F. graminearum and N. crassa are in coding regions and result in changes that are adaptive and beneficial. Many of these editing sites are in genes specifically expressed or upregulated during sexual reproduction. In F. graminearum, 69 genes including the RID1 ortholog essential for repeat-induced point mutation, have a UAG stop codon in their ORFs that requires stage-specific editing to UGG to encode functional proteins in developing perithecia. Xu's group also showed that RNA editing may be functionally related to other sexual stage-specific genetic or epigenetic phenomena such as spore killer, RIP, and meiotic silencing of unpaired DNA. Because fungal genomes lack ADAR orthologs that have both adenosine deaminase and dsRNA binding domains, A-to-I editing in filamentous ascomycetes must involve novel molecular mechanisms or enzymes.
Xu has published 140 peer-reviewed papers since 1993, collectively cited more than 10,000 times. In addition to his voluminous groundbreaking research, Xu has served the scientific community and APS as an editor for journals, mentor to graduate students and postdocs and member of scientific committees. He currently is an editor of PLoS Pathogens and MPMI for APS, served on two APS committees and was associate and senior editor of the APSnet Education Center and the Plant Health Instructor. Xu's outstanding record of scientific achievement and service is highly deserving of recognition as a fellow of APS.
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