Timothy W. McNellis, Ph.D.

  • Associate Professor
Timothy W. McNellis, Ph.D.
318 Buckhout Lab (office)
307 Buckhout Lab (lab)

University Park, PA 16802
Work Phone: 814-863-7646
Fax: 814-863-7217

Areas of Expertise

  • Fire blight resistance in apple trees
  • Biologically-based approaches to fire blight disease control
  • Development of citrus greening-resistant citrus varieties
  • Molecular genetics of Erwinia amylovora pathogenicity
  • Development of tomatoes resistant to bacterial canker disease
  • Understanding rootstock-scion interactions in grafted apple trees


  1. B.A., Biology, Johns Hopkins University, 1989
  2. Ph.D., Biology, Yale University, 1995

Areas of Interest

Molecular basis of plant responses to phytopathogenic bacteria
Molecular mechanisms of bacterial pathogenesis in plants
Fire blight disease of apples

Program Interests

My research group studies the interaction of plants with bacterial pathogens at the molecular level.  The overall goal of our research is to improve our understanding of how plants resist bacterial pathogens and how bacterial pathogens cause disease in plants.  We primarily study the disease of apples and pears called fire blight, which is caused by the bacterium Erwinia amylovora.  Other current research topics include citrus greening disease and bacterial canker of tomatoes.

Recent Publications

Klee, S.M., Mostafa, I., Chen, S., Dufresne, C., Lehman, B.L., Sinn, J.P., Peter, K.A., and McNellis, T.W. (2018) An Erwinia amylovora yjeK mutant exhibits reduced virulence, increased chemical sensitivity and numerous environmentally dependent proteomic alterations.  Molecular Plant Pathology 19:1667-1678

Ramos, L. S., Sinn, J. P., Lehman, B. L., Pfeufer, E. E., Peter, K. A., and McNellis, T. W. (2015).  Erwinia amylovora pyrC mutant is virulent despite pyrimidine auxotrophy.  Letters in Applied Microbiology 60:572-279, DOI:10.1111/lam.12417

Kaja, E., Szczesniak, M. W., Jensen, P. J., Axtell, M. J., McNellis, T. W., and Makalowska, I. (2015)  Identification of apple miRNAs and their potential role in fire blight resistance.  Tree Genetics & Genomes 11:812, DOI 10.1007/s11295-014-0812-3

Ramos, L. S., Lehman, B. L., Peter, K. A., and McNellis, T. W. (2014)  Mutation of the Erwinia amylovora argD gene causes arginine auxotrophy, nonpathogenicity in apples, and reduced virulence in pears.  Applied and Environmental Microbiology 80:6739-6749

Jensen, P. J., Fazio, G., Altman, N., Praul, C., and McNellis, T. W. (2014)  Mapping in an apple (Malus x domestica) F1 segregating population based on physical clustering of differentially expressed genes.  BMC Genomics 15:261

Ramos, L. S., Lehman, B. L., Sinn, J. P., Pfeufer, E. E., Halbrendt, N. O., and McNellis, T. W. (2013) The fire blight pathogen Erwinia amylovora requires the rpoN gene for pathogenicity in apple.  Molecular Plant Pathology 14:838-843

Singh, D. K, Laremore, T. N., Smith, P. B., Maximova, S. N., and McNellis, T. W. (2012) Knockdown of FIBRILLIN4 gene expression in apple decreases plastoglobule plastoquinone content.  PLoS One 7:e47547

Jensen, P. J., Halbrendt, N., Fazio, G., Makalowska, I., Altman, N., Praul, C., Maximova, S. N., Ngugi, H. K., Crassweller, R. M., Travis, J. W., and McNellis, T. W. (2012).  Rootstock-regulated gene expression patterns associated with fire blight resistance in apple.  BMC Genomics 13:9

Singh, D. K., and McNellis, T. W. (2011).  Fibrillin protein function: the tip of the iceberg? Trends in Plant Science 16:432-441

Research Interests

Biology and Ecology of Plant-Microbe and Plant-Environment Interactions
Host Resistance and Crop Biotechnology
Microbial Genomics and Informatics
Microbe-Host Interactions and Ecosystem Effects Faculty

Bacterial interactions with plants during diseases such as fire blight and citrus greening

Microbial Genomics, Evolution and Bioinformatics Faculty

Genomic approaches to understand Erwinia amylovora virulence mechanisms