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United States Department of Agriculture

Agricultural Research Service

ROBERT E. DAVIS

Research Leader

USDA-ARS-PSI-MPPL
robert.davis@ars.usda.gov
(301)504-6290 Robert E. Davis

Phytoplasmas (mycoplasmalike organisms, MLOs) and spiroplasmas are plant pathogenic, cell wall-less bacteria that underwent massive reductions in genome size during their evolution from walled bacterial ancestors. Thus, these unusual microbes possess genomes that are among the smallest known in bacteria, approaching the minimal sets of genes required for cellular life and parasitism in plants and insects. The loss of genetic material over evolutionary time was accompanied by the gain of new capabilities enhancing host adaptation and conferring potentials for pathogenicity in insect vectors and plant hosts.

Areas of my personal research interest in phytoplasmas and spiroplasmas are:

  • Genomic events leading to evolutionary emergence of a new life form-phytoplasmas
  • Gene degradation and the loss of biosynthetic pathways that resulted in small genomes and obligate intracellular life styles
  • Expansion of functions carried out by genes that were retained through evolution
  • Acquisition of genes encoding new functions that enabled host adaptations and pathogenicity in insects and plants
  • Transfer of virulence factors through extrachromosomal DNA
  • Identification of pathogen proteins as potential targets for new, safe disease control measures
  • Molecular markers of genus and species level evolutionary divergence
  • Detection, classification, identification, and taxonomy of phytoplasmas in diseases of unsolved causeLI>

 

Through this research, we look forward to gaining new fundamental understanding of the evolutionary emergence of spiroplasmas and phytoplasmas, and to providing molecular markers and tools for improving detection and identification of the pathogens..

Diseases studied include; grapevine yellows, corn stunt

Our results should help:

  • Predict their pathogenic potentials
  • Improve pathogen detection and molecular taxonomy of wall-less bacteria
  • Target pathogen proteins for molecular disease control 
  • Enhance implementation of quarantine measures and aid disease management.

As Research Leader of the Molecular Plant Pathology Laboratory, I have the privilege to oversee a cutting edge research program that address disease problems due to subcellular pathogens (viruses and viroids) and cellular pathogens (fungi, walled bacteria, and wall-less bacteria). All of these research projects are aimed at gaining new knowledge that will make it possible to devise novel, safe and healthy means to reduce the damage caused by diseases of plants in our agricultural and natural ecosystems. One of these research projects, utilizing virus-based gene vectors to express foreign genes in plants, has the further beneficial objective of enabling vaccine production in plants to protect animal and human health.


 

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Diagrammatic representation of plasmid pSKU146 from Spiroplasma kunkelii strain CR2-3X.  Diagram shows potential protein coding regions (arrows), recognition sites for selected endonuclease enzymes, and locations of DNA sequences potentially forming stem-loop or hairpin structures.  

From: Davis RE, Dally EL, Jomantiene R, Zhao Y, Roe B, Lin S, and Shao J. 2005. Cryptic plasmid pSKU146 from the wall-less plant pathogen Spiroplasma kunkelii encodes an adhesin and components of a type IV translocation-related conjugation system. PLASMID 53:179-190.
picture of Spiroplasma kunkelli Plasmid
Symptoms of grapevine yellows disease in grapevine



Symptoms of grapevine yellows disease in grapevine


Last Modified: 11/5/2010