Agrobacterium tumefaciens increases cytokinin production in plastids by modifying the biosynthetic pathway in the host plant

Proc Natl Acad Sci U S A. 2005 Jul 12;102(28):9972-7. doi: 10.1073/pnas.0500793102. Epub 2005 Jul 5.


Agrobacterium tumefaciens infects plants and induces the formation of tumors called "crown galls" by integrating the transferred-DNA (T-DNA) region of the Ti-plasmid into the plant nuclear genome. Tumors are formed because the T-DNA encodes enzymes that modify the synthesis of two plant growth hormones, auxin and cytokinin (CK). Here, we show that a CK biosynthesis enzyme, Tmr, which is encoded by the Agrobacterium T-DNA region, is targeted to and functions in plastids of infected plant cells, despite having no typical plastid-targeting sequence. Evidence is provided that Tmr is an adenosine phosphate-isopentenyltransferase (IPT) that creates a new CK biosynthesis bypass by using 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate (HMBDP) as a substrate. Unlike in the conventional CK biosynthesis pathway in plants, trans-zeatin-type CKs are produced directly without the requirement for P450 monooxygenase-mediated hydroxylation. Consistent with the plastid localization of Tmr, HMBDP is an intermediate in the methylerythritol phosphate pathway, a plastid-localized biosynthesis route for universal isoprenoid precursors. These results demonstrate that A. tumefaciens modifies CK biosynthesis by sending a key enzyme into plastids of the host plant to promote tumorigenesis.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenine Nucleotides / metabolism
  • Agrobacterium tumefaciens / enzymology*
  • Alkyl and Aryl Transferases / metabolism*
  • Arabidopsis / microbiology*
  • Bacterial Proteins / metabolism*
  • Blotting, Western
  • Cytokinins / biosynthesis*
  • Genetic Vectors
  • Green Fluorescent Proteins
  • Oncogene Proteins / metabolism*
  • Organophosphates / metabolism
  • Plant Tumor-Inducing Plasmids / genetics*
  • Plant Tumors / genetics*
  • Plant Tumors / microbiology


  • 4-hydroxy-3-methyl-2-butenyl diphosphate
  • Adenine Nucleotides
  • Bacterial Proteins
  • Cytokinins
  • LSO protein, Agrobacterium tumefaciens
  • Oncogene Proteins
  • Organophosphates
  • Green Fluorescent Proteins
  • Alkyl and Aryl Transferases
  • adenylate isopentenyltransferase