Opines and Agrobacterium: Molecular Mechanisms that
Drive a Successful Microbe-Host Interaction.
We are interested in the problem of how the Ti plasmid insures that it carries the
genes for the catabolism of precisely those opines that are produced by the crown gall tumors
that it induces. Corollaries to this question include those concerning the origins of these
genes, and how they, and the activities of their products have been altered to provide the
functions required for opine synthesis by the plant and catabolism by the bacterium. To this
end, we have been studying the genes involved in the synthesis by the tumor, and the
catabolism by the bacterium of a family of four mannose-containing metabolites called the
mannityl opines. We have discovered that the three key genes responsible for catabolism of
these four opines are duplicates of the three genes, located in the T-region of the Ti
plasmid, responsible for the production of the opines by the crown gall tumors. These genes
are homologous at the DNA and protein sequence levels, and among two of the pairs, the two
proteins of each exhibit similar enzymatic activities. From an analysis of this system, and
also of a progenitor opine system, we have proposed a step-wise course of evolution of the
mannityl opine system. The evolution of this opine system, we suggest, has occurred as a
response by Agrobacterium to the emergence of other soil microflora that can utilize the
predecessors of the mannityl opines. Thus, in addition to providing us with information on
the current status of a microbe-host relationship, our studies give us clues as to how this
system evolved, as well as hints at the selection pressures in nature that led to this
genetic adaptation.
Recent publications relevant to this theme:
Hong, S.-B., Dessaux, Y., Chilton, W.S., and Farrand, S.K. Organization
and regulation of the mannopine cyclase-associated opine catabolism
genes in Agrobacterium tumefaciens strain 15955. J. Bacteriol.
175:401-410, 1993
Hong, S.-B., and Farrand, S.K. Functional role of the Ti plasmid-encoded
catabolic mannopine cyclase in mannityl opine catabolism by
Agrobacterium. J. Bacteriol. 176:3576-3583, 1994
Hong, S.-B. and Farrand, S.K. Purification and characterization of catabolic mannopine
cyclase encoded by the Agrobacterium tumefaciens Ti plasmid
pTi15955. J.Bacteriol. 178:2427-2430, 1996
Kim, K.-S. and Farrand, S.K. Ti plasmid-encoded genes responsible for
catabolism of the crown gall opine mannopine by Agrobacterium
tumefaciens are homologs of the T-region genes responsible for synthesis
of this opine by the plant tumor. J. Bacteriol. 178:3275-3284,
1996
Kim, K.-S., Chilton, W.S., and Farrand, S.K. A Ti plasmid-encoded enzyme
required for degradation of mannopine is functionally homologous to
the T-region-encoded enzyme required for synthesis of this opine in crown
gall tumors. J. Bacteriol. 178:3285-3292, 1996
Hong, S.-B., Hwang, I., Dessaux, Y., Guyon, P., Kim, K.-S., and Farrand, S. K. A T-DNA gene
required for agropine biosynthesis by transformed plants is functionally and evolutionarily
related to a Ti plasmid gene required for catabolism of agropine by Agrobacterium. J.
Bacteriol. 179:4831-4840, 1997.
Kim,H., and Farrand, S. K. Characterization of the acc operon from
the nopaline-type Ti plasmid pTiC58 of Agrobacterium
tumefaciens strain C58 which encodes utilization of agrocinopines
A+B and susceptibility to agrocin 84. J. Bacteriol.
179:7559-7572, 1997
Kim, H., and Farrand, S. K. Opine catabolic loci from
Agrobacterium plasmids confer chemotaxis to their cognate
substrates. Mol. Plant-Microbe Interact. 11:131-143, 1998.
Dessaux, Y., Petit, A., Farrand, S. K., and Murphy, P. J. Opines and
Opine-Like Molecules Involved in Plant-Rhizobiaceae
Interactions. In: H. P. Spank, A. Kondorosi, and P. J. J. Hooykaas,
(Eds). The Rhizobiaceae. Kluwer Academic Publishing Co.,
Dorrecht, The Neterlands, In press, 1998.