Further extension of the opine concept: Plasmids in Agrobacterium rhizogenes cooperate for opine degradation

Abstract

Primary hairy root tissues as well as aseptic hairy root culture lines contain specific compounds that have been biologically characterized as opines. These substances are agropine, mannopine, mannopinic acid, and agropinic acid; they have been synthesized and their electrophoretic behavior has been studied. Hairy root tissues also contain agrocinopines. According to the opine content of hairy root tissues, two types of Agrobacterium rhizogenes strains have been identified. Agropine-type strains (A4, 15834, HRI) elicit roots containing agropine, mannopine, mannopinic acid, and agropinic acid, whereas mannopine-type strains (8196, TR7, TR101) elicit roots containing only mannopine, mannopinic acid and agropinic acid. A. rhizogenes strains catabolize the opines whose synthesis they induce in the hairy root tissues. However, strain HRI only catabolizes agropine. Except for strain HRI, all A. rhizogenes strains studied contain three plasmids, of which the largest appears to be a cointegrate of the two others. Transconjugants of A. rhizogenes plasmids in A. tumefaciens have been obtained by selection on opines. Their properties have been studied and related to their plasmid content. In the mannopine strain C58C1(pRi8196), the virulence functions and the opine-related functions are located on the same plasmid (pRi8196). In agropine strains the catabolic functions are dissociated: agropine degradation is specified by the virulence plasmid, which also specifies opine synthesis in hairy root tissue, however, mannopine, mannopinic acid and agropinic acid degradation are specified by the smaller plasmid. Strain HRI contains only the virulence plasmid, which explains its inability to degrade mannopine, mannopinic acid, and agropinic acid.