Chemical Studies on the Infection Mechanism of Crown Gall Disease

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1. Agrobacterium tumefaciens is a soil bacterium which induces crown gall tumors in a wide variety of dicotyledonous plants. This tumorigenic interaction between the bacterium and the plant is a natural example of the genetic engineering of eukaryotes. Indeed, the oncogenic bacterium harbors a large Ti plasmid, whose T-DNA region is transferred to and integrated into the plant genome during tumorous transformation. However, very little information is available concerning the early process leading to tumor formation. In order to study further the mechanism of tumor induction, it is necessary to develop a chemical probe that will help in exploring the early steps of tumor formation. We searched transformation inhibitors which do not inhibit the growth of A. tumefaciens and are nontoxic against the transformed plant cells.2. A few esters derived from oxazolomycin isolated from Streptomyces sp. KBFP-2025 as well as two active compounds of bisanthraquinone type, julichrome Q_<1・3> and julimycin B-II, isolated from Streptomyces sp. TM-71, inhibit crown gall formation, but are nontoxic against this bacterium and the host plant.3. These compounds administered to a potato disk 12 - 24 hours after the inoculation of the bacterium hardly inhibited crown gall formation, and no longer necrosed the potato disk. This suggests that these compounds act on any step of transformation process, but have no toxicity toward transformed plant cells whose genome has integrated the T-DNA of A. tumefaciens. It is probable that the transformation process of this system is completed within 12 - 24 hours after the inoculation. For a direct proof of this hypothesis, a quantitative microanalytical method of opines, indices of transformation, has to be established. This method involves HPLC analysis of fluorescent compound formed by reaction of benzoin with guanidino group of the characteristic amino acid. Time course of transformation will be possibly traced by this method.