Succinamopine: a new crown gall opine

Area of Science:

• Microbiology
• Plant Pathology
• Molecular Biology

Background:

• Agrobacterium tumefaciens incites plant tumors by transferring plasmid DNA to plant cells.
• Tumor cells synthesize novel metabolites called opines, which the bacteria can catabolize.
• Opine synthesis and catabolism patterns are determined by genes on the pathogen's tumor-inducing (Ti) plasmids.

Purpose of the Study:

• To investigate anomalous Agrobacterium tumefaciens strains (AT181, EU6, T10/73) whose Ti plasmids encode nopaline degradation but whose incited tumors do not synthesize nopaline.
• To identify the novel opine synthesized by these strains and characterize the genetic basis for its metabolism.

Main Methods:

• Southern blot hybridization was used to compare the DNA of the AT181 Ti plasmid with the nopaline synthase gene of pTi T37.
• Opine analysis was performed on tumors incited by the studied strains.
• Catabolism assays were conducted using various Agrobacterium tumefaciens strains and plasmids to test for the degradation of identified opines.

Main Results:

• Southern blot analysis confirmed that the AT181 Ti plasmid lacks homology to the nopaline synthase gene.
• Tumors incited by strains AT181, EU6, and T10/73 synthesized a novel opine, designated succinamopine, structurally analogous to nopaline.
• The Ti plasmids of strains AT181, EU6, and T10/73 were found to encode the ability to catabolize succinamopine, succinamopine lactam, and succinopine lactam.

Conclusions:

• The studied Agrobacterium tumefaciens strains represent a distinct group characterized by the synthesis and catabolism of succinamopine, rather than nopaline.
• These strains possess novel Ti plasmids, proposed to be designated as succinamopine Ti plasmids.
• This finding expands the known diversity of opine types and their associated genetic determinants in Agrobacterium tumefaciens.