Multiple mutations in the T region of the Agrobacterium tumefaciens tumor-inducing plasmid.

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Abstract
Three genetic loci affecting tumor morphology lie within pTiA6NC T-DNA: tms, tmr and tml. Using deletions and multiple transposon insertions, one constructed tumor-inducing (Ti) plasmids representing every possible double and triple mutant combination. tms tmr and tms tmr tml mutants did not incite tumors on most plants and produced a very weak response on a few other hosts, but tms tml and tmr tml mutants were virulent. tms+ or tmr+ alone can promote significant tumor growth, but tml+ by itself is not sufficient. On hosts where tms mutants induce tumors accompanied by shoot proliferation, addition of a tml mutation reduces or eliminates shoot proliferation, suggesting that tml+ promotes shoot development. The small calli incited by tms tmr and tms tmr tml mutants contain agropine, an indication that these plant cells incorporate T-DNA in the absence of substantial tumor growth.