TEMPERATURE AFFECTS THE T-DNA TRANSFER MACHINERY OF AGROBACTERIUM-TUMEFACIENS

Early studies on Agrobacterium tumefaciens showed that development of tumors on plants following infection by A. tumefaciens was optimal at temperatures around 22 degrees C and did not occur at temperatures abo ve 29 degrees C. To assess whether this inability to induce tumors is due to a defect in the T-DNA transfer machinery, mobilization of an in compatibility group Q (IncQ) plasmid by the T-DNA transfer machinery o f A. tumefaciens was tested at various temperatures. Optimal transfer occurred when matings were performed at 19 degrees C, and transfer was not seen when matings were incubated above 28 degrees C. Transfer of the IncQ plasmid was dependent upon induction of the virB and virD ope rons by acetosyringone but was not dependent upon induction of the tra genes by octopine. However, alterations in the level of vir gene indu ction could not account for the decrease in transfer with increasing t emperature. A. tumefaciens did successfully mobilize IncQ plasmids at higher temperatures when alternative transfer machineries were provide d. Thus, the defect in transfer at high temperature is apparently in t he T-DNA transfer machinery itself. As these data correlate with earli er tumorigenesis studies, we propose that tumor suppression at higher temperatures results from a T-DNA transfer machinery which does not fu nction properly.