Plasmid-dependent temperature-sensitive phase in crown gall tumorigenesis.

Area of Science:

• Plant pathology
• Molecular biology
• Bacteriology

Background:

• Crown gall tumorigenesis is a complex process involving Agrobacterium tumefaciens and its plasmid pTiC58.
• A specific temperature-sensitive (ts) period during tumor development has been observed.
• The role of plasmid maintenance genes in this ts period was previously unclear.

Purpose of the Study:

• To investigate the role of temperature-sensitive (ts) genes on the pTiC58 plasmid in crown gall tumorigenesis.
• To determine if these genes are responsible for the observed 37°C ts period.
• To elucidate the mechanism underlying this temperature sensitivity.

Main Methods:

• Comparative analysis of tumors induced by different Agrobacterium tumefaciens strains with varying plasmid content and temperature resistance.
• Monitoring tumor development and temperature resistance at 32°C and 37°C.
• Incorporation of radiolabeled thymidine to assess plasmid replication at different temperatures.

Main Results:

• Tumors induced by wild-type strain C58 (carrying pTiC58) exhibit temperature sensitivity at 37°C between 96 and 168 hours post-infection.
• Replacing pTiC58 with a temperature-resistant plasmid (B(6)806) eliminated the 37°C sensitivity, with tumors becoming resistant by 96 hours.
• Mutating pTiC58 for temperature resistance at 37°C shortened the ts period, confirming the plasmid's role.
• [(3)H]-thymidine incorporation into pTiC58 was inhibited at 37°C but not 32°C, indicating impaired plasmid replication.

Conclusions:

• The temperature-sensitive period during crown gall tumorigenesis is directly controlled by ts plasmid maintenance genes on pTiC58.
• These genes are crucial for plasmid replication within incipient tumor cells during a specific developmental window.
• The transient nature of the ts period suggests a temporary requirement for these gene products, possibly linked to plasmid DNA integration into plant genetic material.