The regulatory VirA protein of Agrobacterium tumefaciens does not function at elevated temperatures

• Published in: Journal of Bacteriology Vol. 175; no. 21; pp. 6830 - 6835
• Main Authors: Jin, S.G, Song, Y.N, Deng, W.Y, Gordon, M.P, Nester, E.W
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.11.1993
• Subjects: AGROBACTERIUM TUMEFACIENS; Agrobacterium tumefaciens - genetics; Agrobacterium tumefaciens - metabolism; Agronomy. Soil science and plant productions; BACTERIA; Bacterial plant pathogens; Bacterial Proteins - biosynthesis; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; CALOR; CHALEUR; DNA-Binding Proteins; EXPRESION GENICA; EXPRESSION DES GENES; Flowers & plants; FOSFORILACION; Fundamental and applied biological sciences. Psychology; Genes, Bacterial; Genetics; Infections; KALANCHOE; Kinetics; LOCI; LOCUS; Molecules; NEOPLASMAS; NEOPLASME; PHOSPHORYLATION; Phytopathology. Animal pests. Plant and forest protection; Plant Tumors - microbiology; Plants - microbiology; Plasmids; PODER PATOGENO; POUVOIR PATHOGENE; Promoter Regions, Genetic; PROTEINAS; PROTEINE; Restriction Mapping; SINTOMAS; SYMPTOME; Systematics. Structure, properties and multiplication. Genetics; Thermodynamics; Transcription Factors; Virulence Factors; Temperature; Plant pathogen; Crassulaceae; Agrobacterium tumefaciens; Vegetal microorganism relation; Environmental factor; Tumorigenicity; Gene expression; Thermal sensibility; Signal transduction; Dicotyledones; Angiospermae; Bacteria; Spermatophyta; Rhizobiaceae; Inhibition; Kalanchoe
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.175.21.6830-6835.1993

Previous studies have shown that Agrobacterium tumefaciens causes tumors on plants only at temperatures below 32 degrees C, and virulence gene expression is specifically inhibited at temperatures above 32 degrees C. We show here that this effect persists even when the virA and virG loci are expressed under the control of a lac promoter whose activity is temperature independent. This finding suggests that one or more steps in the signal transduction process mediated by the VirA and VirG proteins are temperature sensitive. Both the autophosphorylation of VirA and the subsequent transfer of phosphate to VirG are shown to be sensitive to high temperatures ( 32 degrees C), and this correlates with the reduced vir gene expression observed at these temperatures. At temperatures of 32 degrees C and higher, the VirA molecule undergoes a reversible inactivation while the VirG molecule is not affected. vir gene induction is temperature sensitive in an acetosyringone-independent virA mutant background but not in a virG constitutive mutant which is virA and acetosyringone independent. These observations all support the notion that the VirA protein is responsible for the thermosensitivity of vir gene expression. However, an Agrobacterium strain containing a constitutive virG locus still cannot cause tumors on Kalanchoe plants at 32 degrees C. This strain induces normal-size tumors at temperatures up to 30 degrees C, whereas the wild-type Agrobacterium strain produces almost no tumors at 30 degrees C. These results suggest that at temperatures above 32 degrees C, the plant becomes more resistant to infection by A. tumefaciens and/or functions of some other vir gene products are lost in spite of their normal levels of expression