Cloning and Nucleotide Sequence of TZS a Cytokinin Biosynthetic Locus, from Agrobacterium Tumefaciens Strain T37

Abstract

Production of the phytohormone, trans-zeatin, by the plant pathogen, Agrobacterium tumefaciens, has been previously shown to be a nopaline Ti plasmid function. The gene determining the trans-zeatin secretion phenotype (tzs) in the bacterium has been cloned from the virulence region of pTiT37. The nucleotide sequence has been determined and contains an open reading frame of 729 bp, encoding a 27,545 dalton polypeptide. The tzs sequence shows 50% overall homology to the published T-DNA cytokinin locus, tmr, from pTiT37. While the tzs gene has a prokaryotic promoter and the tmr a eukaryotic promoter, both genes show the cytokinin biosynthetic activity, DNA transferase, by in vitro assay. Additionally, both genes confer the phenotype of trans-zeatin overproduction to their respective host cells (bacterial and plant). The tmr coding sequence has been fused to a phage promoter and bacteria containing this chimeric gene show high levels of trans-zeatin production. Other plant pathogens have been screened for the presence of tzs by both Southern hybridization and by assay for the secretion of trans-zeatin into the culture medium. Several strains from different genera have been found to contain a functional tzs gene.