Agrobacterial ipt gene for cytokinin biosynthesis is found in phototrophic non-sulfur purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris

Abstract

Phototrophic non-sulfur bacteria (PNSB) are close relatives of cytokinin producing agrobacteria. However, the sequenced PNSB genomes do not have the ipt gene sequences involved in the cytokinin biosynthesis. In Rhodobacter sphaeroides and Rhodopseudomonas palustris transformed with ipt, we previously observed the substantial morphological and physiological changes as compared with the original strains. To find associations of these changes with the ipt function, its expression levels were studied in the transformants and the parent strains. Unexpectedly, the ipt transcripts were found in both the transformants and the original untransformed strains, although the ipt expression level was several orders of magnitude lower in the latter compared to the transformants. The ipt sequences amplified from the plasmid DNA templates of the parent PNSB strains showed that they were identical to each other but differed in four nucleotides compared to the ipt gene from the Agrobacterium tumefaciens pTiBo 542 plasmid. The in silico comparison amongst the ipt sequences from the other agrobacterial plasmids, as well as from the other PNSB, demonstrated their low identity. This is the first report on the active gene of the cytokinin biosynthesis found in Rba. sphaeroides and Rps. palustris which is homologous to the agrobacterial ipt gene.