The TR-DNA region carrying the auxin synthesis genes of the Agrobacterium rhizogenes agropine-type plasmid pRiA4: nucleotide sequence analysis and introduction into tobacco plants

Abstract

We have determined the nucleotide sequence of a 6-kilobase fragment of the Agrobacterium rhizogenes plasmid pRiA4 TR-region that carries genes (aux1 and aux2) responsible for auxin biosynthesis in transformed plant cells. Sequence analysis revealed two open reading frames corresponding to proteins of 749 amino acids for the aux1 gene and 466 amino acids for the aux2 gene. We observed significant similarity between the amino acid sequences deduced from the pRiA4 aux genes and those of the auxin biosynthesis genes of A. tumefaciens octopine-type Ti plasmids, the iaaM and iaaH genes of Pseudomonas savastanoi, and different genes of the pRiA4 TL-region; however, the 5'-flanking regions of the pRi and pTi auxin biosynthesis genes were found to be completely different. Transgenic tobacco plants containing this entire 6-kilobase fragment of the pRiA4 TR-region have been obtained. Regenerated plants are phenotypically normal. The aux1 gene is not or is very weakly expressed in these plants, but expression of the aux2 gene leads to a modified root phenotype when plants are grown on medium containing an auxin precursor (naphthalene acetamide).