title: Common evolutionary origin of the central portions of the Ri TL-DNA of Agrobacterium rhizogenes and the Ti T-DNAs of Agrobacterium tumefaciens.
abstract: Analysis of published sequences for Ri TL-DNA (root-inducing left-hand transferred DNA) of Agrobacterium rhizogenes revealed several unsuspected structural features. First, Ri TL-DNA genes are redundant. Using redundancy as a criterion, three regions (left, middle and right) were discerned. The left one, ORFs (open reading frames) 1-7, contains no detectable redundancy. In the middle region a highly diverged gene family was detected in ORFs 8, 11, 12, 13 and 14. The right region contains an apparently recent duplication (ORF 15 =18+17). We interpret the phenomenon of redundancy, particularly in the central region that encodes the transformed phenotype, to be an adaptation that ensures function in a variety of host species. Comparison of Ri TL-DNA and Ti T-DNAs from Agrobacterium tumefaciens revealed common structures, unpredicted by previous nucleic acid hybridization studies. Ri TL-DNA ORF 8 is a diverged Ti T-DNA tms1. Both Agrobacterium genes consist of a member of the diverged gene family detected in the central part of the Ri TL-DNA, but fused to a sequence similar to iaaM of Pseudomonas savastonoi. Other members of this gene family were found scattered throughout Ti T-DNA. We argue that the central region of Ri and the part of Ti T-DNA including ORFs 5-10 evolved from a common ancestor. We present the hypothesis that the gene family encodes functions that alter developmental plasticity in higher plants.
authors.affiliation: Laboratoire de Biologie de la Rhizosphère, Institut National de la Recherche Agronomique, 78000, Versailles, France.
authors.forename: H
authors.initials: H
authors.lastname: Levesque
authors.forename: P
authors.initials: P
authors.lastname: Delepelaire
authors.forename: P
authors.initials: P
authors.lastname: Rouzé
authors.forename: J
authors.initials: J
authors.lastname: Slightom
authors.forename: D
authors.initials: D
authors.lastname: Tepfer