Fasciation induction by the phytopathogen Rhodococcus fascians depends upon a linear plasmid encoding a cytokinin synthase gene.

Abstract

Rhodococcus fascians is a nocardiform bacteria that induces leafy galls (fasciation) on dicotyledonous and several monocotyledonous plants. The wild‐type strain D188 contained a conjugative, 200 kb linear extrachromosomal element, pFiD188. Linear plasmid‐cured strains were avirulent and reintroduction of this linear element restored virulence. Pulsed field electrophoresis indicated that the chromosome might also be a linear molecule of 4 megabases. Three loci involved in phytopathogenicity have been identified by insertion mutagenesis of this Fi plasmid. Inactivation of the fas locus resulted in avirulent strains, whereas insertions in the two other loci affected the degree of virulence, yielding attenuated (att) and hypervirulent (hyp) bacteria. One of the genes within the fas locus encoded an isopentenyltranferase (IPT) with low homology to analogous proteins from Gram‐negative phytopathogenic bacteria. IPT activity was detected after expression of this protein in Escherichia coli cells. In R.fascians, ipt expression could only be detected in bacteria induced with extracts from fasciated tissue. R.fascians strains without the linear plasmid but containing this fas locus alone could not provoke any phenotype on plants, indicating additional genes from the linear plasmid were also essential for virulence. These studies, the first genetic analysis of the interaction of a Gram‐positive bacterium with plants, suggest that a novel mechanism for plant tumour induction has evolved in R.fascians independently from the other branches of the eubacteria.

Bacterial and Plant Signal Integration via D3-Type Cyclins Enhances Symptom Development in the Arabidopsis-Rhodococcus fasciansInteraction

“…The bacteria disturb the plant's hormone balance by producing morphogenic signals, such as auxins and cytokinins, that provoke the outgrowth of existing and the development of new shoot meristems de O Manes et al, 2001;Vandeputte et al, 2005;Pertry et al, 2009), ultimately leading to the establishment of a leafy gall. In strain D188, virulence is conferred by a linear plasmid, pFiD188, that harbors the fasciation (fas) genes essential for cytokinin biosynthesis and symptom development (Crespi et al, 1992;Stange et al, 1996;Pertry et al, 2010). The bacteria secrete a mixture of synergistically acting cytokinins, some of which accumulate in infected plant tissues (Pertry et al, 2009).…”

Physical map of the Clostridium beijerinckii (formerly Clostridium acetobutylicum) NCIMB 8052 chromosome

“…However, several exceptions to this general rule have been described. Some bacteria, such as Borrelia burgdorferi and Rhodococcus fascians, have linear chromosomes (4,20,24), whereas Streptomyces lividans and Streptomyces coelicolor have linear chromosomes that may become circular as a result of deletions spanning both telomeres (34,35). Still others, such as Brucella melitensis and Leptospira interrogans, have segmented genomes (40, 63).…”

Molecular Biology of Borrelia burgdorferi

“…Recently analysis of entire Agrobacterium tumefaciens C58 genome revealed presence of one 2.1-Mb linear and one 3-Mb circular plasmid (Servent et al; and it has been shown that rhodococcus fascians contains 4 Mb linear chromosome (Crespi et al;. Presence of several linear plasmids seems the segmentation of Borrelias DNA to several linear pieces has led to the suggestion that the relatively small linear chromosome and the linear plasmids actually are minichromosoms.…”