LEAFY GALL FORMATION BY RHODOCOCCUS FASCIANS

Abstract

Rhodococcus fascians infects a wide range of plants, initiating the formation of leafy galls that consist of centers of shoot amplification and shoot growth inhibition. R. fascians is an epiphyte but it also can establish endophytic populations. Bacterial signals involved in symptom development initiate de novo cell division and shoot meristem formation in differentiated tissues. The R. fascians signals exert activities that are distinct from mere cytokinin effects, and the evidence points to a process that adopted cytokinin biosynthetic enzymes to form derivatives with unique activity. Genes implicated in leafy gall formation are located on a linear plasmid and are subject to a highly controlling, complex regulatory network, integrating autoregulatory compounds and environmental signals. Leafy galls are considered as centers with specific metabolic features, a niche where populations of R. fascians experience a selective advantage. Such "metabolic habitat modification" might be universal for gall-inducing bacteria.

Taxonomy, Physiology, and Natural Products of Actinobacteria

“…Since then, the symptoms caused by R. fascians in diverse plant species have been described (reviewed by Goethals et al [517]). The bacterium infects both monocot and dicot hosts, many of which are economically important (518).…”

A large, mobile pathogenicity island confers plant pathogenicity on Streptomyces species

“…The fas operon is required for the production of leafy galls by R. fascians on plants and evidently codes for a cytokinin biosynthetic pathway (Goethals et al, 2001). The presence of the fas operon on the S. turgidiscabies PAI was unexpected, as neither this pathogen nor the other species known to cause potato scab produce plant galls.…”

“…Homologues of the six genes in the plant fasciation ( fas) operon in Rhodococcus fascians were identified from the S. turgidiscabies PAI. In R. fascians these genes are located on a linear plasmid and comprise a cytokinin biosynthetic pathway that is required for leafy gall formation on plants (Crespi et al, 1992;Goethals et al, 2001). The S. turgidiscabies fas operon is colinear with the fas operon of R. fascians, with the exception of fas6, which appears to have undergone a rearrangement on the S. turgidiscabies chromosome.…”

Three Types of Antibiotics Produced from Rhodococcus erythropolis Strains

“…In the last few decades, the genus Rhodococcus, a member of Actinobacteria, has received considerable attention for its remarkable ability to degrade persistent chemicals such as polychlorinated biphenyls (PCBs) 14,15) and nitrophenols 4,11) ; the industrial application of nitrile hydratase that is synthesized by the members of this genus 13) has also been investigated. Previous research has also focused on the plant and mammalian pathogenic characteristics of some species belonging to this genus 3,16) . Extensive research and considerable progress have been reported in these fields.…”