RESUMEN
Members of Gram-positive Actinobacteria cause economically important diseases to plants. Within the Rhodococcus genus, some members can cause growth deformities and persist as pathogens on a wide range of host plants. The current model predicts that phytopathogenic isolates require a cluster of three loci present on a linear plasmid, with the fas operon central to virulence. The Fas proteins synthesize, modify, and activate a mixture of growth regulating cytokinins, which cause a hormonal imbalance in plants, resulting in abnormal growth. We sequenced and compared the genomes of 20 isolates of Rhodococcus to gain insights into the mechanisms and evolution of virulence in these bacteria. Horizontal gene transfer was identified as critical but limited in the scale of virulence evolution, as few loci are conserved and exclusive to phytopathogenic isolates. Although the fas operon is present in most phytopathogenic isolates, it is absent from phytopathogenic isolate A21d2. Instead, this isolate has a horizontally acquired gene chimera that encodes a novel fusion protein with isopentyltransferase and phosphoribohydrolase domains, predicted to be capable of catalyzing and activating cytokinins, respectively. Cytokinin profiling of the archetypal D188 isolate revealed only one activate cytokinin type that was specifically synthesized in a fas-dependent manner. These results suggest that only the isopentenyladenine cytokinin type is synthesized and necessary for Rhodococcus phytopathogenicity, which is not consistent with the extant model stating that a mixture of cytokinins is necessary for Rhodococcus to cause leafy gall symptoms. In all, data indicate that only four horizontally acquired functions are sufficient to confer the trait of phytopathogenicity to members of the genetically diverse clade of Rhodococcus.
Asunto(s)
Sitios Genéticos/genética , Genómica , Plantas/microbiología , Rhodococcus/genética , Rhodococcus/patogenicidad , Análisis de Secuencia , Secuencia de Aminoácidos , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Secuencia Conservada , Evolución Molecular , Fusión Génica , Transferencia de Gen Horizontal/genética , Genoma Bacteriano/genética , Isopenteniladenosina/metabolismo , Datos de Secuencia Molecular , Operón/genética , Plásmidos/genética , Polimorfismo Genético , Rhodococcus/metabolismo , Rhodococcus/fisiologíaRESUMEN
The 2D crystal lattice structure and bias-dependent contrast of a chiral electron donor-acceptor-donor triad system, composed of two oligo(p-phenylene vinylene) electron donors and a perylenediimide electron acceptor (OPV4-PDI-OPV4), have been studied by means of scanning tunneling microscopy (STM) at the liquid-graphite interface. OPV4-PDI-OPV4 is ordered in rows and forms a well-ordered 2D crystal lattice structure. The electrical properties of the donor and acceptor parts are distinguished by the contrast in bias-dependent STM imaging.
