The coexistence of symbiosis and pathogenicity-determining genes in Rhizobium rhizogenes strains enables them to induce nodules and tumors or hairy roots in plants.
Bacteria belonging to the family Rhizobiaceae may establish beneficial or harmful relationships with plants. The legume endosymbionts contain nod and nif genes responsible for nodule formation and nitrogen fixation, respectively, whereas the pathogenic strains carry vir genes responsible for the formation of tumors or hairy roots. The symbiotic and pathogenic strains currently belong to different species of the genus Rhizobium and, until now, no strains able to establish symbiosis with legumes and also to induce tumors or hairy roots in plants have been reported. Here, we report for the first time the occurrence of two rhizobial strains (163C and ATCC11325T) belonging to Rhizobium rhizogenes able to induce hairy roots or tumors in plants and also to nodulate Phaseolus vulgaris under natural environmental conditions. Symbiotic plasmids (pSym) containing nod and nif genes and pTi- or pRi-type plasmids containing vir genes were found in these strains. The nodD and nifH genes of the strains from this study are phylogenetically related to those of Sinorhizobium strains nodulating P. vulgaris. The virA and virB4 genes from strain 163C are phylogenetically related to those of R. tumefaciens C58, whereas the same genes from strain ATCC 11325T are related to those of hairy root-inducing strains. These findings may be of high relevance for the better understanding of plant-microbe interactions and knowledge of rhizobial phylogenetic history.
Departamento de Microbiología y Genética, Universidad de Salamanca, Salamanca, Spain. evp@usal.es
Encarna
E
Velázquez
Alvaro
A
Peix
José Luis
JL
Zurdo-Piñeiro
José Luis
JL
Palomo
Pedro F
PF
Mateos
Raúl
R
Rivas
Estefanía
E
Muñoz-Adelantado
Nicolás
N
Toro
Pablo
P
García-Benavides
Eustoquio
E
Martínez-Molina
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D020869:Gene Expression Profiling; D008969:Molecular Sequence Data; D027805:Phaseolus / Q000378:metabolism / Q000382:microbiology; D010802:Phylogeny; D018517:Plant Roots / Q000382:microbiology*; D010957:Plasmids / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012231:Rhizobium / Q000145:classification / Q000235:genetics* / Q000472:pathogenicity* / Q000502:physiology; D013559:Symbiosis / Q000235:genetics*; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S