Symbiotic characterization of isoleucine+valine and leucine auxotrophs of Sinorhizobium meliloti.
Ten isoleucine+valine and three leucine auxotrophs of Sinorhizobium meliloti Rmd201 were obtained by random mutagenesis with transposon Tn5 followed by screening of Tn5 derivatives on minimal medium supplemented with modified Holliday pools. Based on intermediate feeding, intermediate accumulation and cross-feeding studies, isoleucine+valine and leucine auxotrophs were designated as ilvB/ilvG, ilvC and ilvD, and leuC/leuD and leuB mutants, respectively. Symbiotic properties of all ilvD mutants with alfalfa plants were similar to those of the parental strain. The ilvB/ilvG and ilvC mutants were Nod-. Inoculation of alfalfa plants with ilvB/ilvG mutant did not result in root hair curling and infection thread formation. The ilvC mutants were capable of curling root hairs but did not induce infection thread formation. All leucine auxotrophs were Nod+ Fix-. Supplementation of leucine to the plant nutrient medium did not restore symbiotic effectiveness to the auxotrophs. Histological studies revealed that the nodules induced by the leucine auxotrophs did not develop fully like those induced by the parental strain. The nodules induced by leuB mutants were structurally more advanced than the leuC/leuD mutant induced nodules. These results indicate that ilvB/ilvG, ilvC and one or two leu genes of S. meliloti may have a role in symbiosis. The position of ilv genes on the chromosomal map of S. meliloti was found to be near ade-15 marker.
Hassani
Raad
R
Department of Biosciences & Biotechnology, Indian Institute of Technology, Roorkee 247 667, India.
Prasad
C Krishna
CK
Vineetha
K E
KE
Vij
Neeraj
N
Singh
Prachi
P
Sud
Reeteka
R
Yadav
Sangeeta
S
Randhawa
Gursharn S
GS
D004251:DNA Transposable Elements; D007532:Isoleucine / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism*; D000455:Medicago sativa / Q000382:microbiology*; D016296:Mutagenesis; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013559:Symbiosis; D014633:Valine / Q000378:metabolism*
D004251:DNA Transposable Elements; D007532:Isoleucine; D007930:Leucine; D014633:Valine