Indian Journal of Experimental Biology Vol. 41, October 2003, pp. 1095-1100

Milestones in the genetical research on rhizobia

Gursham S Randhawa & Anvita Kumar

Department of Biotechnology, Indian Institute of Technology, Roorkee 247667, India

Phone:. 91-1332-285808; Fax: 91-1332-273560; E-mail: sharntbs@iitr.ernet.in

The first isolation of the rhizobial bacteria from the legume roots was done in 1888. Since then a large number of scientists have made efforts to understand the molecular basis of Rhizobium-legume symbiosis. The important developments of 115 years of genetical research on rhizobia have been listed in this article. •

Keywords: Legume, Nitrogen fixation, Rhizobium, Symbiosis

1888 • Assimilation of atmospheric nitrogen by root nodules demonstrated I • Isolation of root nodule bacteria by pure culture techniques; the name Bacillus radicicola proposed

for these bacteria2

1889 • Root nodule bacteria renamed as Rhizobium3

1921 • Rhizobia divided into fast- and slow- growing groups4

1954 • Gene transfer by transformation with linear DNA reported in Rhizobium by R. Balassa (cited by G. Balassa, 1963)5

1967 • Gene transfer by transduction reported in rhizobia6

• Gene transfer by conjugation reported in Rhizobium leguminosarum bv. trifolii; plasmid control of nodule forming ability suggested7

1968 • Gene transfer by conjugation reported in Rhizobium lupini8

1971 • Specialized transduction reported in Sino rhizobium meliloti9

1973 • Transformation of R. leguminosarum bv. trifolii with plasmid DNA to

1974 • P-group antibiotic resistance plasmid of Pseudomonas aeruginosa transferred by conjugation to R I · It . egummosarum

• Physical evidence for the presence of plasrnids in rhizobia presentedl2

1976 • Chromosomal recombination and mapping in R. leguminosarum reported l3

1977 • Construction of circular linkage map of the chromosome of S. meliloti l4, 15

• Large plasrnids detected in different Rhizobium species 16

1978 • Transposon Tn5 transferred to Rhizobium by the suicide plasmid vector pJB4JI17 ,

• Heat treatment method employed for isolating non-nodulating mutants of R. leguminosarum by. 1/ / trifolii l8

.. /

1096 INDIAN J EXP BIOL, OCTOBER 2003

• Construction of circular linkage map of the chromosome of R. leguminosarum 19

• Discovery of host specificity and nodule forming genes on plasmid pRLlJI of R. leguminosarum2o

1979 • Discovery of nodulation genes on plasmid in R. leguminosarum biovar trijoW21

• Generalized transduction reported in S. melilotp2 • Genes coding for nitrogenase enzyme located on a large plasmid of R. leguminosarum23

• Identification and characterization of large plasmids in S. meliloti24

1980 • Cowpea group Rhizobium species strain NGR234 found to nodulate the non-legume Parasponia25

• Homology of nitrogenase genes of different species of rhizobia demonstrated26

1981 • A general method described for site-directed mutagenesis of rhizobia27

• Nodulation and nitrogen fixation genes located on a megaplasmid in S. melilotP8.29 • R. trijolii plasmid containing nodulation genes transferred to R. leguminosarum and A. tumejaciens30

• S. meliloti nifH gene sequenced31

1982 • Slow-growing rhizobia placed under the genus Bradyrhizobium32 • Fast growing rhizobia isolated from root nodules of soybean in China3

)

• Cloning of nodulation genes of S. meliloti by complementation34

• Mobilization of the S. meliloti megaplasmid carrying nodulation and nitrogen fixation genes into other rhizobia and Agrobacterium35

• Construction of a broad host range cosrnid cloning vector for genetic analysis of Rhizobium36

1983 • Construction of improved suicide plasmid vectors for transposon Tn5 mutagenesis of rhizobia37• 38

• S. meliloti promoters studied by fusion to lacZ gene of E. coli39

• Symbiotic mutations located on chromosome of S. meliloti40

• nifH and nifDK genes found on separate operons in Bradyrhizobiumjaponicum41

1984 • Common nodulation genes of S. meliloti42 and R. leguminosarum43 sequenced • Pseudonodules formed on alfalfa by A. tumejaciens and E. coli containing S. meliloti genes44

• Transposon Tn5 found to specify streptomycin resistance in rhizobia45•46

1985 • Two megaplasmids detected in S. meliloti47

• Identification of nodDABC gene products of rhizobia48•49

• Mutants defective in exo-polysaccharide production found to induce ineffective nodules5o

1986 • Plant flavone, luteolin, found to induce expression of S. meliloti nodulation genes51

• S. meliloti nodulation genes found to be related to virulence genes of A. tumejaciens52

1987 • Plant signal interacting with nodD gene product identified53

• Physical characterization of S. meliloti megaplasmids54

• nijA gene of S. meliloti found to be oxygen regulated55

1988 • New genera Sinorhizobium56 and Azorhizobium57 recognized • C4-dicarboxylic acid transport genes of S. meliloti located58

•59

• Rhizobial extracellular signal (later called nod factor) stimulating mitosis of plant cells detected60• 61

1989 • Subcellular localization of nodD gene product in R. leguminosarum reported62

• A novel exo-polysaccharide having function in nodulation of alfalfa by S. meliloti identified63

RANDHA W A & KUMAR : MILESTONES IN GENETICAL RESEARCH ON RHIZOBIA

1990 • Identification of the molecular signal detennining host specificity of S. melilotl-64 • Genetic map of S. meliloti megaplasmid presented65

1991 • S. fredii gene nole involved in cultivar specific nodulation of soybean characterized66

1992 • Rhizobium species NGR234 strain found to synthesize a family of Nod factors67

• Development of high frequency chromosomal mobilization system in S. meliloti68

• Genetic mapping of symbiotic loci on S. meliloti chromosome69

• Mutational analysis of the S. meliloti nifA promoter70

1993 • Physical map of the genome of S. meliloti 1021 presented71

• Physical and genetic map of B. japonicum 110 genome presented72

1994 • Expression of insecticidal crystal protein gene from Bacillus thuringiensis in rhizobia73

1995 • Molecular analysis of the S. meliloti mucR gene carried oue4

1997 • New genus Mesorhizobium recognized75

• Complete nucleotide sequence of symbiotic plasmid of Rhizobium species NGR234 determined76

1097

• Natural endophytic association between R. leguminosarum biovar trifolii and rice roots discovered77• 78

1998 • A new genus Allorhizobium proposed79

• Succinoglycan found to be required for initiation and elongation of infection threads during nodulation of alfalfa by S. meliloti80

• noLO and noel of Rhizobium species NGR234 characterized81

2000 • Similar requirements of S. meliloti and a mammalian pathogen described82

• A close relation between Agrobacterium and Rhizobium discovered83

• Complete genome of Mesorhizobium loti sequenced84.

85

• Rhizobial inoculation found to increase growth of rice86

• Discovery of the dependence of alfalfa root nodule invasion efficiency on S. meliloti polysaccharides87

2001 • Complete genome of S. meliloti sequenced88, 89. 90

2002 • Complete genome of B. japonicum USDAIlO sequenced91

• Identification of two quorum-sensing systems in S. meliloti92

2003 • Expression of R. leguminosarum bv. viciae genes encoding for amino acid transporters found essential for symbiosis93

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81 Jabbouri S, Relic B, Hann M, Kamalaprija P, Burger U, Pome D, Prome J C & Broughton W J, noLO and noll (Hsn Ill) of Rhizobium sp. NGR234 are involved in 3-D­Carbamoylation and 2-D-Methylation of Nod factors, J Bio Chem, 273 (1998) 12047.

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84 Kaneko T, Nakamura Y, Sato S, Asamizu E, Kato T, Sasamoto S, Watanabe A, Idesawa K, Ishikawa A, Kawashima K, Kimura T, Kishida Y, Kiyokawa C, Kohara M, Matsumoto M, Matsuno A, Mochizuki Y, Nakayama S, Nakazaki N, Shimpo S, Sugimoto M, Takeuchi C, Yamada M & Tabata S, Complete genome structure of the nitrogen­fixing symbiotic bacterium Mesorhizobium loti, DNA Res, 7 (2000) 331.

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90 Barnett M J, Fisher R F, Jones T, Komp C, Abola A P, Barloy-Hubler F, Bowser L, Capela D, Galibert F, Gouzy J, Gurjal M, Hong A, Huizar L, Hyman R W, Kahn D, Kahn M L, Kalman S, Keating D H, Palm C, Peck M C, Surzycki R, Wells D H, Yeh K C, Davis R W, Federspiel N A & Long S R, Nucleotide sequence and predicted functions of the entire Sinorhizobium meliloti pSymA megaplasmid, Proc Natl Acad Sci, 98 (2001) 9883.

91 Kaneko T, Nakamura Y, Sato S, Minamisawa K, Uchiumi T, Sasamoto S, Watanabe A, Idesawa K, lriguchi M, Kawashima K, Kohara M, Matsumoto M, Shimpo S, Tsuruoka H, Wada T, Yamada M & Tabata S, Complete genomic sequence of nitrogen-fixing symbiotic bacterium Bradyrhizobium japonicum USDAllO, DNA Res, 9 (2002) 189.

92 Marketon M M & Gonzalez J E, Identification of two quorum-sensing systems in Sinorhizobium meliloti, 184 (2002) 3466.

93 Lodwig E M, Hosie A H F, Bourdes A, Findlay K, Allaway D, Karunakaran R, Downie J A & Poole P S, Amino-acid cycling drives nitrogen fixation in the legume-Rhizobium symbiosis, Nature , 422 (2003) 722.