Leghemoglobin and Rhizobium Respiration

Appleby, Cyril A.

doi:10.1146/annurev.arplant.35.1.443

Cited by 178 publications

(215 citation statements)

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“…Given the high sequence conservation between the soybean leghemoglobin genes it is all the more interesting that they are not regulated in the co-ordinate manner that seems to be the case for the more divergent alfalfa leghemoglobin genes. However, this might reflect different roles for leghemoglobins in the soybean nodule, since it has been shown that there is a correlation between the oxygen affinity of a particular leghemoglobin and its relative abundance in young versus old soybean nodules [2]. Unfortunately, since oxygen-affinity data are unavailable for alfalfa 769 leghemoglobins we are unable to compare the situation in soybean with that in alfalfa.…”

Section: Discussionmentioning

confidence: 96%

“…However, to date, the functions of only a handful of nodulins have been established. These include uricase from soybean [4], glutamine synthetase from kidney bean [9] and leghemoglobin, the highaffinity oxygen-binding heme protein whose function appears to be both to assure a sufficient flux of oxygen for bacterial respiration and to create the microaerobic environment necessary for nitrogenase activity [2]. Leghemoglobin has been identified in all leguminous plants so far examined and proteins homologous to leghemoglobin have also been found in the Rhizobium-containing nodules of the U1-maceae, Parasponia [1] and the actinorhizal root nodules formed in the N2-fixing symbiosis between Casuarina and the actinomycete Frankia [12].…”

Section: Introductionmentioning

confidence: 99%

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Identification of two groups of leghemoglobin genes in alfalfa (Medicago sativa) and a study of their expression during root nodule development

et al. 1988

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Differential screening of an alfalfa root nodule cDNA library with either root or nodule mRNA resulted in the isolation of two groups of leghemoglobin cDNA which differ significantly in sequence. Analysis of one member of each group revealed a divergence within the coding region of 15% at the nucleotide level and 14% at the amino acid level. The 3' non-coding sequences are 25% divergent but are highly conserved over a stretch of 54 nucleotides which contains two sequence motifs common to leghemoglobin genes from other plant species. Southern blotting analysis with exon-specific probes has shown that there are approximately twice as many leghemoglobin gene copies in the alfalfa genome corresponding to one type of cDNA as compared with the other. Using the same criterium of DNA sequence relatedness these two distinct groups of leghemoglobin genes have also been identified in the genomes of the diploid annual Medicago truncatula and the closely related genus, Melilotus. Transcripts corresponding to both groups of leghemoglobin genes are first detected in alfalfa nodules 9-10 days after Rhizobium inoculation. Thereafter, mRNA levels increase rapidly and synchronously, reaching a maximum approximately 2 days later. There is a 2-3 fold difference in the steady-state levels of the two mRNA populations and this is maintained throughout the subsequent two weeks of nodule growth. The absence of any detectable transcription during the early stages of nodule development and the apparent co-ordinate expression of leghemoglobin genes in alfalfa contrasts with the situation in soybean and suggests that important differences in leghemoglobin gene regulation exist between these two distantly related legume species.

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Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Identification of two groups of leghemoglobin genes in alfalfa (Medicago sativa) and a study of their expression during root nodule development

et al. 1988

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“…The 0, diffusion barrier causes the decrease in free 0, between the atmosphere and the infected zone, while leghemoglobin enables the rapid diffusion of oxygen in a bound form to the terminal oxidase sites throughout the infected zone (Appleby, 1984).…”

Section: Limitations Of Nitrogenase Activitymentioning

confidence: 99%

Measurement of nitrogenase activity in legume root nodules: In defense of the acetylene reduction assay

Vessey

1994

Plant Soil

123

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The closed acetylene reduction assay has been used as a measure of nitrogenase activity and an indicator of N, fixation in Rhizobium/legume symbioses for 25 years. However, starting 10 years ago this assay has come under harsh criticism as being inaccurate. Currently, confusion exists regarding the conditions under which the acetylene reduction assay can be used accurately, or whether it can be used at all as a measure of nitrogenase activity. This article reviews the circumstance that has lead to this confusion. The author argues that under the proper assay conditions and with the appropriate checks, the closed acetylene reduction assay is still a valuable tool in assessing relative differences in nitrogenase activity in Rhizobium/legume symbioses.

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“…The leghemoglobin (lb) genes, encoding proteins involved in oxygen transport in the nodule [1], constitute one of the most highly expressed subclasses of the late nodulin genes. The lb genes have been best studied in the case of soybean (Glycinemax [13,23])and the stem-nodulated, tropical legume Sesbania rostrata [3,15,24].…”

Section: Introductionmentioning

confidence: 99%

Regulation of plant genes specifically induced in nitrogen-fixing nodules: role of cis-acting elements and trans-acting factors in leghemoglobin gene expression

et al. 1989

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Transgenic alfalfa plants harboring a gene fusion between the soybean leghemoglobin (lbc3) promoter region and the chloramphenicol acetyl transferase (cat) gene were used to determine the influence of rhizobial mutants on lb gene expression in nodules. The promoter region of the Sesbania rostrata glb3 (Srglb3) leghemoglobin gene was examined for the presence of conserved motifs homologous to binding site 1 and 2 of the soybean lbc3 promoter region, found to interact with a trans-acting factor present in soybean nodule nuclear extracts (Jensen EO, Marcker KA, Schell J, de Bruijn FJ, EMBO J 7:1265-1271, 1988). Subfragments of the S. rostrata glb3 (Srglb3) promoter region were examined for binding to trans-acting factors from nodule nuclear extracts. In addition to the binding sites previously identified (Metz BA, Welters P, Hoffmann HJ, Jensen EO, Schell J, de Bruijn FJ, Mol Gen Genet 214: 181-191), several other sites were found to interact with trans-acting factors. In most cases the same trans-acting factor(s) were shown to be involved. One fragment (202) was found to bind specifically to a different factor (protein) which was extremely heat-resistant (100 degrees C). The appearance of this factor was shown to be developmentally regulated since the expected protein-DNA complexes were first observed around 12 days after infection, concomitant with the production of leghemoglobin proteins. Fragments of the Srglb3 5' upstream region were fused to the beta-glucuronidase reporter gene with its own CAAT and TATA box region or those of the cauliflower mosaic virus 35S and nopaline synthase (nos) promoters.(ABSTRACT TRUNCATED AT 250 WORDS)

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Leghemoglobin and Rhizobium Respiration

Cited by 178 publications

References 0 publications

Identification of two groups of leghemoglobin genes in alfalfa (Medicago sativa) and a study of their expression during root nodule development

Identification of two groups of leghemoglobin genes in alfalfa (Medicago sativa) and a study of their expression during root nodule development

Measurement of nitrogenase activity in legume root nodules: In defense of the acetylene reduction assay

Regulation of plant genes specifically induced in nitrogen-fixing nodules: role of cis-acting elements and trans-acting factors in leghemoglobin gene expression

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