Publication Date
1993
Description
The establishment of nit.rogen-fixing symbiosis between rhizobia and their plant hosls requires multiple interactions between the two pnrtners, which involves transmission of signal molecules activating gene sets controlling nodule development. Plant roots exude specific Oavonoids which can induce the expression of the nodulation (nod) genes in the appropriate bacterium partner, in conjunction with the constitutively produced activator protein NodD. Additional positive and negative regulatory factors further modulate nod gene expression and this fine tuning of 110d gene expression is required for optimal nodulation of the hosts. Some of these factors mediate the effects of some soil factors, such as (he combined nitrogen level. The products of the majority of nod genes are involved in the synthesis and excretion of a family of structurally related lipo-oligosaccharides, the Nod factors. These molecules stimulate root hair deformation, cortical cell division and nodule induction. Thus, the Nod factors act as morphogens switching on nodule organogenesis. Moreover, they have a key role in determining host specificity. Perturbations of the hormonal balance of the host plant were shown to nffect nodulation drastically, suggesting that the transduction of Nod signals may be associated with the t.ransduction of known plant hormones. Understanding the molecular control of nodule induction may help improving the efficiency of symbiotic associations. Two examples will be presented. First, we showed that by modifying the regulation of 110d gene expression in Rhizobium meliloti the symbiotic partner of alfalfa (Medicago sativa), the nodulation. ability and competitiveness of this strain could be improved. Second, two alfalfa varieties were transformed with different combinations of the ro/A, B, C genes of AgrobacIerium rhizogenes which altered the auxin-sensitivity and the endogenous auxin-cytokinin ratios. Depending on the genes int.roduced, root development was positively influenced and symbiotic nitrogen fixation and plant growth were significantly increased.
Citation
Kondorosi, Adam; Schultze, Michael; Hoffmann, Beate; Koncz, Csaba; Bogre, Laszlo; Cren, Michele; Dusha, Ilona; Dudits, Denes; and Kondorosi, Eva, "Molecular Basis of Legume-Rhizobium Interactions: Potentials for Improving Symbiotic Nitrogen Fixation" (2024). IGC Proceedings (1993-2023). 8.
https://uknowledge.uky.edu/igc/1993/session34/8
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Molecular Basis of Legume-Rhizobium Interactions: Potentials for Improving Symbiotic Nitrogen Fixation
The establishment of nit.rogen-fixing symbiosis between rhizobia and their plant hosls requires multiple interactions between the two pnrtners, which involves transmission of signal molecules activating gene sets controlling nodule development. Plant roots exude specific Oavonoids which can induce the expression of the nodulation (nod) genes in the appropriate bacterium partner, in conjunction with the constitutively produced activator protein NodD. Additional positive and negative regulatory factors further modulate nod gene expression and this fine tuning of 110d gene expression is required for optimal nodulation of the hosts. Some of these factors mediate the effects of some soil factors, such as (he combined nitrogen level. The products of the majority of nod genes are involved in the synthesis and excretion of a family of structurally related lipo-oligosaccharides, the Nod factors. These molecules stimulate root hair deformation, cortical cell division and nodule induction. Thus, the Nod factors act as morphogens switching on nodule organogenesis. Moreover, they have a key role in determining host specificity. Perturbations of the hormonal balance of the host plant were shown to nffect nodulation drastically, suggesting that the transduction of Nod signals may be associated with the t.ransduction of known plant hormones. Understanding the molecular control of nodule induction may help improving the efficiency of symbiotic associations. Two examples will be presented. First, we showed that by modifying the regulation of 110d gene expression in Rhizobium meliloti the symbiotic partner of alfalfa (Medicago sativa), the nodulation. ability and competitiveness of this strain could be improved. Second, two alfalfa varieties were transformed with different combinations of the ro/A, B, C genes of AgrobacIerium rhizogenes which altered the auxin-sensitivity and the endogenous auxin-cytokinin ratios. Depending on the genes int.roduced, root development was positively influenced and symbiotic nitrogen fixation and plant growth were significantly increased.
