Abstract
Biological nitrogen fixation by the Rhizobium-legume symbiosis allows the conversion of atmospheric nitrogen into ammonia within root nodules mediated by the nitrogenase enzyme. Nitrogenase activity results in the evolution of hydrogen as a result of a side reaction intrinsic to the activity of this enzyme. Some rhizobia, and also other nitrogen fixers, induce a NiFe uptake hydrogenase (Hup) to recycle hydrogen produced by nitrogenase, thus improving the efficiency of the nitrogen fixation process. In this work we report the generation and symbiotic behavior of hydrogenase-positive Rhizobium leguminosarum and Mesorhizobium loti strains effective in vetch (Vicia sativa) and birsfoot trefoil (Lotus corniculatus) forage crops, respectively. The ability of hydrogen recycling was transferred to these strains through the incorporation of hup minitransposon TnHB100, thus leading to full recycling of hydrogen in nodules. Inoculation of Vicia and Lotus plants with these engineered strains led to significant increases in the levels of nitrogen incorporated into the host legumes. The level of improvement of symbiotic performance was dependent on the recipient strain and also on the legume host. These results indicate that hydrogen recycling has the potential to improve symbiotic nitrogen fixation in forage plants.
Highlights
Introduction ofH2-Uptake Hydrogenase Genes Into RhizobialStrains Improves Symbiotic NitrogenFixation in Vicia sativa and Lotus corniculatus Forage LegumesEdited by: Bahar S
In order to analyze the potential effect of hydrogen recycling in symbiotic performance of forage legumes, the R. leguminosarum hydrogenase gene cluster was introduced into strains effective in Vicia sativa (R. leguminosarum bv viciae Rlv13 and Rlv21) and in L. corniculatus (Mesorhizobium loti U261, a broad-range Lotus inoculant strain)
Insertion sites were determined for these four derivatives, and derivatives Rlv 13H6 and Rlv21H10, bearing insertions with no predicted effect on bacteroid physiology were selected for the analysis of the effect of hydrogen recycling on vetch productivity
Summary
Introduction ofH2-Uptake Hydrogenase Genes Into RhizobialStrains Improves Symbiotic NitrogenFixation in Vicia sativa and Lotus corniculatus Forage LegumesEdited by: Bahar S. Fixation in Vicia sativa and Lotus corniculatus Forage Legumes. Symbiotic nitrogen fixation, carried out by rhizobia expressing nitrogenase in association with legume plants, allows reducing the use of N fertilizers, positioning legume crops as key players in sustainable agriculture (Laranjo et al, 2014). Common vetch (Vicia sativa) is a multi-purpose, cool season annual legume widely used in low- to medium rainfall areas as source of both forage and grain for animal feeding, due to its high protein content (Huang et al, 2017). V. rhizobia were traditionally placed within Rhizobium leguminosarum species, but systematic analysis of isolates from different regions has revealed that other rhizobial species such as R. sophorae and R. laguerreae, are endosymbionts of this legume (Zhang et al, 2019)
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