AUTHOR=Sotelo Mariana , Ureta Ana Claudia , Muñoz Socorro , Sanjuán Juan , Monza Jorge , Palacios Jose 

TITLE=Introduction of H2-Uptake Hydrogenase Genes Into Rhizobial Strains Improves Symbiotic Nitrogen Fixation in Vicia sativa and Lotus corniculatus Forage Legumes

JOURNAL=Frontiers in Agronomy

VOLUME=3

YEAR=2021

URL=https://www.frontiersin.org/journals/agronomy/articles/10.3389/fagro.2021.661534

DOI=10.3389/fagro.2021.661534

ISSN=2673-3218

ABSTRACT=<p>Biological nitrogen fixation by the <italic>Rhizobium</italic>-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 <italic>Rhizobium leguminosarum</italic> and <italic>Mesorhizobium loti</italic> strains effective in vetch (<italic>Vicia sativa)</italic> and birsfoot trefoil (<italic>Lotus corniculatus</italic>) forage crops, respectively. The ability of hydrogen recycling was transferred to these strains through the incorporation of <italic>hup</italic> minitransposon Tn<italic>HB100</italic>, thus leading to full recycling of hydrogen in nodules. Inoculation of <italic>Vicia</italic> and <italic>Lotus</italic> 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.</p>