The Ammonium Channel NOD26 is the Evolutionary Innovation that Drives the Emergence, Consolidation, and Dissemination of Nitrogen-Fixing Symbiosis in Angiosperms

Increasing evidence indicates that N-fixing symbiosis has evolved several times in the N-fixing clade of angiosperms and that this evolution is driven by a single evolutionary innovation. However, the genetics of this ancestral predisposition to N-fixing symbiosis remains unclear. A natural candidate for such molecular innovation is the ammonium channel NOD26, the main protein component of the symbiosome membrane, which facilitates the plant uptake of the nitrogen fixed by symbiotic bacteria. Here, in concordance with the emergence of N-fixing symbiosis in angiosperms but not in ancestral plants, phylogenetic analysis showed that NOD26 belongs to an angiosperm-exclusive subgroup of aquaporins. Integrated genomic, phylogenetic, and gene expression analyses supported NOD26 occurrence in the N-fixing clade, the increase in the NOD26 copy number by block and tandem duplications in legumes, and the low-copy number or even the loss of NOD26 in non-legume species of the N-fixing clade, which correlated with the possibility to lose N-fixing symbiosis in legume and non-legume lineages. Metabolic reconstructions showed that retention of NOD26 in N-fixing precursor could represent an adaptive mechanism to bypass energy crisis during anaerobic stress by ammonium detoxification. Finally, we discuss the potential use of NOD26 to transfer N-fixation to non-N-fixing crops as cereals. Fil: Frare, Romina Alejandra. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ayub, Nicolás Daniel. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Alleva, Karina Edith. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentina Fil: Soto, Gabriela Cynthia. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación en Ciencias Veterinarias y Agronómicas. Instituto de Genética; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina