Nodulation competitiveness and diversification of symbiosis genes in common beans from the American centers of domestication

O. MARIO AGUILAR1*, MÓNICA M. COLLAVINO2 & ULISES MANCINI1

Scientific Reports

Nature Publishing Group

Año: 2022 vol. 12

2045-2322

Phaseolus vulgaris (common bean), having a proposed Mexican origin within the Americas, comprisesthree centers of diversification: Mesoamerica, the southern Andes, and the Amotape-HuancabambaDepression in Peru-Ecuador. Rhizobium etli is the predominant rhizobium found symbioticallyassociated with beans in the Americasalthough closely related Rhizobium phylotypes have also beendetected. To investigate if symbiosis between bean varieties and rhizobia evolved affinity, firstlynodulation competitiveness was studied after inoculation with a mixture of sympatric and allopatricrhizobial strains isolated from the respective geographical regions. Rhizobia strains harboring nodCtypes α and , which were found predominant in Mexico and Ecuador, were comparable in noduleoccupancy at 50% of each in beans from the Mesoamerican and Andean gene pools, but it is one ofthose two nodC types which clearly predominated in Ecuadorian-Peruvian beans as well as in Andeanbeans nodC type predominated the sympatric nodC type δ. The results indicated that those beansfrom Ecuador-Peru and Andean region, respectively exhibited no affinity for nodulation by thesympatric rhizobial lineages that were found to be predominant in bean nodules formed in thoserespective areas. Unlike the strains isolated from Ecuador, Rhizobium etli isolated from Mexico aswell from the southern Andes was highly competitive for nodulation in beans from Ecuador-Peru, and quite similarly competitive in Mesoamerican and Andean beans. Finally, five gene products associated with symbiosis were examined to analyze variations that could be correlated with nodulation competitiveness. A small GTPase RabA2, transcriptional factors NIN and ASTRAY, and nodulation factor receptors NFR1 and NFR5- indicated high conservation but NIN, NFR1 and NFR5 of beans representative of the Ecuador-Peru genetic pool clustered separated from the Mesoamerican and Andean showing diversification and possible different interaction. These results indicated that both host and bacterial genetics are important for mutual affinity, and that symbiosis is another trait of legumes that could be sensitive to evolutionary influences and local adaptation.