Identification and characterization of common bean (Phaseolus vulgaris) non-nodulating mutants altered in rhizobial infection

Authors: REYERO-SAAVEDRA, MARIA DEL ROCIO - Universidad Nacional Autonoma De Mexico; FUENTES, SARA - Universidad Nacional Autonoma De Mexico; LEIJA-SALAS, ALFONSO - Universidad Nacional Autonoma De Mexico; JIMENEZ-NOPALA, GLADYS - Universidad Nacional Autonoma De Mexico; PELAEZ, PABLO - Universidad Nacional Autonoma De Mexico; RAMIREZ, MARIO - Universidad Nacional Autonoma De Mexico; GIRARD, LOURDES - Universidad Nacional Autonoma De Mexico; Porch, Timothy - Tim; HERNANDEZ, GEORGINA - Universidad Nacional Autonoma De Mexico

Submitted to: Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2023
Publication Date: 3/14/2023
Citation: Reyero-Saavedra, M., Fuentes, S.I., Leija-Salas, A., Jimenez-Nopala, G., Pelaez, P., Ramirez, M., Girard, L., Porch, T.G., Hernandez, G. 2023. Identification and characterization of common bean (Phaseolus vulgaris) non-nodulating mutants altered in rhizobial infection. Plants. 12(6): 1310. https://doi.org/10.3390/plants12061310.
DOI: https://doi.org/10.3390/plants12061310

Interpretive Summary: The symbiotic nitrogen fixation (SNF) process resulting from the legume (plant) and rhizobia (bacteria) interaction is relevant for sustainable agriculture. The characterization of mutants for this symbiotic process, mainly in model legumes, has been instrumental for the discovery of symbiotic genes, but studies in crop legumes are scant. To isolate and characterize common bean symbiotic mutants, a chemical-induced mutant population using the BAT 93 common bean variety was analyzed. Our initial screening revealed different alterations in nodulation in mutants inoculated with the bacteria. We proceeded with the characterization of three non-nodulating (nnod) mutants: nnod(1895), nnod(2353) and nnod(2114). Microscopic analysis revealed different impairments in each mutant in early symbiotic steps. Nnod(1895) formed a decreased number of deformed root hairs and no rhizobia infection. Nnod(2353) produced normal root hair curling and rhizobia entrapment to form infection chambers, but the development of the latter was blocked. Nnod(2114) formed infection threads that did not elongate and thus did not reach the root cortex and it occasionally formed non-infected pseudo-nodules. Current research is aimed at mapping the responsible mutated genes for a better understanding of SNF in this food-important crop. These studies elucidating the symbiotic nitrogen fixation process could result in common bean varieties that require less fertilizer inputs for farmers.

Technical Abstract: The symbiotic N2-fixation (SNF) process in the legume – rhizobia interaction is relevant for sustainable agriculture. The characterization of symbiotic mutants, mainly in model legumes, has been instrumental for the discovery of symbiotic genes, but similar studies in crop legumes are scant. To isolate and characterize common bean (Phaseolus vulgaris) symbiotic mutants, an ethylmethanesulphonate-induced mutant population from the BAT 93 genotype, was analyzed. Our initial screening, of Rhizobium etli CE3 inoculated mutant plants, revealed different alterations in nodulation. We proceeded with the characterization of three non-nodulating (nnod), apparently monogenic/recessive mutants: nnod(1895), nnod(2353) and nnod(2114). Their reduced growth in symbiotic condition was restored when nitrate was added. A similar nnod phenotype was observed upon inoculation with other efficient rhizobia species. Microscopic analysis revealed different impairments in each mutant in an early symbiotic step. nnod (1895) formed a decreased number of effective root hair deformation and no rhizobia infection. nnod (2353) produced normal root hair curling and rhizobia entrapment to form infection chambers, but the development of the latter was blocked. nnod (2114) formed infection threads that did not elongate and thus did not reach the root cortex level; it occasionally formed non-infected pseudo-nodules. Current research is aimed at mapping the responsible mutated genes for a better understanding of SNF in this food-important crop.