The specificity in the symbiotic interaction between legume hosts and rhizobia

O. MARIO AGUILAR

Mar del Plata

Congreso; Reunión de la Sociedad Argentinade Fisiologia Vegetal; 2012

Sociedad Argentina de Fisiología Vegetal

All legume crops are able to establish nitrogen fixing root nodule symbiosis with soil bacteria generically known as rhizobia. The symbiotic interaction shows specificity between the plants and the bacteria because legumes can usually be nodulated by a limited number of rhizobial strains. The plant decision in choosing a bacterial partner is determined by a set of genes which react to a display of bacterial signals and effectors. A key bacterial determinant of host specificity is the structure of the secreted lipochitin oligosaccharide (Nodulation Factor) which is recognized by plant LysM containing NF receptor kinases. A set of functionally related genes in the symbiosis pathway controls the early signaling stages of nodulation, some of them probably recruited from existing functions such as the older arbuscular mycorrhizal symbiosis.  Additional strategies of optimization in compatibility between partners were found in the native habitats of Phaseolus vulgaris and the indigenous bean nodulating rhizobia in the Mesoamerican and Southern Andean centers of host diversification. During the last years, investigation on the P. vulgaris-rhizobia symbiosis was performed in our laboratory. Analysis of nodulation factors produced by strains of R. etli from both centers of diversification and competitiveness by R. etli nolL mutant, suggested that factors other than NF might be involved in strain preference. A host gene coding for a subunit of the NF-Y transcriptional factor was identified in the Mesoamerican beans and found to be activated in response to inoculation with its cognate rhizobia.