New insights in the molecular events underlying actinorhizal nodulation

SVISTOONOFF S; IMANISHI L; GHERBI H; HOCHER V; LALPAZE L; BOGUSZ D; WALL LG; FRANCHE C

Valparaíso

Encuentro; V REUNION DE BIOLOGÍA VEGETAL; 2010

More than 200 species of dicotyledonous plants, mostly trees and schrubs, belonging to eight different families can enter actinorhizal symbioses with the nitrogen-fixing soil actinomycete Frankia. The establishment of the symbiosis involves both specific recognition of symbiotic partners and developmental adaptations of the host plant leading to the nitrogen-fixing nodule. Nevertheless, the key molecules that control specific recognition of the actinomycetal partner by the plant have not been characterized. On the plant side, molecular approaches and genomics have been developed to understand changes in gene expression resulting from the interaction with the actinomycete. Great efforts are currently underway in our team to identify the changes in the global patterns of gene expression occurring during different stages of the symbiotic interaction by using microarray technologies in the actinorhizal plant Casuarina glauca. The goal is to identify key genes involved in the early steps of the symbiotic process, and to perform a comparative analysis in actinorhizal plants and legumes. ESTs that exhibit homology with the early symbiotic genes involved in the Nod factor transduction pathway of Legumes are currently being characterized. A functional analysis of CgSymRK, a gene from Casuarina homologous to the receptor-like kinase gene SymRK/DMI2 from legumes, has been previously reported (PNAS, 2008, 105 :4928-4932). Silencing experiments based on RNA interference technology established that CgSYMRK was necessary for both nodule and mycorhiza (AM) formation in Casuarinaceae. Similar experiments are currently elaborated with CgCCaMK, a calcium-dependant calmodulin kinase-like gene from C. glauca, and with CgNIN, a gene encoding a putative transcriptional regulator necessary for bacterial invasion and nodule organogenesis in legumes. Using two other actinorhizal plants, Alnus glutinosa and Discaria trinervis we are also studying the conservation of molecular mechanisms leading to actinorhizal development.