Frankia-actinorhizal plant symbioses. News from research on South American native plants Discaria trinervis and Alnus acuminata.

WALL LG, VALVERDE C, CHAIA E, ENRICO R, VALDÉS LA HENS D, FERRARI A, RAMIREZ S, LUCKI G, OBERTELLO M, GABBARINI L, MASSA G.

Villa Carlos Paz, Córdoba, Argentina

Workshop; 5th International PGPR Workshop.; 2000

The term “actinorhiza” refers both to the filamentous bacteria Frankia, an actinomycete, and to the root location of the nitrogen fixing nodules. Actinorhizal plants are classified in four subclasses, 8 Families and 25 genera comprising more than 220 species. Basic studies in complex interactions between microorganisms and actinorhizal plants will help us also to increase our knowledge about plant growth regulation and their interactions with microbes in nature. Although ontogenically related to lateral roots, actinorhizal nodules are characterized by differentially expressed genes, supporting the idea of the uniqueness of this new organ. Two pathways for root infection have been described for compatible Frankia interactions: root hair infection, as in Alnus or intercellular penetration, as in Discaria.  Here, we present the different aspects on actinorhizal symbiosis that our group has been studying during the last five years.