Cyanobacterial-plant Symbioses: Signalling and Development
Birgitta Bergman, Liang Ran and David G. Adams
from: The Cyanobacteria: Molecular Biology, Genomics and Evolution (Edited by: Antonia Herrero and Enrique Flores). Caister Academic Press, U.K. (2008)
Cyanobacteria form stable nitrogen-fixing symbioses with diverse eukaryotes. With few exceptions the cyanobacteria belong to the terrestrial and widespread genus Nostoc. This genus has a notable morphological plasticity which may be in part responsible for its symbiotic competence. In contrast, the symbiotic host range is wide, from mosses to angiosperms. The plant symbioses range from less intimate interactions, such as in mosses, to highly intricate symbioses, such as the intracellular symbiosis with the angiosperm Gunnera. In Azolla spp. the relationship is perpetual and maintained between generations. Nostoc is also one of the most developmentally advanced prokaryotes and capable of differentiating several cell types with various functions. Individual vegetative cells of Nostoc may differentiate into nitrogen-fixing heterocysts, and filaments may fragment into hormogonia, a motile life-stage and a prerequisite for plant infection. On internalization, the hormogonia are turned into multi-heterocystous filaments. The high frequency of heterocysts is reflected in their high nitrogen-fixing activities, and in the transfer of the fixed nitrogen to the plant. A sequence of inter-organism communication events between the partners and cellular adaptations is therefore obvious. Our current knowledge about molecular mechanisms involved in these events, and how a full integration has evolved, will be presented with emphasis on recent findings read more ...