Legume small GTPases and their role in the establishment of symbiotic associations with Rhizobium spp

Abstract

Small GTP-binding genes act as molecular switches regulating myriad of cellular processes including vesicle-mediated intracellular trafficking, signal transduction, cytoskeletal reorganization and cell division in plants and animals. Even though these genes are well conserved both functionally and sequentially across whole Eukaryotae, occasional lineage-specific diversification in some plant species in terms of both functional and expressional characteristics have been reported. Hence, comparative phyletic and correlative functional analyses of legume small GTPases homologs with the genes from other Metazoa and Embryophyta species would be very beneficial for gleaning out the small GTPases that could have specialized in legume-specific processes; e.g., nodulation. The completion of genome sequences of two model legumes, Medicago truncatula and Lotus japonicus will significantly improve our knowledge about mechanism of biological processes taking place in legume-rhizobia symbiotic associations. Besides, the need for molecular switches coordinating busy cargo-trafficking between symbiosis partners would suggest a possible subfunctionalization of small GTPases in Fabaceae for these functions. Therefore, more detailed investigation into the functional characteristics of legume small GTPases would be helpful for the illumination of the events initialized with the perception of bacteria by host, followed by the formation of infection thread and the engulfment of rhizobial bacteria, and end with the senescence of nitrogen-fixing organelles, nodules. In summary, a more thorough functional and evolutionary characterization of small GTPases across the main lineages of Embryophyta is significant for better comprehension of evolutionary history of Plantae, that is because, these genes are associated with multitude of vital biological processes including organogenesis.

Keywords: Medicago truncatula; embryophyta; nodulation; small GTPases; symbiosis.

Figure 1

A schematic drawing depicting possible steps where fabaceous small GTPases couldplay role during the development and maintenance of nodules. The dashed arrows indicate the possible addresses of the vesicle-coated cargo and the questions marks limn the locations where small GTPases, identified by us could involve in the regulation of the nodule-specific trafficking. The abbreviations: PM, Plasma Membrane; PBM, Peribacteroid Membrane; CW, Cell Wall; and ER, Endoplasmic Reticulum.