Role of Membrane Rafts during Legume Nodulation

Nodulation is the result of the intimate relationship between rhizobia and legumes. Upon recognition of the two partners, rhizobia will infect root hair cells before to colonize a new root organ, the nodule. In the nodule, differentiated bacteria will fix and assimilate atmospheric nitrogen for the plant. During the past two decades, using forward and reverse genomic tools, researchers characterized the role of many legume genes as regulators of the nodulation process. Among these genes, GmFWL1 (FW2.2-like 1) has been characterized as a regulator of soybean nodulation. While the biological role of GmFWL1 has been described, the molecular function of GmFWL1 is unknown. Here, using molecular, biochemical, comparative genomic and microscopic methods, we characterize GmFWL1 as a membrane raft-associated protein. Specifically, 172 soybean proteins interact with GmFWL1 including proteins which belong to families previously characterized as membrane raft-associated proteins. Notably, using comparative genomics, one GmFWL1 partner was identified as orthologous to MtFLOT2 and MtFLOT4, membrane raft-associated proteins controlling Medicago truncatula nodulation. Additional microscopic observations confirmed the heterogeneous plasma membrane localization of GmFWL1 compatible with its raft localization. Taking advantage of publicly available transcriptomic resources, a significant number of the 172 GmFWL1 protein partners are exclusively expressed during the nodulation process supporting the idea of a specific protein composition of a part of the membrane rafts during the nodulation process. This work thus contributes to a better understanding of the function of GmFWL1 during the nodulation process and confirm the role of membrane rafts in controlling legume nodulation.