Legumes have evolved symbiotic interactions with rhizo-bial bacteria to efficiently utilize nitrogen. Recent pro-gress in symbiosis has revealed several key components of host plants required for nitrogen-fixing nodule organogenesis, in which complicated metabolic and signaling pathways in the host plant are reprogrammed to generate nodules in the cortex upon perception of the rhizobial Nod factor. Following the recognition of Nod factors, plant hormones are likely to be essential throughout nodule organogenesis for integration of developmental and environmental signaling cues into nodule development. Here, we review the molecular events involved in plant hormonal regulation and signaling cross-talk for nitrogen-fixing nodule devel-opment, and discuss how these signaling networks are integrated into Nod factor-mediated signaling during plant-microbe interactions.

Keywords: cross talk, hormone, legume, nitrogen fixing, symbiosis