Positioning the nodule, the hormone dictum

The formation of a nitrogen-fixing nodule involves two diverse developmental processes in the legume root: infection thread initiation in epidermal cells and nodule primordia formation in the cortex. Several plant hormones have been reported to positively or negatively regulate nodulation. These hormones function at different stages in the nodulation process and may facilitate the coordinated development of the epidermal and cortical developmental programs that are necessary to allow bacterial infection into the developing nodule. In this paper, we review and discuss how the tissue specific nature of hormonal action dictates where, when and how a nodule is formed.