OsIDD7 integrates signaling networks for arbuscular mycorrhizal symbiosis

Here, we identify the rice INDETERMINATE DOMAIN (IDD) transcription factor IDD7 as a key regulator of AM symbiosis. IDD7 expression is strongly induced in arbusculated cells, and loss of IDD7 markedly reduces fungal colonization and disrupts arbuscule development.

IDD7 is involved in regulating genes involved in fatty acid biosynthesis, nutrient transport, and symbiotic signaling, and interacts with the transcription factors SLR1 and PHR2 through its conserved TQDFLG domain. Electrophoretic mobility shift assays show that IDD7 binds multiple promoter motifs and, together with SLR1 and PHR2, synergistically activates the promoters of PT11, PHR2, RAM1, WRI5a, and CYCLOPS. Moreover, IDD7 is required for PHR2 expression in arbusculated cells.