ARF5 and hypophysitis: The embryonic root initiation process greatly depends on the antagonistic interaction between MP/ARF5 and its repressor BDL/IAA12 protein (Hamann et al., 2002; Schlereth et al., 2010), and both the loss-of-function mp/arf5 and gain-of-function bdl/iaa12 mutants are defective in hypophysis specification (Hamann et al., 1999).