Figure 2.

Proposed model for the control of the ovule primordia initiation. Auxin triggers ANT and MP expression, which in its turn is required for ANT, CUC1 and CUC2 expression during the early stages of placenta development and ovule primordia formation. ANT expression is also regulated by brassinosteroids (BR), specifically being directly regulated by BZR1. ANT controls cell proliferation in the placenta and ovules, whereas CUC1 and CUC2 establish the boundaries and control PIN1 expression, which is required for primordia formation. Cytokinin (CK) may act downstream of CUC proteins in promoting PIN1 expression. Once the primordia have formed, auxin accumulates at the edge of the developing ovule. An inhibitory loop of auxins on CUC1 and CUC2, as it is postulated for the leaf serration, could be happening at the ovule boundaries. Adapted from Galbiati et al. (2013).