BLADE-ON-PETIOLE interacts with CYCLOIDEA to fine-tune CYCLOIDEA-mediated flower symmetry in Monkeyflowers (Mimulus)

AbstractMorphological novelties, or key innovations, are instrumental to the diversification of the organisms. In plants, one such innovation is the evolution of zygomorphic flowers, which is thought to promote outcrossing and increases flower morphological diversity. We isolated three allelic mutants from two Mimulus species displaying altered floral symmetry and identified the causal gene as the orthologue of Arabidopsis BLADE-ON-PETIOLE. We found that MlBOP and MlCYC2a physically interact and this BOP-CYC interaction module is highly conserved across the angiosperms. Furthermore, MlBOP self-ubiquitinates and suppresses MlCYC2a self- activation. MlCYC2a, in turn, impedes MlBOP ubiquitination. Thus, this molecular tug-of-war between MlBOP and MlCYC2a fine-tunes the expression of MlCYC2a, contributing to the formation of bilateral symmetry flowers, a key trait in angiosperm evolution. One Sentence SummaryMolecular tug-of-war between MlBOP and MlCYC2a fine-tunes the expression of MlCYC2a, contributing to the bilateral flower symmetry formation.