LMI1 and TCP4 homologs form a functional module to regulate lateral petal asymmetric bending in Delphinium...

During the floral evolution of Delphinium (Ranunculaceae), the lineage leading to speciose subgenera of Delphinastrum/Oligophyllon gained a novel trait of asymmetric bending in their lateral petals, which further reinforced the highly specialized petal movement, mirrored helical rotation, during their flower opening. Our previous study in Delphinium anthriscifolium identified DeanLATE MERISTEM IDENTITY1 (DeanLMI1) as a key regulator, but its broad expression suggests that additional co-regulators are required for specifying its function. Here, by screening the transcriptome data from DeanLMI1-silenced lateral petals, together with detailed morphological, functional and interaction studies, we aim to uncover the DeanLMI1-mediated module underlying the evolution of lateral petal asymmetric bending in Delphinium. We identified a class II TCP (TEOSINTE BRANCHED1, CYCLOIDEA, PROLIFERATING CELL FACTORS) family gene, DeanTCP4-1, whose expression overlaps with DeanLMI1 at the hinge region of the lateral petals, where the asymmetric bending initiates. Silencing DeanTCP4-1 alone or together with DeanLMI1 resulted in the loss of this trait. Such a function is supported by direct activation of DeanTCP4-1 by DeanLMI1 and their protein-protein interaction. This work highlights that a functional module formed by LMI1 and TCP4 homologs is required for the evolution of lateral petal asymmetric bending in Delphinium, and also provides insights into the molecular mechanisms underlying diverse flower opening and plant movements.