Format: ORAL

Shihao Su1, Xuan Zhou1, Tetsuya Higashiyama2

1. School of Agriculture, Sun Yat-sen University, Shenzhen, China 2. Department of Biological Sciences, The University of Tokyo, Japan

The three-dimensional shape of a flower is integrated by morphogenesis along different independent axes. Differentiation along the petal proximodistal axis is tightly linked to the specification of pollinators; however, it is still unclear how a petal patterns its proximodistal axis. The corolla of Torenia fournieri, exhibits strong differentiation along the proximodistal axis, including a distal petal lobe region, an intermediate corolla tube, and a proximal corolla neck region that is controlled by an ALOG family homologue, TfALOG3. In this study, we report a floral-specific BOP gene, TfBOP2, which is predominantly expressed in the proximal region of the corolla. CRISPR knockout mutants of TfBOP2 have shorter proximal corolla tubes and longer distal lobe regions, with ectopic growth of conical cells in the fusion boundaries of the corolla tube, consistent with its expression pattern as a proximal regulator. Mutants of BOP homologues in Arabidopsis thaliana also show developmental defects in the petal proximal region, favouring a shared role of BOPs among different species. Genetic analysis demonstrates the interaction between TfBOP2 and TfALOG3 in the control of corolla proximodistal differentiation since double mutants have the shortest proximal corolla tubes while exhibiting normal boundary fusion. We further found that TfALOG3 physically interacts with TfBOP2 and can recruit TfBOP2 to the nuclear region, indicating its possible function as a complex. Our study favours a hypothetical shared BOP-ALOG complex across the core eudicots that is recruited to regulate corolla differentiation in the proximal region axis of T. fournieri.