The Tobacco BLADE-ON-PETIOLE2 Gene Mediates Differentiation of the Corolla Abscission Zone by Controlling Longitudinal Cell Expansion

The BLADE-ON-PETIOLE (BOP) genes of Arabidopsis (Arabidopsis thaliana) have been shown to play an essential role in floral abscission by specializing the abscission zone (AZ) anatomy. However, the molecular and cellular mechanisms that underlie differentiation of the AZ are largely unknown. In this study, we identified a tobacco (Nicotiana tabacum) homolog of BOP (designated NtBOP2) and characterized its cellular function. In tobacco plants, the NtBOP2 gene is predominantly expressed at the base of the corolla in an ethylene-independent manner. Both antisense suppression of NtBOP genes and overexpression of NtBOP2 in tobacco plants caused a failure in corolla shedding. Histological analysis revealed that the differentiation of the corolla AZ was blocked in the transgenic flowers. This blockage was due to uncontrolled cell elongation at the region corresponding to wild-type AZ. The role of NtBOP2 in regulating cell elongation was further demonstrated in Bright Yellow 2 single cells: perturbation of NtBOP2 function by a dominant negative strategy led to the formation of abnormally elongated cells. Subcellular localization analysis showed that NtBOP2-green fluorescent protein fusion proteins were targeted to both the nucleus and cytoplasm. Yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays demonstrated that NtBOP2 proteins interacted with TGA transcription factors. Taken together, these results indicated that NtBOP2 mediated the differentiation of AZ architecture by controlling longitudinal cell growth. Furthermore, NtBOP2 may achieve this outcome through interaction with the TGA transcription factors and via an ethylene-independent signaling pathway.