A leaf-expressed TERMINAL FLOWER1 ortholog from coffee with alternate splice forms alters flowering time and inflorescence branching in Arabidopsis
Perennial, polycarpic species, such as Coffea sp L. (coffee), exhibit asynchronous flowering while maintaining concomitant vegetative growth. This growth dichotomy is associated directly with fruit development and maturation time. To identify molecular components that underlie asynchronous flowering, we isolated phosphatidylethanolamine binding protein (PEBP) homologs expressed in coffee and identified a gene with high similarity to Arabidopsis TERMINAL FLOWER1-like. In Arabidopsis, interaction of TFL1 (AtTFL1) with bZIP transcription factor floral regulator FD (AtFD) forms a floral repressor complex that maintains inflorescence meristems in an indeterminate state. Unlike AtTFL1, which is expressed only in the shoot apical meristem, CaTFL1 transcript was detected exclusively in coffee leaves. Moreover, this transcript retained an intron, which was not reported for AtTFL1. CaTFL1 was characterized through heterologous expression in Arabidopsis and protein interaction analysis. Ectopic overexpression of CaTFL1 in transgenic Arabidopsis plants caused extreme late flowering or prevented flowering. However, the most severe floral repressive activity occurred in transgenic plants that spliced out the extra intron from CaTFL1. Yeast two hybrid assay revealed that CaTFL1 protein encoded by the spliced mRNA interacts with AtFD, as well as Arabidopsis 14-3-3 protein. These findings suggest that CaTFL1 acts as a leaf-expressed floral repressor, whose activity is controlled by alternate splicing, and may contribute to asynchronous flowering in coffee.