Owen Hebb

Coffee is a perennial plant that exhibits asynchronous flowering while maintaining concomitant vegetative growth. This growth dichotomy affects fruit development and maturation time. To better understand flowering in coffee, we characterized a phosphatidylethanolamine binding protein (PEBP) homolog with high similarity to Arabidopsis thaliana TERMINAL FLOWER1 (TFL1). The interaction of TFL1 with floral regulator bZIP transcription factor, FD, forms a floral repressor complex that maintains inflorescence meristems in an indeterminate state. Arabidopsis TFL1 is expressed only in shoot apical meristems, yet CaTFL1a transcripts were detected exclusively in coffee leaves. Moreover, leaf-derived CaTFL1a transcript retains an intron, which has not been reported for TFL1 orthologs in other species. The ectopic expression of CaTFL1a in Arabidopsis causes extreme late flowering or prevents flowering altogether. Notably, the most severe floral repressive activity occurred in transgenic plants that spliced out the extra intron from CaTFL1. Yeast Two-Hybrid assays show that full-length CaTFL1a protein (fl-CaTFL1a) encoded by the fully spliced mRNA interacts with FD and Arabidopsis 14-3-3 protein AtGRF3, whereas truncated protein (tr-CaTFL1a) encoded by transcript that retains an intron does not interact. This evidence suggests that CaTFL1a may affect flowering in coffee by acting as a leaf-derived, long-distance floral repressor whose activity is controlled by alternative splicing.