Phloem-mobile signals affecting flowers: applications for crop breeding

Transport of endogenous macromolecules within and between tissues serves as a signaling pathway to regulate numerous aspects of plant growth. The florigenic FT gene product moves via the phloem from leaves to apical tissues and induces the flowering program in meristems. Similarly, short interfering RNA (siRNA) signals produced in source or sink tissues move cell-to-cell and long distance via the phloem to apical tissues. Recent advances in identifying these mobile signals regulating flowering or the epigenetic status of targeted tissues can be applicable to crop-breeding programs. In this review, we address the identity of florigen, the mechanism of allocation, and how virus-induced flowering and grafting of transgenes producing siRNA signals affecting meiosis can produce transgene-free progenies useful for agriculture.