Plants utilize proteins and RNA as non-cell-autonomously acting signaling macromolecules to mediate local and long-distance regulation over physiological and developmental processes. The cell-to-cell pathway for the trafficking of these non-cell-autonomous proteins and RNA, in the form of ribonucleoprotein complexes, is established by plasmodesmata and phloem. In agiosperms, the phloem sieve tube system is comprised of two main cell types, the sieve elements and their associated companion cells. The impact of non-cell-autonomous trafficking of proteins and RNA on the development of novel agronomic traits will be discussed.