Viruses provide direction on the plant information superhighway

Phloem tubes are made up of aligned cells, called sieve elements, which lack nuclei and therefore must rely on associated companion cells for physiological support and nourishment. Sieve elements and companion cells are connected by plasmodesmata — a network of tiny channels through which molecules such as sugars, hormones and amino acids travel. How these molecules are ushered via plasmodesmata into the long-distance transport systems has eluded researchers until only recently, when viruses have provided some vital clues.