Update: The multiple signals that control tuber formation

Potato is an important food crop, but unlike most of the other major foods, it is a tuber, not a seed. Classic studies showed that there is a mobile, photoperiod-induced signal that moves from the shoot to the stolen tip (an underground, stem-like structure) to initiate tuberization. Experimental studies point to three factors as key in the onset of tuberization. Hannapel et al. review recent evidence for these tuberization signals. StSP6A (an orthologue of “florigen”, FLOWERING LOCUS T) is a phloem-mobile protein produced in the leaf under favorable conditions. StCDF1 functions in the leaf to enhance expression of StSP6A. BEL5 moves as a phloem-mobile RNA from leaf to stolon, where it is translated and serves as a transcription factor.  This review also discusses factors upstream and downstream of these three key factors, and unresolved issues. Plant Physiol. 10.1104/pp.17.00272