Potato Tuber Induction is Regulated by Interactions Between Components of a Tuberigen Complex

Abstract

Photoperiod-regulated flowering and potato tuber formation involve leaf-produced mobile signals, florigen and tuberigen, respectively. The major protein component of florigen has been identified as the FLOWERING LOCUS T (FT) protein. In rice, an FT-like protein, Heading date 3a (Hd3a), induces flowering by making the florigen activation complex (FAC) through interactions with 14-3-3 and OsFD1, a rice FD-like protein. In potato, StSP6A, an FT-like protein, was identified as a major component of tuberigen. However, the molecular mechanism of how StSP6A triggers tuber formation remains elusive. Here we analyzed the significance of the formation of a complex including StSP6A, 14-3-3 and FD-like proteins in tuberization. Yeast two-hybrid, bimolecular fluorescence complementation and in vitro pull-down assays showed that StSP6A and StFDL1, a potato FD-like protein, interact with St14-3-3s. StSP6A overexpression induced early tuberization in a 14-3-3-dependent manner, and suppression of StFDL1 delayed tuberization. These results strongly suggest that an FAC-like complex, the tuberigen activation complex (TAC), comprised of StSP6A, St14-3-3s and StFDL1, regulates potato tuber formation.

The Multiple Signals That Control Tuber Formation

“…The current model proposes the existence of two TACs working in concert, an StBEL5/StKNOX complex and another composed of StSP6A, StFDL1, and a 14-3-3 protein ( Fig. 4; Teo et al, 2017).…”

“…Through interactions of FT with a different protein partner that regulates a unique set of targets, the FAC model provides the molecular basis for creating multiple functions for FT beyond flowering (Tsuji and Taoka, 2014). Similar interactions among StSP6A, a 14-3-3 protein, and an StFD1-like protein appear to be functional as the tuber activation complex (TAC; Teo et al, 2017). Transgenic lines that constitutively express either StSP6A or Hd3a exhibited enhanced production of flowers from the shoot apical meristem and tubers from the stolon tips (Navarro et al, 2011).…”

“…Recent work by Teo et al (2017) has elucidated important aspects of a specific TAC that promotes tuber induction. Protein-binding assays demonstrated that, similar to the FAC of rice, the tuberigen complex that functions locally in stolon tips is composed of StSP6A, a 14-3-3 protein, and an FD-like (FDL) protein.…”

“…Overall, these results strongly suggest that the components of this complex are a local trigger for tuber formation. No effect on tuberization was reported, however, upon overexpression of StFD1 (Teo, 2015). In the more recent study (Teo et al, 2017), tuberization was measured by the percentage of plants that tuberized at discrete time points without regard for overall tuber yields.…”

“…No effect on tuberization was reported, however, upon overexpression of StFD1 (Teo, 2015). In the more recent study (Teo et al, 2017), tuberization was measured by the percentage of plants that tuberized at discrete time points without regard for overall tuber yields. This suggests that the components of this complex regulate the onset of tuberization but do not necessarily affect overall tuber yield.…”