Control of flowering and storage organ formation in potato by FLOWERING LOCUS T

Abstract

Seasonal fluctuations in day length regulate important aspects of plant development such as the flowering transition or, in potato (Solanum tuberosum), the formation of tubers. Day length is sensed by the leaves, which produce a mobile signal transported to the shoot apex or underground stems to induce a flowering transition or, respectively, a tuberization transition. Work in Arabidopsis, tomato and rice (Oryza sativa) identified the mobile FLOWERING LOCUS T (FT) protein as a main component of the long-range 'florigen', or flowering hormone, signal. Here we show that expression of the Hd3a gene, the FT orthologue in rice, induces strict short-day potato types to tuberize in long days. Tuber induction is graft transmissible and the Hd3a-GFP protein is detected in the stolons of grafted plants, transport of the fusion protein thus correlating with tuber formation. We provide evidence showing that the potato floral and tuberization transitions are controlled by two different FT-like paralogues (StSP3D and StSP6A) that respond to independent environmental cues, and show that an autorelay mechanism involving CONSTANS modulates expression of the tuberization-control StSP6A gene.

The Multiple Signals That Control Tuber Formation

“…Overall, these results suggest that StSP6A is involved in the initial activation of tuberization but probably not long-term tuber morphology. Consistent with this premise, StSP6A expression was strongest in an early-maturing variety and relatively lower in a latematuring variety (Navarro et al, 2011). Induction of StSP6A using an inducible promoter led to the activation of several tuber marker genes, including StGA2OX1.…”

“…These include bud dormancy in Vitis vinifera (Vergara et al, 2016), seasonal control of growth in Populus spp. (Böhlenius et al, 2006;Tylewicz et al, 2015), bud dormancy in conifers (Gyllenstrand et al, 2007), meristem growth termination in tomato (Solanum lycopersicum; Shalit et al, 2009), and tuberization in potato (Navarro et al, 2011). Overall, these observations suggest that FT orthologs may function as mobile signals in meristem-associated transitions in nonfloral pathways.…”

“…StSP3D controls the floral pathway, StSP6A regulates tuber initiation, and StSP5G represses tuber formation by suppressing StSP6A activity (Abelenda et al, 2016). Utilizing transgenic analysis and heterografting experiments, StSP6A has been established as a candidate for the mobile tuber signal (Navarro et al, 2011). Overexpression lines of StSP6A tuberized earlier and under noninductive LD.…”

“…Based on published experimental evidence, the three most important signals that regulate the onset of tuber formation in potato are CYCLING DOF FACTOR1 (StCDF1), StSP6A, and StBEL5 (Banerjee et al, 2006; (Banerjee et al, 2006;Navarro et al, 2011). In this review, we will discuss how these signals regulate the timing and development of tuberization.…”

A reverse genetics approach identifies novel mutants in light responses and anthocyanin metabolism in petunia

“…In day-neutral tomato, the FT ortholog, SINGLE FLOWER TRUSS (SFT ), has been demonstrated to trigger the systemic signal responsible for pleiotropic regulation of growth and flowering (Lifschitz et al 2006). In potato, the ectopic expression of a rice FT gene elucidated the role of CO in controlling the photoperiodic processes flowering and tuberization (Navarro et al 2011). The mutation identified in petunia CO ortholog is similar to the 4-bp deletion in the CCT domain of the Arabidopsis late-flowering co-5 and co-7 mutant alleles (Koornneef et al 1991), generating a peptide lacking the P and R conserved residues (Fig.…”