Four Tomato FLOWERING LOCUS T-Like Proteins Act Antagonistically to Regulate Floral Initiation

Abstract

The transition from vegetative growth to floral meristems in higher plants is regulated through the integration of internal cues and environmental signals. We were interested to examine the molecular mechanism of flowering in the day-neutral plant tomato (Solanum lycopersicum L.) and the effect of environmental conditions on tomato flowering. Analysis of the tomato genome uncovered 13 PEBP (phosphatidylethanolamine-binding protein) genes, and found six of them were FT-like genes which named as SlSP3D, SlSP6A, SlSP5G, SlSP5G1, SlSP5G2, and SlSP5G3. Six FT-like genes were analyzed to clarify their functional roles in flowering using transgenic and expression analyses. We found that SlSP5G, SlSP5G2, and SlSP5G3 proteins were floral inhibitors whereas only SlSP3D/SFT (SINGLE FLOWER TRUSS) was a floral inducer. SlSP5G was expressed at higher levels in long day (LD) conditions compared to short day (SD) conditions while SlSP5G2 and SlSP5G3 showed the opposite expression patterns. The silencing of SlSP5G by VIGS (Virus induced gene silencing) resulted in tomato plants that flowered early under LD conditions and the silencing of SlSP5G2 and SlSP5G3 led to early flowering under SD conditions. The higher expression levels of SlSP5G under LD conditions were not seen in phyB1 mutants, and the expression levels of SlSP5G2 and SlSP5G3 were increased in phyB1 mutants under both SD and LD conditions compared to wild type plants. These data suggest that SlSP5G, SlSP5G2, and SlSP5G3 are controlled by photoperiod, and the different expression patterns of FT-like genes under different photoperiod may contribute to tomato being a day neutral plant. In addition, PHYB1 mediate the expression of SlSP5G, SlSP5G2, and SlSP5G3 to regulate flowering in tomato.

Pivotal Roles of Cryptochromes 1a and 2 in Tomato Development and Physiology

“…The promotion of flowering in the cry1a/cry2 mutant is probably mediated by SP5G. This gene, belonging to the large family of FT-like genes, is expressed at very high levels in LD and at low levels in SD photoperiods (Cao et al, 2016); SP5G is an inhibitor of flowering, as indicated by the fact that Arabidopsis overexpressors show retarded flowering and that virus-mediated silencing of the SP5G gene in tomato resulted in early flowering of tomato plants under LD conditions (Cao et al, 2016). SP5G mutants obtained by gene-editing exhibit rapid flowering and enhance the compact determinate growth habit of field tomatoes (Soyk et al, 2017).…”

FT and florigen long-distance flowering control in plants

“…The balance of activity of florigens and antiflorigens is important for overall growth, architecture, and/or flowering. This was first elucidated for FT and TFL1-like genes in the tomato model [18][19][20]. iv.…”

The FT/FD‐dependent initiation of flowering under long‐day conditions in the day‐neutral species Nicotiana tabacum originates from the facultative short‐day ancestor Nicotiana tomentosiformis

“…During vegetative growth, expression of the floral activator BvFT2 is repressed by BvFT1 and flowering is initiated only following the vernalization-dependent downregulation of BvFT1 expression (Pin et al, 2010). In tomato, the FT homolog SlSP5G represses flowering under LD conditions, whereas the FT homologs SlSP5G2 and SlSP5G3 repress flowering under SD conditions (Cao et al, 2016). Floral differentiation is usually repressed by members of the TERMINAL FLOWER 1 (TFL1)-like clade of the PEBP family.…”