Mobility of FLOWERING LOCUS T protein as a systemic signal in trifoliate orange and its low accumulation in grafted juvenile scions

Abstract

The long juvenile period of perennial woody plants is a major constraint in breeding programs. FLOWERING LOCUS T (FT) protein is an important mobile florigen signal that induces plant flowering. However, whether FT can be transported in woody plants to shorten the juvenile period is unknown, and its transport mechanism remains unclear. In this study, trifoliate orange FT (ToFT) and Arabidopsis FT (AtFT, which has been confirmed to be transportable in Arabidopsis) as a control were transformed into tomato and trifoliate orange, and early flowering was induced in the transgenic plants. Long-distance and two-way (upward and downward) transmission of ToFT and AtFT proteins was confirmed in both tomato and trifoliate orange using grafting and western blot analysis. However, rootstocks of transgenic trifoliate orange could not induce flowering in grafted wild-type juvenile scions because of the low accumulation of total FT protein in the grafted scions. It was further confirmed that endogenous ToFT protein was reduced in trifoliate orange, and the accumulation of the transported ToFT and AtFT proteins was lower than that in grafted juvenile tomato scions. Furthermore, the trifoliate orange FT-INTERACTING PROTEIN1 homolog (ToFTIP1) was isolated by yeast two-hybrid analysis. The FTIP1 homolog may regulate FT transport by interacting with FT in tomato and trifoliate orange. Our findings suggest that FT transport may be conserved between the tomato model and woody plants. However, in woody plants, the transported FT protein did not accumulate in significant amounts in the grafted wild-type juvenile scions and induce the scions to flower.

A bZIP transcription factor (CiFD) regulates drought‐ and low‐temperature‐induced flowering by alternative splicing in citrus

“…However, some transgenic plants from two AS transcripts did not display early flowering phenotype. We speculated that this may be caused by the expression of CiFDα and CiFDβ not reaching the threshold required for plant flowering, similar to the transgenic plants of CiFT in citrus (Wu et al, 2022).…”

Functional diversification and molecular mechanisms of FLOWERING LOCUS T/TERMINAL FLOWER 1 family genes in horticultural plants

“…In trifoliate orange, its early flowering was induced in the transgenic tomato as well as trifoliate orange plants transformed with ToFT . However, the rootstocks of transgenic trifoliate orange could not induce flowering of grafted wild-type (WT) juvenile scions because of their low accumulation of total FT protein (Wu et al, 2022 ). That finings suggests the expression of FT must reach a certain threshold to induce flowering.…”

Regulatory frameworks involved in the floral induction, formation and developmental programming of woody horticultural plants: a case study on blueberries

“…Intriguing insights have indicated from transgrafting experiments involving FT-CX materials, underscoring the role of FT-CX in signaling the onset of flowering. In several instances, the FT-CX generated within transgenic leaves, functioning as either a direct or an indirect florigenic signal, exhibited the remarkable capacity to promote flowering in nontransgenic scions through long-distance transportation ( Ye et al., 2014 ; Song et al., 2019 ; Wu et al., 2022 ). This phenomenon diverges distinctly from parallel transgrafting studies where FT-CX produced in transgenic roots and stems (in the absence of transgenic leaves) failed to incite flowering in nontransgenic scions ( Zhang et al., 2010 ; Srinivasan et al., 2012 ; Wenzel et al., 2013 ; Bull et al., 2017 ).…”