Early flowering phenotype of the Arabidopsis altered meristem program1 mutant is dependent on the FLOWERING LOCUS T-mediated pathway.

Controlling the flowering time is crucial for propagating plant species and crop production. ALTERED MERISTEM PROGRAM1 (AMP1) in Arabidopsis thaliana encodes a putative carboxypeptidase, and an AMP1 mutant (amp1) was found to cause highly pleiotropic phenotypes including a short plastochron, an enlarged shoot apical meristem, and reduced apical dominance. Although amp1 also shows an early flowering phenotype, its mechanism has not been investigated in detail. The most important floral integrator or florigen gene, FLOWERING LOCUS T (FT), has a close relative, TWIN SISTER OF FT (TSF). In this report, we generated a new allele of tsf using a genome-editing technique and produced ft tsf double and amp1 ft tsf triple mutants. The flowering time of amp1 ft tsf was equally as late as ft tsf under long-day conditions. In addition, the expression level of FT in amp1 was 2.4-fold higher than that in wild-type, even five days after germination under long-day conditions. These results suggest that the elevated expression level of FT is responsible for the early flowering phenotype of amp1. Furthermore, expression of FLOWERING LOCUS C (FLC), a negative regulator of FT expression, is severely repressed in amp1, raising the possibility that low expression levels of FLC contributes to upregulation of FT expression and the early flowering phenotype of amp1.