Mutations in the floral regulator gene HUA2 restore flowering to the Arabidopsis trehalose 6-phosphate synthase1 (tps1) mutant

Plant growth and development are regulated by many factors, including carbohydrate availability and signaling. Trehalose 6-phosphate (T6P), which is synthesized by TREHALOSE-6-PHOSPHATE SYNTHASE 1 (TPS1), is positively associated with and functions as a signal that informs the cell about the carbohydrate status. Mutations in TPS1 negatively affect the growth and development of Arabidopsis (Arabidopsis thaliana), and complete loss-of-function alleles are embryo-lethal, which can be overcome using inducible expression of TPS1 (GVG::TPS1) during embryogenesis. Using ethyl methane sulfonate mutagenesis in combination with genome re-sequencing, we have identified several alleles in the floral regulator gene HUA2 that restore flowering in tps1-2 GVG::TPS1. Genetic analyses using an HUA2 T-DNA insertion allele, hua2-4, confirmed this finding. RNA-seq analyses demonstrated that hua2-4 has widespread effects on the tps1-2 GVG::TPS1 transcriptome, including key genes and pathways involved in regulating flowering. Higher order mutants combining tps1-2 GVG::TPS1 and hua2-4 with alleles in the key flowering time regulators FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), and FLOWERING LOCUS C (FLC) were constructed to analyze the role of HUA2 during floral transition in tps1-2 in more detail. Our findings demonstrate that loss of HUA2 can restore flowering in tps1-2 GVG::TPS1, in part through activation of FT, with contributions from the upstream regulators SOC1 and FLC. Interestingly, we found that mutation of FLC is sufficient to induce flowering in tps1-2 GVG::TPS1. Furthermore, we observed that mutations in HUA2 modulate carbohydrate signaling and that this regulation might contribute to flowering in hua2-4 tps1-2 GVG::TPS1.HUA2 represents an important genetic link between energy management and flowering time regulation by modulating T6P-dependent carbohydrate signaling and activating the floral integrator FLOWER LOCUS T.