The AtFLC-AtFT Pathway Is Involved in the Early Flowering Promoted by Loss of AtHO1 Function in Arabidopsis

Although previous studies have indicated that heme oxygenase 1 (HO1/HY1) regulates the flowering time via the photoperiod pathway, the specific mechanism is still elusive. Here, we found that the Arabidopsis hy1-100 mutant displayed early flowering, and the characteristic expression patterns of several master genes involved in the autonomous pathway were altered. Notably, the transcript levels of FLOWERING LOCUS C (AtFLC) gene declined developmentally in both wild-type and hy1-100 mutant, with a more pronounced fold reduction observed in the mutant. Genetic evidence further underlined that hy1-100/FLCOE plants partially reversed the early flowering phenomenon of hy1-100 mutant, suggesting that AtHO1 regulated flowering at least partially through the AtFLC-involved autonomous pathway, as supported by changes in FLOWERING LOCUS T (AtFT) and SUPPRESSOR OF OVEREXPRESSION OF CO1 (AtSOC1) transcripts. Further analysis of hy1-100/ft mutants revealed that hy1-100/ft and ft mutants displayed similar late flowering phenotypes, accompanied by downregulated APETALA1 (AtAP1) and AtSOC1, indicating that AtFT played a crucial role in AtHO1-regulated flowering. Two key conclusions are drawn: first, the loss of AtHO1 function promotes early flowering in Arabidopsis, which was genetically linked to the autonomous pathway regulating AtFLC expression; second, AtFT was an essential downstream factor mediating AtHO1-regulated flowering.