A Plant biostimulant prepared from Ascophyllum nodosum Induces Flowering by Regulating the MIR156‐mediated Age Pathway in Arabidopsis

Flowering, the change from vegetative development to the reproductive phase, represents a crucial and intricate stage in the life cycle of plants, which is tightly controlled by both internal and external factors. In this study, we investigated the effect of Ascophyllum nodosum extract (ANE) on the flowering time of Arabidopsis. We found that a 0.1% concentration of ANE induced flowering in Arabidopsis, accompanied by the upregulation of key flowering time genes: FT (FLOWERING LOCUS T), SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1), and LFY (LEAFY). Further investigation showed that ANE specifically promotes flowering through the MIR156‐mediated age pathway. ANE treatment resulted in the repression of negative regulator genes, MIR156, while simultaneously enhancing the expression of positive regulator genes, including SPLs and MIR172. This, in turn, led to the downregulation of AP2‐like genes, which are known as floral repressors. It is worth noting that ANE did not alleviate the late flowering phenotype of MIR156‐overexpressing plants and spl mutants. Furthermore, ANE‐derived fucoidan mimics the function of sugars in regulating MIR156, closely mirroring the effects induced by ANE treatments. It suppresses the transcript levels of MIR156 and AP2‐like genes while inducing those of SPLs and MIR172, thereby reinforcing the involvement of fucoidan in the control of flowering by ANE. In summary, our results demonstrate that ANE induces flowering by modulating the MIR156‐SPL module within the age pathway, and this effect is mediated by fucoidan.