Abstract: Mitogen-activated protein kinase (MAPK) cascades play vital roles in regulating plant growth, development, and stress responses. Nevertheless, the complete MAPK cascade that regulates the flowering time of Arabidopsis thaliana has not been established. A MAPK module comprising MAPKKK18, MAPKK3, and MAPK1/2/7/14 accelerates flowering in Arabidopsis. Through direct interaction, MAPK1/2/7/14 phosphorylates the S²⁴ residue of NF-YB2. Phosphorylated NF-YB2 enhances the stability of the heterotrimeric CO ~ NF-YB2 ~ NF-YC3/C9 complex and the expression of FT. Accumulation of NF-YB2 significantly promotes flowering, whereas the role of NF-YB2^S24A in this process is less pronounced. Compared with the transgenic plants overexpressing MAPKKK18 in the wild-type (WT) background, the nf-yb2 plants overexpressing MAPKKK18 bolt considerably later. Taken together, the MAPKKK18-mediated signaling cascade exerts tight control over the flowering time of Arabidopsis by modulating the phosphorylation status of NF-YB2, unveiling a flexible regulatory pathway to fine-tune plant development.

Key words: CO, ?owering time, FT, MAPKKK18, NF‐YB2, phosphorylation