摘要Sphingolipids are the structural components of membrane lipid bilayers and act as signaling molecules in many cellular processes.Serine pal-mitoyltransferase(SPT)is the first committed and rate-limiting enzyme in the de novo sphingolipids biosynthetic pathway.The core SPT enzyme is a heterodimer consisting of LONG-CHAIN BASE1(LCB1)and LCB2 subunits.SPT activity is in-hibited by orosomucoid proteins and stimulated by small subunits of SPT(ssSPTs).However,whether LCB1 is modified and how such mod-ification might regulate SPT activity have to date been unclear.Here,we show that activation of MITOGEN-ACTIVATED PROTEIN KINASE 3(MPK3)and MPK6 by upstream MKK9 and treat-ment with Flg22(a pathogen-associated molec-ular pattern)increases SPT activity and induces the accumulation of sphingosine long-chain base t18:0 in Arabidopsis thaliana,with activated MPK3 and MPK6 phosphorylating AtLCB1.Phosphor-ylation of AtLCB1 strengthened its binding with AtLCB2b,promoted its binding with ssSPTs,and stimulated the formation of higher order oligo-meric and active SPT complexes.Our findings therefore suggest a novel regulatory mechanism for SPT activity.