Auxin acts as a key hormone in plant that determines many developmental processes by the typical concentration dependent way.Local auxin concentration is precisely controlled by both polar auxin transport and auxin biosynthesis in response to both developmental and environmental cues.However,the intense studies had illustrated how the regulation of polar auxin transport determined the local concentration of auxin,but the regulation of auxin biosynthesis is largely unknown.Interestingly,by mass-spectrum we firstly identified a phosphorylation site on TAA1 protein,a key enzyme in auxin biosynthesis.The phosphorylation of this plant well-conserved site of TAA determined the on-off switch of its enzyme activity,phosphorylation switch-off and non-phosphorylation switch-on,which illustrated a