The chemical reactions and pathways resulting in the formation of rhizobactin 1021, (E)-4-((3-(acetylhydroxyamino)propyl)-amino)-2-hydroxy-(2-(2-(3-(hydroxy(1-oxo-2-decenyl)amino)propyl)amino)-2-oxoethyl)-4-oxobutanoic acid, a siderophore produced by Sinorhizobium meliloti.