Isoprenoids are a hugely diverse family of compounds derived from the C5 precursors isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP).Although all free-living organisms synthesize isoprenoids,they are particularly abundant and diverse in plants,with tens of thousands structures known to date.The highest variety of plant isoprenoids are specialized (secondary) metabolites that participate in the interaction of plants with their environment.These include pigments,volatiles,and defense compounds,some of which have applications in industry and agriculture.For example,isoprenoid drugs are used against cancer (taxol) or malaria (artemisin).But plants also synthesize isoprenoids with essential (primary) functions in respiration (ubiquinone),photosynthesis (carotenoids,chlorophylls,tocopherols,phylIoquinones,plastoquinone),membrane architecture (sterols),and growth regulation (brassinosteroids,cytokinins,gibberellins,abscisic acid,strigolactones).Despite their economic importance and biological relevance,our knowledge of the core pathways for the production of the universal isoprenoid precursors IPP and DMAPP in plant cells remained incomplete until the mid-1990s.Impressive progress in the last decade has resulted in the complete elucidation of several isoprenoid pathways,the identification of regulatory mechanisms,the discovery of new functions and properties of specific isoprenoids,and the successful manipulation of isoprenoid biosynthesis in a number of metabolic engineering approaches.In this update article,we will discuss some of the most recent advances in the plant isoprenoid field,focusing on the pathways supplying the C5 precursors in plant cells and the novel insights into regulatory matters.