摘要Plant isoprenoids are formed from precursors synthesized by the mevalonate (MVA) pathway in the cytosol or by the methyl-D-erythritol 4- phosphate (MEP) pathway in plastids.Although some exchange of precursors occurs,cytosolic sesquiterpenes are assumed to derive mainly from MVA,while plastidial monoterpenes are produced preferentially from MEP precursors.Additional complexity arises in the first step of the MEP pathway,which is typically catalyzed by two divergent 1-deoxy-D-xylulose 5-phosphate synthase isoforms (DXS1,DXS2).In tomato (Solanum lycopersicum),the SIDXS1 gene is ubiquitously expressed with highest levels during fruit ripening,whereas SIDXS2 transcripts are abundant in only few tissues,including young leaves,petals,and isolated trichomes.Specific down-regulation of SIDXS2 expression sor allocation.