XVI International Botanical Congess

Plant isoprenoid biosynthesis is a complex multibranched pathway. IPP, the structural precursor of all isoprenoids, is synthesized by two alternativepathways: the mevalonate pathway (located in the cytosol) and the recently discovered deoxyxylulose-5P pathway (located in the plastids). HMG-CoA reductase (HMGR) is one of the best characterized enzymes of the pathway. HMGR is under the control of complex transcriptional and post-transcriptional mechanisms. In Arabidopsis the specific role of the different HMGR isoforms has been studied in transgenic plants with altered levels of the enzyme. The genes encoding other early enzymes of the isoprenoid pathway have been recently cloned and characterized. The role of these enzymes in the control of the pathway is currently being studied in transgenic plants with altered enzyme levels.