Abstract
Plants produce a variety of isoprenoids. All isoprenoids are synthesized via the cytosolic mevalonate (MVA) pathway and the plastidic non-MVA pathway. HMG-CoA reductase (HMGR) catalyzes the early step in the MVA pathway. Arabidopsis has two genes encoding HMGR, HMG1 and HMG2. To understand the roles of HMG1 and HMG2, we have isolated and characterized hmg1 and hmg2 mutants. hmg1 mutant showed dwarf due to reduced cell elongation, early senescence and male sterile phenotypes, suggesting that hmg1 is a mutant reduced brassinosteroid or cytokinin that are isoprenoid-type hormones. However several experiments revealed that hmg1 is not such a mutant. The pleiotropic phenotypes were rescued by squalene. Experiments using inhibitors of enzymes in the MVA pathway suggested that different triterpenes regulate cell elongation and senescence, respectively. Quantification-analysis revealed decreased sterol contents in hmg1. These findings suggested that HMG1 is important for the biosynthesis of triterpenes involved in cell elongation, senescence and fertility.
