13. hmg1 変異体はステロール欠損変異体か?

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In higher plants, isoprenoids are synthesized via mevalonate pathway (MVA pathway) and non-mevalonate pathway. 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) is a key enzyme of MVA pathway and is encoded by two genes, HMG1 and HMG2,in Arabidoposis. To understand the role of HMGR on plant development, we analyze hmg1 and hmg2 mutants. hmg1 mutant showed dwarf, male sterile and early senescence phenotypes. The microscopic analysis and the gene expression analyses revealed that dwarf phenotype of hmg1 is due to the inhibition of cell elongation. Sterility in hmg1 is due to a loss of the ability of germination in pollen. It was found that the lipids supplied from tapetum cells are important for the development of pollen. HMG1 is expressed in tapetum cells and organelles rich in lipids are decreased in hmg1 tapetum cells. Therefore, it was suggested that hmg1 pollen can not germinate because of decreased lipids supplied from tapetum cells. SAG12,the senescence marker gene, is expressed earlier in hmg1 than in a wild type (WT). Exogenously applied trans-cytokinins, hormones known to inhibit senescence, inhibited the early induction of SAG12 expression in hmg1,however, levels of trans-cytokinins were not lower in hmg1. WT plants treated with squalene synthase inhibitor mimicked hmg1 phenotypes but WT plants treated with brassinosteroids synthase inhibitor did not show similar phenotype with hmg1. Chemical complementation also showed triterpenoids downstream of squalene is contribute to the pleiotropic phenotype of hmg1. The sterol levels in hmg1 mutants were lower than in the WT. These findings suggest that HMG1 is a critical role in triterpene biosynthesis, and that sterols and/or pentacyclic isoprenoids contribute to cell elongation, senescence and fertility.
植物化学調節学会の論文
2003-10-10

13. hmg1 変異体はステロール欠損変異体か?

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