HMG2
3-Hydroxy-3-methylglutaryl-CoA
reductase (HMGR) catalyzes the first committed step
in the cytosolic isoprenoid
biosynthesis pathway in higher plants. To understand the contribution of HMGR
to plant development, we isolated T-DNA insertion mutants for HMG1 and HMG2.
The hmg1 and hmg2 mutants were both more sensitive than the wild type (WT) to lovastatin, an inhibitor of HMGR. The hmg2 mutant showed no
visible phenotype under normal growth conditions. In contrast, the hmg1 mutant
exhibited dwarfing, early senescence, and sterility. Expression of
senescence-associated genes 12 (SAG12), a marker gene for senescence, was
induced in the hmg1 mutant at an earlier stage than in the WT. Levels of trans-cytokinins - hormones known to inhibit senescence - were
not lower in hmg1. The mutant did not have the typical appearance of brassinosteroid (BR)-deficient mutants, except for a dwarf
phenotype, because of the suppression of cell
elongation. The expression of several genes involved in cell elongation was
suppressed in hmg1. WT plants treated exogenously with inhibitors of sterol
biosynthesis had similar gene expression and sterility characteristics as the
hmg1 mutants. Pleiotropic phenotypes were rescued by
feeding with squalene, the precursor of sterols and triterpenoids. The sterol levels in hmg1 mutants were lower
than in the WT. These findings suggest that HMG1 plays a critical role in triterpene biosynthesis, and that
sterols and/or triterpenoids contribute to cell
elongation, senescence, and fertility.
PMID: 14871314 [PubMed - as supplied by publisher]