Abstract
The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the early step in the cytosolic isoprenoid biosynthesis pathway. We isolated T-DNA insertion mutants, hmg1 and hmg2, in Arabidopsis. The hmg1 exhibited male sterility, while the hmg2 exhibited normal fertility. It was revealed that the HMG1 transcript was present in tapetum and microspores. The hmg1 exhibited stunting of tapetosomes, which are characteristic lipid-rich organelles in tapetum. In contrast, the hmg1 male gametophyte displayed normal intracellular structure. We propose that the sterol deficiency of tapetal cells in the hmg1 caused stunting of the tapetosomes, leading to inadequate hmg1 pollen coat materials for pollen germination. Furthermore, we tried to produce hmg1 hmg2 double mutants. Crossing experiments and microscopic analysis showed that the development of hmg1 hmg2 male gametophyte was abnormal, but hmg1 hmg2 female was normal. This result may suggest that only HMG1 or HMG2 is necessary for the male gametophyte development for the supply of sterols.
