Department of Biology, Genetics Institute, University of Florida, Gainesville, FL 32610, USA.
New Phytol. 2011 Jan;189(1):160-75. doi: 10.1111/j.1469-8137.2010.03460.x. Epub 2010 Sep 14.
• Isopropylmalate dehydrogenases (IPMDHs) catalyze the oxidative decarboxylation of 3-isopropylmalate (3-IPM) in leucine biosynthesis in microorganisms. The Arabidopsis thaliana genome contains three putative IPMDH genes. • IPMDH2 and IPMDH3 proteins exhibited significantly higher activity toward 3-IPM than IPMDH1, which is indicative of a pivotal role in leucine biosynthesis. Single mutants of IPMDH2 or IPMDH3 lacked a discernible phenotype. Genetic analysis showed that ipmdh2 ipmdh3 was lethal in male gametophytes and had reduced transmission through female gametophytes. The aborted pollen grains were small, abnormal in cellular structure, and arrested in germination. In addition, half of the double mutant embryo sacs exhibited slowed development. • The IPMDH2/ipmdh2 ipmdh3/ipmdh3 genotype exhibited abnormal vegetative phenotypes, suggesting haplo-insufficiency of IPMDH2 in the ipmdh3 background. This mutant and a triple mutant containing one allele of IPMDH2 or IPMDH3 had decreased leucine biosynthetic enzyme activities and lower free leucine concentrations. The latter mutant showed changes in glucosinolate profiles different from those in the ipmdh1 mutant. • The results demonstrate that IPMDH2 and IPMDH3 primarily function in leucine biosynthesis, are essential for pollen development and are needed for proper embryo sac development.
• 异丙基苹果酸脱氢酶（IPMDHs）在微生物的亮氨酸生物合成中催化 3-异丙基苹果酸（3-IPM）的氧化脱羧。拟南芥基因组包含三个假定的 IPMDH 基因。• IPMDH2 和 IPMDH3 蛋白对 3-IPM 的活性明显高于 IPMDH1，这表明它们在亮氨酸生物合成中起着关键作用。IPMDH2 或 IPMDH3 的单突变体缺乏明显的表型。遗传分析表明，ipmdh2 ipmdh3 在雄性配子体中是致命的，并且通过雌性配子体的传递减少。退化的花粉粒体积小，细胞结构异常，发芽受阻。此外，一半的双突变体胚囊中显示出发育缓慢。• IPMDH2/ipmdh2 ipmdh3/ipmdh3 基因型表现出异常的营养表型，这表明 IPMDH2 在 ipmdh3 背景下存在单倍体不足。该突变体和包含一个 IPMDH2 或 IPMDH3 等位基因的三重突变体的亮氨酸生物合成酶活性降低，游离亮氨酸浓度降低。后一种突变体显示出不同于 ipmdh1 突变体的硫代葡萄糖苷图谱变化。• 结果表明，IPMDH2 和 IPMDH3 主要在亮氨酸生物合成中起作用，是花粉发育所必需的，并且是适当的胚囊发育所必需的。
