Department of Genetics and Cell Biology , College of Life Sciences, Nankai University, and Tianjin Key Laboratory of Protein Sciences, Tianjin 300071, China.
Plant Physiol. 2013 Oct;163(2):713-20. doi: 10.1104/pp.113.224501. Epub 2013 Aug 6.
In all eukaryotic cells, the endoplasmic reticulum (ER) forms a tubular network whose generation requires the fusion of ER membranes. In Arabidopsis (Arabidopsis thaliana), the membrane-bound GTPase ROOT HAIR DEFECTIVE3 (RHD3) is a potential candidate to mediate ER fusion. In addition, Arabidopsis has two tissue-specific isoforms of RHD3, namely RHD3-like (RL) proteins, and their function is not clear. Here, we show that a null allele of RHD3, rhd3-8, causes growth defects and shortened root hairs. A point mutant, rhd3-1, exhibits a more severe growth phenotype than the null mutant, likely because it exerts a dominant-negative effect on the RL proteins. Genetic analysis reveals that the double deletion of RHD3 and RL1 is lethal and that the rhd3 rl2 plants produce no viable pollen, suggesting that the RL proteins are redundant to RHD3. RHD3 family proteins can replace Sey1p, the homolog of RHD3 in yeast (Saccharomyces cerevisiae), in the maintenance of ER morphology, and they are able to fuse membranes both in vivo and in vitro. Our results suggest that RHD3 proteins mediate ER fusion and are essential for plant development and that the formation of the tubular ER network is of general physiological significance.
在所有真核细胞中，内质网（ER）形成管状网络，其生成需要 ER 膜的融合。在拟南芥（Arabidopsis thaliana）中，膜结合的 GTPase ROOT HAIR DEFECTIVE3（RHD3）是一种潜在的候选蛋白，可介导 ER 融合。此外，拟南芥有两种组织特异性的 RHD3 同工型，即 RHD3-like（RL）蛋白，但其功能尚不清楚。在这里，我们发现 RHD3 的一个 null 等位基因 rhd3-8 导致生长缺陷和根毛缩短。一个点突变体 rhd3-1 表现出比 null 突变体更严重的生长表型，可能是因为它对 RL 蛋白表现出显性负效应。遗传分析表明，RHD3 和 RL1 的双缺失是致死的，而 rhd3 rl2 植物产生的花粉没有活力，这表明 RL 蛋白对 RHD3 是冗余的。RHD3 家族蛋白可以取代 Sey1p，即酵母（Saccharomyces cerevisiae）中 RHD3 的同源物，在维持 ER 形态方面，它们能够在体内和体外融合膜。我们的结果表明，RHD3 蛋白介导 ER 融合，对植物发育至关重要，管状 ER 网络的形成具有普遍的生理意义。
