State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
State Key Laboratory of Plant Genomics and National Plant Gene Research Center, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China.
J Integr Plant Biol. 2018 Nov;60(11):1051-1069. doi: 10.1111/jipb.12694. Epub 2018 Sep 3.
Cell-wall deposition of cellulose microfibrils is essential for plant growth and development. In plant cells, cellulose synthesis is accomplished by cellulose synthase complexes located in the plasma membrane. Trafficking of the complex between endomembrane compartments and the plasma membrane is vital for cellulose biosynthesis; however, the mechanism for this process is not well understood. We here report that, in Arabidopsis thaliana, Rab-H1b, a Golgi-localized small GTPase, participates in the trafficking of CELLULOSE SYNTHASE 6 (CESA6) to the plasma membrane. Loss of Rab-H1b function resulted in altered distribution and motility of CESA6 in the plasma membrane and reduced cellulose content. Seedlings with this defect exhibited short, fragile etiolated hypocotyls. Exocytosis of CESA6 was impaired in rab-h1b cells, and endocytosis in mutant cells was significantly reduced as well. We further observed accumulation of vesicles around an abnormal Golgi apparatus having an increased number of cisternae in rab-h1b cells, suggesting a defect in cisternal homeostasis caused by Rab-H1b loss function. Our findings link Rab GTPases to cellulose biosynthesis, during hypocotyl growth, and suggest Rab-H1b is crucial for modulating the trafficking of cellulose synthase complexes between endomembrane compartments and the plasma membrane and for maintaining Golgi organization and morphology.
纤维素微纤丝的细胞壁沉积对于植物的生长和发育至关重要。在植物细胞中，纤维素的合成是由位于质膜中的纤维素合酶复合物完成的。复合物在内质网隔室和质膜之间的运输对于纤维素的生物合成至关重要；然而，这个过程的机制还不是很清楚。在这里，我们报告说，在拟南芥中，高尔基体定位的小 GTPase Rab-H1b 参与了纤维素合酶 6（CESA6）向质膜的运输。Rab-H1b 功能的丧失导致 CESA6 在质膜中的分布和运动发生改变，纤维素含量降低。具有这种缺陷的幼苗表现出短而脆弱的黄化下胚轴。rab-h1b 细胞中 CESA6 的胞吐作用受损，而突变细胞中的内吞作用也显著减少。我们还观察到在 rab-h1b 细胞中，异常高尔基体周围有囊泡积累，高尔基体中内质网的数量增加，这表明 Rab-H1b 功能丧失导致内质网稳态失调。我们的发现将 Rab GTPases 与质膜上的纤维素生物合成联系起来，在幼苗下胚轴的生长过程中，Rab-H1b 对于调节纤维素合酶复合物在内质网隔室和质膜之间的运输以及维持高尔基体的组织和形态至关重要。
