Zhuang X, Xu Y, Chong K, Lan L, Xue Y, Xu Z
Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, CAS, Beijing, China.
Plant Cell Environ. 2005 Feb;28(2):147-56. doi: 10.1111/j.1365-3040.2004.01253.x.
Arf (ADP-ribosylation factor) proteins, which mediate vesicular transport, have little or no intrinsic GTPase activity. They rely on the action of GTPase-activating proteins (GAPs) and guanine nucleotide exchange factors (GEFs) for their function. In the present study the OsAGAP gene in rice, which encoded a protein with predicted structure similar to ArfGAP, was identified. The purified OsAGAP-GST fusion protein was able to stimulate the GTPase activity of rice Arf. Furthermore, OsAGAP can rescue the defect of vesicular transport in the yeast gcs1 delta glo3 delta double-mutant cells. Transgenic Arabidopsis with OsAGAP constitutively expression showed reduced apical dominance, shorter primary roots, increasing number of longer adventitious roots. Many of the phenotypes can be phenocopied by treatment of exogenous indoleacetic acid level (IAA) in wild-type plants. Determination of whole-plant IAA level showed that there is a sharp increase of free IAA in OsAGAP transgenic Arabidopsis seedlings. In addition, removal of the 4-day-old shoot apex could inhibit the adventitious root formation in the transgenic seedlings. These results suggest OsAGAP, an ARF-GAP of rice, maybe involved in the mediation of plant root development by regulating auxin level.
Arf（ADP核糖基化因子）蛋白介导囊泡运输，其内在的GTP酶活性很低或没有。它们的功能依赖于GTP酶激活蛋白（GAPs）和鸟嘌呤核苷酸交换因子（GEFs）的作用。在本研究中，鉴定了水稻中的OsAGAP基因，该基因编码一种预测结构与ArfGAP相似的蛋白质。纯化的OsAGAP-GST融合蛋白能够刺激水稻Arf的GTP酶活性。此外，OsAGAP可以挽救酵母gcs1δglo3δ双突变细胞中囊泡运输的缺陷。组成型表达OsAGAP的转基因拟南芥表现出顶端优势降低、主根变短、不定根数量增加且变长。许多这些表型可以通过在野生型植物中处理外源吲哚乙酸水平（IAA）来模拟。对全株IAA水平的测定表明，OsAGAP转基因拟南芥幼苗中的游离IAA急剧增加。此外，去除4日龄的茎尖可以抑制转基因幼苗中不定根的形成。这些结果表明，水稻的ARF-GAP OsAGAP可能通过调节生长素水平参与植物根系发育的调控。
