Hunter Christine A, Aukerman Milo J, Sun Hui, Fokina Maria, Poethig R Scott
Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6018, USA.
Plant Physiol. 2003 Aug;132(4):2135-43. doi: 10.1104/pp.103.023309.
Los1p/exportin-t (XPOT) mediates the nuclear export of tRNAs in yeast and mammals. The requirements for this transport pathway are unclear, however, because los1 mutations do not affect yeast growth, and the phenotype of XPOT mutations in mammals is unknown. Here, we show that PAUSED (PSD) is the Arabidopsis ortholog of LOS1/XPOT and is capable of rescuing the tRNA export defect of los1 in Brewer's yeast (Saccharomyces cerevisiae), suggesting that its function has been conserved. Putative null alleles of PSD disrupt the initiation of the shoot apical meristem and delay leaf initiation after germination, the emergence of the radicle and lateral roots, and the transition to flowering. Plants doubly mutant for psd and hasty, the Arabidopsis ortholog of exportin 5, are viable but have a more severe phenotype than either single mutant. These results suggest that PSD plays a role in tRNA export in Arabidopsis, but that at least one-and perhaps several-additional tRNA export pathways also exist. The PSD transcript is broadly expressed during development and is alternatively spliced in the 3'-untranslated region. No temporal or spatial difference in the abundance of different splice forms was observed. We propose that the mutant phenotype of psd reflects defects in developmental events and cell/tissue types that require elevated levels of protein synthesis and are therefore acutely sensitive to a reduction in tRNA export.
Los1p/exportin-t（XPOT）介导酵母和哺乳动物中tRNA的核输出。然而，这种转运途径的具体要求尚不清楚，因为los1突变并不影响酵母生长，而哺乳动物中XPOT突变的表型未知。在此，我们表明PAUSED（PSD）是拟南芥中LOS1/XPOT的直系同源物，并且能够挽救酿酒酵母（Saccharomyces cerevisiae）中los1的tRNA输出缺陷，这表明其功能具有保守性。PSD的推定无效等位基因会破坏茎尖分生组织的起始，并延迟萌发后叶片起始、胚根和侧根的出现以及向开花的转变。psd和hasty（拟南芥中exportin 5的直系同源物）的双突变体植株是可存活的，但具有比任一单突变体更严重的表型。这些结果表明PSD在拟南芥的tRNA输出中发挥作用，但至少还存在一条——也许还有几条——额外的tRNA输出途径。PSD转录本在发育过程中广泛表达，并在3'非翻译区发生可变剪接。未观察到不同剪接形式丰度的时间或空间差异。我们提出，psd的突变表型反映了发育事件以及需要高水平蛋白质合成的细胞/组织类型中的缺陷，因此对tRNA输出的减少极为敏感。
