VACUOLAR PROCESSING SYSTEM IN HIGHER PLANTS

液泡处理酶(VPE)是一种半胱氨酸蛋白酶，负责植物各种液泡蛋白的成熟。在粗面内质网上合成的较大的VPE前体在液泡中转化为一种活性酶。我们在酿酒酵母的Pep4菌株中表达了蓖麻豆VPE的前体，以研究VPE的激活机制。我们的发现表明，在内质网合成的非活性VPE前体被运输到酵母细胞的液泡中，然后在液泡内通过自催化蛋白分解加工成活性VPE。拟南芥有三个液泡加工酶(VPEs)。研究发现，β-葡萄糖醛酸苷酶报告基因的启动子能在转基因拟南芥的种子、花粉和根尖中表达。另一方面，αVPE基因和伽马VPE基因的启动子都被发现显著地指导了衰老组织中的衰退。伤害、乙烯和水杨酸处理诱导了α-VPE和γ-VPE基因的表达，而茉莉酸诱导了α-VPE和γ-VPE基因的表达，这些结果表明，营养VPE可能调节了营养液泡中某些功能蛋白的激活。

Vacuolar processing enzymes (VPE) are cysteine proteinases responsible for maturation of various vacuolar proteins in plants. A larger precursor to VPE synthesized on rough endoplasmic reticulum is converted to an active enzyme in the vacuoles. We expressed a precursor to castor bean VPE in a pep4 strain of the yeast Saccharomyces cerevisiate to examine the mechanism of activation of VPE.Our findings suggest that an inactive VPE precursor synthesized on the endoplasmic reticulum is transported to the vacuoles in the yeast cells and then processed to make an active VPE by self-catalytic proteolysis within the vacuoles.Arabidopsis has three vacuolar processing enzymes (VPEs). The promoter of the betaVPE gene was found to direct the expression of the beta-glucuronidase reporter gene in the seeds, the pollen and the root tip of a transgenic Arabidopsis. On the other hand, the promoters of both the alphaVPE and gammaVPE genes were found to direct remarkably the eression in senescent tissue. Treatment with wounding, ethylene and salicylic acid induced the gene expression of the alphaVPE and gammaVPE genes, while jasmonate slightly induced that of the gammaVPE.Taken together, the results suggest that vegetative VPEs might regulate the activation of some functional proteins in the vegetative vacuoles.