Graduate School of Environmental Sciences, Gene Research Center, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8572. Japan.
J Exp Bot. 2011 May;62(8):2773-86. doi: 10.1093/jxb/erq451. Epub 2011 Jan 31.
In plant cells, many vacuolar proteins are synthesized as precursors in the endoplasmic reticulum and are subsequently transported to the vacuole. These precursors are subject to post-translational modifications to allow the active mature forms to be produced. Vacuolar processing enzyme (VPE) has been identified as a family of cysteine proteases involved in protein maturation in the vacuole. In this study, novel VPE genes were isolated from tomato (Solanum lycopersicum), and they were designated SlVPE1-SlVPE5. Phylogenic analysis suggested that SlVPE1 and SlVPE2 were categorized as the seed coat type, SlVPE4 was categorized as the seed type, and both SlVPE3 and SlVPE5 were categorized as the vegetative type. Expression analysis demonstrated that these genes were expressed during fruit development, and that their expression profiles agreed with this classification. High VPE enzyme activity was observed during tomato fruit development; the enzyme activity was correlated with the SlVPE mRNA levels, indicating that the SlVPE encoded active VPE proteins. The total sugar content was higher in RNA interference (RNAi) lines compared with the control plants, suggesting negative roles for SlVPE in sugar accumulation. The quantitative expression analysis of each SlVPE gene in the RNAi lines suggested that the suppression of SlVPE5 probably had the strongest effect on the sugar accumulation observed. The suppression of SlVPE did not influence the total amino acid content, suggesting that the molecular targets of SlVPE were mainly involved in sugar accumulation.
在植物细胞中，许多液泡蛋白作为内质网中的前体合成，随后被运输到液泡中。这些前体经历翻译后修饰，以产生有活性的成熟形式。液泡加工酶（VPE）已被鉴定为一种半胱氨酸蛋白酶家族，参与液泡中的蛋白质成熟。在这项研究中，从番茄（Solanum lycopersicum）中分离出了新的 VPE 基因，并将其命名为 SlVPE1-SlVPE5。系统发育分析表明，SlVPE1 和 SlVPE2 被归类为种皮型，SlVPE4 被归类为种子型，而 SlVPE3 和 SlVPE5 则被归类为营养型。表达分析表明，这些基因在果实发育过程中表达，其表达谱与这种分类一致。在番茄果实发育过程中观察到高 VPE 酶活性；酶活性与 SlVPE mRNA 水平相关，表明 SlVPE 编码有活性的 VPE 蛋白。与对照植物相比，RNA 干扰（RNAi）系中的总糖含量更高，表明 SlVPE 在糖积累中起负作用。在 RNAi 系中对每个 SlVPE 基因的定量表达分析表明，SlVPE5 的抑制可能对观察到的糖积累产生最强的影响。SlVPE 的抑制并不影响总氨基酸含量，表明 SlVPE 的分子靶标主要参与糖积累。
