Lisón Purificación, Rodrigo Ismael, Conejero Vicente
Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas, 46022 Valencia, Spain.
Plant Physiol. 2006 Nov;142(3):1329-39. doi: 10.1104/pp.106.086587. Epub 2006 Sep 29.
Proteinaceous aspartic proteinase inhibitors are rare in nature and are described in only a few plant species. One of them corresponds to a family of cathepsin D inhibitors (CDIs) described in potato (Solanum tuberosum), involving up to 15 isoforms with a high sequence similarity. In this work, we describe a tomato (Solanum lycopersicum) wound-inducible protein called jasmonic-induced protein 21 (JIP21). Sequence analysis of its cDNA predicted a putative function as a CDI. The JIP21 gene, whose protein has been demonstrated to be glycosylated, is constitutively expressed in flowers, stem, and fruit, and is inducible to high levels by wounding and methyl jasmonate in leaves of tomato plants. The genomic sequence of JIP21 shows that the gene is intronless and reveals the presence of both a methyl jasmonate box (TGACT) and a G-box (CACGT) in the promoter. In contrast to the presumed role of JIP21 based on sequence analysis, a detailed biochemical characterization of the purified protein uncovers a different function as a strong chymotrypsin inhibitor, which questions the previously predicted inhibitory activity against aspartic proteinases. Moreover, Egyptian cotton worm (Spodoptera littoralis) larvae fed on transgenic tomato plants overexpressing JIP21 present an increase in mortality and a delay in growth when compared with larvae fed on wild-type plants. These larvae belong to the Lepidoptera family whose main digestive enzymes have been described as being Ser proteases. All these results support the notion that tomato JIP21 should be considered as a chymotrypsin inhibitor belonging to the Ser proteinase inhibitors rather than a CDI. Therefore, we propose to name this protein tomato chymotrypsin inhibitor 21 (TCI21).
蛋白质类天冬氨酸蛋白酶抑制剂在自然界中很罕见，仅在少数植物物种中有描述。其中之一是马铃薯（Solanum tuberosum）中描述的组织蛋白酶D抑制剂（CDIs）家族，该家族包含多达15种具有高度序列相似性的同工型。在这项研究中，我们描述了一种番茄（Solanum lycopersicum）伤口诱导蛋白，称为茉莉酸诱导蛋白21（JIP21）。对其cDNA的序列分析预测其具有作为CDI的假定功能。JIP21基因的蛋白质已被证明是糖基化的，它在花、茎和果实中组成性表达，并且在番茄植株的叶片中受到伤口和茉莉酸甲酯的诱导可高水平表达。JIP21的基因组序列表明该基因无内含子，并揭示其启动子中存在茉莉酸甲酯盒（TGACT）和G盒（CACGT）。与基于序列分析推测的JIP21的作用相反，对纯化蛋白的详细生化特性分析揭示了其作为强胰凝乳蛋白酶抑制剂的不同功能，这对先前预测的对天冬氨酸蛋白酶的抑制活性提出了质疑。此外，与取食野生型植物的幼虫相比，取食过量表达JIP21的转基因番茄植株的埃及棉铃虫（Spodoptera littoralis）幼虫死亡率增加且生长延迟。这些幼虫属于鳞翅目，其主要消化酶已被描述为丝氨酸蛋白酶。所有这些结果支持这样一种观点，即番茄JIP21应被视为属于丝氨酸蛋白酶抑制剂的胰凝乳蛋白酶抑制剂，而不是CDI。因此，我们建议将该蛋白命名为番茄胰凝乳蛋白酶抑制剂21（TCI21）。
