Tahara Ko, Milkowski Carsten, Oda-Yamamizo Chihiro
Department of Forest Molecular Genetics and Biotechnology, Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki 305-8687, Japan.
Martin Luther University Halle-Wittenberg, AGRIPOLY: International Graduate School in Agricultural and Polymer Sciences, Betty-Heimann-Straße 3, D-06120 Halle, Germany.
Plant Biotechnol (Tokyo). 2024 Sep 25;41(3):203-212. doi: 10.5511/plantbiotechnology.24.0601a.
Hydrolyzable tannins (HTs) are a class of polyphenols produced mostly in core eudicot plants. They accumulate in various plant tissues and are considered to function as defense compounds that protect against herbivory, infections, and toxic metals (specifically aluminum ions). Moreover, HTs have industrial and pharmaceutical uses that benefit humans. Elucidating and reconstituting the biosynthesis of HTs is necessary for genetically engineering in planta functions and for efficiently producing HTs for human use. The biosynthesis of HTs is initiated by the formation of gallic acid from the shikimate pathway intermediate 3-dehydroshikimic acid, which is catalyzed by bifunctional dehydroquinate dehydratase/shikimate dehydrogenases (DQD/SDHs). In the second step, UDP glycosyltransferases (UGTs) esterify gallic acid with glucose to form β-glucogallin (1--galloyl-β-D-glucose). β-glucogallin is then converted to 1,2,3,4,6-penta--galloyl-β-D-glucose through a series of galloylation steps that are catalyzed by galloyltransferases, using β-glucogallin as a galloyl donor. Laccases subsequently catalyze the oxidative coupling between adjacent galloyl groups to form hexahydroxydiphenoyl (HHDP) groups, which are characteristic components of ellagitannins. Furthermore, monomeric ellagitannins can undergo oligomerization via intermolecular oxidative coupling, which is also catalyzed by laccases. To reconstitute the HT biosynthetic pathway in HT-non-accumulating plants, /s and s from were heterologously co-expressed in leaves, which resulted in the production of gallic acid and β-glucogallin. In future studies, this transgenic system will be used to identify genes encoding galloyltransferases and laccases to further elucidate and reconstitute the HT biosynthetic pathway.
可水解单宁（HTs）是一类主要在核心真双子叶植物中产生的多酚。它们积累在各种植物组织中，被认为起着防御化合物的作用，可抵御食草动物、感染和有毒金属（特别是铝离子）。此外，HTs在工业和制药方面对人类有益。阐明并重建HTs的生物合成对于在植物中进行基因工程功能研究以及高效生产供人类使用的HTs是必要的。HTs的生物合成起始于莽草酸途径中间体3 - 脱氢莽草酸形成没食子酸，这一过程由双功能脱氢奎尼酸脱水酶/莽草酸脱氢酶（DQD/SDHs）催化。第二步，尿苷二磷酸糖基转移酶（UGTs）将没食子酸与葡萄糖酯化形成β - 葡萄糖没食子酸（1 - 没食子酰基 - β - D - 葡萄糖）。然后，β - 葡萄糖没食子酸通过一系列由没食子酰基转移酶催化的没食子酰化步骤转化为1,2,3,4,6 - 五没食子酰基 - β - D - 葡萄糖，其中β - 葡萄糖没食子酸作为没食子酰基供体。漆酶随后催化相邻没食子酰基之间的氧化偶联形成六羟基二苯甲酰（HHDP）基团，这是鞣花单宁的特征性成分。此外，单体鞣花单宁可通过分子间氧化偶联进行寡聚化，这一过程也由漆酶催化。为了在不积累HTs的植物中重建HT生物合成途径，来自[具体来源未给出]的[具体基因未给出]和[具体基因未给出]在[具体植物未给出]叶片中异源共表达，从而产生了没食子酸和β - 葡萄糖没食子酸。在未来的研究中，这个转基因系统将用于鉴定编码没食子酰基转移酶和漆酶的基因，以进一步阐明和重建HT生物合成途径。
