Wakabayashi Takatoshi, Joseph Benesh, Yasumoto Shuhei, Akashi Tomoyoshi, Aoki Toshio, Harada Kazuo, Muranaka Satoru, Bamba Takeshi, Fukusaki Eiichiro, Takeuchi Yasutomo, Yoneyama Koichi, Muranaka Toshiya, Sugimoto Yukihiro, Okazawa Atsushi
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.
Department of Applied Biological Science, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-8510, Japan.
J Exp Bot. 2015 Jun;66(11):3085-97. doi: 10.1093/jxb/erv116. Epub 2015 Mar 28.
Root parasitic weeds in Orobanchaceae cause serious damage to worldwide agriculture. Germination of the parasites requires host-derived germination stimulants, such as strigolactones, as indicators of host roots within reach of the parasite's radicles. This unique germination process was focused on to identify metabolic pathways required for germination, and to design a selective control strategy. A metabolomic analysis of germinating seeds of clover broomrape, Orobanche minor, was conducted to identify its distinctive metabolites. Consequently, a galactosyl-sucrose trisaccharide, planteose (α-d-galactopyranosyl-(1→6)-β-d-fructofuranosyl-(2→1)-α-d-glucopyranoside), was identified as a metabolite that decreased promptly after reception of the germination stimulant. To investigate the importance of planteose metabolism, the effects of several glycosidase inhibitors were examined, and nojirimycin bisulfite (NJ) was found to alter the sugar metabolism and to selectively inhibit the germination of O. minor. Planteose consumption was similar in NJ-treated seeds and non-treated germinating seeds; however, NJ-treated seeds showed lower consumption of sucrose, a possible intermediate of planteose metabolism, resulting in significantly less glucose and fructose. This inhibitory effect was recovered by adding glucose. These results suggest that planteose is a storage carbohydrate required for early stage of germination of O. minor, and NJ inhibits germination by blocking the supply of essential glucose from planteose and sucrose. Additionally, NJ selectively inhibited radicle elongation of germinated seeds of Orobanchaceae plants (Striga hermonthica and Phtheirospermum japonicum). Thus, NJ will be a promising tool to develop specific herbicides to the parasites, especially broomrapes, and to improve our understanding of the molecular mechanisms of this unique germination.
列当科的根寄生杂草对全球农业造成严重损害。这些寄生虫的萌发需要宿主衍生的萌发刺激物，如独脚金内酯，作为宿主根在寄生虫胚根可及范围内的指标。这一独特的萌发过程成为研究重点，以确定萌发所需的代谢途径，并设计一种选择性控制策略。对小花列当萌发种子进行代谢组学分析，以鉴定其独特的代谢产物。结果，一种半乳糖基蔗糖三糖，蔗果三糖（α-d-吡喃半乳糖基-(1→6)-β-d-呋喃果糖基-(2→1)-α-d-吡喃葡萄糖苷），被鉴定为一种在接受萌发刺激物后迅速减少的代谢产物。为了研究蔗果三糖代谢的重要性，检测了几种糖苷酶抑制剂的作用，发现亚硫酸诺吉霉素（NJ）可改变糖代谢并选择性抑制小花列当的萌发。NJ处理的种子和未处理的萌发种子中蔗果三糖的消耗相似；然而，NJ处理的种子中蔗糖（蔗果三糖代谢的可能中间体）的消耗较低，导致葡萄糖和果糖显著减少。通过添加葡萄糖可恢复这种抑制作用。这些结果表明，蔗果三糖是小花列当萌发早期所需的储存碳水化合物，NJ通过阻断蔗果三糖和蔗糖提供必需的葡萄糖来抑制萌发。此外，NJ选择性抑制列当科植物（独脚金和日本地黄）萌发种子的胚根伸长。因此，NJ将成为开发针对这些寄生虫，尤其是列当属杂草的特效除草剂以及增进我们对这种独特萌发分子机制理解的有前景的工具。
