Sugiyama Akifumi, Yamazaki Yumi, Hamamoto Shoichiro, Takase Hisabumi, Yazaki Kazufumi
Research Institute for Sustainable Humanosphere, Kyoto University, Uji 611-0011, Japan.
Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8567, Japan.
Plant Cell Physiol. 2017 Sep 1;58(9):1594-1600. doi: 10.1093/pcp/pcx084.
Isoflavones play important roles in rhizosphere plant-microbe interactions. Daidzein and genistein secreted by soybean roots induce the symbiotic interaction with rhizobia and may modulate rhizosphere interactions with microbes. Yet despite their important roles, little is known about the biosynthesis, secretion and fate of isoflavones in field-grown soybeans. Here, we analyzed isoflavone contents and the expression of isoflavone biosynthesis genes in field-grown soybeans. In roots, isoflavone contents and composition did not change with crop growth, but the expression of UGT4, an isoflavone-specific 7-O-glucosyltransferase, and of ICHG (isoflavone conjugates hydrolyzing beta-glucosidase) was decreased during the reproductive stages. Isoflavone contents were higher in rhizosphere soil than in bulk soil during both vegetative and reproductive stages, and were comparable in the rhizosphere soil between these two stages. We analyzed the degradation dynamics of daidzein and its glucosides to develop a model for predicting rhizosphere isoflavone contents from the amount of isoflavones secreted in hydroponic culture. Conjugates of daidzein were degraded much faster than daidzein, with degradation rate constants of 8.51 d-1 for malonyldaidzin and 11.6 d-1 for daidzin, vs. 9.15 × 10-2 d-1 for daidzein. The model suggested that secretion of isoflavones into the rhizosphere is higher during vegetative stages than during reproductive stages in field-grown soybean.
异黄酮在根际植物 - 微生物相互作用中发挥着重要作用。大豆根部分泌的大豆苷元和染料木黄酮可诱导与根瘤菌的共生相互作用，并可能调节与微生物的根际相互作用。然而，尽管它们具有重要作用，但关于田间种植大豆中异黄酮的生物合成、分泌和归宿却知之甚少。在此，我们分析了田间种植大豆中异黄酮的含量以及异黄酮生物合成基因的表达。在根中，异黄酮的含量和组成并未随作物生长而变化，但在生殖阶段，异黄酮特异性7 - O - 葡萄糖基转移酶UGT4和异黄酮共轭物水解β - 葡萄糖苷酶ICHG的表达下降。在营养生长阶段和生殖阶段，根际土壤中的异黄酮含量均高于非根际土壤，且这两个阶段根际土壤中的异黄酮含量相当。我们分析了大豆苷元及其糖苷的降解动态，以建立一个根据水培培养中分泌的异黄酮量预测根际异黄酮含量的模型。大豆苷元的共轭物降解速度比大豆苷元快得多，丙二酰大豆苷的降解速率常数为(8.51 d^{-1})，大豆苷为(11.6 d^{-1})，而大豆苷元为(9.15×10^{-2} d^{-1})。该模型表明，田间种植的大豆在营养生长阶段向根际分泌的异黄酮比生殖阶段更高。
