Department of Biology, University of Texas, Arlington, Texas, USA.
Appl Environ Microbiol. 2012 Apr;78(8):2896-903. doi: 10.1128/AEM.07336-11. Epub 2012 Feb 3.
Flavonoids, secondary plant metabolites which mainly have a polyphenolic structure, play an important role in plant-microbe communications for nitrogen-fixing symbiosis. Among 10 polyphenolic compounds isolated from soybean roots in our previous study, coumestrol showed the highest antioxidant activity. In this study, its effect on the soybean nodulation was tested. The soybean symbiont Bradyrhizobium japonicum USDA110 pretreated with 20 μM coumestrol enhanced soybean nodulation by increasing the number of nodules 1.7-fold compared to the control. We also tested the effect of coumestrol on B. japonicum biofilm formation. At a concentration of 2 μM, coumestrol caused a higher degree of biofilm formation than two major soybean isoflavonoids, genistein and daidzein, although no biofilm formation was observed at a concentration of 20 μM each compound. A genome-wide transcriptional analysis was performed to obtain a comprehensive snapshot of the B. japonicum response to coumestrol. When the bacterium was incubated in 20 μM coumestrol for 24 h, a total of 371 genes (139 upregulated and 232 downregulated) were differentially expressed at a 2-fold cutoff with a q value of less than 5%. No common nod gene induction was found in the microarray data. However, quantitative reverse transcription-PCR (qRT-PCR) data showed that incubation for 12 h resulted in a moderate induction (ca. 2-fold) of nodD1 and nodABC, indicating that soybean coumestrol is a weak inducer of common nod genes. In addition, disruption of nfeD (bll4952) affected the soybean nodulation by an approximate 30% reduction in the average number of nodules.
类黄酮是植物次生代谢产物，主要具有多酚结构，在固氮共生植物-微生物通讯中发挥重要作用。在我们之前的研究中从大豆根部分离出的 10 种多酚化合物中，香豆雌酚表现出最高的抗氧化活性。在这项研究中，测试了它对大豆结瘤的影响。与对照相比，用 20μM 香豆雌酚预处理大豆共生菌根瘤菌（Bradyrhizobium japonicum）USDA110 可将大豆结瘤数增加 1.7 倍，从而增强大豆结瘤。我们还测试了香豆雌酚对根瘤菌生物膜形成的影响。在 2μM 的浓度下，香豆雌酚引起的生物膜形成程度高于两种主要的大豆异黄酮，染料木黄酮和大豆苷元，尽管在每种化合物的 20μM 浓度下没有观察到生物膜形成。进行了全基因组转录分析，以获得根瘤菌对香豆雌酚反应的综合快照。当细菌在 20μM 香豆雌酚中孵育 24 小时时，总共 371 个基因（139 个上调和 232 个下调）在 2 倍截止值和 q 值小于 5%时差异表达。在微阵列数据中没有发现共同的结瘤基因诱导。然而，定量逆转录-PCR（qRT-PCR）数据显示，孵育 12 小时导致 nodD1 和 nodABC 适度诱导（约 2 倍），表明大豆香豆雌酚是常见结瘤基因的弱诱导剂。此外，nfeD（bll4952）的缺失会导致大豆结瘤减少约 30%，平均结瘤数减少。
