Molecular analysis of ultraviolet (UV)-B signal transduction and a mechanism of UV-tolerance in agronomical plants.

黄酮类化合物被认为在抵御生物和非生物攻击方面发挥着重要作用。本研究的主要目的是阐明大豆黄酮类生物合成响应外界刺激的分子机制。查尔酮合酶(CHS)是大豆黄酮类生物合成的第一步酶，由7个基因编码。在本研究中，我们定量分析了每个成员在大豆幼苗中的表达水平。Chs7的表达很早就被诱导，在吸胀后6h达到高峰。在吸胀的24小时内，该基因家族的紫外线(UV)-B反应被发现，这表明萌发胚胎的机械发育受到控制。在3天暗培养的幼苗中，所有7个基因都对白光有反应，并受到UV-B的上调，但成员之间的反应有很大差异。一些黄酮类化合物也被报道具有诱导根瘤菌与豆科植物共生的作用，但这一作用被生长介质中的硝酸盐抑制。我们研究了大豆中CHS基因的表达是否受介质中硝酸盐存在的调节，发现基因7的表达受到硝酸盐的抑制，这种对氮化合物的反应仅在豆科植物中观察到。除了最不敏感的基因chs2外，大多数对光响应的chs基因都含有一个H-box。据报道，H-box被玉米中的MYB同源P元件识别，该元件在反式类黄酮类基因中激活。在这个项目中，我们分离了大豆NYB同源基因Gmmyb10和Gmmyb29的整个区域，它们的表达被UV-B上调。我们打算利用这些基因来调控豆类黄酮的生物合成。

Flavonoids are belived to play an important role in protection against biotic and abiotic attacks. The primary aim of this project is to elucidate the molecular mechanism of flavenoid biosynthesis in response to the emviromnental stimuli.Chalcone synthase (CHS), the first step enzyme of flabonoid biosynthesis, is encoded by seven genes in soybean. In this research, we quantitatively analyzed the expression levels of each member in soybean seedlings. Expression of chs7 was induced very early reaching its peak within 6 hours post imbibition. Ultraviolet (UV) -B response of the gene family was found to emerge during 24 hours of imbibition, suggesting a developmental control of the machinery in the germinating embryo. In three-day-dark-grown seedlings, all the seven genes responded to white light and showed up-regulation by UV-Bwith substantial variation in their response among the members.Some flavonoids are also reported to function as inducer of Rhizobium-legume symbiosis and this is inhibited by nitrate in the growth medium. Here we investigated if expression of CHS genes in soybesn is regulated by the presence of nitrate in the medium and found that expression of gene 7 was inhibited by nitrate and that this kind of response to the nitrogen compound was specifically observed in legume plants.Most of the light-responsive chs genes contain an H-box except for the least responsive gene, chs2. The H-box is reported to be recognized by MYB-homologous P element in maize, which activates in trans flavonoid genes. In this project, we isolated the whole region of the soybean NYB-homologous genes, Gmmyb10 and Gmmyb29, whose expression was found up-regulated by UV-B.We intend to use thses genes to manipulate flavonoid biosynthesis in legume.