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起着重要作用。查尔酮合成酶（Chalcone synthase，CHS）是大豆黄酮类化合物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。chs 7的表达被诱导得非常早，在吸胀后6小时内达到峰值。紫外线（UV）-B反应的基因家族被发现出现在24小时的吸胀，这表明在萌发的胚胎中的机器的发育控制。在黑暗生长三天的幼苗中，所有7个基因都对白色光有反应，并被UV-B上调，但成员之间的反应差异很大。在这里，我们调查了CHS基因在soybesn中的表达是否受培养基中硝酸盐的存在的调节，发现基因7的表达被硝酸盐抑制，并且这种对氮化合物的反应在豆科植物中特异地观察到。据报道，玉米中的MYB同源P元件识别H-box，其激活反式黄酮基因。在本项目中，我们分离了大豆NYB同源基因Gmmyb 10和Gmmyb 29的整个区域，发现它们的表达被UV-B上调。我们打算利用这些基因来操纵豆科植物类黄酮的生物合成。

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.