von Lintig J, Welsch R, Bonk M, Giuliano G, Batschauer A, Kleinig H
Institut für Biologie II, Zellbiologie, Albert-Ludwigs Universität Freiburg, Germany.
Plant J. 1997 Sep;12(3):625-34. doi: 10.1046/j.1365-313x.1997.00625.x.
In chloroplasts, carotenoids are essential pigments involved in photosynthesis. During-photomorphogenesis, a coordinated increase in the amounts of chlorophylls and carotenoids, in conjugation with other components, leads to the formation of a functional photosynthetic apparatus. To investigate the regulation of carotenoid biosynthesis during this process at the molecular level, GGPS, PSY and PDS cDNAs have been cloned from white mustard (Sinapis alba L). GGPS encodes a key enzyme in plastid isoprenoid metabolism, while the products of PSY and PDS catalyse the subsequent steps in carotenoid biosynthesis. Due to the low mRNA levels of the genes involved, the use of a RT-PCR protocol was necessary to measure gene expression during photomorphogenesis. With light, there is an up-regulation of PSY expression, the first gene within the carotenoid biosynthetic pathway, while PDS and GGPS expression levels remain constant. Treatment with different light qualities reveals a phytochrome-mediated regulation of PSY expression in developing white mustard seedlings. To obtain more detailed information on the light-regulation, Arabidopsis thaliana wild-type and phytochrome mutants were utilized. Continuous far-red and red light both increase the expression of PSY in wild-type seedlings, demonstrating that both light-labile and light-stable phytochromes are involved in PSY regulation. The response to far-red light is completely abolished in the phyA mutant, showing that PHYA mediates the increase in PSY transcript levels under these light conditions. In the phyB mutant, the red light response is normal, indicating that PSY expression is not controlled by PHYB but by other light-stable phytochromes. Measurement of chlorophylls and carotenoids under the same light regimes shows that the up-regulation of PSY expression does not necessarily result in an increase of the carotenoid content. Only those light conditions which allow chlorophyll biosynthesis lead to a significant increase of the carotenoid content. Therefore, it is proposed that up-regulation of PSY mRNA levels leads to an increased capacity for the formation of carotenoids. However, this only takes place under light conditions leading to protochlorophyllide photoconversion.
在叶绿体中，类胡萝卜素是参与光合作用的必需色素。在光形态建成过程中，叶绿素和类胡萝卜素含量的协同增加，与其他成分共同作用，导致功能性光合装置的形成。为了在分子水平上研究该过程中类胡萝卜素生物合成的调控，已从白芥（Sinapis alba L）中克隆了GGPS、PSY和PDS的cDNA。GGPS编码质体类异戊二烯代谢中的关键酶，而PSY和PDS的产物催化类胡萝卜素生物合成的后续步骤。由于所涉及基因的mRNA水平较低，因此需要使用RT-PCR方案来测量光形态建成过程中的基因表达。光照下，类胡萝卜素生物合成途径中的第一个基因PSY的表达上调，而PDS和GGPS的表达水平保持不变。用不同光质处理揭示了发育中的白芥幼苗中PSY表达受光敏色素介导的调控。为了获得关于光调控的更详细信息，利用了拟南芥野生型和光敏色素突变体。持续的远红光和红光均增加野生型幼苗中PSY的表达，表明光不稳定和光稳定的光敏色素均参与PSY的调控。在phyA突变体中，对远红光的反应完全消失，表明PHYA介导了这些光照条件下PSY转录水平的增加。在phyB突变体中，红光反应正常，表明PSY的表达不受PHYB控制，而是受其他光稳定的光敏色素控制。在相同光照条件下对叶绿素和类胡萝卜素的测量表明，PSY表达的上调不一定导致类胡萝卜素含量的增加。只有那些允许叶绿素生物合成的光照条件才会导致类胡萝卜素含量显著增加。因此，有人提出PSY mRNA水平的上调导致类胡萝卜素形成能力的增加。然而，这仅在导致原叶绿素酸酯光转化的光照条件下发生。
