Meier Stuart, Tzfadia Oren, Vallabhaneni Ratnakar, Gehring Chris, Wurtzel Eleanore T
Department of Biological Sciences, Lehman College, The City University of New York, 250 Bedford Park Blvd, West, Bronx, NY 10468, USA.
BMC Syst Biol. 2011 May 19;5:77. doi: 10.1186/1752-0509-5-77.
The carotenoids are pure isoprenoids that are essential components of the photosynthetic apparatus and are coordinately synthesized with chlorophylls in chloroplasts. However, little is known about the mechanisms that regulate carotenoid biosynthesis or the mechanisms that coordinate this synthesis with that of chlorophylls and other plastidial synthesized isoprenoid-derived compounds, including quinones, gibberellic acid and abscisic acid. Here, a comprehensive transcriptional analysis of individual carotenoid and isoprenoid-related biosynthesis pathway genes was performed in order to elucidate the role of transcriptional regulation in the coordinated synthesis of these compounds and to identify regulatory components that may mediate this process in Arabidopsis thaliana.
A global microarray expression correlation analysis revealed that the phytoene synthase gene, which encodes the first dedicated and rate-limiting enzyme of carotenogenesis, is highly co-expressed with many photosynthesis-related genes including many isoprenoid-related biosynthesis pathway genes. Chemical and mutant analysis revealed that induction of the co-expressed genes following germination was dependent on gibberellic acid and brassinosteroids (BR) but was inhibited by abscisic acid (ABA). Mutant analyses further revealed that expression of many of the genes is suppressed in dark grown plants by Phytochrome Interacting transcription Factors (PIFs) and activated by photoactivated phytochromes, which in turn degrade PIFs and mediate a coordinated induction of the genes. The promoters of PSY and the co-expressed genes were found to contain an enrichment in putative BR-auxin response elements and G-boxes, which bind PIFs, further supporting a role for BRs and PIFs in regulating expression of the genes. In osmotically stressed root tissue, transcription of Calvin cycle, methylerythritol 4-phosphate pathway and carotenoid biosynthesis genes is induced and uncoupled from that of chlorophyll biosynthesis genes in a manner that is consistent with the increased synthesis of carotenoid precursors for ABA biosynthesis. In all tissues examined, induction of β-carotene hydroxylase transcript levels are linked to an increased demand for ABA.
This analysis provides compelling evidence to suggest that coordinated transcriptional regulation of isoprenoid-related biosynthesis pathway genes plays a major role in coordinating the synthesis of functionally related chloroplast localized isoprenoid-derived compounds.
类胡萝卜素是纯类异戊二烯，是光合机构的重要组成部分，在叶绿体中与叶绿素协同合成。然而，对于调节类胡萝卜素生物合成的机制，以及将这种合成与叶绿素和其他质体合成的类异戊二烯衍生化合物（包括醌、赤霉素和脱落酸）的合成相协调的机制，我们知之甚少。在此，对单个类胡萝卜素和类异戊二烯相关生物合成途径基因进行了全面的转录分析，以阐明转录调控在这些化合物协同合成中的作用，并鉴定可能在拟南芥中介导这一过程的调控成分。
一项全局微阵列表达相关性分析表明，编码类胡萝卜素生成过程中第一个专用限速酶的八氢番茄红素合酶基因，与许多光合作用相关基因高度共表达，包括许多类异戊二烯相关生物合成途径基因。化学和突变体分析表明，萌发后共表达基因的诱导依赖于赤霉素和油菜素内酯（BR），但被脱落酸（ABA）抑制。突变体分析进一步表明，许多基因的表达在黑暗生长的植物中被光敏色素相互作用转录因子（PIF）抑制，而被光活化的光敏色素激活，光活化的光敏色素反过来降解PIF并介导基因的协同诱导。发现PSY和共表达基因的启动子富含假定的BR-生长素反应元件和G-盒，它们与PIF结合，进一步支持BR和PIF在调节基因表达中的作用。在渗透胁迫的根组织中，卡尔文循环、甲基赤藓糖醇4-磷酸途径和类胡萝卜素生物合成基因的转录被诱导，并与叶绿素生物合成基因的转录解偶联，其方式与ABA生物合成中类胡萝卜素前体合成增加一致。在所有检测的组织中，β-胡萝卜素羟化酶转录水平的诱导与ABA需求的增加相关。
该分析提供了令人信服的证据，表明类异戊二烯相关生物合成途径基因的协同转录调控在协调功能相关的叶绿体定位类异戊二烯衍生化合物的合成中起主要作用。
