Pan Ya-Jie, Liu Jia, Guo Xiao-Rui, Zu Yuan-Gang, Tang Zhong-Hua
The Key Laboratory of Plant Ecology, Northeast Forestry University, Harbin, 150040, China.
Protoplasma. 2015 May;252(3):813-24. doi: 10.1007/s00709-014-0718-9. Epub 2014 Oct 26.
Research on transcriptional regulation of terpenoid indole alkaloid (TIA) biosynthesis of the medicinal plant, Catharanthus roseus, has largely been focused on gene function and not clustering analysis of multiple genes at the transcript level. Here, more than ten key genes encoding key enzyme of alkaloid synthesis in TIA biosynthetic pathways were chosen to investigate the integrative responses to exogenous elicitor ethylene and copper (Cu) at both transcriptional and metabolic levels. The ethylene-induced gene transcripts in leaves and roots, respectively, were subjected to principal component analysis (PCA) and the results showed the overall expression of TIA pathway genes indicated as the Q value followed a standard normal distribution after ethylene treatments. Peak gene expression was at 15-30 μM of ethephon, and the pre-mature leaf had a higher Q value than the immature or mature leaf and root. Treatment with elicitor Cu found that Cu up-regulated overall TIA gene expression more in roots than in leaves. The combined effects of Cu and ethephon on TIA gene expression were stronger than their separate effects. It has been documented that TIA gene expression is tightly regulated by the transcriptional factor (TF) ethylene responsive factor (ERF) and mitogen-activated protein kinase (MAPK) cascade. The loading plot combination with correlation analysis for the genes of C. roseus showed that expression of the MPK gene correlated with strictosidine synthase (STR) and strictosidine b-D-glucosidase(SGD). In addition, ERF expression correlated with expression of secologanin synthase (SLS) and tryptophan decarboxylase (TDC), specifically in roots, whereas MPK and myelocytomatosis oncogene (MYC) correlated with STR and SGD genes. In conclusion, the ERF regulates the upstream pathway genes in response to heavy metal Cu mainly in C. roseus roots, while the MPK mainly participates in regulating the STR gene in response to ethylene in pre-mature leaf. Interestingly, the change in TIA accumulation does not correlate with expression of the associated genes. Our previous research found significant accumulation of vinblastine in response to high concentration of ethylene and Cu suggesting the involvement of posttranscriptional and posttranslational mechanisms in a spatial and temporal manner. In this study, meta-analysis reveals ERF and MPK form a positive feedback loop connecting two pathways actively involved in response of TIA pathway genes to ethylene and copper in C. roseus.
对于药用植物长春花中萜类吲哚生物碱（TIA）生物合成的转录调控研究，主要集中在基因功能方面，而未涉及转录水平上多个基因的聚类分析。在此，选择了十多个编码TIA生物合成途径中生物碱合成关键酶的关键基因，以研究其在转录和代谢水平上对外源诱导子乙烯和铜（Cu）的综合响应。分别对乙烯诱导的叶片和根中的基因转录本进行主成分分析（PCA），结果表明，乙烯处理后，以Q值表示的TIA途径基因的整体表达呈标准正态分布。基因表达峰值出现在15 - 30 μM乙烯利时，且未成熟叶片的Q值高于未成熟或成熟叶片及根。用诱导子Cu处理发现，Cu对TIA基因整体表达的上调作用在根中比在叶中更明显。Cu和乙烯利对TIA基因表达的联合作用强于它们各自的作用。已有文献记载，TIA基因表达受转录因子（TF）乙烯响应因子（ERF）和丝裂原活化蛋白激酶（MAPK）级联的严格调控。长春花基因的载荷图与相关性分析表明，MPK基因的表达与异胡豆苷合成酶（STR）和异胡豆苷β - D - 葡萄糖苷酶（SGD）相关。此外，ERF的表达与裂环马钱子苷合成酶（SLS）和色氨酸脱羧酶（TDC）的表达相关，特别是在根中，而MPK和原癌基因（MYC）与STR和SGD基因相关。总之，ERF主要在长春花根中响应重金属Cu调节上游途径基因，而MPK主要在未成熟叶片中响应乙烯参与调节STR基因。有趣的是，TIA积累的变化与相关基因的表达不相关。我们之前的研究发现，高浓度乙烯和Cu会导致长春花中长春碱大量积累，这表明转录后和翻译后机制以时空方式参与其中。在本研究中，荟萃分析揭示ERF和MPK形成了一个正反馈环，积极连接参与长春花TIA途径基因对乙烯和铜响应的两条途径。
