BMC Genomics. 2013 Apr 8;14:227. doi: 10.1186/1471-2164-14-227.
Agarwood is an expensive resinous heartwood derived from Aquilaria plants that is widely used in traditional medicines, incense and perfume. Only wounded trees can produce agarwood, and the huge demand for the agarwood products has led all Aquilaria spp. being endangered and listed in the Appendix II of the CITES (http://www.cites.org). The major components of agarwood are sesquiterpenes and phenylethyl chromones. Owing to a lack of genomic information, the molecular basis of wound-induced sesquiterpenes biosynthesis and agarwood formation remains unknown.
To identify the primary genes that maybe related to agarwood formation, we sequenced 2 cDNA libraries generated from healthy and wounded A. sinensis (Lour.) Gilg. A total of 89,137 unigenes with an average length of 678.65 bp were obtained, and they were annotated in detail at bioinformatics levels. Of those associated with agarwood formation, 30 putatively encoded enzymes in the sesquiterpene biosynthesis pathway, and a handful of transcription factors and protein kinases were related to wound signal transduction. Three full-length cDNAs of sesquiterpene synthases (ASS1-3) were cloned and expressed in Escherichia coli, and enzyme assays revealed that they are active enzymes, with the major products being δ-guaiene. A methyl jasmonate (MJ) induction experiment revealed that the expression of ASS was significantly induced by MJ, and the production of sesquiterpenes was elevated accordingly. The expression of some transcription factors and protein kinases, especially MYB4, WRKY4, MPKK2 and MAPK2, was also induced by MJ and coordinated with ASS expression, suggesting they maybe positive regulators of ASS.
This study provides extensive transcriptome information for Aquilaria spp. and valuable clues for elucidating the mechanism of wound-induced agarwood sesquiterpenes biosynthesis and their regulation.
沉香是一种从沉香属植物中提取的昂贵树脂心材，广泛应用于传统药物、香薰和香水。只有受伤的树木才能产生沉香，对沉香产品的巨大需求导致所有沉香属植物都濒临灭绝，并被列入《濒危野生动植物种国际贸易公约》附录二（http://www.cites.org）。沉香的主要成分是倍半萜和苯乙基色酮。由于缺乏基因组信息，沉香中倍半萜生物合成和沉香形成的分子基础仍不清楚。
为了鉴定可能与沉香形成有关的主要基因，我们从健康和受伤的白木香（Lour.）Gilg 中测序了 2 个 cDNA 文库。共获得 89137 个平均长度为 678.65bp 的 unigenes，并在生物信息学水平上进行了详细注释。其中与沉香形成相关的 30 种倍半萜生物合成途径中的推定酶，以及少数转录因子和蛋白激酶与伤口信号转导有关。克隆并在大肠杆菌中表达了 3 个全长倍半萜合酶（ASS1-3）cDNA，酶活性测定表明它们是活性酶，主要产物为δ-愈创木烯。茉莉酸甲酯（MJ）诱导实验表明，MJ 显著诱导 ASS 的表达，相应地提高了倍半萜的产量。一些转录因子和蛋白激酶的表达，特别是 MYB4、WRKY4、MPKK2 和 MAPK2，也被 MJ 诱导，并与 ASS 表达协调，表明它们可能是 ASS 的正调控因子。
本研究为沉香属植物提供了广泛的转录组信息，为阐明伤口诱导沉香倍半萜生物合成及其调控机制提供了有价值的线索。
