論文標題：Tandem gene duplications drive divergent evolution of caffeine and crocin biosynthetic pathways in plants
期刊：BMC Biology
作者：Zhichao Xu, Xiangdong Pu et.al
發表時間：2020/06/18
數字識別碼：10.1186/s12915-020-00795-3
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近期，發表在BMC Biology上的一篇文章報告了利用牛津納米孔測序和Hi-C技術獲得的產生西紅花苷的物種--梔子的染色體級基因組組裝。
植物進化出一系列專門的代謝物以增加其環境適應性。其中兩個例子是咖啡因（一種嘌呤類精神生物鹼）和西紅花苷（一組糖基化的類胡蘿蔔素色素）。這兩類化合物都存在於少數幾個遠親植物屬中（咖啡因來自咖啡屬、山茶屬、泡林藤屬和冬青屬植物；西紅花苷來自番紅花屬、醉魚草屬和梔子屬），它們可能是通過趨同進化而來的。密切相關的咖啡屬和梔子屬屬於茜草科，分別在其果實中合成咖啡因和西紅花苷。
圖1
通過基因組學和功能測定，我們首次在某種植物中完全解讀了紅素生物合成的專用途徑。通過與Coffea canephora和其他裸子植物基因組的比較分析，我們發現咖啡屬中咖啡鹼合成酶和梔子屬合成紅素時的第一個專用基因GjCCD4a，分別是通過最近兩個不同屬的串聯基因重複進化而來的。相比之下，編碼梔子花紅素途徑後期步驟的基因ALDH和UGT則是通過更古老的基因重複進化而來的，據推測，它們是在GjCCD4a基因進化後才參與到西紅花苷的生物合成途徑中。
該研究表明，咖啡屬（茜草科）內兩條特徵性次級代謝途徑--咖啡因和西紅花苷生物合成--從一個不具備這兩條完整途徑的共同祖先開始，發生了基於重複的趨異進化。這些發現為串聯重複在植物特化代謝進化中的作用提供了重要的啟示。
圖2
BMC Biology is an open access journal publishing outstanding research in all areas of biology, with a publication policy that combines selection for broad interest and importance with a commitment to serving authors well.
摘要：
Background
Plants have evolved a panoply of specialized metabolites that increase their environmental fitness. Two examples are caffeine, a purine psychotropic alkaloid, and crocins, a group of glycosylated apocarotenoid pigments. Both classes of compounds are found in a handful of distantly related plant genera (Coffea, Camellia, Paullinia, and Ilex for caffeine;Crocus, Buddleja, and Gardenia for crocins) wherein they presumably evolved through convergent evolution. The closely related Coffea andGardenia genera belong to the Rubiaceae family and synthesize, respectively, caffeine and crocins in their fruits.
Results
Here, we report a chromosomal-level genome assembly of Gardenia jasminoides, a crocin-producing species, obtained using Oxford Nanopore sequencing and Hi-C technology. Through genomic and functional assays, we completely deciphered for the first time in any plant the dedicated pathway of crocin biosynthesis. Through comparative analyses with Coffea canephora and other eudicot genomes, we show that Coffea caffeine synthases and the first dedicated gene in theGardenia crocin pathway, GjCCD4a, evolved through recent tandem gene duplications in the two different genera, respectively. In contrast, genes encoding later steps of the Gardenia crocin pathway, ALDH and UGT, evolved through more ancient gene duplications and were presumably recruited into the crocin biosynthetic pathway only after the evolution of the GjCCD4a gene.
Conclusions
This study shows duplication-based divergent evolution within the coffee family (Rubiaceae) of two characteristic secondary metabolic pathways, caffeine and crocin biosynthesis, from a common ancestor that possessed neither complete pathway. These findings provide significant insights on the role of tandem duplications in the evolution of plant specialized metabolism.
（來源：科學網）
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