Li Han, Liang Jiubo, Chen Hu, Ding Guangyu, Ma Bi, He Ningjia
State Key Laboratory of Silkworm Genome Biology, Southwest University, Beibei, Chongqing, 400715, People's Republic of China.
BMC Genomics. 2016 Aug 4;17:540. doi: 10.1186/s12864-016-2843-7.
Type III polyketide synthases are important for the biosynthesis of flavonoids and various plant polyphenols. Mulberry plants have abundant polyphenols, but very little is known about the mulberry type III polyketide synthase genes. An analysis of these genes may provide new targets for genetic improvement to increase relevant secondary metabolites and enhance the plant tolerance to biotic and abiotic stresses.
Eighteen genes encoding type III polyketide synthases were identified, including six chalcone synthases (CHS), ten stilbene synthases (STS), and two polyketide synthases (PKS). Functional characterization of four genes representing most of the MnCHS and MnSTS genes by coexpression with 4-Coumaroyl-CoA ligase in Escherichia coli indicated that their products were able to catalyze p-coumaroyl-CoA and malonyl-CoA to generate naringenin and resveratrol, respectively. Microsynteny analysis within mulberry indicated that segmental and tandem duplication events contributed to the expansion of the MnCHS family, while tandem duplications were mainly responsible for the generation of the MnSTS genes. Combining the evolution and expression analysis results of the mulberry type III PKS genes indicated that MnCHS and MnSTS genes evolved mainly under purifying selection to maintain their original functions, but transcriptional subfunctionalization occurred during long-term species evolution. Moreover, mulberry leaves can rapidly accumulated oxyresveratrol after UV-C irradiation, suggesting that resveratrol was converted to oxyresveratrol.
Characterizing the functions and evolution of mulberry type III PKS genes is crucial for advancing our understanding of these genes and providing the basis for further studies on the biosynthesis of relevant secondary metabolites in mulberry plants.
III型聚酮合酶对黄酮类化合物和各种植物多酚的生物合成很重要。桑树含有丰富的多酚，但对桑树III型聚酮合酶基因了解甚少。对这些基因的分析可能为遗传改良提供新靶点，以增加相关次生代谢产物并增强植物对生物和非生物胁迫的耐受性。
鉴定出18个编码III型聚酮合酶的基因，包括6个查尔酮合酶（CHS）、10个芪合酶（STS）和2个聚酮合酶（PKS）。通过与4-香豆酰辅酶A连接酶在大肠杆菌中共表达，对代表大多数MnCHS和MnSTS基因的4个基因进行功能表征，结果表明它们的产物能够分别催化对香豆酰辅酶A和丙二酰辅酶A生成柚皮素和白藜芦醇。桑树种内的微共线性分析表明，片段重复和串联重复事件导致了MnCHS家族的扩张，而串联重复主要导致了MnSTS基因的产生。结合桑树III型PKS基因的进化和表达分析结果表明，MnCHS和MnSTS基因主要在纯化选择下进化以维持其原始功能，但在长期物种进化过程中发生了转录亚功能化。此外，紫外线-C照射后桑叶中氧白藜芦醇能快速积累，表明白藜芦醇被转化为氧白藜芦醇。
表征桑树III型PKS基因的功能和进化对于增进我们对这些基因的理解以及为进一步研究桑树中相关次生代谢产物的生物合成提供基础至关重要。
