HDR.fas

<b>Background</b>Isoprenoids are the most ancient and essential class of metabolites produced in all organisms, either via mevalonate (MVA)-and/or methylerythritol phosphate (MEP)-pathways. The MEP-pathway is present in all plastid-bearing organisms and most eubacteria. However, no comprehensive study reveals the origination and evolutionary characteristics of MEP-pathway genes in eukaryotes.<b>Results</b>Here, detailed bioinformatics analyses of the MEP-pathway provide an in-depth understanding the evolutionary history of this indispensable biochemical route, and offer a basis for the co-existence of the cytosolic MVA- and plastidial MEP-pathway in plants given the established exchange of the end products between the two isoprenoid-biosynthesis pathways. Here, phylogenetic analyses establish the contributions of both cyanobacteria and Chlamydiae sequences to the plant’s MEP-pathway genes. Moreover, Phylogenetic and inter-species syntenic block analyses demonstrate that six of the seven MEP-pathway genes have predominantly remained as single-copy in land plants in spite of multiple whole-genome duplication events (WGDs). Substitution rate and domain studies display the evolutionary conservation of these genes, reinforced by their high expression levels. Distinct phenotypic variation among plants with reduced expression levels of individual MEP-pathway genes confirm the indispensable function of each nuclear-encoded plastid-targeted MEP-pathway enzyme in plant growth and development.<b>Conclusion</b>Collectively, these findings reveal the polyphyletic origin and restrict conservation of MEP-pathway genes, and reinforce the potential function of the individual enzymes beyond production of the isoprenoids intermediates.<b>研究背景</b>类异戊二烯（isoprenoids）是所有生物通过甲羟戊酸（MVA）途径和/或甲基赤藓糖醇磷酸（MEP）途径产生的最古老且不可或缺的一类代谢物。MEP途径存在于所有拥有质体的生物以及大多数真细菌中。然而，目前尚无全面研究阐明真核生物中MEP途径基因的起源与演化特征。<b>研究结果</b>本研究通过对MEP途径的详细生物信息学分析，深入解析了这一不可或缺的生化通路的演化历程，并鉴于两类异戊二烯生物合成途径终产物的已知交换机制，为植物中胞质MVA途径与质体MEP途径的共存现象提供了理论依据。系统发育分析证实，蓝细菌（cyanobacteria）和衣原体（Chlamydiae）的序列均对植物MEP途径基因做出了贡献。此外，系统发育与种间共线性区块分析表明，尽管经历了多次全基因组复制（WGD）事件，陆地植物中的7个MEP途径基因中有6个仍主要维持单拷贝状态。替换速率与结构域分析显示这些基因具有进化保守性，其高表达水平进一步验证了这一点。当单个MEP途径基因的表达水平降低时，植物会出现明显的表型变异，这证实了每个由细胞核编码、靶向质体的MEP途径酶在植物生长发育过程中不可或缺的功能。<b>研究结论</b>综合来看，本研究的结果揭示了MEP途径基因的多系起源与受限的保守性，并进一步阐明了单个酶除生成类异戊二烯中间产物之外的潜在功能。