Knock-down of the MEP pathway isogene 1-deoxy-D-xylulose 5-phosphate synthase 2 inhibits formation of arbuscular mycorrhiza-induced apocarotenoids, and abolishes normal expression of mycorrhiza-specific plant marker genes
Knock-down of the MEP pathway isogene 1-deoxy-D-xylulose 5-phosphate synthase 2 inhibits formation of arbuscular mycorrhiza-induced apocarotenoids, and abolishes normal expression of mycorrhiza-specific plant marker genes
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DOI：
10.1111/j.1365-313x.2008.03575.x
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发表时间：
2008-10-01
期刊：
影响因子：
7.2
通讯作者：
Walter, Michael H.
中科院分区：
文献类型：
--
作者：
Floss, Daniela S.;Hause, Bettina;Walter, Michael H.
质体甲基戊糖磷酸（MEP）途径的第一步由1-脱氧-D-木酮糖5-磷酸合酶的两种异构体（DXS 1和DXS 2）催化。在蒺藜苜蓿中，MtDXS 1和MtDXS 2基因表现出完全不同的表达模式。最突出的是，定植丛枝菌根（AM）真菌诱导积累的某些脱辅基类胡萝卜素（环己烯酮和mycorradicin衍生物）与MtDXS 2的表达，但不是MtDXS 1。为了证明DXS 2的独特功能，在转基因的M毛状根中进行了MtDXS 2表达的选择性RNAi方法。蒺藜抑制MtDXS 2一贯导致降低转录水平的菌根根，并伴随着减少AM诱导的脱辅基类胡萝卜素的积累。MtDXS 1的转录水平在RNAi植物中保持不变，并且在非AM植物中没有观察到表型变化。AM共生的后期阶段受到不利影响，但仅在强烈阻遏时，残留的MtDXS 2 -1转录水平保持在约10%以下。这种情况下导致MtPT 4，AM特异性植物磷酸盐转运蛋白基因，以及大量其他AM诱导的植物标记基因的转录水平大幅下降，如转录组分析所示。这是伴随着一个比例增加的退化和死亡的灌木在牺牲成熟的。这些数据揭示了DXS 2依赖的MEP途径为基础的类异戊二烯产品，以维持在共生后期的菌根功能的要求。他们进一步验证了DXS 2在次级代谢中的独特作用的概念，并提供了一种新的工具，通过靶向其前体供应来选择性地操纵次级类异戊二烯的水平。
The first step of the plastidial methylerythritol phosphate (MEP) pathway is catalyzed by two isoforms of 1-deoxy-D-xylulose 5-phosphate synthase (DXS1 and DXS2). In Medicago truncatula, MtDXS1 and MtDXS2 genes exhibit completely different expression patterns. Most prominently, colonization by arbuscular mycorrhizal (AM) fungi induces the accumulation of certain apocarotenoids (cyclohexenone and mycorradicin derivatives) correlated with the expression of MtDXS2 but not of MtDXS1. To prove a distinct function of DXS2, a selective RNAi approach on MtDXS2 expression was performed in transgenic hairy roots of M. truncatula. Repression of MtDXS2 consistently led to reduced transcript levels in mycorrhizal roots, and to a concomitant reduction of AM-induced apocarotenoid accumulation. The transcript levels of MtDXS1 remained unaltered in RNAi plants, and no phenotypical changes in non-AM plants were observed. Late stages of the AM symbiosis were adversely affected, but only upon strong repression with residual MtDXS2-1 transcript levels remaining below approximately 10%. This condition resulted in a strong decrease in the transcript levels of MtPT4, an AM-specific plant phosphate transporter gene, and in a multitude of other AM-induced plant marker genes, as shown by transcriptome analysis. This was accompanied by an increased proportion of degenerating and dead arbuscules at the expense of mature ones. The data reveal a requirement for DXS2-dependent MEP pathway-based isoprenoid poducts to sustain mycorrhizal functionality at later stages of the symbiosis. They further validate the concept of a distinct role for DXS2 in secondary metabolism, and offer a novel tool to selectively manipulate the levels of secondary isoprenoids by targeting their precursor supply.