ABSTRACT

Phylloquinone (vitamin K1) is a thylakoid-embedded electron carrier essential for photosynthesis. Paradoxically, we found that phylloquinone biosynthesis is retained in the nonphotosynthetic holoparasite Phelipanche aegyptiaca (Egyptian broomrape). The phylloquinone pathway genes are preferentially expressed during development of the invasive organ, the haustorium, and exhibit strong coexpression with redox-active proteins known to be involved in parasitism. Unlike in photoautotrophic taxa, the late pathway genes of the holoparasite lack the chloroplast-targeting sequence and their proteins are targeted to the plasma membrane instead. Plasma membrane phylloquinone may enable Phelipanche to sense changes in the redox environment during host interactions. The N-truncated isoforms are conserved in several other Orobanchaceae root holoparasites, and interestingly, in a number of closely related photoautotrophic species as well. This suggests an ancient origin of distinct phylloquinone pathways predating the evolution of parasitic plants in the Orobanchaceae. These findings represent exciting opportunities to probe plasma membrane phylloquinone function and diversification in parasitic and nonparasitic plant responses to external redox chemistry in the rhizosphere.

摘要

叶醌（维生素 K1）是光合作用必需的类囊体嵌入电子载体。矛盾的是，我们发现叶绿醌生物合成保留在非光合作用全寄生虫Phelipanche aegyptiaca（埃及列日菜）中。叶绿醌途径基因在侵入性器官吸器的发育过程中优先表达，并与已知参与寄生的氧化还原活性蛋白表现出强烈的共表达。与光合自养类群不同，全寄生虫的晚期途径基因缺乏叶绿体靶向序列，并且它们的蛋白质而是靶向质膜。质膜叶绿醌可能使Phelipanche能够感知宿主相互作用期间氧化还原环境的变化。N-截短的亚型在其他几种列当科根全寄生物中是保守的，有趣的是，在许多密切相关的光合自养物种中也是如此。这表明独特的叶绿醌途径的古老起源早于列当科寄生植物的进化。这些发现为探索质膜叶绿醌功能以及寄生和非寄生植物对根际外部氧化还原化学反应的多样化提供了令人兴奋的机会。