Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
Trends Plant Sci. 2014 Aug;19(8):501-7. doi: 10.1016/j.tplants.2014.02.013. Epub 2014 Mar 26.
As a hub for plant metabolism, plastids extensively exchange metabolites with the extraplastid environment. For polar metabolites, membrane transporters mediate this exchange, but for many plastid-synthesized nonpolar compounds, such transporters remain elusive. Here, we discuss recent data from transorganellar complementation studies that demonstrate that enzymes in one organelle can directly access nonpolar metabolites from a companion organelle. We propose that a mechanism, based on hemifused-membranes at plastid-endoplasmic reticulum (ER) contact sites, facilitates interorganellar interactions and allows enzymes direct, transporter-independent access to a range of nonpolar compounds in both organelle membranes. In a wider context, interorganellar metabolism at hemifusion interfaces would allow evolution of membrane-spanning pathways for the many thousands of nonpolar metabolites in the plant kingdom to be uncoupled from coevolution with nonpolar metabolite transporters.
作为植物代谢的中心，质体与质外体环境广泛地交换代谢物。对于极性代谢物，膜转运蛋白介导这种交换，但对于许多质体合成的非极性化合物，这种转运蛋白仍然难以捉摸。在这里，我们讨论了来自跨细胞器互补研究的最新数据，这些数据表明一个细胞器中的酶可以直接从伴细胞器中获取非极性代谢物。我们提出，一种基于质体-内质网（ER）接触位点半融合膜的机制，促进了细胞器间的相互作用，并允许酶直接、无需转运蛋白就能进入细胞器膜中一系列非极性化合物。在更广泛的背景下，半融合界面处的细胞器间代谢可以使植物王国中数千种非极性代谢物的跨膜途径的进化与非极性代谢物转运蛋白的共同进化脱钩。
