[原生質絲] 沒有通道的隧道，反而暢行無阻？ 20191001 Nature Plants

Plasmodesmata
Oct 1, 2019
2 min read

Sphingolipid biosynthesis modulates plasmodesmal ultrastructure and phloem unloading

Dawei Yan, Shri Ram Yadav, Andrea Paterlini, William J. Nicolas, Jules D. Petit,, Lysiane Brocard, Ilya Belevich, Magali S. Grison, Anne Vaten, Leila Karami, Sedeer el-Showk, Jung-Youn Lee, Gosia M. Murawska9,10, Jenny Mortimer, Michael Knoblauch11, Eija Jokitalo, Jonathan E. Markham1, Emmanuelle M. Bayer and Ykä Helariutta

During phloem unloading, multiple cell-to-cell transport events move organic substances to the root meristem. Although the primary unloading event from the sieve elements to the phloem pole pericycle has been characterized to some extent, little is known about post-sieve element unloading. Here, we report a novel gene, PHLOEM UNLOADING MODULATOR (PLM), in the absence of which plasmodesmata-mediated symplastic transport through the phloem pole pericycle–endodermis interface is specifically enhanced. Increased unloading is attributable to a defect in the formation of the endoplasmic reticulum–plasma membrane tethers during plasmodesmal morphogenesis, resulting in the majority of pores lacking a visible cytoplasmic sleeve. PLM encodes a putative enzyme required for the biosynthesis of sphingolipids with very-long-chain fatty acid. Taken together, our results indicate that post-sieve element unloading involves sphingolipid metabolism, which affects plasmodesmal ultrastructure. They also raise the question of how and why plasmodesmata with no cytoplasmic sleeve facilitate molecular trafficking.

鞘脂的生合成調節了原生質絲的構造以及韌皮部的輸出功能

摘要

植物的韌皮部在輸出物質的時候，多重細胞間的傳輸使得有機物質能夠輸送到根尖的幹細胞區域。雖然，從篩管細胞運輸到韌皮域周鞘細胞的輸出機制，已經受到一定程度的瞭解，我們對於在篩管細胞之後的運輸機制，還是知道的很少。在此，我們報導一個新的基因，稱為韌皮部輸出調節基因（PLM)。在PLM缺失的時候，經由原生質絲，從韌皮部周鞘細胞，再到內皮層經的運輸有特別的增加。而這個運輸增加的現象，是由於在原生質絲形成過程中，內質網與細胞膜間的連結有所缺陷，進而造成原生質絲缺少細胞質“袖套”（原生質絲中，內質網膜與細胞膜間的空隙，大多數人認為物質的運輸是經由這個區域）。PLM基因蘊含著一個推定為有鞘脂生合成功能的酵素，主要可形成非常長鏈的脂質。總結而言，我們的結果顯示了，鞘脂因為影響了原生質絲的整體構造中，而參與了後篩管細胞的輸出功能。這些結果更引發出了一個問題，原生質絲在沒有細胞質袖套的狀態下，是為何又如何促進物質的運輸的呢？