Sphingolipid biosynthesis modulates plasmodesmal ultrastructure and phloem unloading.

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Yadav, Shri Ram 
Nicolas, William J 
Petit, Jules D 

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.

Arabidopsis, Arabidopsis Proteins, Genes, Plant, Glucans, Green Fluorescent Proteins, Membrane Proteins, Mutation, Phloem, Plant Roots, Plasmodesmata, Sphingolipids, Transferases (Other Substituted Phosphate Groups)
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Nat Plants
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Springer Science and Business Media LLC
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European Research Council (323052)
Gatsby Charitable Foundation (GAT3395/PR3)
Biotechnology and Biological Sciences Research Council (BB/N013158/1)
Finnish Centre of Excellence in Molecular Biology of Primary Producers (decision #271832) Gatsby Foundation (GAT3395/PR3) National Science Foundation Biotechnology and Biological Sciences Research Council grant (BB/N013158/1) University of Helsinki (award 799992091) ERC Advanced Investigator Grant SYMDEV (No. 323052)