title: Microtubules contribute to tubule elongation and anchoring of endoplasmic reticulum, resulting in high network complexity in Arabidopsis.
abstract: The endoplasmic reticulum (ER) is a network of tubules and sheet-like structures in eukaryotic cells. Some ER tubules dynamically change their morphology, and others form stable structures. In plants, it has been thought that the ER tubule extension is driven by the actin-myosin machinery. Here, we show that microtubules also contribute to the ER tubule extension with an almost 20-fold slower rate than the actin filament-based ER extension. Treatment with the actin-depolymerizing drug Latrunculin B made it possible to visualize the slow extension of the ER tubules in transgenic Arabidopsis (Arabidopsis thaliana) plants expressing ER-targeted green fluorescent protein. The ER tubules elongated along microtubules in both directions of microtubules, which have a distinct polarity. This feature is similar to the kinesin- or dynein-driven ER tubule extension in animal cells. In contrast to the animal case, ER tubules elongating with the growing microtubule ends were not observed in Arabidopsis. We also found the spots where microtubules are stably colocalized with the ER subdomains during long observations of 1,040 s, suggesting that cortical microtubules contribute to provide ER anchoring points. The anchoring points acted as the branching points of the ER tubules, resulting in the formation of multiway junctions. The density of the ER tubule junction positively correlated with the microtubule density in both elongating cells and mature cells of leaf epidermis, showing the requirement of microtubules for formation of the complex ER network. Taken together, our findings show that plants use microtubules for ER anchoring and ER tubule extension, which establish fine network structures of the ER within the cell.
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hamada
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Haruko
authors.initials: H
authors.lastname: Ueda
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kawase
authors.affiliation: Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan ihnishi@gr.bot.kyoto-u.ac.jp.
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D016547:Kinesins / Q000235:genetics / Q000378:metabolism; D008870:Microtubules / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D009218:Myosins / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D009218:Myosins; D016547:Kinesins