title: ERMO3/MVP1/GOLD36 is involved in a cell type-specific mechanism for maintaining ER morphology in Arabidopsis thaliana.
abstract: The endoplasmic reticulum (ER) has a unique, network-like morphology. The ER structures are composed of tubules, cisternae, and three-way junctions. This morphology is highly conserved among eukaryotes, but the molecular mechanism that maintains ER morphology has not yet been elucidated. In addition, certain Brassicaceae plants develop a unique ER-derived organelle called the ER body. This organelle accumulates large amounts of PYK10, a β-glucosidase, but its physiological functions are still obscure. We aimed to identify a novel factor required for maintaining the morphology of the ER, including ER bodies, and employed a forward-genetic approach using transgenic Arabidopsis thaliana (GFP-h) with fluorescently-labeled ER. We isolated and investigated a mutant (designated endoplasmic reticulum morphology3, ermo3) with huge aggregates and abnormal punctate structures of ER. ERMO3 encodes a GDSL-lipase/esterase family protein, also known as MVP1. Here, we showed that, although ERMO3/MVP1/GOLD36 was expressed ubiquitously, the morphological defects of ermo3 were specifically seen in a certain type of cells where ER bodies developed. Coimmunoprecipitation analysis combined with mass spectrometry revealed that ERMO3/MVP1/GOLD36 interacts with the PYK10 complex, a huge protein complex that is thought to be important for ER body-related defense systems. We also found that the depletion of transcription factor NAI1, a master regulator for ER body formation, suppressed the formation of ER-aggregates in ermo3 cells, suggesting that NAI1 expression plays an important role in the abnormal aggregation of ER. Our results suggest that ERMO3/MVP1/GOLD36 is required for preventing ER and other organelles from abnormal aggregation and for maintaining proper ER morphology in a coordinated manner with NAI1.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: Ryohei Thomas
authors.initials: RT
authors.lastname: Nakano
authors.forename: Ryo
authors.initials: R
authors.lastname: Matsushima
authors.forename: Atsushi J
authors.initials: AJ
authors.lastname: Nagano
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Masayuki
authors.initials: M
authors.lastname: Fujiwara
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D013058:Mass Spectrometry; D009154:Mutation; D001617:beta-Glucosidase / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C580914:ERMO3 protein, Arabidopsis; D002265:Carboxylic Ester Hydrolases; C473372:PYK10 protein, Arabidopsis; D001617:beta-Glucosidase