title: Mechanisms of functional specificity among plasma-membrane syntaxins in Arabidopsis.
abstract: Syntaxins and interacting SNARE proteins enable membrane fusion in diverse trafficking pathways. The Arabidopsis SYP1 family of plasma membrane-localized syntaxins comprises nine members, of which KNOLLE and PEN1 play specific roles in cytokinesis and innate immunity, respectively. To identify mechanisms conferring specificity of action, we examined one member of each subfamily-KNOLLE/SYP111, PEN1/SYP121 and SYP132-in regard to subcellular localization, dynamic behavior and complementation of knolle and pen1 mutants when expressed from the same promoters. Our results suggest that cytokinesis-specific syntaxin requires high-level accumulation during cell-plate formation, which necessitates de novo synthesis rather than endocytosis of pre-made protein from the plasma membrane. In contrast, syntaxin in innate immunity does not need upregulation of expression but instead requires pathogen-induced and endocytosis-dependent retargeting to the infection site. This feature of PEN1 is not afforded by SYP132. Additionally, PEN1 could not substitute for KNOLLE because of SNARE domain differences, as revealed by protein chimeras. In contrast, SYP132 was able to rescue knolle as did KNOLLE-SYP132 chimeras. Unlike KNOLLE and PEN1, which appear to have evolved to perform specialized functions, SYP132 stably localized at the plasma membrane and thus might play a role in constitutive membrane fusion.
authors.affiliation: ZMBP, Entwicklungsgenetik, Universität Tübingen, Auf der Morgenstelle 3, 72076 Tübingen, Germany.
authors.forename: Ilka
authors.initials: I
authors.lastname: Reichardt
authors.forename: Daniel
authors.initials: D
authors.lastname: Slane
authors.forename: Farid
authors.initials: F
authors.lastname: El Kasmi
authors.forename: Christian
authors.initials: C
authors.lastname: Knöll
authors.forename: Rene
authors.initials: R
authors.lastname: Fuchs
authors.forename: Ulrike
authors.initials: U
authors.lastname: Mayer
authors.forename: Volker
authors.initials: V
authors.lastname: Lipka
authors.forename: Gerd
authors.initials: G
authors.lastname: Jürgens
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000166:cytology / Q000382:microbiology / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001203:Ascomycota / Q000472:pathogenicity; D002462:Cell Membrane / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D008561:Membrane Fusion; D030821:Plants, Genetically Modified; D050765:Qa-SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C097724:KNOLLE protein, Arabidopsis; C479425:PEN1 protein, Arabidopsis; D050765:Qa-SNARE Proteins; D011993:Recombinant Fusion Proteins; D050600:SNARE Proteins; C568818:SYP132 protein, Arabidopsis