Arabidopsis ARF-GTP exchange factor, GNOM, mediates transport required for innate immunity and focal accumulation of syntaxin PEN1

Mads Eggert Nielsen*, Angela Feechan, Henrik Böhlenius, Takashi Ueda, Hans Thordal-Christensen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

147 Citations (Scopus)


Penetration resistance to powdery mildew fungi, conferred by localized cell wall appositions (papillae), is one of the best-studied processes in plant innate immunity. The syntaxin PENETRATION (PEN)1 is required for timely appearance of papillae, which contain callose and extracellular membrane material, as well as PEN1 itself. Appearance of membrane material in papillae suggests secretion of exosomes. These are potentially derived from multivesicular bodies (MVBs), supported by our observation that ARA6-labeled organelles assemble at the fungal attack site. However, the trafficking components that mediate delivery of extracellular membrane material are unknown. Here, we show that the delivery is independent of PEN1 function. Instead, we find that application of brefeldin (BF)A blocks the papillary accumulation of GFP-PEN1 - labeled extracellular membrane and callose, while impeding penetration resistance. We subsequently provide evidence indicating that the responsible BFA-sensitive ADP ribosylation factor - GTP exchange factor (ARF-GEF) is GNOM. Firstly, analysis of the transheterozygote gnom B4049/emb30-1 (gnomB/E) mutant revealed a delay in papilla formation and reduced penetration resistance. Furthermore, a BFA-resistant version of GNOM restored the BFA-sensitive papillary accumulation of GFP-PEN1 and callose. Our data, therefore, provide a link between GNOM and disease resistance. We suggest that papilla formation requires rapid reorganization of material from the plasma membrane mediated by GNOM. The papilla material is subsequently presumed to be sorted into MVBs and directed to the site of fungal attack, rendering the epidermal plant cell inaccessible for the invading powdery mildew fungus.

Original languageEnglish
Pages (from-to)11443-11448
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number28
Publication statusPublished - 10 Jul 2012


  • Defense
  • Fungal penetration
  • GTPase
  • Pathogen
  • Vesicle transport

ASJC Scopus subject areas

  • General


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