High impact information on GN

• In plants harboring this fully functional GNOM variant, PIN1 localization and auxin transport are no longer sensitive to BFA, while trafficking of other proteins is still affected by the drug [1].
• In this paper, we show that GNOM localizes to endosomes and is required for their structural integrity [1].
• We engineered a BFA-resistant version of GNOM [1].
• In this issue of Cell, Geldner et al. demonstrate that the Arabidopsis ARF activator GNOM localizes to endosomes where it controls the polarized trafficking of the auxin efflux carrier PIN1 to the basal plasma membrane [2].
• The Arabidopsis protein GNOM is a brefeldin A (BFA) sensitive ARF-GEF that is required for the proper polar localization of PIN1, a candidate transporter of the plant hormone auxin [1].

Biological context of GN

• Molecular data and microscopy studies of emb30 seedlings presented here indicate that EMB30 affects cell division, elongation, and adhesion and functions in seedling and adult plants as well as during embryogenic pattern formation [3].
• We have cloned the EMB30 gene, and it encodes a protein that has similarity to the yeast Sec7 protein and to two other open reading frames identified in clones from humans and C. elegans [3].
• In addition, pectin, a complex polysaccharide important for cell adhesion, appears to be abnormally localized in emb30 plants [4].
• Four fully complementing gnom alleles carry missense mutations in conserved regions, seven partially complementing alleles have premature stop codon mutations and two non-complementing alleles have splice-site lesions [5].
• Although the predicted 163 kDa GNOM protein has a conserved domain in common with the yeast secretory protein Sec7p, it is most closely related in size and overall similarity to the product of the yeast YEC2 gene, which is not essential for cell viability [5].

Anatomical context of GN

• We show that emb30 mutants have a cell wall defect that sometimes allows material to be deposited into the interstitial space between cells instead of being restricted to cell corners [4].
• In contrast, localization of epitopes associated with xyloglucan or arabinogalactan was similar in wild-type and emb30 tissues, and the localization of a marker molecule to vacuoles appeared normal [4].
• Mutations in the GNOM gene alter the asymmetric division of the zygote and interfere with the formation of distinct apical-basal regions in the developing embryo [5].

Associations of GN with chemical compounds

• Our results demonstrate that GNOM is required for the recycling of auxin transport components and suggest that ARF-GEFs regulate specific endosomal trafficking pathways [1].
• GNOM is a membrane-associated guanine-nucleotide exchange factor on ADP-ribosylation factor G protein (ARF GEF) [6].
• However, POLARIS was expressed in the basal part of hydra embryos lacking an embryonic root and in the basal parts of both hydra and emb30 seedlings [7].

Other interactions of GN

• Genetic analysis of 8 of these mutant lines indicated that vein pattern formation in these lines resulted from monogenic recessive mutations in 7 different genes, designated VAN1 through VAN7 [8].

Analytical, diagnostic and therapeutic context of GN

• In root cells, we further show that AtSNX1 localizes to an endosomal compartment distinct from GNOM-containing endosomes, and that PIN2 accumulates in this compartment after treatment with the phosphatidylinositol-3-OH kinase inhibitor wortmannin or after a gravity stimulus [9].

References