Edinburgh, Scotland, United Kingdom - TAIR

Small GTPases in post-Golgi and endocytic
membrane traffic in Arabidopsis
The endomembrane organelles and their associated trafficking pathways
synthesise some of the most biologically and commercially important structures
in plants. Circumstantial evidence suggests that intracellular membrane trafficking
pathways diversified independently in the plant kingdom but documented
examples are rare. Rab GTPases are essential regulators of membrane identity
and membrane targeting specificity in eukaryotic cells. Rab GTPase families
have diversified independently in the animal and plant lineages. We show that
in Arabidopsis root tips, the Rab-A2 and Rab-A3 subclasses define a novel post-
Golgi membrane domain that communicates with the plasma membrane and
early endosomal system and contributes substantially to the cell plate during
cytokinesis. In contrast to the Rab-A2 and –A3 subclasses, Rab-A5 proteins
define compartments with a distinct and apparently unique distribution at the
periphery of root meristematic cells.
We have also employed a screen based on accumulation of secreted GFP to
identify mutations that affect biosynthetic membrane traffic in Arabidopsis. Using
this screen we identified mutants in the GBF-family Arf GEF GNOM-LIKE1
(GNL1). We show that GNL1 is a BFA-resistant GBF protein that functions
together with a BFA-sensitive Arf GEF both at the Golgi and in endocytic
trafficking of PIN2 but not of other plasma-membrane markers. The evolution of
endocytic trafficking in plants was apparently accompanied by neofunctionalisation
within the GBF family while in other kingdoms it occurred independently
by elaboration of additional Arf GEF families. A TILLING screen of additional
seedling-lethal secretory mutants suggests that several will identify components
of the trafficking machinery that are not previously well characterised.
41
L16
Friday 11:00 - 11:30
Cell Biology
Ian Moore
University of Oxford
UK