Download The exocyst, an octameric protein complex conserved among all

The exocyst, an octameric protein complex conserved among all eukaryotes, mediates
tethering of the vesicle prior to its fusion with the target membrane. Apart from the function
of exocyst in exocytosis, new studies from both mammalian and plant fields report its
involvement in the cellular self-eating process called autophagy. In land plants the number
of paralogs of some exocyst subunits is extraordinarily large. There are 23 paralogs of Exo70
subunit in Arabidopsis thaliana. It is supposed that these paralogs have acquired functional
specialization during the evolution – including involvement in autophagy. Using yeast twohybrid assay it is shown here that Exo70B1 and Exo70B2, but not other Arabidopsis Exo70
paralogs interact with Atg8, an autophagosomal marker. The proximity of these two paralogs
and Atg8 in vivo was confirmed by independent Förster resonance energy transfer (FRET)
method. Interestingly, interaction of Atg8f with Exo70B2 paralog appears to be stronger
than with Exo70B1. Exo70B1-mRUBY expressed under the natural promoter shows punctate
membrane structures that are mostly static. That changes after the tunicamycin treatment movement of some of these dots was induced.
Homology modeling of Exo70B1 and Exo70B2 proteins tertiary structure in combination with
bioinformatic prediction based on results suggests sites of the interaction with Atg8 and
render possible explanation of Exo70B2 being stronger interacting partner.