Autophagy is an essential quality control pathway that mediates the recycling of damaged
cellular components that would otherwise harm the cell. It involves encapsulating the
damaged macromolecules in a double membrane vesicle termed the autophagosome, which
is then carried to the vacuole for recycling. Despite extensive molecular studies in yeast and
metazoans, in plants, how autophagosomes are transported and fuse with the vacuole
remain largely unknown. Intriguingly, although the core autophagy machinery is highly
conserved, plant genomes lack some of the key players that are involved in autophagosome
transport. This suggests that the green lineage may have evolved novel means to deliver
autophagic cargo to the vacuole. To unravel the molecular mechanism of autophagic cargo
delivery in plants, we focused on identification of the autophagy adaptors that are recruited
to autophagosomes by interacting with ATG8 proteins on the outer autophagosome
membrane. Through extensive fractionation-coupled mass spectrometry experiments, we
identified two candidate autophagy adaptors that are critical for autophagic flux in
Arabidopsis. We have obtained preliminary evidence suggesting both of these proteins
directly interact with ATG8 proteins via short linear motifs termed ATG8 interacting motifs. In
this proposal, we will use functional cross-complementation assays in Arabidopsis and
Marchantia to elucidate the molecular functions and evolution of these adaptor proteins. We
will also establish correlative light and electron microscopy (CLEM) techniques to visualize
these autophagy adaptors on outer autophagosome membranes at the ultrastructural level.
Finally, we will perform recovery assays to see if increasing the level of these autophagy
adaptors could facilitate autophagy and thereby enhance stress tolerance in plants.
Altogether, our studies will shed light on a hitherto unknown group of molecular players in
plant autophagy and reveal if they can be modulated to engineer more robust plants.