The lipid flippase Drs2 regulates anterograde transport of Atg9 during autophagy

Abstract

Macroautophagy/autophagy is a conserved catabolic pathway during which cellular material is sequestered within newly formed doublemembrane vesicles called autophagosomes and delivered to the lytic compartment of eukaryotic cells for degradation. Autophagosome biogenesis depends on the core autophagy-related (Atg) machinery, and involves a massive supply and remodelling of membranes. To gain insight into the lipid remodelling mechanisms during autophagy, we have systematically investigated whether lipid flippases are required for this pathway in the yeast Saccharomyces cerevisiae. We found that the flippase Drs2, which transfers phosphatidylserine and phosphatidylethanolamine from the lumenal to the cytosolic leaflet of the limiting membrane at the trans-Golgi network, is required for normal progression of autophagy. We also show that Drs2 is important for the trafficking of the core Atg protein Atg9. Atg9 is a transmembrane protein important for autophagosome biogenesis and its anterograde transport from its post-Golgi reservoirs to the site of autophagosome formation is severely impaired in the absence of Drs2. Thus, our results identify a novel autophagy player and highlight that membrane asymmetry regulates early autophagy steps.

Deficiencies in cluster‐2 ALA lipid flippases result in salicylic acid‐dependent growth reductions

“…For example, Arabidopsis mutants deficient in autophagy are known to display SA‐dependent early senescence and autoimmunity phenotypes (Yoshimoto et al, 2009), and it is possible that cluster‐2 ALAs are required for the proper localization of one or more proteins in the autophagy machinery. In yeast, Δdrs2 flippase mutants are autophagy‐deficient due to the impaired trafficking of a lipid scramblase named Autophagy 9 (ATG9) (Matoba et al, 2020; Kriegenburg et al, 2022), which supports the potential that ala flippase mutations might trigger a similar deficiency in plant autophagy. This would add to the many examples in which ala mutations have resulted in altered trafficking and localization of membrane proteins, including auxin‐effluxing PIN proteins, the ABC‐transporter PEN3, and LURE peptide receptors (Underwood et al, 2017; Zhang et al, 2020; Zhou et al, 2020; Yang et al, 2022).…”