Stress Granules Sequester Autophagy Proteins to Facilitate Plant Recovery from Heat Stress

The autophagy pathway regulates the degradation of misfolded proteins caused by heat stress (HS) in the cytoplasm, thereby maintaining cellular homeostasis. Although previous studies have established that autophagy (ATG) genes are transcriptionally upregulated in response to HS, the precise regulation of ATG proteins at the subcellular level remains poorly understood. In this study, we provide compelling evidence for the translocation of key autophagy components, including the ATG1/ATG13 kinase complex (ATG1a, ATG13a), PI3K complex (ATG6, VPS34), and ATG8-PE system (ATG5), to HS-induced stress granules (SGs) in Arabidopsis thaliana. As HS subsides, SGs disassemble, leading to the re-translocation of ATG proteins back to the cytoplasm, thereby facilitating the rapid activation of autophagy to degrade HS-induced ubiquitinated aggregates. Notably, autophagy activation is delayed in the SG-deficient (ubp1abc) mutants during the HS recovery phase, resulting in an insufficient clearance of ubiquitinated insoluble proteins that arise due to HS. Collectively, this study uncovers a previously unknown function of SGs in regulating autophagy as a temporary repository for ATG proteins under HS and provides valuable insights into the cellular mechanisms that maintain protein homeostasis during stress.